One solution I’ve heard of for the problem of spacers and shafts moving when switching wheels is to use a light-duty clamping shaft collar as the last spacer before the wheel. That way taking off the wheel doesn’t allow the shaft and spacers to move freely because they’re still constrained by the axial tapped bolt on one end and the shaft collar on the other. I’ve never actually used it myself because we’ve never really had a problem with this but it seems like a simple solution.
I highly recommend standardizing on a 1/4" screw with a nylon patch for all tapped shaft ends. Something like https://www.mcmaster.com/92360A310/.
Toss and replace each time you remove it. They can be reused several times but it is hard to keep track of which ones have been reused.
Agreed that either this or Ricky’s solution above are the way to go for the actual problem we were facing, and would likely be what we actually implement since we don’t have the resources to make a wheel like this very easily anyway.
I’m curious, does any one use a drilled axle and R-pins (or similar) as a positive means of wheel retainment?
In 2019 we’ve used a similar method to the AndyMark performance wheels, with a zip tie going through both ends of the tread and hooked onto the wheel near the hub. We changed the design a bit, making the notch the same width as the treads so that we could tighten it using the zip tie, and having the ziptie hook onto a bolt instead of twisting around into a hole. Replacing all 4 treads took less than 40 seconds for two pit crew members. Treads never came off(except for one instance where the hole on the tread was drilled way too close to the edge) and the bump where they enter the wheel wasn’t noticeable at all.
This is very similar to the tread concept I have been playing around with on the latest version of my swerve module. I like the feature you built in to be able to take one half of the wheel off to swap the tread while keeping the wheel on the shaft.
In your post you said the tread would be injection molded. Are you actually planning to make that? How are you justifying the tooling cost of molding it? I am currently playing around with 3d printing TPU filament for the tread on my swerve version.
Last year (2019) we 3D printed our traction wheels, and designed them with holes for 8-32 screws at regular intervals, on the inside of each of the holes is a slot for an 8-32 nylock nut. The tread is held in place much like how a wheel with riveted tread would be, except instead of rivets, it uses screws.
To change the tread, all you have to do is unscrew the 4x-5x screws holding it in place, replace it with another piece of tread that’s already been pre-drilled (since the holes are the exact same on every wheel, you can use a template), and screw it back on.
This is particularly convenient if you’re not using a WCD since you can replace the tread relatively easily without removing the wheel from the shaft.
This is how the Thrifty Swerve wheels work and how 2767 did it this year. Also how Patrick’s swerve wheels work.
Is it bad that we reuse but never really replace the nylon unless visibly worn down?
I wonder if there would be a market for a cast-your-own version of this? Someone could sell hubs with standard interfaces, outer moulds with various tread patterns, and be a distributor for various casting resins in a variety of durometers. Customers could pick the resin, customize it with something if desired (soft rubber chunks in high-durometer matrix? why not?), and cast their own into the wheel so the T-slot is captive. If they don’t like the properties, they can try again with a different compound.
(To cast directly into the T-slot profile, there would probably need to be some riser holes to avoid air pockets.)
An L rather than a T should hold fine with some compression in the design, and lets you skip the risers on the mold.
This overall sounds like selling a science experiment rather than a competition product though, which is risky.
You could also cast it in a different orientation to avoid the risers.
However this process is a bit outside of my wheelhouse, so there may be reasons not to do that.
I’ve been toying around with the idea of making a cast polyurethane version or perhaps 3D printed polyurethane version just as an experiment. I suspect the cost benefit on this is not very favorable unless this became a production part that was made in large enough quantities to justify the tooling and even then probably need to prototype via casting or printing before committing to a tread pattern/design and making a mold.
After spending some time actually thinking about how to make this concept much more economical/scalable, I came up with the following revised concept. Same type of structure in terms of the two part wheel hub, but the tread will be waterjet from whatever 1" thick rubber/TPU/Neoprene/SBR is deemed to be optimal. The tread will have alignment and torque transfer nubs that will interface with the two part wheel hub. Overall weight as shown is .65 lbs per full assembly including hardware, though I’m sure that can be further optimized.
I think this greatly simplifies the concept and shifts the cost-benefit ratio to a more favorable position. I’m sure there is also a lot of room to experiment with different durometer treads and different tread patterns as well. I’m also fairly confident that with some geometry modification/optimization to the part that interfaces with the shaft, the wheel hubs can be 3D printed on a Markforged. This would likely require thicker spokes, heat set inserts for the screws, and a metal insert for the hex shaft interface.
This also solves, in my eyes, a potential problem with the T-shaped slot - rolling of the tread when the wheel is pushed sideways. A molded or all rubber part without the hard backing that comes on a nitrile tread is likely going to want to lift at the edges when its skidding perpendicular to the floor. Over time the rubber could even stretch to a point where the edges of the wheels are loose.
The new version will do a much better job of keep the the tread flat against the wheel.
Idea: what if you eliminated the 6 fasteners and their holes. Then I think the front and back could be identical. Then put an exterior thread on the hex shaft and use a castle nut to compress the two halves together and secure the assembly to the axle. This would also double the area in which the hex shaft drives the wheel. Also only one fastener to remove and split the wheel.
There are some very good adhesives that could essentially glue tread to some kind of rim. An interesting variation might be to have a disposable rim that would be changed out with the tread, but to reuse the main part of the wheel. You could apply this to the current design to provide different tread options, while allowing the middle (“tread”) part to be made from materials that don’t make good treads, but do make good rims.
I think the simple answer is that your method is proven until you start seeing screws come loose. Don’t fix a problem that isn’t a problem, lol.
Do you have some photos you can post? This would be a great upgrade for designs based on parallel plates, like the KOP chassis.
Actually, I can do you one better than that, here’s some pictures AND the CAD models…
If I had to make one upgrade to this design it would be to make the nylock nut slots a bit deeper so they stay in place better. Still it worked fine for us that year (and this year we had pneumatic wheels so we didn’t need them).