Metal muscles exist, but robots mostly use motors, hydrolic, or pneumatic.
We will talk about motors here.
Your nice hobby type 130 motor and the like, brushed, and most brushless, with two wires, are dumb motors, with no feed back or control.
They run, roughly proportionally, to the power supplied. Traditional model trains run this way with a dial on the power supply. A fancier version of model train power supply...
Not really suitable to robotics, since we want precise control and feedback.
Stepper motors are a step up. With seperate coils in each pole, for which it has multiple. With decent controller, it can move with precision, to exact number of turns (built from adding the steps.) Provided there nothing is stuck, beyond measuring current draw, there is no way to tell if the movement train is stuck or slipping.
Then there are servos. With an encoder, it knows precisely how many degrees it had moved. This allows for precise movement and basic feedback on if those movement actually happened. So it can tell if the movement train is stuck. (or conversely, if the rotation is higher than what is expected on a load, we can deduce there is slippage.)
To prevent damage, the best solution is to add a load cell that measure the applied force at the end point. This can prevent damage and allows for full feedback.
7/29/26