Synchronizing the speeds of two DC motors

[Molectric]

Hello,

I have a project where I have to synchronize the speeds of two DC motors, the master motor and the slave motor. I will have to manually adjust the speed of the master motor and the slave motor should follow the speed of the master( They should both rotate with the same speed). I would like to know if there is a specific reference on motor speed synchronization theory that anyone might know.

I have tried to google the topic, but failed to find a suitable reference on this.

It is a requirement that I use a dsPIC microcontroller. Both the motors will be driven from separate PWM output port pins of the microcontroller. What I would like to know also, is how to verify that the motors will not be driven from the same signal, without using wireless control to show that the slave DC motor is indeed following the master DC motor.

This is my first time working with motors and having to control them.

 

[FvM]

if there is a specific reference on motor speed synchronization theory

I don't see a field of "motor speed synchronization theory". It's all about basic control theory.

how to verify that the motors will not be driven from the same signal

I don't understand which problem you are referring to. You will in fact achieve best dynamic behaviour if the setpoint signal is fed to both controllers in parallel. Making one controller follow the other involves a systematical asymmetry which should be avoided if ever possible.

 

[Molectric]

It's all about basic control theory.

At the moment to me the control is not that basic. If you know of any reference that I can use please help. The reason for the references is that it will help in providing proper documentation of the whole project, as my evaluation is based on a working system and a good technical report of home I designed and implemented my system.

I don't understand which problem you are referring to.

I am referring to when demonstrating my system to the examiners. How do I show them that changing the speed of the master motor to 200rpm ( for example) will make the slave to follow with the same 200rpm. There should not necessarily be a delay in the slave motor changing speed. A suggestion was that I use a wireless control for the slave motor, which is as the master motor speed changes are made synchronization with the slave motor speed will be done wirelessly. In this way I would have proven that I am not feeding the motors from the same PWM signal. However because I am not good with microcontrollers (programming them) I do not want to use wireless communication as the control design and implementation of the project is already too much for me. Hence I needed a detailed theory on motor speed synchronization.

 

[albbg]

I think you could try using a PID (Proportional-Integral-Derivative) controller. The two inputs will be the two speeds while the output will be sent to the slave motor PWM controller.

Of course the two motors have to be both equipped with a tachimetric dynamo (or an encoder), in order to sense the istantaneous speed.

The PID can be realized either in hardware (a board with opamp properly configured) or in software. In this last case you need to acquire the two tachimetric outputs and the sampling time will limit the maximum acceleration of the master you can follow.

Usually a certain amount of time has to be foreseen to tune the three PID parameters and avoid instability. Roughly, the proportional constant will play a major role while the derivative will improve the behaviour during high acceleration (e.g.: starting from zero speed) and the integral will remove a static error (f.i. a DC bias due to imperfections in speed sensing).

You can prove you teachers that the motors are not driven by means of the same signals, playing with PID constants, then modifiyng the speed response ogf the slave motor with respect to the master.

I don't think you need wireless control.

 

[Molectric]

You can prove you teachers that the motors are not driven by means of the same signals, playing with PID constants, then modifiyng the speed response ogf the slave motor with respect to the master.

What I understand from PID control is that the control constants are adjusted such that the response signal approaches the set point quick enough with less overshoot and oscillation as possible. So you (albbg) are saying that I should run tests with different, Kp, Kd and Ki values and record the speeds of the motors. By showing that the system responds differently (maybe with other/different parameters the slave may not correctly follow master) with different Kp, Kd, Ki parameters I would have then shown that the motor drivers are not fed with the same signal.

Please let me know if what I am saying impractical and wrong. Anything that would lead me away from using wireless communication would be gladly appreciated.