 Welcome to the third video of the STEVAL FCU001V1. In this video, we will cover the ESC configuration. Here is the flight controller board mounted on a typical racing drone frame. Let's see the differences with the smaller version of drone already presented in previous videos. The overall weight. The small one is below 100 grams, while the bigger racing ones weight usually is in the order of 200 to 300 or 400 grams. The other key point is the type of motor used. For the small one, DC motors are used. While for the bigger one, DC brushless motors are used. So, here in this schematic, you can see the configuration when DC motors are used. The motors and W1 cell battery are directly connected to the FCU board. In case of DC brushless motors with external ESC, the battery, usually two, three or four cell type, is connected to the ESC. In case the ESC has the BEC option, basically an onboard DC to DC converter, the 5 volt to the FCU is supplied by the external ESC. From the FCU, we have also the four PWM signals to the motors. You can also see that a small hardware modification to the PCB is needed. We need to change a few resistors in order to bypass the MOSFETs on the FCU and avoid burning the microcontroller present on the ESC. After having done the necessary modifications to the resistors, you just have to connect the flight controller unit to the ESC. Here, we show how to connect the FCU to the ST electronic speed controller reference design, the ST eval ESC001V1, which is able to drive three phase motors up to a maximum RMS output current of 20 amps and 30 volts. Please note that four ESC are needed, one for each propeller. Let's come back to the racing drone. Please note the connector for the battery whose voltage and capability varies depending on the weight and size of the drone. The PDB, the power board with DC to DC converters, mounted below the FCU and the ESC mounted on the arms of the drone's frame. As explained before, the ESC is taking power directly from the battery while the FCU takes 5 volts from the PDB board. Here is a typical 3-cell battery for a racing drone and we can easily see the difference in size compared to the one-cell battery used for the small drone. Please also note that on both drones, we have a small board that is the RF receiver of the remote controller. We strongly recommend that you use an external remote controller when using an external ESC configuration because the drone will be much faster and will need a precise control which is unachievable with a smartphone or tablet app. Also, the maximum distance of the Bluetooth low energy is around 15 meters which is not optimal for outdoor use of the racing drone. Let's see how to program and debug the FCU with external ESC configuration. Here is an ST link that I will connect to the FCU in order to program it and debug the firmware code. I am using an ST link in the video but you may use other JTAG boards like the one present in the Nucleo board. Here we connect a battery checker with a beeper always connected to the LiPo battery when we are working on the firmware. It's important to check the voltage level of the battery because you may spend a long time working on the firmware and if the voltage drops below a certain level you risk damaging the LiPo battery permanently. So, let's open the firmware project of the FCU board and let's see which modifications are needed. First, let's go to motor.h file. Here we can see in the initial part of the code a define for the motor DC configuration or for the motor ESC configuration. Also, we can see here that we have a different range for the value of the PWM signal going from the FCU to the ESC different from the ones we had in the case of DC motors. In fact, in the case of the DC motors we just give a PWM to modulate MOSFETs switching. While in the case of the ESC we need to give a specific frequency, in this case 400 Hz with the specific TON timing that will define the speed of the motor. Usually TON equals 1 ms for minimum speed and TON equals 2 ms for maximum speed. We can also see that in the case of a signal with the TON timing less than 1 ms the ESC will be disarmed in which condition usually they emit an audible alarm beep sound. While if we are over this threshold the ESC will be armed and ready to spin the motors. The values that we need to change in the FCU firmware are the PWM TON values related to the minimum throttle and the maximum throttle and the frequency typically varying from 50 to 400 Hz. When we power the FCU board we are in a kind of standby mode in which the PWM is already generated and sent to the ESC to put them in arm mode. But before spinning the motors and hence flying the drone we need to calibrate the sensors with the drone on a flat surface and with the joysticks of the remote controller in a specific position. Then the next step will be to enable or arm the motors. In this case, arming the motors means that when we change or increase the throttle value the motors will spin. So let's do these two things. Launch the sensor calibration and arm the motors. The LED on the FCU will change from blinking to staying on. You can see that while increasing the throttle the motors are spinning. There are a few other parameters that we may need to fine tune. At first the PID. In fact, the PID can be quite different from the mini drone because we have very different mechanical frame motors and propellers. Another point to fine tune is the slope of the rate of the throttle versus the input value. In this case, GTHR from the remote controller receiver. Also in this case we may need a very different slope from the one used in the mini drone so that we can fly the drone easily. So, we have seen all the basic modifications and fine tuning that we need for the use of the FCU with external ESC. As you can see, we have done all the tests with the battery checker always connected and the propellers not mounted to the motors for safety reasons. The next step will be to go outdoors in a wider space and with the propellers mounted test the drone in flight condition and eventually make further fine tuning of the PID and Remicon throttle slope as explained before.