My application is a small robot-ic head - lets say for a scarecrow. It is going to be moved around frequently, during operation too.

I obtained a lot of these "hobby" servos that are used in RC planes/cars/helicopters...

My problem begins here - when I tried to fabricate the head using the design I had in mind, the model came out heavier than I expected.

Now on paper these motors (TowerPro MG996r CLONES) have good torques, but I want to believe during operation they might burn out and I will be left with a dummy head in one hand and resignation in the other.

So I thought I will use 2 motors for one axis. The motors will have to be coupled but at the same time facing each other - which means they will have to run opposite to each other.

I am thinking of using some aluminium couplings on one of the motors to reduce backlash. Software will have to be modified to (as close as possible) send opposite signals to both the servos... so that their torque actually helps each other.

Now for my question: Does this all make sense? Or is it not possible even theoretically? Is it a stupid idea?

P.S.: I am using a Pi-zero W (ABSOLUTELY LOVE IT) and a PCA9685 servo controller board (clone again :( ) - for information.

Thanks a lot O' lovely forum. I am getting entertained and educated going through all of the posts, hope to contribute soon.


closed as off-topic by Chris Stratton, PeterJ, Wesley Lee, Voltage Spike, Dmitry Grigoryev Jul 25 '17 at 16:26

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  • \$\begingroup\$ Get some active cooling instead perhaps, heat sink + fan. \$\endgroup\$ – Harry Svensson Jul 25 '17 at 5:08
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    \$\begingroup\$ I'm voting to close this question as off-topic because it is about mechanical issues, not electronic design. \$\endgroup\$ – Chris Stratton Jul 25 '17 at 5:22
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    \$\begingroup\$ You don't want to try to get two servos to cooperate. First balance (and if necessary, counterbalance the head. Then if you're still worried, buy a stronger servo - lots of projects happen with the tiny ones, the "ordinary" ones are more powerful, and then there are the "giant scale" ones. Mounting the head on some bearings and using pull-pull cables or even a timing belt on 3d printed sprockets isn't a bad idea though. \$\endgroup\$ – Chris Stratton Jul 25 '17 at 5:24

Your difficulty will not be lining up the motors initially, or dialling in the opposite drive operation, it will be maintaining that alignment when faced by the mechanical and electrical position drift of the servos over time.

Servos don't have a torque output, they have a position output, though their torque when trying to get to that new position is limited. This means if the positions are mismatched beyond their deadzone, they will keep on driving, fighting each other, using power and getting hot. You would be creating the very situation you are trying to avoid.

If you have room for two small servoes, then you have room for one larger servo. Use a bigger one with adequate specification.


One possibility is to mount the motors one behind the other, both driving the same shaft through belts for example - this, at least, would avoid the need to invert the signal. Also, it may be easier to "adjust" for each motor characteristic that way.


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