 So, let me come to the second half of the lecture. Now, again I am showing you the what you call our rhino robot. Now, in this lecture, we will have a look at the transmission systems. How is the motion transmitted from the actuator? This is the mechanical detail. I am just giving you some. So, here you can see that in this rhino robot, the motion is being transmitted by chains. This particular educational robot, motion is being transmitted by chains. All the motors are at the base. You can see this. See these motors. These motors, the black unit on the motor is the encoder. It is a magnetic encoder. I think you must have been told about encoders yesterday. It is a magnetic encoder. So, that way they have reduced the weight here, but of course, they did not escape some of these motors here. It is not always. As I said, robot has several degrees of freedom and for each degree of freedom, there is an actuator. So, fingers and grippers are not counted as degrees of freedom. Now, sometimes what happens is when I had told you that when you want to trace a straight line, you first use the robot as a measuring device. Take the end point of the robot to the first point on the line, one end point on the line. Then we call it the end effector. The gripper which grips, we call it the end effector. The general name for that is the end effector. The end effector might be a gripper, might be a tool, might be a tool like a welding gun, might be anything. So, we take it to the point A, the first point on the straight line, the end point of the straight line, then record all the joint angles. Go to point B, record all the joint angles. Then compute the x, y coordinates of A and B. Then draw the line A, B. I mean, obtain the equation of the line A, B. Cut it into pieces along that line. From individual locations on that line, you work back the joint angles. That is the inverse kinematics. That is what we do. Now, this becomes quite a tedious task. Solving the equations becomes tedious. So, what we do in mechanical engineering geometry of the, engineering geometry of the robot is so adjusted that it becomes easier for you to do the inverse kinematics. So, here is one example. You can see there are three tubes here. There are two tubes, R 1 and R 2 and a pair of bevel gears and ring gears. So, this is the, what is known as a three-roll wrist. By driving these two, you can obtain the rotations, this rotation. See, you have a set of gears. Many of you must have seen the differential in an automobile. It is a multi-degree of freedom system. Essentially, that is converted into a single degree of freedom system. So, through use of bevel gears and all that, we have developed, they have developed what is known as the three-roll wrist. Now, there are several advantages in using the three-roll wrist. The actuators can be kept far away and the rotations, the three rotations, the axis of rotation, three rotations, they intersect. See, in a wrist, I told you there are three motions, one this way, another this way and a third this way. These three intersect, the axis of rotation. See, you can always have a wrist with this motion here and this motion could be around an axis which is here rather than here. That can always happen. In that case, it is difficult to calculate backwards once the position is given the various angles, but if the three axis intersect, it is much easier. So, that these tricks are adopted by mechanical engineers in order to reduce the computational complexity and speed up the computation. When the three axis intersect, it is equivalent to a spherical joint, a ball and socket. So, in a ball and socket joint, you can position it at any angle you like. So, the idea was why not make the ball and socket joint a stepper? You know the stepper motor, you give it a pulse, set of a stream of pulses, it goes through some 1.8 degrees or 0.9 degrees. Why not have a ball and socket joint? People have been working on this. People have been working on ball and socket joint. So, right now, the capability of fit to lift much weight is limited, but still people have been working on it. So, the whole mechanical complexity is reduced by going in for this. At the same time, computational complexity is also simultaneously reduced. So, stator coils are on one side and you have the magnetic grid on the ball and by energizing the stator coils, you can move it in various ways. People have been attempting. Another way to reduce what you call that, bring the motor down and reduce the torque on motors, which you should essentially lift the payload rather than lifting up what you call the other motors is through use of this carajer robot. You see, this arm rotates around this axis and this arm, portion of the arm rotates around this axis. This motor drives this up and down. As I told you, this carajer, the Japanese have used it very successfully. So, what they have done is they have used the steel, the motors are here and they have used the steel band in order to drive that. One more motor is here and this drives through a steel band, this one. Since the whole thing is moving in a plane, the motors are not being lifted up and down. Only when you move the motors up and down, do you need energy? So, everything is moving in a plane. So, motors are not being lifted up and down and there is a screw joint here, which will lift this fellow up and down. The motor is stationary. It is not moving up and down. They have used steel bands. See, when you have a chain, when you move the output velocity fluctuates slightly. About the mean velocity point, there is a fluctuation. Even in gearing, you get it. If you see tape recorders, you will find that they do not use gear drives in order to get the tape drive. They do not use gear. They use belts. They do not use chains because whenever a chain or a gear tooth engages and disengages, then you have velocity changing. So, the sound quality will change. You will not get proper sound if you use a gears or chains in a tape recorder. You will not get the proper sound. So, instead, you use belts, very smooth. So, they have used steel belts. And if you are wondering where the steel belts exist, you must have seen in the workshop, the dual machine. There is a band saw, where they use a steel band. Similar bands are used. And the motors are what are known as direct drive motors, which are essentially low speed high torque motors. See, typically DC servos and servo motors run at about 3000 rpm. Whereas, your arm movement is slow, much slower comparative. So, you have to have a huge reduction. A lot of energy loss, efficiency, loss of efficiency in the entire system. So, if you use a slower motor to begin with, then the reduction required is not much. And you can attain higher efficiencies. So, that is why they have used what are known as direct drive. There are joint encoders are here. It is a very fast robot. In assembly operations, the time required to fetch the object to be assembled to the assembly point is a wasted time. You should spend more time assembling than fetching the object. So, that is why they want to move very fast from that point here, cut down the time there and spend more time assembling. At the same time when it reaches this end position, it should not oscillate there. So, all these are met by this sort of designs. Unfortunately, these belts are not available in India, but timing belt also has teeth. So, again that problem of vibration, you have to worry about that. So, this is known as that. This is a schematic of the adept robot, which is a very fast robot, which is used for assembly of several components. The Sony Walkman, for example, such a, historically it is a historic product. It was the first which was assembled using robots. The Walkman, Sony Walkman. Yes, obviously, like any belt