Holding a position in our arm

[Ben Englert]

You can't move the arm at a single hardcoded speed and then suddenly reverse it when you pass your target - you will overshoot, as I'm sure you've noticed. While full-fledged PID (PD, anyway) control would be best here, I understand you're short on time so you can implement a rudimentary version of P control like this:

You will need a PWM-limiting function that takes an integer and bounds it between 0 and 254, because otherwise the unsigned char that representes a PWM setting will roll over and you will find your motors moving backwards.

targetVal = 180;
float pGain = 0.5;
int sensor = Get_Analog_Value(foo);
pwm02 = pwm_Limit((pGain*(targetVal-sensor))+127);

And then, just tweak the pGain up or down in small increments until your arm movement is acceptable.

Again, PID feedback is great, so if you have the time to do it properly I definitely would, but you can get away with this in a pinch.