Wheel Drive Motor Gearbox Swap for JPL Open Source Rover

It’s a lot of fun to run the JPL Open Source Rover across rough terrain, seeing its rocker-bogie suspension system at work. But it is possible to play too rough and break some gears in the wheel drive gearbox. Some rover builders on the forum who ran into this problem decided they wanted sturdier motors and upgraded all six drive motors to something bigger and beefier. I understand this upgrade was done for the JPL-owned example as well. But that can be an expensive proposition.

If a rover is not strictly required to traverse rough terrain, we can decide to stay with kinder gentler terrain. Returning to the official parts list we see they are Pololu’s item number 4888, 172:1 Metal Gearmotor LP 12V with 48 CPR Encoder. As of this writing, $35 each. The easy solution is to buy more of them but I hunted for a less expensive proposition.

My first question is: “Can we make replacement gears?” and I quickly decided it was not practical. These gears are too small for consumer grade FDM 3D printers to handle and demands more strength than 3D-printed plastic can deliver. I don’t have a machine shop with metal gear cutting equipment.

The next question is: “Can we buy replacement gears?” And I had no luck here as I didn’t know how to navigate the manufacturing industry landscape to find who might be willing to sell small numbers of these gears to individual consumers.

Following that: “Can we buy replacement gearboxes?” The best I found was a company selling them with a minimum order quantity of 1000. I suppose I could buy a pallet and go into business selling replacement gearboxes to rover builders, but that’s not my idea of entrepreneurship today. (UPDATE: While sharing this information to OSR forums, I found a vendor on Amazon(*) selling them at $16 each. For lowest cost, I also found a company on Alibaba willing to sell individual gearboxes as samples at $2.79 each.)

What’s left? Well, Pololu’s product chart shows item 3256 is the same motor and gearbox, but without the encoder. As of this writing, these are $20 each, a significant discount for not buying another encoder.

It offers a lower cost alternative to direct replacement. I had two broken gearboxes on hand. They correspond to the two front wheels on a rover that took too big of a drop off a curb. I bought two #3256 gearmotors without encoder, and swapped their gearboxes out with the rover’s two #4888 gearmotors with encoders, bringing the rover back up and running.


(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

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