One of our students figured out how to use the CNC Shark router at our build space and cut this wheel from a piece of scrap lumber. It is designed to mount a VersaHub to interface with a 1/2" hex shaft, and the blue nitrile tread is attached with CA glue and staples.
How creative! Have you done any strength tests on it yet? How much does it weigh?
We haven’t done any testing yet. According to my cheesy kitchen scale this one minus the hub and hardware is just over 120 grams, and there’s a lot of room for cutting more material out.
What are the dimensions of the wheel? I’m impressed with how light it is; a 4" HiGrip wheel from AndyMark is 140 grams, and this seems like it’s of comparable (greater?) strength to the commonly used plastic wheels.
Being a team that works with wood a tremendous amount, you probably know… but is a .5" hex sufficient for a wood drive wheel (even if it’s only ~4" diameter)? I would think you’d at least want to make sure the interface didn’t have slop.
It sounds like the intent is to place a hub in these wheels.
I believe this is the answer (emphasis mine):
As I read it, the hex hole in the wood isn’t for torque transfer, but presumably for alignment.
Yep… good thing you guys can read! (unlike me)
Hey now! I can read perfectly fine!!!
Looks cool! Can’t tell if you have flange(s) to help hold tread in place, or perhaps you don’t need it?
It’s flanged on one side. I’d be interested in seeing how the glue holds up, it might be enough as is.
Also, if the flanged side is towards the inside of the robot, it should help handle the sideways load on the tread in the worst condition (being pushed sideways by another robot). Most of the load in that case is taken by the center wheel opposite the side that’s being pushed. Maybe just one flange would be okay.
Do you have an old operable robot base you can swap these onto and test them out? Not a bad idea for teams that lack machine shop capabilities.
For BEST one year (Warp XX - 2012) we needed a large winch spool to wind up the cable we were climbing. I took the largest hole saws we had (3.5" and 3" I think) to some plywood and acquired 4 disks of wood of equal diameter and 2 larger disks for outer guards. I used a .25" pilot bit in the saw, so I aligned all 6 disks on a 1/4-20 all-thread with glue between each layer and clamped overnight. I then chucked the all-thread into the drill press using it as a lathe to sandpaper the edges smooth. It worked fantastically.
A few more steps and you could have basically this wheel on nothing more than a drill press. The hex broach is unlikely, so maybe a versa hub on both sides.
If you have a CNC shark router, you have at least some machine shop capabilities, no?
Not at the moment. We may in the next couple of weeks and will for sure early in build season.
We actually have pretty substantial machining capabilities in-house: a Bridgeport mill, a lathe, the router and a Trotec Speedy 300 laser cutter. We use the laser whenever we can, since making parts with it is much faster than using the other tools.
188 has had a lot of experience and success with wood wheels on FRC drivetrains. Most were turned on a wood lathe, no CNC, DROs etc. They tended to be dead-axle with sprockets bolted directly to the wheel. I don’t think they’ve ever needed to put flanges on the wheels to keep the tread in place, but I’m sure that will help. They do securely rivet or screw the tread on to the wheel. Special care is needed for the rivets at the end of the tread. It’s hard to explain, but they put two rivets at the ends, but cut notches into the ends so that a half-width of the start of the tread sits beside a half-width of the end of the tread, and the ends “overlap” (not on top of each other, but beside each other). The two rivets go right beside each other, one into the start of the tread, one into the end, in the middle of the overlap. Very clean, and prevents any gaps in the tread - there’s at least half-width at the gap.
Version 2 of the wheel. Improvements include:
-Reduced machining time from ~30 min to ~15 min with better toolpath generation and faster feed rate
-Reduced weight to 38 g vs 71 g for the original wheel (some of the variation may be due to different materials)
-Smaller diameter match 4" Vex Pro Traction Wheels
-Recessed hub keeps hardware from protruding past the wheel.
We haven’t yet been able to test them on a chassis.
Very interesting! I’m curious how the hub goes on though; do you drill holes after putting it in for the screws or do you just glue it in and forgo screws altogether?
I’m guessing they attach it with wood screws.