loadmotorservo
Can a Servo motor (or any electric motor) be used as a load on a system ? meaning can it reprisent for example a certain dead weight ?
In the picture below you can see a motor driving 3 gears, to apply a certain load on the system could i put another motor on the other end ? will that burn the motor ? how would the load be applied should the second motor receive current ? or run in reverse ?
First, let's get straight that you are actually talking about small "hobby servo motors". The word "servo" has a different and general meaning having to do with a control loop method.
I didn't look at your particular hobby servo motors, but if they are like most others the unit includes a motor, position sensor, and some kind of electronics that performs servo control such that the motor is driven to a particular position. The usual means this is communicated to the electronics is by sending a pulse between 1 and 2 ms in length, with 1 ms indicating one end of travel and 2 ms the other. These pulses need to be repeated usually every 20-50 ms for smooth operation.
Due to the fact that these units perform closed loop control of the motor position, the power to the motor will be dynamically adjusted as needed to get to and hold the indicated position. The motor will automatically be driven harder when it is off position, or something is trying to force it off position. Depending on the exact servo algorithm, small deviations may not produce as much torque from the motor initially, but it may produce more and more force over time if a small position deviation persists.
The system is not about moving X degrees, but holding the motor at X degrees.
If these are typical hobby servos, you don't implement a PID loop to control them. That's what the servo controller in the unit already does. You simply send it commands what to do and it will drive the motor as necessary to follow those commands within its limits of speed and torque.
You misunderstand the implementation of a PID controller.
The PID controller wants to make its Error \$e(t)\$ equal to 0.
Your implementation determines which way the actuator goes.
Take setpoint 40 while actual 0 degree. The Error is 40.
Take kP to be 5, then U will be 40*5 = 200.
Your process, the motor controller, then outputs 200, in positive direction.
But setpoint -40 while actual 0 degree. The Error is -40.
When kP is 5, U will be -40*5 = -200.
Your motor controller then outputs -200, in negative direction.
If you invert this, the PID will output 200, but error will increase. Creating a loop until something clips or breaks.
Best Answer
Geared servo motors generally do not like being run in reverse. You may damage the geartrain. Simple DC motors are better for that, although not at low speed. Connect a power resistor across the terminals and it will dump energy from the shaft speed into the resistor.
You might be better off with a mechanical friction brake of some kind. Or dump the energy into a fluid. A set of paddles rotating in the air is a common small test load. For lower speeds and higher torque, put a paddle in a liquid such as water or oil.