pic: Flipped Vex Clamping Gearbox Omni Drive

The title may seem like a mouthful at a glance, but it really was the best name I could come up with for this idea I had earlier this morning. This is what I came up with after wanting something that was more low profile than the WCP SS Gearbox. I wanted something that didn’t take up as much height and interior space in a robot, something that was easy to fabricate, and something comparable in price to the WCP SS Gearbox. (That is a really tall order considering how affordable that gearbox is as well as how versatile it is in terms of gear ratios.) After playing around with multiple ways to do this I feel like this is a pretty good solution to what I wanted without going fully custom. The motors do not sit higher than the bumpers which are 1" above the ground. It really is hard to beat something this simple in terms of fabrication. This drivetrain should be pretty bullet proof, easy to work on, and comparably fast to some other FRC drivetrains. Feel free to post any questions you may have about my decisions in this design, as well as make suggestions to improve the design.

Our 2016 robot had chains inside the frame, similar to how you have the belts.
The chains being there really were annoying because we couldn’t mount stuff to this side rails without having to work around the chains.

Traction wheels on one end would make this a more viable machine in a pushing match. You could also potentially run the belts (or chain, which would work better with the 2"x1") inside the tube, freeing up even more space.

My team ran something similar in 2016, but with only 2CIMs per side, and was bulletproof, as you say. Maintanance was negligible, and space was abundant.

Nice work!!

I like the layout, ease of building, price.

I am sightly worried about using the clamp-on boxes in a drive train. We used them in our climber this year and they worked great for that, but we only used them 4 seconds a match. My main complaint is you could not really get them tight to the frame. The nuts are recessed in the plastic (a molded hex) and when you try to snug them up the nut could start spinning even after being pretty careful. Once you got to that point they became very difficult to get on an off because you could not put a wrench on them and the nut would just spin.

I’m sure there are people on here that have used them in drive trains and can comment on the durability or ability to stay located when clamped under a belt or gear load for an entire match.

Also don’t forget to remind programmers that the middle motor needs to turn opposite from the others.

Overall I like it and would be interested in the results if you try to build and test one of these.

We ran them in our drivetrain throughout the Northern AZ and Colorado Regionals, and at champs. We kept that machine running through the first part of this build season for demos and drive practice. The clamping boxes gave us no grief, ever. If there was a year for something to break that was going to break, Stronghold was probably it.

Here is a link to a video of our 2016 practice bot that shows the gearbox configuration pretty well.

Pictured in this setup is 35 chain with 12t sprockets. They are just modeled in the assembly as an extrusion to simulate weight and space taken up. I see your concern with not being able to mount stuff to the frame easily but there are ways around this that I am fully confident in dealing with. I have run a WCD style drive similar to this (in terms of chain and wheel placement) for many years.

On paper chain in tube looks good but I am still not comfortable trying it. I don’t like having to worry about something going terrible wrong, like having rivet ends get stuck in the tube with the chain because students (or myself) forget it is in there.

I agree that adding traction wheels to one side would make it more viable at pushing but I disagree with “pushing” defense in general. There are much easier ways to play defense that DO NOT involve “pushing matches”. Also all omni drives are very maneuverable when driven well, and can deliver just as much functionality in most situations.

In regards to making sure one motor spins the opposite direction flipping one signal in code will work, but the easier solution in terms of logic that still provides the same function is to flip the leads on the motor controller going into the motor. We like to send the same signal to the motor controllers on the same side of the drivetrain. We make custom pwm splitters so we use less pwm outputs on our rio.

This looks super clean! Traditional WCD for a much lower price, especially given that there’s only 2 bearing blocks. I’ll be sure to try this in the offseason if I can.
The only small downside I can see is having to use 6 miniCIMs instead of 4 CIMs, which adds a little bit of weight and cost due to the setup if somebody doesn’t own 6 miniCIMs.

Any worry about the bumpers bowing in after enough hard hits and putting stress on the CIM motor body? I would be a little worried with outside stress on the plastic clamping gearbox.

Nice design, Cooper. It should be fast and easy to build sufficiently accurately and get working properly.

If you are fast and maneuverable enough, pushing matches become irrelevant. I also don’t think spending the whole match pushing other robots around and not participating in the scoring does not match the style of play that your team prefers.

What is the length of the standoffs? If it is 2", I would recommend adding some pieces of 2"x1" oriented vertically, one in front of the motors and one behind, to support the bumpers over their full height. This would prevent the top part of the bumpers bending inwards and hitting your motors. Alternatively, you can put a piece of 1"x1" tube across the chassis and attached to your side tubes. This might get in the way of your scoring mechanisms or might be a good mounting point.

If you are really worried about wiring or pneumatic tubing getting snagged by the chains, install a piece of thin 1"x2" Al angle to form a wall where needed.

The front and rear cross tubes block access to the two side tubes so a chain in tube implementation will be problematic. Chain in tube also restricts your ability to just screw or rivet things to the side tubes.

DO NOT, DO NOT, DO NOT overtighten the socket cap screws that hold the motors onto the clamping gearboxes. One of the Disco students who didn’t know any better overtightened those screws and they pulled through the plastic and popped out the other side. Of course, the motor was no longer attached. The clamping gearbox was ruined and could not be reused since the hole was now too big.

If you are worried about the nuts getting twisted out of place in the plastic gearboxes as chadr03 experienced, replace them with STEEL standoffs. With how you are installing the gearboxes, put the standoffs on the outside of the frames for easy access with a socket or nutdriver.

Wow. Really nice design!
We used clamping gearboxes this year in our mecanum wc frame and had no problems.
In addition to the Vex frame design (linked) we added 2 short pieces of 1x2 tubes to each side to add bumper support and to comply with FIRST rules.