drive and smooth. See, velocity ratio is constant, but on that average velocity, there is a slight fluctuation. Supposing, you know, your motor is handed rpm, you have a reduction of 10, then your output rotates at 10, but what will happen due to gear teeth is it will slow. Around that speed, it will be a slight fluctuation like this, even as it moves, because there is a gear teeth engaging and disengaging, or chain and sprocket engaging and disengaging. They give you a fluctuation in velocity. That is why in tape recorders, they use a smooth belt. Same band is equivalent to the belt, that is all, except that it is measured. Now, typically the servo motor consists of a tachometer, which measures the velocity. Then there is a speed reducer and there could be a potentiometer or an encoder in order to measure the position. The tachos, this is in control system, you have PID controls and all. The tacho information is required. Sometimes the tacho information, velocity information is obtained from the position. I mean the encoder itself, sometimes it is obtained, sometimes you have a tacho, both are there, sometimes both are there. Then the D to A and A to D converters will convert it into a form suitable for the microprocessor. So, processing that is how it is done. There is a servo amplifier, which will sense the error and then feed a signal, so that the motion occurs according to the proportional to the error. They have also used the cables in order to drive these fingers. Cycle cable, brake cable you have. Similar cables are used. Cables and pulleys have been used to drive these fingers. You can see this, 3 degree of freedom of fingers and the cables and the activities are remotely positioned through the cables they drive. Now, there is a famous, there are many, there is a lot of work on this in the sense that not only in the laboratory, they have gone to the floor also, shop floor also. Some of these cable drive units, pumps, which will pick up objects, gone to the shop floor also. Then in some of the welding robots, you want to go into the interior of a car and weld. You know through the window, you want to go in, weld or do some task. The whole arm must be clean. There should not be too many, you saw the rhino, it had so many things sticking out, want to be clean. So, what you do is you position the motors here and through linkages you drive this. All the motions you obtain through these linkages. Now, it all depends on whether you are willing, how much error you are willing to tolerate in the positioning. This all depends, your decision on how much error. Now, reduction in speed is always a big problem. If you want to reduce speed, so what do they do? They have what is known as the inverted slider crank. Many of you who are mechanical engineers will be able to know that. If you look at a dump truck or the bulldozer, there is a shiny hydraulic piston. Now, the piston is driven by oil going into the cylinder and so that is what is known as an inverted slider crank configuration. Now, instead of the piston and cylinder, you use a screw and a nut. Now, when you rotate the screw, the nut will translate just like the piston moves, translates and that you connect in place of the hydraulic cylinder and this. Hydraulics is not preferred because if oil leaks on the shop floor, there could be accidents and fire and all these things and you need a hydraulic power pack. The oil has to be kept dry. Once oil moisture goes in, the oil will deteriorate. Then oil has to be very clean filtered because these are very sensitive servo valves are used for the servo control and they are susceptible to damage if there is a lot of dust in the oil. So, lot of care has to be taken about the oil. You need an oil tank and all that. So, increasingly people have shifted from oil to sealing is another problem. So, increasingly people have resorted to use of these electric drives which consists of a DC motor driving a ball screw. In the ball screw between the screw and the nut, there are spherical balls which cut down the friction. Efficiency is could be as high as 85, 87 percent, 85 percent. In the laboratory, we found that conventional screw drive, unless you finish it accurately, it goes up to about 30, 35 percent efficiency, drive efficiency. Whereas, the ball screw drive gives you about 80 to 85 percent. They are expensive, ball screw drive. In nut raj, we use the ball screw drives because otherwise, you know, nut raj has to carry its own power pack and you need lot of. So, we had no choice but to worry about the efficiency. So, we use the ball screw drive and we use a similar configuration in order to drive it. Now, independent actuation, you see, now I want to move this as well as this. This is the shoulder and this is elbow. I would like to move both. So, I have the inverted slider cranks here. We have the piston and cylinder. I have just shown as a sort of a schematic. So, if I drive this, this fellow moves up. Obviously, he carries the whole lot of these things, but I can change this angle independent of this angle, right? Between these two links, the angle can be changed with this, these two links. So, I have independent actuation of both the axes. Though, the motion of the end effector when this fellow moves and this fellow moves, when this fellow moves, the motion end effector will go somewhere. Then, I have to readjust along using this particular action. Also, you see, these are some of the mechanical designs we play. When you want to hold an object, which is of this shape, you would like the finger to move from here to here, here parallel to itself. So, we use linkages. Otherwise, if you use a scissor like thing, the fingers are not moving parallel. Difficult to grasp a rectangular or squarish object, prismatic object. Whereas, if the fingers move parallel to each other, then what is the grip you have to exert? Because there is a weight. You must have sufficient friction in order to keep it from falling. Or, when the robot is picked up the object and is accelerating, the object should not be thrown. Safety is a very important. There have been accidents when the object was thrown. Let us say, one or two kilo object you are carrying. The object is thrown. Then, it can cause damage. So, these have power failure in India in particular. Suddenly, if the power fails, the robot will come down. So, all the motors must have safety brakes. If the power fails, the brake will come on automatically. Otherwise, let us say the worker is examining something and then the robot comes down due to power failure. It could be a safety hazard. Now, if you want to look at an object and then decide something, whether it is properly positioned and all, you can use ultrasonic range finders inside the gripper itself. You can see this. These are parallel motion. When you know that you have touched it, a piezoelectric sensor or even a small micro switch will do. Many times, these simple devices enhance the capability of the robot. Otherwise, the robot once programmed, whether it grips up an object or not, it will go through its motions. But, supposing you put a micro switch here and in the program you have this, unless this micro switch is on, only then continues the motion, then it will wait and alert you saying that there is no object here. You have to make sure that the object is there. In any robotic system, presentation of the object to the robot is very important. You cannot just throw the robot at any, throw the object and hope that the robot will present, pick it up properly. It has to know if the fingers have to close on to two surfaces, you have to know which surfaces it has to close on to. If the surface is curved and the finger is a flat shape, it may not grip it properly. You have to select the surfaces. So, if you have to