It’s a one-speed gearbox that has a roughly 8.5 gearing ratio, (for games like recycle rush or whatever that don’t need high speeds) and the drive motors are 2 Mini-CIMs. The front plate and back plate are identical for the sake of simplicity.
Cheers!
Looks good as far as I can see. You are probably going to want to add some retaining clips for the Mini Cim gears, though.
Sorry for another reply, I cant edit posts yet. But, another thing is some of those internal angles on the face plate, especially near the bearing. They look too sharp to be machinable with any decent sized endmill. Consider throwing some larger radius fillets on those spots.
Thanks, I actually noticed that too. I was planning on adding another set of fillets there, but forgot. heh.
Also, if you don’t have them already, make sure to add holes for mounting the gearbox onto some sort of frame. It might be a good exercise to do them for a KOP or some sort of standard frame.
It has a set of clearance holes for a wcp bearing block kit (from vex) on either side of the bearing. This gives it one attachment point to the frame via the bearing block, which I think should be enough. I was considering adding another set of mounting hole, though, as I’ve had experiences with gearboxes sagging towards the center as the season progresses.
It’s usually a good idea to have a separate set of mounting holes for the gearbox alongside those on the WCP bearing block (from WCP) to help take the load of the gearbox weight, so that way the bearing block isn’t supporting the entire load of the gearbox.
A good example of this is the WCP DS transmission - check it out if you get the chance!
From experience, it is somewhat iffy to use the bolts holding the gearbox together as an additional attachment point - tightening them enough to provide significant support tends to bind up the gearbox.
That’s why you have rock-solid spacers between the plates and don’t overtighten everything. Some forethought and moderation can go a long way in design :).
It would be very nice if the COTS gearbox had these “rock-solid spacers” you speak of.
As it is, attempting to use those bolts as a solid attachment on an unmodified WCP gearbox is not likely to work very well.
I know that worked fine for several teams this season. I can’t imagine how else the WCP DS would even be held together because the bolt head would hit the tube. How would it cause the gearbox to pop?
You can drill clearance holes for the bolt heads. You can also put the bolts through the tube wall, but you can’t tighten them enough to have them make much of a difference in the sturdiness of the mounting.
It doesn’t cause the gearbox to “pop,” it causes it to bind - tightening those bolts past a certain (not very tight) point will severely increase the friction in the gearbox by introducing clamping force to the various parts on the gearbox shafts.
How is that different from doing it with clearance holes?
It’s not - it’s basically the same either way, which is the point. In either case, the bolts cannot really contribute to the sturdiness of the gearbox mounting, because even if you pass them through the tube plate, they can’t be tightened very much.
Sorry, I meant clearance holes for the bolt head. Or did you mean you should never tighten gearbox bolts all the way anyway?
They do - if you’ve had failures you should contact [email protected]. The team there is fantastic at answering any questions thrown their way and assisting with issues that arise from product misuse. I’ve used this method of gearbox attachment for years, as have many others, to much success. I’m sure if you provide more details about your implementation of the gearbox and how it didn’t work well, someone will be able to help you figure out what changes to your application will help get better results in the future.
Kaorin, your design is pretty rock solid for a first time custom gearbox - nice! A helpful trick I learned from using the WCP SS is to use at least one set of your CIM mounting bolts to hold your gearbox plates together. Just run a standoff between the plates and thread a bolt long enough to get through both plates and the standoff into the motor and you can get a pretty great connection while utilizing already-existing geometry! You also don’t need to use hex shaft for standoffs unless you’re planning on threading into the shaft and need to tighten it down - round standoffs will do in this case!
Keep up the great work, we can’t wait to see your next iteration!
Gotta agree with Andrew here. Our WCP Flipped DS are mounted with bearing block and the bolts through the gearbox. Worked excellently and had no issues through 2 regionals and 50+ hours of outreach demos and practice. And as stated, WCP has great support and they stand by their products.
An alternative to adding a second set of bolts would be to run some thunderhex or churro across the bot from gearbox to gearbox so that they support each other. I have no idea how this would work out, just an idea.
The distance in CAD and actual distance didn’t end up being exactly the same for whatever reason and we had to shove in a washer, but otherwise it works fine.
The kitbot actually used to be that way (it may still be - I haven’t worked with the recent kitbots too much). It definitely works, and it’s something many teams use to great success to add stiffness to their drivetrains. I personally avoid it because I like clearing up the center of my drivetrain for other things, and my personal experiences have shown it’s not too necessary, but again that’s me - your experiences may vary.
