[joelg236]

You can use a sensor (potentiometer, encoder, etc) to determine where the motor is, and use a control loop (PID, bang-bang) to keep it at that position.

Now, if there is a lot of weight on that arm / mechanism, you likely don't want to be stalling your motor, gearbox, etc. You could easily damage the components or brown out, as you said.

From a programming perspective, the sensor+control loop works, from a design one, be cautious of an application that requires this to keep something in the air. Could be fine, but be sure you're not headed down the wrong road.