select the surfaces, you have to present the object to the robot in a proper way. The presentation systems in robotics can be more expensive than the robot itself. Once you are presented from the next station, the robot will position it properly for the next robot to pick it up. So, at the first station, invariably you require a proper presentation. Of course, if you are carrying it from there to elsewhere, there again you will start requiring a presentation system. There are many vibrating bowl feeders and many pieces of automation currently used on shop floor are used as presentation systems. They make sure the object is in the right position. Otherwise, the robot will not know what to do, presentation systems are. Here these are more sophisticated presentation systems. These things appropriate control on the forces by looking at the forces on the piece of crystal. You can make sure that your robot fingers do not crush an egg. They can hold an egg and the same fingers can also be asked to hold some other hard object. It can be done much more firmly. So, you have incorporated some amount of decision making at this place itself, at the finger level itself. So, this is one more thing that is being done nowadays. These have become fairly common now in the shop floor. Now, most of the robot we saw were serial chains. That means, one motor driving the shoulder, another motor in the elbow and like that. There are what are known as parallel chain robots. Here you have a crystalline cylinder, six of them. This plate moves relative to this plate. There are ball and socket joints at either end. In one end of course, ball and socket as as usually it is universal joints, different joints. So, you get a one degree freedom and this is object being manipulated. The reach may not be much, but orientation capability is there and it is very stiff. Stiff in the sense, if you apply a force, it will not yield. This fellow, all the servos must be lying in order to see that it does. Now, let us say I am using the conventional rhino to drill. Then the forces, when you drill, you have to press against the object, right? So, there will be a force on the robot. These forces are taken up by the servos. Here it will be a stiffer one. That is why these are used now in order to do this PCB drilling and all that. Because they are very stiff, so you can get a, they will not deflect backwards under the parallel close chain robots. This is the same thing that is used in aircraft simulators. When pilots are trained, they sit on this and they are trained. Now, such platforms are being built for training in racing car drivers. It will also simulate or drive, when you drive vehicles on terrain, off the road, you know, all sorts of terrain. Now, you have to train. For example, many drivers have to be trained to drive in Kashmir. So, lot of petrol is, fuel is used for training the drivers itself. So, why not train them on this? So, that has begun. There are some companies in Hyderabad which are making those trainers. It will look like the cab of a truck. You sit in it and then it will simulate the terrain there. You suddenly the vehicle will fall. Suddenly it will raise all these things, the rival experience and how to handle the car. Because when such a thing happens, if you think you are going this way, because of that reason some pothole or something, it will suddenly turn the other way. So, he has to anticipate. He has to be, get trained. So, these trainings are imparted on this before he is put on the actual truck and then some more training before. So, these are being used now. When we want to reach very high speeds of operation like in the Skara, there are lot of problems. What will happen is your links will deflect under the massive inertia forces as you accelerate and decelerate. So, we were trying in our lab of very high speed manipulation. What happens is when some object is moving, you know that mass into acceleration, the inertia forces and all these come into picture. We were trying to cancel them out. When this particular robot, when this will move, they move opposite to each other so that these forces cancel out and allows you to move at very high speeds. So, part of a PhD, a student who worked with Professor Bharat Seth, he did his PhD, he built this setup to check up and to decide on the control strategies and all, very high speed. You can attain much higher speeds than people are trying to attain higher and higher speeds so that the throughput on the shop floor increases. You can do the task faster and faster. Again, as I told you, I had earlier told, see here is a special mechanism used to design the leg for a walking machine. This one will move the foot on a D-shaped curve. The foot will go like this, raise and then fall forward. This one, the foot will raise, go and fall forward on a D-shaped curve. So, when the machine is on the ground, for some time you find the foot on the ground, the machine moves forward, then the foot is raised. Some other three feet are supporting the machine. When one foot is raised, you look at the way you walk. You stand on one foot and you throw one foot forward in a D-shaped curve. That is what you do. Now, I had told you that in Natraj, when we move one motor, the foot moves up and when we move the other motor, the foot moves forward and backward. So, this is the scheme which we utilize. So, this is the linkage we utilize, this particular one. We had explored various possible linkages and finally settled for this one. This is the one. Now, you can see that here we have depicted our ball screw driven linear actuator in the form of a piston and cylinder just as a sort of a schematic. So, when we move this, this fellow moves up and when we move this, this fellow moves backward and forward. The advantage that way we did not have to overload our computer with calculating things. If I have to move the arm like this, I told you about the direct and inverse kinematics. All those calculations have to take place. If I want the foot to move on a D-shaped curve, which is the typical curve for the foot trip when you are walking. So, we did not want to go through because until it completes the computation, the machine cannot move forward and till it completes the computation and tells the motor you do this, you cannot move forward. You will be waiting. It is pointless and of course, elsewhere what people have done is they have done the computation and then, but many in case of walking machines, many have adopted this sort of a strategy that one motor lifts the foot, another motor moves it forward. So, you sit on this motor, it lifts, you sit on the other motor, it will move forward much easier. Now, the question that comes up is what has actuators being used here? You see you have seen the Natrage actuator. See how big it is huge. What about actuators being used here? So, lot of mechanical engineering linkage design is critical when you design these systems, particularly walking machines, particularly walking machines. Now, here you will see two fingers manipulating an object. Now, what is the requirement here? As the object is manipulated, I am manipulating this object. My fingers are touching the object, three fingers or maybe two because I have soft fingers I can get away with two. If these are hard fingers, I cannot get away with two, soft fingers. Now, as I move the object, I have to do my inverse kinematics, direct kinematics and all this. Also, see what are the forces between these two? If the force is zero, that means I have lost contact with the object. So, the computation load when you do this is much more heavier. So, there are sensors here which hold, give him a feel of what is the force between the workpiece and the finger and that is factored into the computation of the various