I would like to know how to synchronize two (nearly)-identical DC motors (approx. 1 Amp/12 VDC each) with permanent magnet, while they are driving on the same surface (railroad Track). The problem is that 2 motors of the same brand and type always have somewhat different characteristics at different speeds, resulting in (unnecessary) heating of one of the engines and its bearings. I'd like to sync them in an elect(ron)ic way as simple as possible. Thanks for help. A.

  • $\begingroup$ I am not sure what you mean by "synchronize". Are you saying you need them to run at the same speed? Could you explain what you mean by "unnecessary heating" and why you think this is happening? What are you using to power these motors? Are you running them open-loop (apply voltage and they go) or closed loop (with some kind of velocity/position feedback)? $\endgroup$ Feb 14, 2017 at 20:49

2 Answers 2


Answer to: How to synchronize the motor

For a precise synchronization of the two motors (electronically), a closed loop is required:

  • The rotation is captured by a sensor
  • The sensor input a microcontroller
  • The MCU drive the motor

The typical mechanism consists of a few permanent magnets on the motor rotor, which field is detected by a hall-effect sensor.
An MCU with a Analogic-to-digital converter would sample this input at high frequency (at very least twice the maximum RPS of the motors).
The MCU drive the motors, this depends on the type of motors: for a simple DC engine, the electric circuit is pulsed (PWM) to achieve the correct speed without reducing power.

Answer to: What seem the problem

The rail contact against the wheels naturally synchronize their rotation, trying to synchronize front and rear wheels electronically would just be useless.

If any of the two motors overheat compare to the other, it is probably a malfunction of some component (motor or driver circuit). I suggest swapping the motors and see if it's the motor or the driver. In any case, replace the part if needed.
In most of the cases, a little difference is acceptable.


I do not know if you are still interested in this, but I started working on this issue right now and found two solutions, principally one drive is master and another is set to follow it either as position control (I preferer this) or as torque control. I have found these on this topic:

Equipment. 2 x Control Techniques Unidrves (Whatever size) 2 x 1024 PPR Encoders (Compatible with Unidrive) 1 x Control Techniques Second Encoder module

The encoders go on the motors. The "Slave" Drive is to be fitted with the 2nd encoder module.

The encoder signals from the master motor is then also taken to the 2nd encoder Module on the slave drive.

The UNIDRIVE has pre-set macros for use. The slave needs to be set up for the digital lock macro.

Then, the slave will follow the master according to position (not speed) so that they will be synchronised with less than a degree of rotation.

The following ratio is also setable.



The Master slave configuration is basically used for load sharing purposes when 2 identical motors connected to two different drives are coupled to a common load e.g. pinch rolls in Cold rolling mills as well as some transfer cars.

The underlying concept is One drive is defined as the Master and is configured for running in the Speed Control mode whereas the other defined as Slave is configured for running in Torque control mode.

https://support.industry.siemens.com/tf/WW/en/posts/synchronising-with-two-motors/45018?page=0&pageSize=10 https://support.industry.siemens.com/tf/ww/en/posts/what-is-master-slave/45039/?page=0&pageSize=10#top




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