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I would like to synch two small DC motors so they run at the same rpm but in opposite directions. Is there a straightforward (and light) way to do this from a single battery pack? My goal is to turn a pair of props for a model aircraft. Obviously the weight is an issue due to it being an aircraft and the reason for the same speed rotation is to maximise stability.

Edit: I dunno on the subject of brush vs. brushless because I haven't even started this. It's just that I realised the synching is important because this is a free-flight model. It's an A-frame https://amablog.modelaircraft.org/amamuseum/tag/a-frame-twin-pusher/

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    \$\begingroup\$ Define the instability caused by speed mismatch then detect the instability caused by speed mismatch then modify one motor's speed to reduce instability. Rinse and repeat. \$\endgroup\$
    – Andy aka
    Commented Jun 26, 2019 at 14:07
  • \$\begingroup\$ If I understood your problem correctly, you have one motor output from your RC receiver and want to hook up two motors to it. You can simply do this in an antiparallel fashion. Given the motors are identical and the countertorque from the propeller is identical, the speed will be the same to a very small difference. \$\endgroup\$
    – Janka
    Commented Jun 26, 2019 at 14:22
  • \$\begingroup\$ Are these brushed motors, or BLDC? \$\endgroup\$
    – Phil G
    Commented Jun 26, 2019 at 14:33
  • \$\begingroup\$ I don't think the RPM matters, you want to control your airplane, so look at the system as a whole instead of your arbitrary definition of a partial good control which you believe is same RPM. - Why don't I think that RPM matters? Or rather, why do I think that other factors play a larger role? - Size of propeller, direction of wind entering the propeller, distance from center of gravity for each propeller. You might be able to sync them, but you're probably going to control your airplane just as good if it wasn't synced. \$\endgroup\$
    – Harry Svensson
    Commented Jun 26, 2019 at 16:42
  • \$\begingroup\$ This is really unnecessary, but it is also a solved problem especially with brushless. This belongs somewhere like rcgroups not here. \$\endgroup\$
    – Chris Stratton
    Commented Jun 26, 2019 at 17:10

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Even with the same RPM, props are not identical so mechanically linking them or using putting encoders or tachs (which would require both a motor and a ESC that can accept them) won't work. I would use a yaw gyro or side slip sensor. Or trim carefully and rely on your horizontal stabilizer.

Note that brushless ESCs, especially helicopters ESCs have an internal speed governor that you could also use. Trimming still required though.

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  • \$\begingroup\$ I am coming round to the "trimming" solution as the motor speeds are not going to be the only asymmetry going on. \$\endgroup\$
    – NickM
    Commented Jun 26, 2019 at 16:16

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