Problems controlling servos

[PauliusLiekis]

I purchased 4 MG90S servos, Raspberry pi and 16 channel servo driver and I'm having problems making servos rotate full 180 degrees. I used sample Python code from the tutorial, modified frequency to 50Hz and servo_min/servo_max to 205/409 (I also tried 250/500 - that's what you get if you used INTs to calculate those values), but servos seem to rotate only ~80-90 degrees total. Physically I can rotate it full 180 degrees (although it isn't easy). If the physical angle is (-90 to 90), then sending 1ms/1.5ms/2ms signal will correspond to (-90/-45/0) compared to physical angle on my servos.

I tried using C++ code - same results.

I tried controlling a servo through RPi GPIO pin by emulating PWM signal using code like this:

Code: Select all

while (True)
    GPIO.output(pin, 1)
    time.sleep(t)
    GPIO.output(pin, 0)
    time.sleep(0.02 - t)

I get the same results.

Any ideas why my servos won't do full 180?

[adafruit_support_bill]

Do all 4 servos behave the same?

1ms/1.5ms/2ms signal will correspond to (-90/-45/0)

If you extend the range of pulse widths, does the movement range increase at all?

[PauliusLiekis]

Yes, all servos behave the same.

The servo min/max seem to be close to border values, i.e. if I increase to 450/150 the servo stops reacting to the signal.

BTW: it looks like 200/400 range is mapped approximately to 90 degrees, because if send signals 220, 240, 260, etc, I can see that the servo moves 10 times, each time moving roughly 1/10th of the 90deg rage.

[adafruit_support_bill]

Yes, all servos behave the same.

Let me check some servos from stock and see if we can reproduce that here.

[adafruit_support_bill]

Update - I have some servos here now & will be testing them shortly.

[adafruit_support_bill]

OK. I was able to reproduce the problem exactly as you described. Looks like the servo control loop is out-of-whack for the whole lot. We'll have to straighten this out with the Mfgr.

In the mean-time, you can contact [email protected] with a link to this thread, and we'll refund you for the servos.