trajectories as you workpiece. As the workpiece is rotated, you can rotate. You see what the hand is capable of. You can rotate it like this. I want to rotate the workpiece like this. How do I do it? I should not do this contact. So, I have to continuously monitor the forces that come under the hybrid control. You monitor both the forces as well as the positions and keep on controlling so that you have not lost contact and you move the object the way you desire. It is more like an ant crawling over the workpiece somewhat analogous to. So, if I know walking machines, then I know how to handle this also. Though of course, there I do not worry about forces, here I have to start worrying about. See this Stanford arm, you can see these whitish fingers tips. They are piezoelectric crystals and it is holding a wine glass. The wine inside is, you know, it has tilted the glass. So, but you get the feeling that it is not a straight glass. It is there is a break in the glass. You get that feeling. And you can manipulate this glass by feeling the forces and see the cable drives. The cables are here and the actuators are remote, small motors which move forward and backward. I think I will now go to. So, I will now close this session. This I mean they show and show you some movies and there I will explain to you some of the things which you have. Now, first is I am showing you a robot where this sort of motion of decoupling that means in the sense that if I move one motor, it will move in the x direction. If I move another motor, it will move in the y direction. Mind you, you cannot get it exactly on the x and y directions unless you use what is known as a gantry robot. A gantry robot is nothing but a gantry crane which is automated. A gantry crane, you know, moves in the x, y and z directions. It is very easy to figure out the inverse kinematics in a gantry crane. How much distance should I move if the object has to move from xa to xb? It is very easy to figure out just the difference between the two positions. It is not difficult. So, that is why we like that. But when you have these joints which move forward and backward, prismatic joints, there are numerous problems though they are very stiff. In the case of NC machines, you use these xy motions. They are very stiff for metal cutting. Yes, very stiff. But elsewhere, they are bulky. They are not compact. You want to reach out. Otherwise, God would have built us also like gantry robots if they had not been like that. So, we have to do something, you know. I will show you what we did. Now, you see this. One actuator is moving. This red line is actuator. This is a simulation. You can see the object is being moved up and down, though around the circle of a large radius. I will play it again. This is one motion. It is moving more or less on a straight line on the ground. I am moving this actuator now. So, I have interposed the mechanism between the load and the actuator in order to get this. So, if I want to move the object wherever I want, I move one actuator at a time. It makes my life easier. Is it okay? I move one actuator at a time. Play it again. All right. Now, if you are having a robot where you have an arm sitting on top of a mobile vehicle, the vehicle has come to a spot and there it spots an object. And the operator wants to move the gripper to the object. The vehicle, he will park the vehicle. Then he has to move. Supposing I give him something like a human arm, then he moves this motor, then moves this motor, and he reaches it. Right? We had seen that. When we wanted to teach the robot the position of an object, what did we do? We carried the end effector, took it there, but supposing the end effector or the load being carried itself or the gripper is itself about 30, 40 kilos, you may not be able to do it. So, you will have to depend on motors. You press a button. The motor will move. The arm will move like this. Press the other button. This portion will move. Again, press this move. So, you keep on playing with these two motors till you reach. Now, supposing for each of these motion, this fellow goes on the X-Y plane. Is it easier for you to reach the object or is it easier if you have to move along the circular arcs? It's easier if this fellow moves on the X-Y. That's what we have done. Because this is going to be operated by a human who will operate these two from remotely and through a TV camera he will be watching and he will go and pick up the object. We are building this. So, this is what is known as decoupling of motions. Here it is weakly decoupled, not exactly X-Y, but if I put an X-Y, then it will get out of my machine. The machine here will be sitting somewhere here. It's a very tiny machine. I have shown you that with belts and all. A track machine. That is a tiny machine compared to this. This distance is roughly about 3 meters. You can imagine. In 20 kilos. There are cameras to show the operator that he is going to hit an obstruction. See, if we want to build in that level of sophistication where what you essentially do is you build to the extent possible bearing in mind the cost. Maintenance is a very big... If they phone us every time for a repair, then it is no point. So, essentially our philosophy is build something rugged. Now we could have relegated this to the electronics and build this on. We could have done that. Then servo motors. Servo motors are expensive. Each thing adds up to the cost. So you have to look at the target and then decide which way you want to. So, we decided on this because we thought we would put it on the mechanical system and make life easier for the operator. When human interaction comes, you have to think a lot more carefully. Now, when an obstacle comes, it is the operator who decides how to go around the obstacle. If I wanted to do autonomously, now one of the reasons why Japan succeeded in heavily robotizing their shop floors is they said it is another piece of machinery. Americans said it is fantastic. It will do what a human wants. A simple example is like this. If you want to make a cylinder, you will go to the lathe. Will you try to make the cylinder on a shaper? If you want to make a cube, you will go to the shaper. You will not try to make it on a lathe. So, every machine has its capability and you should work within that capability. Some people will say the tool on the lathe can be moved like this. I will hold it in the chuck and I will make a plane surface. But you are not utilizing it in the proper sense. So, you have to make sure that you utilize the capability of them in the proper way. So, what the Japanese said is another piece of machine. This poor fellow has to be shown where the object is. He has to be told everything. Let us treat him like that and let us design the workplace so that it is comfortable to him, to this robot. So, one thing I can do is I want to assemble this ball pen. It consists of several pieces. I dump all the pieces together in a heap. I have two vision cameras. One vision camera, the cameras look and they say this is a clip. Then I take the clip, heap it here. Then again I look, I find this portion, I take it and heap it here. There is one way of doing it, from a heap. Even if I ask you to do, you will tell me that what is this nonsense? You definitely say. Whereas, supposing I keep a heap of these in one corner, another heap of these in one corner, a heap of this in one corner, then even if I tie you blindfolded, you will pick this, pick this, pick this, put it away. That is what the Japanese said. Let us make life comfortable for the robot. Treat him with respect, know his capability and give him a task consistent with his capability. It will work. That is the philosophy one should follow. That is a very important philosophy. That is why they succeeded in