I need to connect two servo motors (with internal position control) to rotate one shaft (to control its position), is that possible? and how to avoid synchronization problems?

the servo motor

I am making a robotic arm, my problem here is that the servos are internally controlling position, which means that if only one of them arrived to the target and the other one haven't yet, it will still try to get to it (even if it is just 0.5 degree away).. i am afraid that this will make the system vibrate around the required position , or make one motor to continuously drag current, or it might hurt the servo shafts and gears, I am thinking of using pulleys and a synchronous belts to connect the servos to the shaft, this could absorb the bad effects. so please let me know if you consider this to be safe, or if there is something i can do to improve the performance and the reliability of the system.

  • $\begingroup$ Welcome to Robotics user17023, but I'm afraid that it is not clear what you are asking. We prefer practical, answerable questions based on actual problems that you face, so it's a good idea to include details of what you want to achieve, what you tried, what you saw & what you expected to see. Please take a look at How to Ask & tour for more information on how stack exchange works and work through the Robotics question checklist to edit your question to make it clearer. $\endgroup$
    – Mark Booth
    May 22, 2017 at 12:07
  • 1
    $\begingroup$ He wants to use two motors to drive one shaft. It's a rather specific and answerable question imho. $\endgroup$
    – FooTheBar
    May 23, 2017 at 6:23
  • $\begingroup$ thank you for your attention.. I edited the question and pleas let me know if it still not clear $\endgroup$ May 23, 2017 at 11:14
  • $\begingroup$ Thanks for your edit @FadiALMasalmah but it would be really useful to know why you are trying to connect two servos to one shaft. Are the two motors to rotate the shaft in a single plane, or are you trying to get multi axis movement with them? Are you attempting to increase torque, speed, movement range, redundancy or have some other effect? If you connect them via a compliant coupling, you will most likely get the effects you describe, so if you need higher torque/speed/range, you may be better off selecting a single motor which has a higher spec rather than jury rig two motors together. $\endgroup$
    – Mark Booth
    May 23, 2017 at 14:18
  • $\begingroup$ I am making a robotic arm that can play table tennis as graduating project, I just have to minimize the cost and time, and there are two motors available, so I have to use them to get the required torque.. I am thinking of using pulley and a synchronous belt to connect the servos to the shaft, this could absorb the bad effects. $\endgroup$ May 23, 2017 at 21:02

1 Answer 1


One bigger servo is better.

You can just hook them both to the same shaft. If you give them the same command, they will fight each other a bit and waste some energy but should work. To improve performance you can calibrate one motor to the other. For each command value of motor A find the command that moves servo B to the same position.

  • $\begingroup$ thank you very much for your answer, it is helpful.. but I edited the question to make it more precise (the internal position control issue).. could you pleas check it and see if you have more details to add!! $\endgroup$ May 23, 2017 at 8:29
  • $\begingroup$ Could drive both with same motor specs but one at a lower voltage than the other, yea? $\endgroup$
    – nimig18
    Jul 16, 2021 at 14:44

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