Our team has the programming and mechanics of using Mecanums down perfectly, so now it’s time to start shedding weight and costs. Here’s what happens when you limit yourself to only things you can get from McMaster, and limit each part to only a few ops on a manual Mill.
The center hub is 2inch Hex stock, and the roller units are made of C channel. The rollers can be lathed from the rubber stock McMaster carries, or custom poured if the budget comes through. The rollers are on 1/4 20 bolts, and the C channel is held to the hub with two #10-24 countersunk screws.
I like this my team does another comp other than FIRST called BEST and has been looking at how to implement mecanums with the limited kit you are given, I think this might be the solution. Really beautifully simple.
Nice design! It is apparent that you took practical considerations into account as the primary design factor. There was a recent thread on CD, in contrast, discussing a mecanum wheel that the designer took aesthetic considerations into account as the primary factor… but as a result the wheel needed to be made on a 5 axis CNC mill in his opinion.
I can guess which one is more likely to show up on a robot!
As for the bumpy factor in the ride, you could always (at this cost) build 8 wheels, and attach them in tandem, with one rotated 30 degrees from it’s partner… much the same way you can use two omnis to smooth out the ride.
For even less necessary machining, you could not mill out the inside of the hex stock, and instead thread-tap the holes where the counter-sunk screws go in. This makes it a bit heavier, but you wouldn’t need a mill to make the wheel.
Then, you could also drill the KOP hub bolt-circle pattern into the side, eliminating the necessity of having to make a key way.
To take this even further, instead of counter-sunk screws you could use half-head-height machine bolts, eliminating the need to create the extra dimple after the initial hole is drilled.
Not sure. Next time I boot my Mac into windows to do some CAD, I’ll throw together a different version with smaller hex. But to be honest, I’m not sure I’d feel comfortable making it any smaller. The team I’m mentoring has an affinity for Banebots transmissions, so I think the goal is to keep to wheels that can be direct driven off a BB tranny.
There are definitely many revisions that could be made to seriously reduce machining time, but this is really just a 1.0 wheel. I’m debating changing the milling operation on the hex to be entirely one sided, so the “dishing” of the wheel would be done in a single Mill op. I’ll have to do some FEA tests to see how the strength would stack up.
Also, for the rough ride concerns: Once I make the wheel wider, and thus the rollers longer, the wheel actually smooths out a good bit.
I think what you have here is just fine. If you’re using a CNC mill, the same program would be used for both sides, so there could be time savings there. Another option would be to incorporate a spoke pattern something like our 4" tread wheel design. It might help if you plan on making the wheel wider.
Sure, let me grab a render real quick. I’ll edit this post in a minute with it.
There’s two renders here: My 1.0 ultra-cheap design, which is with 6 rollers. It’s outer diameter is around 4, 4-5 inches. Next is the 8 roller one, a bit smoother, and a little bit larger with a effective diameter of 6 inches.
Great design. Do the nuts and bolt ends miss the carpet? You may want to look into tapping one end of the c-section and countersinking the clearance on the other. Then you could use a flat head screw and match the length of the screw to the c-section width. Then you should be able to avoid any hardware overhang and further reduce the weight. Typically you should have at least three full threads for any bolted joint.
Keep up the great work and please post your final version!