Finding Mecanum Wheels

[Creator Mat]

My team is looking into using a Mecanum drive train. However after doing some research we found that normal Mecanum Wheels can't function properly on a sloped surface going side to side. But there is a mecanum variant that can function when when on a sloped surface going side to side. We just can't find where to buy these wheels. The reason we want this type of mecanum wheel is because without them (using normal mecanum wheels from andymark) we can only go over the hump head on with little room for alignment error. So does anyone else know where to buy these versions of the mecanum wheel?

Note: please read this paper (http://ftp.mi.fu-berlin.de/Rojas/omn...eter-Tlale.pdf) for explanation why a normal mecanum wheel can't function when on a sloped surface and for what this alternative mecanum wheel might look like.

Also we did find this type of mecanum wheel here (http://letsmakerobots.com/node/10282) but it is to small for us to use and plus the plastic might not be able to stand up to competition.

[billfunk29]

Our team is looing at the mecanum drives as well. One thought we had was to put a clutch on the small rollers to lock them.

Most of these type wheels have adjustable friction on the small rollers. If the two Stampings were pulled together the friction would increase.

Another possibility is to put a bladder (inner tube) inside the wheel. Inflate it to push on the inside of the rollers to lock them.

[scottydoh]

The only ones ive seen like that in FIRST were fabricated by the teams in their own shop. THis is the first time 810's using mecanum wheels too, but my guess is they should work good enough to get over the bump. And I don't really foresee a need to travel parallel to the bump.

[alicen]

today, my team actually took our mechanum drive from three years ago and gave it a face lift. we moved some things around so that it had higher clearance and then tried to drive it over the bump. when we weren't aligned quite right, the robot actually fixed itself and drove straight up the ramp.

i wouldn't be too worried about locking the rollers

[joek]

Originally Posted by Creator Mat

My team is looking into using a Mecanum drive train. However after doing some research we found that normal Mecanum Wheels can't function properly on a sloped surface going side to side. But there is a mecanum variant that can function when when on a sloped surface going side to side. We just can't find where to buy these wheels. The reason we want this type of mecanum wheel is because without them (using normal mecanum wheels from andymark) we can only go over the hump head on with little room for alignment error. So does anyone else know where to buy these versions of the mecanum wheel?

Note: please read this paper (http://ftp.mi.fu-berlin.de/Rojas/omn...eter-Tlale.pdf) for explanation why a normal mecanum wheel can't function when on a sloped surface and for what this alternative mecanum wheel might look like.

Also we did find this type of mecanum wheel here (http://letsmakerobots.com/node/10282) but it is to small for us to use and plus the plastic might not be able to stand up to competition.

those were for FTC, andymark sells mechanum wheels for FRC

[mathman05]

I don't see why you would be worried about getting your mecanums stuck on the ramp. I understand the metal of the wheels would be touching the ramp, but you shouldn't be going up the ramp sideways in the first place.

[JesseK]

Originally Posted by mathman05

I don't see why you would be worried about getting your mecanums stuck on the ramp. I understand the metal of the wheels would be touching the ramp, but you shouldn't be going up the ramp sideways in the first place.

I believe he means strafing while on the ramp, not strafing in order to climb up the ramp. In any case, any sort of drive train will have issues climbing the bump at an off angle unless there's a suspension system. At an off angle it's guaranteed that at least 1 wheel will come off of the ground. If you want to go mecanum and climb the ramp, you will have tradeoffs to consider regardless of how you design it.

Those mecanums are pretty cool; actually in hindsight 4 sets of those little mecanums would have been perfect for our drive train since I'm sure they can handle 20lbs per wheel (for $85, they better!). Hmm, actually at 50A durometer the rollers might rip themselves apart... though it may be worth some offseason testing nonetheless.

[mathman05]

Originally Posted by JesseK

I believe he means strafing while on the ramp, not strafing in order to climb up the ramp. In any case, any sort of drive train will have issues climbing the bump at an off angle unless there's a suspension system. At an off angle it's guaranteed that at least 1 wheel will come off of the ground. If you want to go mecanum and climb the ramp, you will have tradeoffs to consider regardless of how you design it.

Right, sorry. You are correct.

There was a team, though, that posted a video of strafing while on the bump. I forget who posted it at the moment. And I don't see how the metal sides of the mecanums would get in the way of strafing like that.

However, if any robot is caught sideways (meaning your drive wheels are parallel with the bump) (it's probably bottomed-out, firstly) on the bump, it's pretty much immobile until someone hits it off the top of the bump. Even then, you will likely roll over when you get pushed off (unless you have omni's (with large rollers?)? and if you have mecanums, it will be less likely, but still likely) At least, that's what I think.

In other words, if you're going to go up the bump, don't try to go over diagonally; things may not work out the way you want them to.

[efoote868]

Team 868 fabricated wheels like that for the 2006 game, Aim High. We were not able to go up the ramp at any angle other than head on, and once on the ramp we were not able to strafe from side to side, there was too much slippage.

Here's a picture of one of the wheels:
http://i111.photobucket.com/albums/n...te/5wheels.jpg

To be fair, I believe the ramp surface that year was diamond plate, so with a different surface you may have different results.

Best of luck.

[smistthegreat]

Does anyone know where i might be able to purchase some small (<4" Diameter) mecanum wheels. They dont have to bear any weight or do anything cool, just be small mecanum wheels. The cheaper the better

[joek]

i don't think anyone make small mechanum wheels, except for FTC, you'd have to make your own to get small mechanum

[Jon Stratis]

I think your best bet is going to be making your own, if you have the capability.