2

I'm working on a quadcopter controlled by a Raspberry Pi 3 and I'm having some issues controlling the Electronic Speed Control (ESC). I'm a bit of a newbie so please be patient.

I bought the Afro Race Spec Mini 20Amp Multi-Rotor Speed Controller with BEC that is supposed to work with a 1Khz freq, and I managed to control the speed of the motor using the GPIO.PWM module with poor results: the signal sent apparently is not very accurate and the motor spinning is quite noisy and irregular.

Then I switched to the RPIO module and after many nights I managed to make it work with the Raspberry Pi 3 by cloning the metachris version:

git clone https://github.com/metachris/RPIO.git --branch v2 --single-branch

The code I'm trying to use is something like:

import time from RPIO import PWM PIN = 18 servo = PWM.Servo() #using default pulse with 20ms -> 50Hz servo.set_servo(PIN, 1200) time.sleep(5) servo.stop_servo(PIN)

I was expecting some kind of movement of the motor but nothing is happening.

Since the ESC is supposed to work at 1Khz frequency, should I set the pulse width accordingly? In this case should be:

 servo = PWM.Servo(1000)

If so, I can't do this because the minimum value appears to be 3000 microseconds.

Can I do anything to overcome this issue? Am I doing something wrong?

Also, during a series of tests I managed to control the motor setting: 

servo = PWM.Servo(8000)

and changing the servo with random values:

servo.set_servo(PIN, random_value)

but I'm not able to replicate how I did it!

My questions are:

  • If the ESC is supposed to work with a 1000Hz frequency how come did it work with a pulse-width 8000 -> basically 125 Hz ?

  • Is there something I'm missing? ESC calibration, wrong values or anything?

Any help or suggestion would be much appreciated

Improve this question

2 Answers 2

Reset to default
2

Try the following from the command line. I'm assuming you mean Broadcom GPIO 18 (pin 12).

sudo pigpiod # start the pigpio daemon pigs pfs 18 1000 # set 1kHz PWM on GPIO 18 pigs prs 18 1000 # set duty cycle range 0-1000, (same as micros) pigs p 18 500 # send 500 micro pulses pigs p 18 200 # send 200 micro pulses pigs p 18 700 # send 700 micro pulses

Experiment with the pulse lengths.

Improve this answer
1
  • Thank you very much, your suggestion has been really helpful. Commented Feb 8, 2017 at 10:11
2

Thanks to the comment from joan I was able to make it work and I want to share my solution. Apparently it's all about calibrating/initializing the ESC.

In my example I've used the library PIGPIO that you can find at http://abyz.me.uk/rpi/pigpio/

Once you install the library and start the daemon with

sudo pigpiod # start the pigpio daemon

you're ready to send signals to the GPIO pins. In my case I set the frequency to 1Khz and the range 0-1000

pigs pfs 18 1000 # set 1kHz PWM on GPIO 18 pigs prs 18 1000 # set duty cycle range 0-1000, (same as micros)

Then you need to find the right pulse in order to initialise your ESC. After many attempts I found the value 155 was good for mine.

pigs p 18 155 #send 155 micro pulses

This initialises the ESC and you can hear a long beep indicating the ESC is ready to work.

From now on any value in the range 165-300 let the motor move at a specific speed (the steps are 5 micro pulses, so 165-170-175...)

Hope it helps someone else as well.

Improve this answer
1
  • Just a couple of notes. You can use servoblaster and RPIO.GPIO as well as pigpio to control servos/ESCs. The pigs utility is useful for testing. If you need better resolution you can start the pigpiod daemon with 2, or 4 µs steps (-s option). Servoblaster and RPIO.GPIO will have similar options. Commented Feb 8, 2017 at 10:38

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.