[0:00] Hey Everyone,
[0:01] In our last project, we built a voice-controlled robot.
[0:05] To drive the robot we used a couple of servos.
[0:08] I thought it might be good to a bit of a look into driving servos from the ESP32.
[0:14] Servos come in all sorts of shapes and sizes with some very high precision industrial versions available.
[0:21] We’re going to be looking at the low-end hobby RC Servos.
[0:25] These are readily available and very cheap.
[0:28] Typically these consist of a DC motor, reduction gearing and a potentiometer.
[0:34] The potentiometer is used as a position sensor to feedback to the embedded controller and
[0:39] motor driver to tell it what position the servo is in.
[0:43] There are plenty of breakdowns online on what’s inside a servo. Just google “what’s inside a servo”.
[0:50] You’ll find some quite good articles.
[0:52] Wiring a servo is pretty straightforward.
[0:55] Though confusingly the color-coding depends on the manufacturer with three dominant schemes.
[1:03] Most servos that you’ll encounter will require a 5-6V supply.
[1:07] For the demonstrations in this video, I’m using the same power supply as the ESP32,
[1:13] but you may want to use a separate power supply if you are driving multiple servos or have
[1:17] some high torque servos you want to use.
[1:21] Controlling servos is pretty straightforward, you need to provide a 50Hz PWM signal.
[1:27] Sending pulses with a width of 1ms will put the servo at 0 degrees.
[1:33] Sending pulses with a width of 1.5ms will put the servo in its middle position
[1:39] - this will be 45 degrees for servos that have a 90-degree range.
[1:43] And sending pulses with a width of 2ms will put the servo at its extreme range - 90 degrees or 180 degrees.
[1:52] You can go outside the 1ms to 2ms pulse with range and overdrive your servo
[2:01] but this can cause damage and strip the gears in the mechanism or even burn out the motor.
[2:08] Let’s have a look at a servo in action.
[2:10] I’ve wired up my oscilloscope to the control line.
[2:13] You can see that we are sending a signal at 50Hz with 20ms period.
[2:19] If we zoom in on the pulses we can see that as the pulse width changes the servo changes position.
[2:28] We also have available continuous servos
[2:32] these servos don’t have the potentiometer and can spin 360 degrees continuously.
[2:37] Setting the pulse with to 1.5ms will cause no movement to happen.
[2:44] Setting it between 1ms and 1.5ms will cause the servo to rotate counterclockwise.
[2:50] And setting it to between 1.5ms and 2ms will cause the servo to rotate clockwise.
[2:56] The speed of the rotation is determined by how far away from 1.5ms you set your pulse width.
[3:02] Continuous servos also have a trim pot to let you fine-tune the dead zone pulse width.
[3:09] Let’s have a look at one of these servos in action.
[3:12] As you can see when the pulse with is at 1.5ms the servo stops and as we move away from 1.5ms the servo speeds up.
[3:22] So, how is this done on the ESP32?
[3:26] Controlling servos from the ESP32 is really easy
[3:30] The ESP32 has 16 led channels that can output PWM signals to the GPIO pins.
[3:37] To set things up we call the “ledcSetup” function.
[3:41] We pass in the frequency of 50Hz and we pass in the resolution we want to use for setting the duty cycle.
[3:48] In this example, I’m using 16 bits which will let us set a value between 0 and 65535.
[3:54] With 0 being 0% duty cycle and 65535 being 100% duty cycle.
[4:02] Once we’ve called the setup function we just connect the LED channel to a GPIO pin.
[4:08] You can actually connect multiple GPIO pins to the same LED channel if you want.
[4:13] So you can drive multiple servos from the same LED channel.
[4:17] To set the angle of the servo we need to calculate the duty cycle.
[4:22] We can work out the ms value for the duty cycle - this calculation assumes that you
[4:27] want to go from 0 to 90 degrees.
[4:29] If you have a 180-degree servo then change the 90 to 180.
[4:35] We can then work out the value to send to the LED controller.
[4:40] Finally, we just send the value using ledcWrite specifying the LED channel that we want to update.
[4:49] So, that’s really it, It’s really easy to control servos from the ESP32.
[4:54] There are 16 LED channels so potentially we could control 16 independent servos.
[5:01] There are several libraries out there to make this all a bit easier.
[5:06] You should be careful about overdriving servos - you can get more movement range, but you
[5:10] might strip the gears or burn out the motors.
[5:13] It’s also worth bearing in mind that there are more sophisticated servos available.
[5:18] Some servos provide a feedback wire so you can monitor the servo position, there are
[5:22] programmable servos and there are industrial servos.
[5:26] Anyway, that’s it for this video, I hope you found it useful and enjoyable.
[5:31] If you did, please subscribe and hit the bell so you never miss out on a video.
[5:36] Thanks for watching and I’ll see you in the next video!