[Kevin Sevcik]

What you're describing is called open loop control. Programmatically, your control system has no idea what the arm is doing, so it can't stop the arm from moving or falling. All it can do is take the command you're giving it and send power to the motor to match what you're telling it to do. There's no loop of information, commands come from you, go to the controller and then to the arm. No information travels the other direction, thus the term "open loop."

To get your arm to stay in one place via programming, you must close this loop by providing your controller with information about the position of the arm. The controller then decides on its own how much power to send to the motor based on the information of where the arm is now, and the input of where you want the arm to be. If you want the arm to stand still, and the controller sees the arm moving, it will send power to the motor to stop the arm. This is closed loop control because the controller gets information back from the arm and uses this information to control how much power to send to the motor. There's an actual loop of information coming from the arm, affecting the power to the motors, which affect the position of the arm, which means new information from the arm, which changes the power to the motors further, which.... and so on. Closed loop control is the PID control you'll see people talking about here.

So, if you truly want your program to stop the arm from falling you need to add a sensor to the arm and connect this to your controller to implement PID control on the arm. Another option is to use one of the window motors to mechanically stop the arm from falling since these motors are not backdriveable. Your final option is to move the Brake/Coast jumper on your Victor 884 from BC to AB to enable dynamic braking. This will slow the motor down while the victor is in neutral. Unfortunately it slows the motor down more the faster the motor spins. This means it's not actually capable of stopping the arm from falling. It can potentially slow it down by a large amount, however.