Steps to "Hack" a Dynamixel Motor
Work done by: Carlos Prados and Mateo Agustoni
Either because a Dynamixel motor has burned out or because we want to increase its power, in this article, we present the replacement of the inner DC motor of one of them.
In this case, we have used Dynamixel MX-64AT, whose inner motor reference is Maxon RE-max 416440, to be replaced by Maxon DC-max 5308419. Unfortunately these last ones were significantly bigger than the original ones, reason why we decided to modify the servo motor shell in order to make them fit.
Notice the pinions were replaced by some 13T 0.3M copper ones, with the needed 2mm inner diameter that works with the motors.
These are the steps to perform the “hack” process:
- Open the back shell by taking out its four long screws
- Remove both screws that hold the electronic module
Open the front shell and loosen both screws that hold the motor
- Put back on the front shell to prevent dropping any gears and take out the motor-PCB module.
Using the NEW DC motor as reference, carefully file wider the motor hole until it fits a bit tightly. We recommend covering the pinion hole to avoid messing the gears with plastic residues, otherwise you’ll have to clean them up later.
Pull out again the front shell and drill a hole for the pinion, which is going to work inside so it must be at least 6mm diameter.
- Detach the old DC motor from the electronic module and solder in the new one.
You can now fit in the motor and PCB back, screwing them and closing the front shell. Make sure the pinion gets in good contact with the rest of the gears.
Some more room will be needed to close the back shell, so drill it until the back of the motor fits through.
- Finally, screw back the four long screws and cover the new holes to prevent dust coming in. You can use either a simple sticker or design a 3D cover that fits your application like we did.
This modification leads to a significant improve in maximum torque. Dynamixel promises a theoretical performance of 6Nm @ 4.1A, while our tests peaked the original motor at 3.46Nm @ 4A. Same tests on the modified motor showed up of 4.24Nm @ 2.7A, unveiling an increased torque with a reduced power consumption.
Results for both motors (previous and hacked are shown in the following picture in the left and right respectively):