applying robotics rapidly. I have seen one movie in which the worker is working on a list. He completes the job, puts it here. That fellow comes, the robot is just like a helper. He puts it in another tray and from the second tray, this one for him to pick up and load it. Sorry, it loads it onto the machine. This is how things happen. Japanese. That is two. In the area of mechatronics and all these things, a lot of innovation is still currently possible. I will show you one. A mechanical digital logic device, an end gate. Here is an input A, here is an input B. A is now at zero. If I move it forward, it will come to one. Input B is now moving to one. It has moved to one. See the output Z, it is where it is. It is not moved. It is at zero. Now B has gone back to zero. I will move A. Output Z will remain where it is. We captured it from our simulation. I have got the device there in the lab. I can show you the device sometime. Output Z remains where it is because in an end gate, unless A and B go high, you are not going. Go or move both. It is very slow. This can also become the out gate. All I have to do is, it is a zero one here. I will say zero one here. It is consistent. I can build a small circuit out of this. Now this. Now professor Gandhi has built it in MEMS. This has been built in MEMS. I do not know whether he showed it to you yesterday when he gave the lecture on MEMS. I will ask him if he has some time to show it to you. He has built it in MEMS, this particular device. Because in MEMS, you need logic, but you do not only use electronics. Now there are a wide variety of applications for this. Now one application is there. Imagine this is the corridor. This is your office. Your office is air conditioned and clean. You do not want that to come in. So you open this door. Come here. This is an airlock. Then close this door. Then only you should be able to open this door. Then come in. Now supposing I block this. I do not allow Z to move. Just put my finger on top. Then what will happen? When I open this, it is possible to open this because when A goes to one, B is at zero. Z is at zero itself. So you come here. Then close this. Only when you close this can you open this. Because if you try to open this, it will not allow. That is locked. So numerous devices can be built. There is a huge scope for innovation in all these things. Now robotics has gone to a higher level. You go to other planets. You look at things and you do so many things. And I will show you the... Yeah. This is the micro mouse. You know what a maze is. One has to solve a maze. In this competition what they do is they keep the maze is kept secret from you. You have to build the mouse. So you have to come to the centre of the maze from the beginning. The mouse starts from there. It senses the gap, comes, plans, it memorises the route. If it does not reach first time, it will go back and again start all over again. So it has found the route. Now the record here is nine seconds. Unknown maze. Believe you. Unknown maze. What does he do? He has got a mobile robot. He has got sensors which look for this gap. Now the mouse is turning. Then I alpha comes into picture. Mass moment of inertia into alpha. If you do not properly plan the turn and send the sufficient torques, the mouse will overshoot. See the speed at which it turns. If you look at the speed at which it turns. Very fast. Now if you do not control it, the acceleration properly. The second thing is, when it senses a gap it stops. Now there are two wheels on either side. There are four wheels. Now the wheels may bang in the front and the back. So that design has to be very carefully done. So mass into acceleration is properly. The torques are calculated. So there is a lot of... See many a time what I find is youngsters who build these micro-mouse and all do not address these points at all. They do not even know what is the speed and torque of the motor they have. You cannot expect them to come out with a good design. See here all these problems have been addressed to cut down every second. You come down to nine seconds. All right. That is one portion. The other portion is from here how do you know this? See the whole... This is a problem artificial intelligence or whatever you call it. The whole of this maze is divided into sectors. Several rectangles. The central most one is the one you want to reach. So he goes from one to another and then takes a decision. He should always go inwards. So when he spots this, okay, a gap. See the gap is of... All gaps are of equal size. That is very important. Spots a gap. He knows where he is and he knows where the center is. Then he plots his next strategy. Again, repeats it. So first run it may be 15 seconds. Second run it will do it. It will come back. Usually the competition is like this. Start here. Unknown maze. First run. Come back. Second run. I mean you come back and start again. Then second run is the one that is counted. He takes about 8 seconds, 9 seconds. First run may be about 10 to 12 unless he is very late. And we have made this a standard competition because we want students to build. But many of them ignore these and under those severe accelerations the connectors and all become loose if they don't do a proper job of it. And many of them tend to have hanging wires and all it never works. It goes like a bullock cart. Slowly the mouse creeps. Whereas you see this. This boy worked for nearly 4 years before he perfected the mouse. It's not one day's job. Many of us seem to think that one month may a sab ho sakta hai. It's not one day's job. He perfected it over nearly 4 years. First I remember because very first year he showed me and he it was very slow. Then all the whatever he start in the classroom was carefully applied and he reached this level. Similarly the other boy who built that device which will you know 2-wheeler like the Segway. Lot of time was consumed. It's not just overnight job. And we spent 6 years on Natrage because we had to do a lot of computation. We had to do a lot of testing. There were no motors available. First of all of course we have the course on robotics. And typically this is the introduction I give to the robotics course. Here and there I talked about inverse kinematics. What is its importance and all these things. Now first let us look at it in this way. First is the mechanical device. First let me look at the mechanical device. One the decisions are one is whether it's going to be a stepper or a servo. This is typically what one has to decide. Now what happens is when you the drain. Now it depends on what is available to you. If you have I am assuming that you are going to the level where you are asking them to build something. So if you have stepper motors at your disposal look at them. If you have servo motors you look at them. Now each of these motors has its own characteristics. Many a time the stepper motor characteristics locally available once you do not get those characteristics at all. Whereas when you get the important ones you have the supplying the characteristics. That is a very important thing. Pull out torque, pull in torque. Otherwise it will miss steps. Now with the servo DC, servo DC is what you get. DC servos, many students tend to fashion out DC servos from what you call that existing small DC motors. They are usually typically by these DC motors in there. Many of the gear boxes are of no use which you get with those small DC motors with little gear boxes. Many of the gear boxes are of no use. The first thing you have to realize is you may have a motor with 5 watt capacity or 10 watt or whatever it is or 50 watt or 100 watt capacity and you will calculate that you need so much speed and torque. So you will find out the wattage you need. That means the load speed, the speed