Servos in reverse

Unfortunately the high torque servos I bought for the knee and hip joints turn in the opposite direction to the standard ones so either Marty falls over when he walks or he walks backwards when the left and right leg wiring is switched.

Is there a way to reverse the direction of servos in the firmware with calibration (I couldn't find this feature)? Is this likely to be added in a future release or do you have any plans to release the firmware source code so that improvements such as this can be added by the community?

Obviously I could flip the joints round but that would look a bit untidy and it seems such a shame when its only a few lines of code.


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2 Responses

GreenGiraffe OP

Thanks for the update Sandy. I switched his legs and flipped them round as one (or you could say put his head on backwards) which was easier than I expected. I first thought that I would have to completely disassemble each leg. Now everything's working well with the new servos: they no longer cutout. He can even follow a ball now.

I'm using the PowerHD 1810MG which have bit more torque compared to the kit servos. They fit perfectly in the mounts, although I wouldn't recommend them for people without a 3D printer as the servo horn is not interchangeable with the standard servos so I had to redesign and reprint the "servo link" (I can share the stl files if anyone is interested). Also the cable is only just long enough for the left knee. Once that is sorted they work very nicely.

20:27:30, 11th February 2018   |   Permalink   |   View Source
sandy STAFF

Hi there,

I'm afraid the functionality to flip motor polarity (and change scaling factors etc) is not exposed as a command to the outside interfaces yet. It's definitely something we should have, so I'll get it marked as an issue and scheduled for the next firmware update.

That's not really gonna help too much immediately for you though - so probably the easiest thing to do is actually to rotate the hip motors 180 degrees, so that the servos point to Marty's right rather than left. There shouldn't be much of a visual impact, and you can leave the rest of the leg as they are

Out of interest - which servos have you gone for?

All the best,


17:18:43, 03rd February 2018   |   Permalink   |   View Source