Threw together something that my team could do this season based upon discussions we’ve had. It doesn’t really attempt to improve any existing design, but rather emulate WCD-like features in a block that can be produced separate from our drive setup. We’ve practiced and will continue to practice a could of things implemented in this design, including the patterned holes and countersunk bolts. Inspired by Madison from a few years ago.
Box extrusion is 1/8" wall, with 3/16" holes every 1"
1/2" hex bearing isn’t shown
Plates may be cut with waterjet, or manually milled in house. If it’s in-house, things will be more square.
There is a 1"x1" aluminum block that is tapped with several #10 holes
The round pieces that go through the extrusion are 3/8" standoffs tapped with #10 holes
I’d add bearing bores to the block so both bearings sit in the same piece and they are 100% sure to be concentric and can’t be tweaked/shifted due to tension, applied load, etc…
Also, if you have a manual mill in house and are willing to mill all these pieces, doing a more conventional west coast drive is trivially different. Our bearing blocks are pretty much what you drew in terms of time to make (possibly a bit simpler even).
Not sure what your frame looks like but I would be a little worried about the torsional load on that piece of bar stock. If your wheels are cantalievered, remember they work like levers and can be used to twist that bar as your robot bounces/drives around. It would be awful to loose a chain because the bar twisted and your sprockets went out of alignment. I believe this is one of the reasons most WCDs use 1 by 2 bar stock.
It seems to me if you can mill this out, a normal WCD in 2x1 wouldn’t be a problem at all. What’s the reasoning behind this design rather than a regular bearing block and clamping plates?
edit: Sorry, just read read the second part of Adam’s post asking this as well.
This may just be me, but I tend to get really cautious about milling tensioning slots for bolts to slide along in something that experiences a lot of load. How tight would this be clamping onto the frame?
Thanks for the responses. Something to keep in mind is that I have a group of mentors with input into the overall decision process, so going to WCD just because team XYZ does it hasn’t worked. The group didn’t really seem open to physics proving that 6WD was as good as 8WD and I had a really really hard time explaining that putting omnis on the corners would cause oversteer and for us to be turned very easily. So I’ve had to stick with what we’ve experienced as a team for a starting point.
If we can use water jet, I’d rather use it on parts that need precision and save quite a bit of time. I can water jet 5/32" holes in the plate, then use a transfer punch to punch holes in the block, drill/ream/tap and come out with a more accurate part than I can if I tried making the holes in a block and milling out large rectangles on 2x1. This is also based on a recommendation from the waterjet sponsor stipulating that water cutting a 1" thick block will leave sloppy edges on the backside of the piece – not something we want when we’re putting bearings into it.
We’ve done something similar to the transfer punch setup in the past with a drill press while we were kicked out of the school for snow. Heh, that same year we made fairly decent ‘slots’ with 2 holes and some files.
If we can’t get to the waterjet in the first week (we’ll know before kickoff), we may just stick with a variant of the KOP drive train that direct-drives the middle wheel. At that point we might not even do 2-speeds. We’ll see.
The wall thickness of the aluminum is 1/8", which partially accounts for that. I can also adjust the positions of cross members to help. The particular block shown is for an outer wheel, without gussets in place yet. The middle wheel block would have cross members in place already since the direct drive super shifters mount there, similar to what 973 did in 2008.
The block beneath the frame and the two round standoffs are 0.99" wide per an anecdote. Basically, I could file or lightly sand the parts down to get the desired interference for a good clamp. I might also add a regular nut to the tension bolt to satisfy another mentor’s concern that it’ll jiggle loose.