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After a week of searching...

I have built a robotic arm run by a Pi 3. It has 5 servos, as well as a stepper motor. I have code written see, (Pastebin). And I am not able to get each servo motor to move incrementally when the key press function is called. I can make the servos move to positions, but not move in between whenever I press the button.

Ideally the code would call a servo up function, and the servo would move up by increments of 20 every time the function is called.

This is the main focus:

def shoulder_up():
    for spwm in range(1000, 2000, 20):
        pi.set_servo_pulsewidth(shoulderpin, spwm)
        time.sleep(0.4)
        pi.set_servo_pulsewidth(shoulderpin, 0) 

When this is called, I need the servo to move a small increment to the left. This means closer to a 1000 pwm signal value. I cannot determine how to make it move the increment every time based on the previous movement. The code currently just moves the servo through the defined range.


Update:

I would like to try to use this, but I cannot get the variables to change.

def shoulder_up():
global spwm
global nspwm
spwm = nspwm
pi.set_servo_pulsewidth(shoulderpin, spwm)
nspwm = spwm + 20

Every time the loop runs, I want spwm to change and become 20 higher. For some reason I cant get it to change. It goes to 1520 every time.


Any help on this would be appreciated. Yes my code is in alpha, so it is messy and a little nonuniform.

  • 1
    You seriously want us to review over 200 lines of your code? Could you try to isolate the problem to a smaller section of code please? – Darth Vader Jun 9 '17 at 14:29
  • Yes. Of course. – Dylan Hewitt Jun 9 '17 at 14:33
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Did more testing, and here is my final code. I determined that I was failing to reference a global variable properly. I have included the final code for those who are in the same boat. PasteBin Robotic Arm Thank you to those who tried to help!

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Seems like you need to define some persistent servo position variables, and then increment/decrement them (be sure to clamp the positions to limits when inc/dec)

for example something like:

servo_positions=[0,0,0,0,0]

def clamp(n, minn, maxn):
    return max(min(maxn, n), minn)

def inc_servo(nServo):  #nServo 0-4
    global servo_positions
    newPos = servo_positions[nServo]+10
    servo_positions[nServo] = clamp(newPos, -90, +90)

now in your key_loop, when '+1' pressed use inc_servo[1]

  • I am trying to follow what you have done. What variables do I need to change to reflect my setup? – Dylan Hewitt Jun 12 '17 at 12:27
  • I have tried to implement but to no avail. Here is what I have done. [pastebin.com/0hG9j2Xb] – Dylan Hewitt Jun 12 '17 at 12:54

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