pic: Enclosed Delrin Transmission



a fully enclosed 3 cim plastic transmission milled out of a 13.5 in by 1.5 in by 2.5 in piece of delrin made for a drive train.

Interesting design. How much is the overall weight?

Very interesting. What advantage does the milled block provide over two parallel delrin (or aluminum) plates? Are you worried about double loading the pinions? Are those two sides to the same gearbox that bolt together, or are they two separate gearbox enclosures where the open face bolts directly onto the chassis?

Am I looking at this right? I see everything here except the two small gears on the cluster shafts as the first stage, and this gearbox will have two output shafts about 10" apart?

If so, I’m assuming you’re not making a 6-CIM robot with a 10" wheelbase. How to you plan to get the torque to the wheels? Eight wheel drive in a “Double West Coast” configuration?

Interesting approach, looks like it would be easier to keep lubricated if nothing else. Like cad321 I’m also a bit curious how much this weighs.

10" is about the right spacing between the center wheel and an outside wheel on a 6WD chassis. Running a chain from the center wheel and the remaining wheel should work.

This was made for a eight wheel drive base, the gearbox has two outputs and is essentially two double reduction gearboxes geared together I will post a picture when the drive rail is assembled. The gearbox is centered on the rail with two colesons on the two drive shafts with 15mm vex belt leading to omni wheels on the outside.

It weighs 9/10s of a pound

The advantages to this over two parallel plates is having a fully enclosed gearbox that can be run and completely finished in one program in our cnc mill, I’m not worried about overloading the pinions. we did a transmission like this but with aluminum plates on our 2017 robot and had no problems. The other side of the gearbox is milled into one side of the driverail which is a ⅛ wall tube of 2 by 1.5 in aluminum. The gearbox bolts directly to the side of the driverail

Yep, that’s what I pictured. Especially if you go with cantilevered wheels, I again suggest the name “Double West Coast Drive” because it has two direct-drive axles, or as you’re not far south of Lake Ontario, “North Coast Drive”.

The double loading is in the first stage, which is where you want it if you’re going to do that. It appears that you have 14 tooth CIM pinions, which is also good - I suspect that many of the broken pinions over the years have been smaller, or not steel.

Now I like it even better! If I’m picturing this correctly, you can replace a single CIM without removing the gearbox from the chassis -or putting the tool inside the chassis volume- using a ball-end allen driver, and you don’t have to worry about dropping the bolt inside as with some COTS gearboxes. Sliding the new CIM in will require a bit of finagling, but should still be simpler than pulling and replacing the gearbox.

OBTW, the delrin block shown to the right in OP is not the same as the one with the gears, right? It appears that the cutaways to get to the head of the CIM retainer bolts haven’t been made on that piece, and the face showing appears to be the one which goes against the tube, not the CIMs.

Edit: definitely not intended as a negative, and not worth a rework of this box, but it looks like you could shave another ounce or so without reducing strength noticeably by rounding the outside corners of the gearbox with about a 3/4" to 1" radius.

Edit2: And OBTW, why is the tubing 1-1/2"? What’s the advantage that justified something wider than the “FRC standard” 2"x1" tubing?

“Space Coast Drive” might be more appropriate. 233 ran this style in 2011 and 2012 (and maybe 2010 also). That was before we could have 6 of any given motor though, so it wasn’t quite as clean as you can make it now.

Edit: here’s a better pic of just their transmission: https://farm6.static.flickr.com/5172/5523552199_307c792905_b.jpg

It’s possible there may have been others before that even. We (Apex Robotics 5803) ran the same style last year too (linear gearbox, 3 MiniCIMs with two output shafts for the middle wheels, chain to the outside). I highly recommend this architecture for a compact single speed transmission.

The belt run to the omni wheels is inside the tubeing you can’t fit a 15mm belt inside of a 1 in thick tube, I know we could use 9mm belt in a 1 inch tube but with 15mm belt we can be more confidant that it won’t slip and a big factor is that this is an offseason project so we are useing belts pullys and metal that we already have.

Are we talking per module here? Including all the gears or just the Delrin parts (obviously not including the CIMs)?

What is your total output ratio and what size wheels are you planning to use with it?

the delrin block is 9/10s of a pound according to cad for only one transmission, that is just the delrin block, and there is still a lot of material that can be removed to lower the weight. The output wheel size is a 4 in wheel with a 6.8 to 1 gear ratio, using the JVN design calculator the free speed is 13.52 ft per second.