Compact Flipped NEO Gear in Tube Gearbox

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This is a near-complete concept that stemmed from one of those “what if” moments that seemed all too common during the NEO gearbox craze a few months ago. Inspired partially by a few other designs, NEOs are placed between the wheels outside the frame of a WCD, and the 1st stage of reduction is inside the frame tube. This flipped configuration also made Vex’s ballshifter* mechanism package a bit better as the output shaft than in a “standard” gearbox.

Some numbers:

  • 6.6 fps L, 19.3 fps H (adjustable, to an extent) anticipating 2014-type game
  • 8.95" from back of NEO to back of air cylinder
  • 5.65" from inside face of frame tube to back of air cylinder
  • 5.7" horizontally from edge to edge of the plates
  • I’m not 100% sure how light this is, but I think “very” is a good estimate if you exclude the frame tube

This was intended to be used on an actual robot as a compact replacement for the VexPro Ballshifting gearbox, and was designed with our machining capabilities in mind. Everything can be made on a manual mill if you don’t care about lightening too much, plus three parts that should be turned (which you could get around if necessary).

Seeing the uncertainty of NEOs and the added complexity of making this design work with 6" wheels, we decided to shelve the concept for the 2019 season. There are a few modifications I would have made for assembly purposes and gear ratio adjustments before slapping this onto a robot, but those probably won’t happen anytime soon. Feel free to adapt this design as you wish, and I can provide CAD files if requested.

*For those concerned about using the ballshifter as an output stage: we were unable to force the balls to slip or otherwise fail on a test chassis with ~200lbs of normal force on 8, 4" colsons and 6 CIMS with aggressive, high-speed shifting and pushing on the field walls.


My biggest concern with this design is that all of the standoffs/axles are basically in a line, meaning there is only support in that plane. Any forces outside of that plane (like the normal force on the wheel) have little resisting them. I think adding additional standoffs at the top and bottom of the tube will help add support in the vertical axis to keep everything from bending under load.

Other than that, looks like a nice design!

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That was ours as well. Passing the standoffs through the tube and clamping against the inside face of the outer wall, as well as intentionally placing the standoffs with the maximum vertical offset from each other should alleviate most of the issue. Chain routing is quite an annoyance, but a third plate could be added on the tube face at the cost of ~0.5" of space inside the frame if absolutely necessary.

A few people were asking for CAD files, so I figured I would just post the Google drive link here as well.


Troy you’re a god.

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