of the load and the torque required. You will calculate. You will find that if you have a reduction of some 300 or 400 both the torque and speed requirements are met. Unfortunately that is not true. Many a time when you multiply the torque it becomes massive at the end. The shaft system and the gears are not designed for that torque. The limiting factor is what the gears and the shaft. Yeah, plastic gears are all. They can take up much torque. So, irrespective of the wattage or the torque of the motor what decides is that this motor will function properly only up to a certain level of torque which are far less than what the gear ratio shows. Far, far less. You should not try to overload them. So you will procure these. Whether you want what sort of mounting you want and all these things. Then you have to decide whether you are going to build a mobile robot the arm, robotic arm or a walking machine. These are the three things which you typically would like your student to do. Sometimes you will say that why do not you usually students will approach you saying that I want to build a walking machine. Remember in a walking machine the power pack is to be carried by the machine. If you cannot then you have to supply external power through a pair of cords. That is what happens in typically in walking machines. If you wanted to carry its own then the efficiency of all these things you select must be very high. You should try to touch as much as 75 to 80% efficiency. Otherwise it is pointless. You may make one you will find that it will not be able to lift its own weight. It is pointless. Now it comes to the arm. A similar thing applies. Try to bring a hallway design where most of the motors are at the base as far as possible to the base. Chains if you use or timing belts or other weight is a consideration. Because you are typically building a small one. Weight is a consideration. The motor has to accelerate the chain also. That mass you have to take into account. Similarly for mobile robots you have to accelerate the whole thing. Now whether it is a wheeled robot what sort of wheels we are finding it difficult to find those. When you look up western websites you will find those they have a variety of wheels available for them. Whereas here our this is very restricted. So then there is the steering also here. Steering most students tend to adopt differential steering. What they will do is the wheels on the one side of the vehicle will be run at a higher speed compared to the wheels on the other side or they will switch off one side and the vehicle will turn. There is a lot of skidding and all. The correct way is you have to have a different velocity so that you get a smooth turn. Not just shut off. Then it will spin around that particular wheel. Not just shut off. But most students tend to do this. Very few students try to make their steering regular steering as in a car or something. Very few students because as a learning exercise I would say it is excellent. It will be very good if they can do that. It will be very good if they can do that. Many a time they have adopted steering plus differential velocity. See what is the condition for correct steering? There you have to start with the mechanics. What is the condition for correct steering? Pure rolling of the wheels. But what is the condition in a... See I look at this as an exercise where you are teaching children all the students all these things. The condition for correct steering is the axis if you know supposing this is the vehicle and it is moving in this direction. The condition for correct steering is the axis of this front wheel the axis of the two wheels which have been steered should intersect. All these should intersect at one point. In other words the wheel rolls on concentric circles. The four wheels roll on concentric circles. Now to get this condition you have to have the acraments steering mechanism. So I asked them to design the acraments steering to meet this condition. So that is the design exercise there. Now remember on the steering the whole wheels are overrun. So the design has to be carried out. Otherwise the whole steering will collapse if you do not. So you know a four bar linkage the acraments steering is a four bar linkage and the linkage is here. Something like this it is and the wheel is here. The load on the wheel comes here. This way. Load. Load downwards. Load. Down. Maybe it may be a ton in case you are designing a truck. And acraments steering is this is the chassis of the vehicle. So you see the wheel is overhung. Load is coming. There is of course an upward reaction that will tend to bend the wheel and then your acraments steering will go and if you do not properly design all these joints the load is of course you know upwards reaction on the wheel is upwards. So I teach them how to so this wheel when this wheel moves through a particular angle this fellow should move through. Now some student may come and tell me I will design a more sophisticated device. Go ahead. So I make sure that they work from first principles. That is the most important thing in my opinion. Do not worry about whether he uses what you call that sophisticated FEM software or not. It is not necessary. Let them work. Make sure that the first principles are observed right from the beginning. Many of them tend to ignore first principles. In fact my experience is most engineers in the country do not look at first principles. The trouble is most engineers in industry do not look at revisit. And we teachers we do not go and design for industry. This is the problem. Both do not match. So my suggestion is that ask them to work from first principles. For example in designing this micro mouse which I told you the mouse has to turn is the mouse. The mouse has to turn like this. There is a mass movement of inertia. How do you know the mass movement of inertia of this mouse? You see how the mouse is. So he has to approximate it or he has to conduct an experiment to determine the mass movement. Now many a time what they will do is they will draw what is that called you know just on the computer. Solid model. Solid model they will create and then they will calculate the mass movement of inertia. You can do it in 5 minutes using a string. You see that they have to we have to inculcate into the students. Finding mass movement of inertia is very easy to find. Instead of that what you do is you spend 3 days making a solid model which will never you do not know the density of the materials you are using some approximations go on like this. Whereas you have the actual object in your hand you have neglected it. It is like saying you know I will try to calculate the strength of this yield point of this steel. When you have the steel in your hand and the UTM sitting nearby you go to FAM and do that. No you can't it is not the way. So you know theory can take you up to some point but it bases on some experimental facts. This is the very important thing I keep stressing on whenever these students design. Now would this theory mechanism fit the micro mouse if I want to turn so fast that's the question I have to address. Yeah the radius of turning here it has to it turns on the spot so the moment the task demands that it turn on the spot you have to address it in a different way. You may not be able to use this theory. So that is something judgment which you have to gently tell the student. So then comes whether you should use a usually what the student does is first the moment he gets one idea he says that is the best idea and he sticks to it. He doesn't want to come out of it. Sometimes it is better to let him burn his fingers his or her fingers the students fingers in case it is not going to cost you much but if it is going to cost you much you have to think or