Controlling a DC Motor via an analog PID circuit

Question

I am trying to design a 1 DOF copter as in this drawing:

For this circuit there is a stick connected to a DC motor and potentiometer. The potetiometer can be rotated. I need to control the position of the motor with analaog PID circuit using another potentiometer.

My PID circuit is as below:

The first potentiometer controls the angle. The output potentiometer should give feedback.

I am newbie and this circuit does not work, that means my motor does not work when I supply power.

I checked without the motor connected. There is a voltage and everything is okay but after connecting the motor, the voltage is zero and the system does not work.

Because of the pandemic situation, I cannot use the lab equipment to power supply. I think there is not enough current.

• How can I increase the current?
• How can I make sure the PID circuit is working correctly?

Some information my circuit components:

• All op-amps UA741cp
• Other component same with the designed circuit in picture
• My motor is 820 coreless brushed motor set 3.3V =35000-37000 RPM, 5V = 50000 RPM , Size:8 x 20mm, working current min = 0.15A, weight 6.5gr

Answer 1

To increase the current, I suggest to use PWM-signal by using output (voltage) signal compare with saw-tooth or triangle signal. Then you can feed PWM signal to Motor drive module or FET to drive motor. This PWM method produce less heat compare linear method.

^{simulate this circuit – Schematic created using CircuitLab}

If you really want to drive motor with voltage you can try linear voltage regulator with loss a lot of power to heat as follow.

^{simulate this circuit}

If you want to make sure that your PID control work currectly , you can test open-loop response with signal generator and osciloscope.

Answer 2

High current from an op amp with or without transistors?

As for testing. Break the problem down into sections and test each section. To test the control loop, that gets a bit tricky, so start with just the P term. Then add the I term. The D term is last. Adjust the coefficients at each stage.

Understand that adjusting a real PID system is not trivial, so expect to make mistakes.

Answer 3

This circuit works well for me. I use five LM741 op-amps and one power BJT for motor driving.