Preload Chain-bar idea.

VEX V5 Technical Support
1

So I was thinking, and I know I could just test this but I don’t want to waste that much time programming this just for it not to work. Could you use potentiometers to hold a chain-bar at the correct height to get pre-loads. I think it would work something like this:

while(Btn6U = true) //while button is pressed
{
if(SensorValue[potentiometer] > 150) // if arm is farther than a little less than straight up
{
motor[armmotors] = -127; // then arm goes down
}
else if(SensorValue[potentiometer] < 90) // if arm is less than straight out
{
motor[armmotors] = 63; // then the arm goes up with lower power
}
else if(SensorValue[potentiometer] < 40) // if arm is lowered all the way, or almost all the way
{
motor[armmotors] = 127; // then the arm goes up with full power
}
else // if none of the above are true
{
motor[armmotors] = 30; //then the arm uses a little power to counteract gravity and stay in place
}
}

assuming the values are correct, could this work.

2

If you mean match load and the idea it to keep the arm at the right height, then yes, absolutely, go for it. I’d suggest using a simple P-controller over your hand-coded discrete bands, but you can go full PID if necessary.
Just keep in mind that the pot doesn’t read in degrees, it rather maps its movement range (about 260deg) to the analog input range of 0-4095. Thus about 15 units per degree.

3