whether what you should do in order to stop him from spending a lot of money and believe me we stick to first principles all these advance this will come when I want to perfect this product and I am going to send millions of them. Supposing the whole world wants this micro mouse then I will use all my FEM and all that to cut down the cost to redesign the product but in the first case and that is where we come in as teachers make sure that they use the first principle properly the rest they will learn by themselves they don't need you ultimately your aim should be that the student should not come back and keep on telephoning you from all over the world how do I design this bolter that is the aim of the teacher you can't have him dependent on you so first principles you insist he will learn the rest yeah song just tap it and say yeah correct now suddenly it turns but then you imagine the size mass of the car and mass moment of inertia it's going to be a tough job it's a massive one space yeah you want to but then speed is not speed of turning is not important you will gently turn and you can go back you see yeah actually now they have come out with automated devices which will take you and allow you to take over virtually that parallel parking which is a very difficult thing they have come out with automated devices they have got ultrasonic range sensors in the front and back and the car is steered by that I have read about it they have come out with those devices but speed is not important there you see in fact in a parking lot you should be very slow rapid turns you don't want here is the rapid turn is one of the important things which he and sudden acceleration and sudden deceleration when he stops if he wants to cut down one second and he solves the maze pardon cars are there yeah yes that is already that is being sold no no but that one what it will do is it will keep sensing the various positions of other cars and keep on reversing forward reverse turn for see there is another problem like for example what you are saying is let me in this micro mouse the front he has two wheels on the side here it is a ball and one more here it is a ball ball and socket now why why why what is this problem look at a cycle if you turn the wheel through 90 degrees the front wheel through 90 degrees you steer it through 90 degrees you can't move the cycle the back wheel in a child's tricycle if you turn the front wheel by 90 so that means the if this is the front wheel of a cycle okay alright the traction vector is on the back is at the back wheel this is the back wheel okay the traction vector is here I think I will take another paper and show you this is what I mean when I keep telling look at the basics I will just take a second okay this is the front wheel and I have to write larger it appears this is the rear wheel okay the cycle and the seat is here okay now when in the in the convention cycle the traction vector is here that is what pushes against the ground push okay you push against the ground and the the velocity is like this when the wheel is in this position when you steer the wheel the velocity is like this and the push is in this direction traction is okay actual push is cut this out so you are pushing in this direction see the velocity vector is in this direction you are pushing in this direction if the velocity vector or direction of rolling velocity slash is not in the same direction of the push, obviously. If you turn it and bring it here, if your front wheel, if your pedal, then both will be always in the same direction. That is why all these modern cars have front wheel drive. So, you get excellent steering. So, these things have to, one has to pay attention to all these things before here. In modern cars, you see, it is a front wheel which is driven and again the engine weight also comes on the wheel, traction improves, grip or whatever you call it improves. So, these points have, we pay attention to. Second thing is motors. You have to develop, we ask them to come out and test the motors. Many of them come back to me and tell me that they wind a string around the motor, let it run and they find the velocity of the motor by finding out, there is a weight at the end of the string. As it rotates, they find the velocity of the motor like that and the weight tells you how much is the torque. So, torque speed characteristics, they try to plot like that. That is, I mean, if you have not been able to provide them a method of determining the torque speed characteristics, obviously that is what they will do, but small dynamometer. So, you have to induce them to build that. See, our youngsters, they want everything, you know, they want the torque speed. Build it. You have to induce them to build it and then the motor speed characteristics, that they are linear. Since they are linear, two points will suffice for you to establish, at least to a reasonable extent what you think at various voltages. So, this you have to insist. Now, whenever they design an arm, the specific question you ask was when they come to you, what do you do? First, I tell them to come out with this system level, all these things first. Then, you have to assume, you know the payload. Let us say, you have decided on a payload. Now, it is a very difficult thing to decide on these things because you do not know what motors you have. So, it has to be back and forth and give and take. So, we decide on the workspace. How much is this space? So, you want the robot to work within a, to have, to be able to access points within a cube of certain dimension that we decide first. Typically, I keep it small so that the whole robot becomes as small as possible. Now, once they have decided that workspace, then work out the geometry of the links. How much should be the size, length of each links? Not yet the material and cross sections, just the length of links. Then, make sure that you are meeting the workspace requirements. Now comes the difficult part because whether to build it out of aluminum or steel or preferably out of aluminum, they would say because the weight is less. But aluminum is difficult. The material that is available, unless you go for high quality aluminum, joints and all tend to give way, particularly when you screw in something, take it out and you try to put the screw back, it is all gone. So, what I do is, I tell them, all right, aluminum. For example, for designing nutrage, we had to spend a lot of time because the loading in certain instances on the leg was of the order of 1.5 tons, 1.5 tons in certain positions, depending on how many feet are on the ground and all, 1.5 tons was the loading on the end. It is away from the base of the machine when the leg is stretched out. So, imagine the bending moments and all. If I can avoid bending and if I can avoid compression, I would be very happy. Unfortunately, you cannot avoid. See, these are the two which decide where tension is very easy to handle. Most material are strong in, engineering material are strong in tension. But bending and this, that ultimately decides the weight you are going to get. So, I pay extra attention to the bending. Try to see if I can design. In our nutrage, the ball screws are under tension. We have cleverly looked at the kinematics to keep the ball screws throughout under tension. Buttling is not a problem, right? Yeah. Yeah, you know, the car sections will increase, the weight of the machine will increase. But we could not get the hollow ball screws which we wanted, okay. So, when the student comes to you with the payload, ask him to come out with the geometry. Once he has come out with the geometry, now he has to compute what are the weights of the links and decide whether the motors he has in his hand will be able to lift those weights and whether