SIMPLE 3 Neo Drive Gearbox [Rev 2]

Rev 2- switched to gears for reasonable reduction and general improvements.

I look forward to hearing feedback as I continue to iterate.


I’m nervous about hanging motors over wheels like that, since we got knocked out of Champs elims in 2018 due to an opposing robot running into one of our drive motors just right. Bent the motor inwards, and killed our driving pretty much entirely.

Having a single plate holding the middle gear worries me, but I guess the pinions and output gear are holding it in place radially. Interesting idea!

1 Like


How are you aligning your plate to your tube? Clearance holes aren’t really adequate. My first thought is to counterbore the plate to the point where the bearing OD itself sticks into the tube and use that to align with the other bearing on precision holes machined into the tube that are presumably inline.

Also, my personal preference is screws and nylocks rather than tapping holes in a plate.

I have the same concerns about cantilevering a shaft/gear.

How do you keep the middle gear from sliding along the bearing?

Hanging motors over wheels has been done for years by many teams. Especially this year with the high bumpers, it was easy to protect them from harm. I would be equally as worried about another robot reaching an extra 2" and hitting motors that aren’t flipped. The plate could be made 3/8" thick or more to help resist bending though.
+1 to counterboring the plate more. You’d probably be fine without that, but better safe than sorry I suppose, especially with #25 chain in there. Nylon-patch screws are a good alternative to nylocks.

Interesting design. Out of curiosity, what wheel size and gear ratios is this running? Also, for the middle gear, is there a bearing in the plate or have you just bolted the hex shaft onto the plate itself? I’m guessing the latter, as there appears to be a bearing seated in the middle gear already. Very curious as to how that would hold up to a seasons abuse, as I can think of a few scenarios where that method could help me in packaging some designs…

Your reduction isn’t anywhere near high enough, run it through JVN. You can use counterbores to set the bearings flush. The chain will probably interfere slightly with the mounting bolts. The top gear isn’t fully retained (will slide towards the motors). May as well use a third neo mounting screw. Clearance between wheel and motors should be at least 1/4" if possible, can’t see if it is or not

With esimated gear sizes of 14 teeth and 56 teeth and a 4 inch wheel that ratio ends up getting them around 17 fps. That’s well within the realm of fast but acceptable drivetrains. If that’s a 3.5 inch wheel the speed is around 15.

I think people may have gotten to used to the multiple-gear reductions in shifting gearboxes, or those that were done for positioning of the motors etc. So when they see a gearbox like this their immediate response is that the reduction isn’t large enough. It is easy now to make a single reduction drivetrain like this one within a wide range of ground speeds, especially with the lower tooth-count pinions vex has made available.


If I were making this gearbox, I’d probably make that lower interfacing gear out of steel. It’s pretty low to the ground and could be a pain to swap once it’s in an actual FRC robot with other stuff near it if it gets damaged.

This is definitely a neat concept. I’d have some hesitation of cantilevering everything off the gearbox plate, but you can always design up a very minimal support plate as a backup plan that could use your existing holes, standoffs and longer bolts.

Some other things I’d look at -

  • Using the 32dp gears, trying a 5:1 reduction overall and see what that looks like - 20t CIM pinion to 100t 32dp gear.

  • Using the 9t CIM pinion gear against that 56t gear with a 2 motor setup if 3 is too crowded. With a 3.5" or 4" wheel this is an extremely reasonable speed. Now you’ve got me thinking about possibilities :thinking:

  • Design for maintenance / accessibility. Can you fit tools and swap items in a few minutes? How much clearance is required to do that between stuff inside your robot vs. the gearbox itself?

Nice work! Keep cranking at it.

1 Like

Ryan - you’ll find that you can make a single gear reduction for pretty much any reasonable ground speed you want with the new pinions. The only thing you have to insure is that your wheel is larger than your larger driven gear. Ask me what I worked on this summer…


4 NEO drive gearbox?

It’s an 11:54 ratio - plenty reasonable for a drive gearbox.

1 Like

Why Tom, what did you work on this summer?

:joy: Our head mentor worked on single reduction gearboxes using all the new pinions from vex. They are nothing ground breaking, but they are definitely lighter than anything you can buy. Also found out the hard way that while the bolt mounting circle may be the same, cims and minicims have just a slightly larger diameter than Neos. We found that out after the version 1 plates had been cut. In addition when Craig drew them he integrated them into the side of the frame rail. This year is the first year we’ll be able to do that type of fancy machining, since we’re gaining some new capability. We’re all pretty excited to be able to make our own gearboxes.

The simplicity of marcus’s design above reminds me very much of what we are building, though our axles are supported on both sides.