non-cantilevered wheels are easier to mount (just drill two holes and poke a bolt thru them). They also have an outside frame member that protects the wheels from damage, or from getting flat tubes tangled up on them.
Cantilevered wheels can be easier to work on, since there’s no frame member in the way. They also can offer more tipping resistance, as they can be located at the outer edge of the 28" wide robot footprint.
We went with cantilevered mecanum wheels with hex bores. We did this for ease of maintenance on the wheels, so we could easily take them off. We had bumpers (that had abs blocks that slid into the chassis aluminum tubing) around its perimeter to protect the wheels.
We had addition reduction with another gearbox on the output of the banebots planetary. Disassembling this drive to check for maintenance was no problem because everything just slid apart after we loosened some nuts and bolts.
Our team had been sort of scared of cantilevered wheels and the effects it would have on the shaft, chassis, bearings, and such. It turned out working really well.
After 4 years of cantilevered wheels I have to say that we haven’t had an issue with them yet. They are easy to maintain and totally the best way to show off your rims. Can’t forget the fact that if you have hex shafts (i.e. 968/254) changing out a wheel takes about 5 seconds.
-guy
I’ve heard 254/968/4 say the same thing - that it helps them replace wheels. But how often do you have to replace your wheels :ahh:? Its not a problem I’ve ever experienced.
I do agree that cantilevered wheels will definitely help with stability. And using bumpers is an easy way to protect the wheels.
Conveyor tread can wear out quickly in competition, and usually the quickest way to swap the tread is to just stick on another wheel with new tread. I know that by the end of our first regional our robot had nearly bald center wheels.
We change the tread on our wheels anywhere between one and three times during a competition, depending on how it’s wearing. Being able to swap out every wheel in under a minute is a huge advantage.
696 has used cantilevered wheels for the past three years. It ends up saving a good deal of space and weight, as well as giving a wider footprint for better stability and turning moment, and it allows the wheels to come off easily for replacing tread. The only downside is if someone pushes a bumper up against your wheels, you might be stuck goin no where. But you can put in gaurds for that if you’d like.
One thing that hasn’t come up yet is the loading on the axles. Cantilevered axles have a much higher load bending loads on on them than axless that are supported on both sides. We opted to go with cantilevered shafts for the wider base and ease of maintenance (which proved to to be the right choice for us.) But we looked at the math and planned accordingly when picking shafts - 5/8" Igus shafting. :eek:
Despite some of the other problems we had relating to keyways and such, we never bent a shaft.
Thanks for your advice everybody.
If you use cantilevered drive wheels you probably a live axle(right). But how do you attach the wheel to the axle, and have good support? And keep the wheel from falling off?:eek:
Assuming you have a key or use hex shaft, then transferring rotation to the wheel is done by rotating the shaft, There are two common ways of fastening the wheel to the axle: the first is by attaching a hub with a flange onto the axle, then the wheel is screwed on or off when needed. The second way is to machine an integral hub onto the axle, like this
(Yes, CD members, I know this picture is for a different part of the robot) Then the wheel with a matching hole profile is put on the shaft/hub.
As for keeping the wheel on the hub, you can use retaining rings that clip into a circular groove around the end of the shaft, or screw the wheel onto the hub.
Our 2006 shooter bot used cantalievered wheels on our track systems, If any of you remember us having issues with tracks getting walked off if we were being pushed around a turn, we fixed that in the off season.
The fix was, always use two ball bearings, not one, even if the specs say it can take the torsional loads…
Anyhow, yes, cantaliever wheels do take a little more work (we had to design and machine our axles) but they make the robot extremely easy to work on.