he should position the motors at the base or the joints, okay. Now, if the motors are unable to lift, either you go for a bigger motor or reduce the weight of your entire system, reduce the payload and start all over again. We have no choice unless you are able to import the right motor which you desire because you may get the motor with the necessary power but you may not get the gearbox which you want. So, it is a huge compromise you have to make back and forth, back and forth. Then, if massive speeds are involved, better pay attention to the accelerations and the loads that are associated with it, okay. Then, when you look at the motors, look at the voltage versus at every voltage torque versus speed characteristics you have to examine, okay. Motor speed will drop the moment it is loaded, you will have to see what is the torque versus speed characteristics and see that you operate within the, then you have the efficiency, okay, efficiency also. Operate within high efficiency, close to the high efficiency point, as close as possible, it is not always possible. Then, we ask them to design the servo motors that will be told to you how to go about, we have to estimate all the masses, mass, these are what are, here the motion is the servo motion, usually typically what is it, the robot is required to pick up an object, move at certain speeds, many of the servos will move at different speeds, leave the object here. That means it has gone from zero speed to certain high velocity and then come down. So, acceleration, deceleration will come into picture, okay, left it there and again come. Now, this is what is called as incremental, incremental, now intermittent motion, not incremental, intermittent motion. So, for intermittent motion, how do you select and size the motors? So, that itself is another, many a time catalogs of companies will tell you how to determine the size of the motor, torques and all that given this sort of intermittent motion, you can do that. So, anything else? That is a part of a lifetime experience, it is not overnight, 40, 35 years of working in kinematic source, see there I am finding one thing when it comes to mechanism design, either you have it or you do not have it, simple. Your experience, your interest, passion, it is a passion with me. I can sketch a mechanism which will give you what you want, minutes, why? I have spent 35 years doing that, you are asking. Somebody, people have to have a passion for that, sit down, go through books, look at mechanisms, how many of us when we walk around, look at the bulldozer and wonder what sort of a mechanism is used. I do not know, what students think of me, they might have spotted me many a time watching that road repairing machine, wondering what is this fellow doing. I am keenly observing where are the revolute pads, where are the prismatic pads, where are the screw pads, number of links, I count them, sometimes the link is hidden. So, obviously that will come out. There are doors, they close in all sorts of funny combinations, you close the window, then you pull the lever this way, the window opens this way, you see, the window typically opens, the current window, windows will open usually like this, you see. Then you close the window, you pull the lever in another position, now the window will open like this. So, I was observing how, what sort of a device is this, is it a serial chain, is it a parallel chain, a closed chain? These sort of questions come. Now, everywhere you will see this, it has to be your passion, that is all. If somebody has a passion to go and see all movies of Rajnikant or whoever it is, first show, first seat, first ticket, my passion is watching mechanisms. So, that one has to build up over a period of time. And many students do it, there are some students, there was one student of mine, for example, on the logic gates, once I had evolved it, I called one of my students, I worked with me. First time he came to me and said, sir, I have some ideas about something, he indeed knew what I was doing. I knew that this fellow had the flair for mechanisms. Then he one day came and told me, I want to do my project with you. I said, I took out the logic gate, I had built a small sample and I gave it to him. And I said, I want to design this airlock, two door problem, what shall I do? Immediately he gave me the answer, block this. Immediately, then I knew I had this fellow. He has worked on advanced mechanisms for suspension systems for his PhD at MIT. So, I knew, he had it in him, that is all. Geometric sensitivity, that is what I call and a passion for. So, everyone of us has something, you know, develop that, that is all. In a team, somebody may have, like me, may have a geometric sensitivity and a passion for mechanism, somebody else might have a passion for electronic design. So, we have put all these trends together, you get what you want. Based on this particular, this, you know, we have developed further on this mechanical logic, we developed further. We found a very, very interesting thing. All your circuit breakers, which you use are either end or or gates. So, that means, starting with an end gate, I can come out with a series of circuit breakers. They have certain performance characteristics. Starting with an OR gate, I can come out with a series of circuit breakers, mechanical or gates. So, that again with the same boy from MIT, that was his BTEC project. We sat together and we said, it took us one year to figure out what was going on, because when I first saw the circuit breaker, I could not understand. I knew it was a mechanism. I knew how it worked, but it was, the question I asked myself is, how did the fellow who built this first conceive it in the first place? Then, to answer that question, I went to this Boolean algebra and logic. I thought I could crack it through sequential circuits. It did not happen. Then, one day I realized that I do not need anything except the end and the OR gate. You can crack it. So, it is a passion that you have to do. There are many books. If you ask me, I will give you the list, but many of them are out of print now. Many of them are out of print, because everybody thinks with electronics anything can be done. Unfortunately, that is going to cause problems one day or other. Come on. Around a room or whatever it is, avoiding obstacles and all that. Then, the same characteristics which you find in inverse kinematics for robots, you will find there. You want to go from point A to point B along a particular path. If you know the initial orientation of your vehicle, by some means you should know that. What is the initial orientation? Then, you have to decide, I have to go in this direction. Then, how much the wheels are to turn or the motor speeds are to be adjusted in order to turn in that direction. That is equivalent to the inverse kinematics. I am in this direction. I want to go in this. What should I do to the wheels? Should I turn them by 20 degrees? That is inverse kinematics. Same principles can be applied here. So, that is another class of problems students would like to attack. They would like to go around. This is the base. Base is fairly regular, though of course unknown, but they would also like to go around a room, avoiding obstacles. Then, more sophisticated, map the room and where the obstacles are using movements. That is much more, one more level up. Map the room means find out the map of the room with the location of all the furniture and furniture and all that by letting the robot move around. But, what sort of a strategy are you going to adopt? Will you scan or whatever it is? Then, you have to go into the domain of software, but you also need the inverse kinematics and all to determine if you want to turn this much. How much is the angle by which?