3928 is proud to present the drivetrain that we have been working on this pre-season. We designed this drivetrain to take up a minimal footprint, use minimum weight, and to be reflexive, so future changes can be made quickly. Note: the bumper mounts on the side have not been designed yet. We appreciate comments, questions and feedback.
Is that gearbox made out of 2x1? Thats super cool! only thing i’d be careful about is the tolerance on the wall thickness depending on who you buy from. My only concern is the support of the other end of that output shaft, but it looks like you have a bearing in the main tube. Also, i can’t really tell, but it looks like your using a screw to retain that main bearing. As long as you dont plan on any thrust load on that shaft (which there probably won’t be), you dont need to worry about it. Looks good and I like the 2x1 gearbox!
One thing I would think about. 64 tooth gears are 3.3 inches in diameter. If one is centered in a tube, it will stick out 0.65 inches (3.3/2-1). Thus, it will be 0.35 inches above the carpet. Without any protection, it will suck up everything from carpet threads to screws. They will also get stuck on a cable protector (if they have one this year) This will lead to issues. You should look at covering it or doing a 2 stage gearbox.
I recommenced enlarging this hole here and putting a spacer on the shaft between the gear and the sprocket to prevent the gear boss and sprocket boss from rubbing on the inside of the tube.
Also, adding some sort of polycarb cover over top the slot above the center drive sprocket will help prevent things from getting sucked into the drive tube. Tapping 4 of the holes on the top of the drive tube to secure a cover would be a quick and easy way to go about this. Though, as someone who has done multiple CIT drivetrains, I don’t really see a point in having the slot there.
I’m always really hesitant when I see teams make big cuts in the top and bottom flanges of the drive rail. The middle of the tube is where the biggest bending moment will be, and the flanges are taking all of that load (not to mention all of the side-to-side shear loads). Consider eliminating that hole and feeding the sprockets in from the end.
Chain in tube is very easy to assemble, especially now with double sprockets being readily available. You assembly the chain run outside the tube, drop the entire thing in, and stick the shafts through. There really isn’t any need to add any extra pockets for “hand access”.
It is a press-fit, the screw is just there as a fail-safe. We have used this method of retaining bearings with no problems.
Thanks for your concern, but we have run 72 tooth gears with 4 inch wheels in the past without issues. It will not get stuck on the cable protector because in that case it will just act like a 3.3in wheel.
That sounds like a great idea, we will probably end up doing that.
This was the plan, I just never bothered to put it into Cad yet. All the holes in the drive tubes that don’t have a specific purpose are .159" and will be tapped for 10-32 so that we can avoid drilling rivets out into the chain.
We have also done CIT in 2016, 2018, 2019 and have found those access holes useful. In 2016 we did not have access holes, and had a problem with it being very difficult to assemble, especially if the chain breaks.
That seems like the way to go, and especially because it makes it easier to assemble than from the top.
