We like to use Denso window motors for mechanism arms because their worm gearing prevents backdriving, eliminating the need for a brake to hold the arm in a raised position. The window motor speed is adequate for arm rotation, but it normally lacks the required output torque. In the past we’ve used chain and sprockets to increase the torque output. The odd shape of the window motor and output coupler required multi-part custom brackets and spacers to properly align the chains and sprockets. In Aerial Assist we wanted to use window motors to rotate our intake mechanism. We designed a chain and sprocket system that worked, but we were worried that it wouldn’t be robust enough to survive the expected heavy defense in that game. We had a lot of old Toughbox parts and a good 3D printer so the Window Motor Gearbox was born!
You can download the gearbox from GrabCAD. There are three 3D printed parts in the gearbox: the housing, output coupler and a bushing. The housing integrates motor mounting and gear alignment into a compact single part. The output coupler mates the window motor splines with a small hex shaft. The bushing captures a bearing that mounts to the aluminum mounting plate. Mirrored housings were made for right and left side gearboxes. This two-stage gearbox has an overall gear reduction of 12.8:1. The gearboxes functioned perfectly and survived the brutal defense played at the Hawaii regional. A post-regional teardown showed only one failure, a crack in the 3D printed bushing. I suspect that crack occured because the fit with the bearing was too tight.
The gearbox worked so well that we used the concept again for our intake arms in Recycle Rush. We only needed a single-stage 4:1 gear reduction for this application. The gearboxes performed well again although one of the housings did crack which we quickly swapped out with a spare. I haven’t tried to analyze why this housing cracked. Files for the single-stage gearbox are here.
We’re running low on our supply of Denso motors and Toughbox parts so I’m not sure if we’ll reuse these designs in the future, but I can see easily adapting this concept to other worm gear motors and maybe even mating them to a Versaplanetary gearbox.