Prototyping rotary stringed instrument bow with Pololu wheels

HI everyone and thanks for checking out my first post. I am prototyping a rotary bow for playing stringed instruments using Pololu 90mm wheels with the D-shaft fitting. All the wheels I’ve ordered so far have a beveled edge that is too narrow for my purposes, so I had a 3D file altered to create a wider and flat outer rim of 1/2" (12.7 mm). You can see that wheel in action here: Scott Hampton on Instagram: "Super jazzed about this new wheel that a friend 3D printed for me!! it’s the closest thing so far to a horse hair bow, which, as I explain in the video, is just a happy accident! #rotobow #bowedguitar #guitarviol #diyinstruments #instrumenthack #uniqueinstruments #happyaccident #3dprinting #prototyping"

I sent a message about this to and never received a response so I thought I would try here. I’m wondering if it’s possible to have some additional wheels printed to these specifications and what materials might work for this application? I found that the PETG material is better because it’s a bit softer than the original wheels, and the PETG strands have a texture similar to a horsehair bow.
I also noticed that the 3D file I found for the 90 mm wheel actually has a flat outer rim. Is that something you can buy off the shelf or just an anomaly in the design file?
Eventually I would like to develop some variable speed functionality, I was thinking using a pressure sensor but I think I need one that has more than just positive and ground leads? The controller I’m using now to control speed has three connections so it doesn’t seem like it would work with a standard ribbon pressure sensor.
Thanks for any insight you can provide!


I am sorry that you did not receive a response to your email. To clarify, our wheels are injection molded, not 3D printed, and we do not offer custom 3D printing services.

It is not entirely clear to me what bevel you are referring to. The outer profile of those wheels is designed to be flat, but there is a small amount of draft added to help release from the mold (along with a fillet on the edges). Please note that the 3D STEP models we provide under the “Resources” tab of the wheel’s product page does not show this draft, and the wheel is merged with an approximation of the rubber tire after it has been stretched over and installed.

As far as adding variable speed control, if you can post more details about what you are using now (i.e. controller, motor, and power supply), we might be able to offer some suggestions.