Kitbot with 8 inch wheels

Potentially very stupid question. My team is essentially trying to turn our 2020 kitbot into a kitbot on steroids for 2021. The first change we though of was trying to put on a 3 motor gearbox. However, when doing the CAD for this, we realized that the gearbox we chose ( the vexpro single speed single reduction one) makes our ground clearance pretty much zero. We would be open to using a different gearbox, but we don’t have a press, so the evo gearboxes are pretty much out of the question. So, the idea I had to fix this was to “hide” the gearbox inside the space taken up by the wheel so that we don’t smash it on things. However, it doesn’t quite fit within a 6 inch wheel. So, to the big question of the day, is it possible to use 8 inch wheels on the am14u4 chassis? The biggest potential issue I see with this is that it might elevate the bumpers out of the bumper zone.

Is it possible to use 8" wheels? Yes, you can…but you may need to rework your bumper mounting to suit. Engineering is all about tradeoffs.

Also consider Thrifty Bot’s 3-motor setup, which is derived from the Toughbox Mini’s gears and shafts. That should keep things fairly clear of the ground, and do so thriftily. I’d have to pull both into Onshape to verify the differences.


Related: Here’s a Thrifty plate up against a Toughbox Mini housing, aligned on the cluster and output shaft bearing holes (because they’re identical since TTB’s uses the AM gears)

So ground clearance should not be a further issue, though obviously it may create issues up top depending on your mechanisms.


Thank you so much! I think we’ll end up going with the thrifty bot gearboxes, because they shouldn’t cause any issues that I can think of off the top of my head, and solve the current problem. This is also actually ideal for us, because we bought a bunch of Toughbox gear reductions at the beginning of the season that won’t go to waste now!


If you do switch to 8in wheels, Make sure you pay attention to your gearbox ratios too so the robot is still controllable. With the stock gear ratio, 6in wheels will drive slower than 8in ones.


you can buy a press for less money than a gearbox, can’t you? :slight_smile:

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Bench vises also work as a makeshift bearing press

They can, but the results may leave a bit to be desired…

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Correct, though with six motors you should gain a tiny bit of acceleration.

The best way to determine this is to model it. The ILITE Drivetrain Simulator has been illuminating in how we make decisions on drivetrains.

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Please enlighten me!

Here you go.

Just a general observation…I can see not having an expensive piece of equipment driving the design strategy, but a press just doesn’t meet that definition, to me.

I should have been more explicit - a press which meets OP’s need:

That is, able to press an EVO pinion onto a CIM - 3 tons with 6.664+ inches throat height (5.912 for the CIM, 0.75 for the pinion).

(OP: another option is to buy the CIMs from AM with the pinion pre-installed.)

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We are aware of that option, but we want to use the neos that we have and didn’t end up using in 2020 because we built the drive out of the KOP without thinking about it, and didn’t want to change it

Would we have to cover up the spaces of the TTB gearbox? The main reason we didnt use it was we werent sure if it would be ruled a safety issue on the bot.

This would certainly be no more of an issue than anyone using a Vex clamp-on gearbox, or any other open or semi-open gearbox (e.g. the toughbox with two side plates and two open sides, and all of the EVO gearboxes). As long as it doesn’t reach outside the frame perimeter and/or isn’t likely to entangle people or other robots, open gears, chains, and timing belts are pretty normal, subject to your LRI of course. If you thought it was an issue, adding a bit of polycarbonate or other material to restrict access to the exposed gears is well within most teams’ capabilities.

If you’re looking for modifications for the kop drivetrain, I put together a set of upgrades you can find here – the biggest improvement you can make to the is probably tube axles and riveted nuts for axles and bumpers

I have a wraparound 3D printed cover designed that snaps onto the 4 spacers. I guess now is a good time to iterate it and put it out there :thinking:

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