Very nice. There is so much I don't know about this stuff. I didn't know you could do this with photocells. I'd love to get the article/info on how to build this if you still have it. Nice job.
Nope! The derivative was calculated using a single capacitor. The 555 timer controls the pulses needed for the servo. The photocells are the sensor input. Between the photocells and the 555 timer input is a resistor and capacitor in parallel (15K ohm, .1 or .2 uF) that is used for proportional (resistor) control and derivative (capacitor) control.
A wide range of PD controllers can be made with just a simple resistor and capacitor at the input to a PWM.
Cheap photocells were used. There's a light above the robot and that's the only reference. The photocells provide both proportional and derivative (through a capacitor) information. You must use derivative information to make the system stable.
Yes, only a 555 timer was used. It's set up as a pulse generator and those pulses control the actions of a servo modified for continuous rotation. A modified servo is a full proportional bi-directional device.
The 555 timer is used as a crude but highly functinal PID controller (only PD was used in this robot). You can email me at:
tom ((at) newschooltch ((dot) com
and I'll email you an article on how to build this robot with schematics.
so cool.
it seems that analog is really useful. Not all workable things are digital.
praiseslow 5 months ago
Very nice. There is so much I don't know about this stuff. I didn't know you could do this with photocells. I'd love to get the article/info on how to build this if you still have it. Nice job.
Soulrider2012 1 year ago
God! I knew the 555 timer was usefull but this is by far the coolest project iv'e seen!
Hail to you!!!
kurtcomet 2 years ago 5
Great job, that really took some creative thinking. I love seeing analog circuits put together instead of slapping a microcontroller on everything.
Pilotgeek 3 years ago 4
Cool stuff! Are you using op-amps to calculate the derivative?
markthemech 3 years ago
Nope! The derivative was calculated using a single capacitor. The 555 timer controls the pulses needed for the servo. The photocells are the sensor input. Between the photocells and the 555 timer input is a resistor and capacitor in parallel (15K ohm, .1 or .2 uF) that is used for proportional (resistor) control and derivative (capacitor) control.
A wide range of PD controllers can be made with just a simple resistor and capacitor at the input to a PWM.
roboanalogtom 3 years ago
hey, very cool robot. do you have the schematic or any documentation?
davidbball13 3 years ago
Just curious, what did you use to sense the inclination?
felineboy 4 years ago
Cheap photocells were used. There's a light above the robot and that's the only reference. The photocells provide both proportional and derivative (through a capacitor) information. You must use derivative information to make the system stable.
roboanalogtom 4 years ago
D'oh, the email is:
tom ((at) newschooltech ((dot) com
roboanalogtom 5 years ago
Yes, only a 555 timer was used. It's set up as a pulse generator and those pulses control the actions of a servo modified for continuous rotation. A modified servo is a full proportional bi-directional device.
The 555 timer is used as a crude but highly functinal PID controller (only PD was used in this robot). You can email me at:
tom ((at) newschooltch ((dot) com
and I'll email you an article on how to build this robot with schematics.
roboanalogtom 5 years ago
actually a 555 makes sense if its set to switch something back and forth right ? very cool
boxa888 5 years ago
this is really impressive, do you have anymore details?? you only ussed the 555??
jlewis184 5 years ago