We use dc motor to control the arm but when we released the button arm starts to fall. Motors have enough power but I need to change software. I tried to PID control but it didn't work. What should I try to prevent arm from falling?

Thanks.

PID control should solve this problem. What do you mean by "it didn't work"? Could you explain your steps precisely, and perhaps post your code?

Arm fall even though the PID.
nMotorPIDSpeedCtrl[arm] = mtrSpeedReg;
.
.
.
if(joy1Btn(6) == 1)
{ motor[arm] = 50;
}
else
if(joy1Btn(8) == 1)
{
motor[arm] = -40;
}
else
motor[arm] = 0;
This code didn't work ,arm was falling slowly again. Then I tried to give 5 instead of 0 (it was a really big mistake) arm starts to raise continously and slowly which shows PID works but it can't hold the arm same position.