Re: Problems with Vex Pro mecanum wheels
 

LOL:D... Maybe we will try switching the wheels on Wednesday back to the Andymark one? We have to take the transmissions off to swap gears anyways.

Re: Problems with Vex Pro mecanum wheels
 

I don't think he's joking around. I see no reason why a standard traction tank drive wouldn't be more advantageous for you to use instead of mecanums.

Re: Problems with Vex Pro mecanum wheels
 

Let the battle begin!

Re: Problems with Vex Pro mecanum wheels
 

Make sure to check every roller, last year we had a strafing issue and it was because one roller was stuck. Our issue looked more like an intermittent speed issue is strafing.

I would also check if each wheel can rotate forward and backwards at full speed with the robot off the ground. Hopefully you have the encoders hooked up to each gear box to see the counts per second. At least this can sort out programing versus mechanical issues.

Just to be clear how loose our rollers are on our 2012 robot, the rollers will spin a couple time after flicking them.

Re: Problems with Vex Pro mecanum wheels
 

That's fine, but we could just put real traction wheels on if we are taking the transmissions of anyways.

Re: Problems with Vex Pro mecanum wheels
 

Ok thanks, I'll test all of this out Wednesday. I would prefer to keep mecanum for this year.

Re: Problems with Vex Pro mecanum wheels
 

Problem is, the rollers can appear to be free-spinning when not under load, and then bind up when they are loaded.

There is a lot of axial force on the roller under real-world operating conditions. It is prohibitively expensive to put high-quality thrust ball bearings on FRC mecanum wheel rollers. I've never seen the VEX mecanum wheels. What provision is in the design to react the high axial forces without creating excessive friction? IOW, what two materials are scrubbing against each other when the roller is axially loaded?

Re: Problems with Vex Pro mecanum wheels
 

Another potential problem with staffing is if your frame isn't square - ie, loads on the wheels have too much difference. We had that problem this year - we shimmed one gearbox and the staffing was fine after that.

Re: Problems with Vex Pro mecanum wheels
 

Yeah I was going to caution that a wheel unloaded will be different from a loaded wheel. My team never came up with a good test method for this.

I am sure you know this Ether, but so others can follow, I will be a bit more detailed. On the andy mark wheels, there is a bushing in the wheel. This rotates on a bolt. Between the wheel and hub plates are washers. If one is too zealous, one can tighten the bolts too much compressing the washers and wheels until the wont move. We had to play with this a bit because once the wheels are on the ground, the deflection of parts can create binding too. I think if its too loose, the hub plates could touch the roller. I forget how much it took to cause the failure mode, but gut tells me that situation required the bolts of be barely tighten.

I am guessing the Vex wheels are similar with a shoulder bolt or screw that supports the rollers. Thus i may be possible to over tighten the screw until the rollers bind. The roller would be compressed by the head of the screw and the hub ( plus a few washers in there).

Re: Problems with Vex Pro mecanum wheels
 

We switched to VEX mecanum wheels for our octocanum drive this year, and had no issues whatsoever with their performance. (And the added maneuverability was very useful in lining up to the feeder slot!)

Re: Problems with Vex Pro mecanum wheels
 

So I was thinking along the same lines as Ether as well,
But we have a 28"x28" robot with a center of mass right in the middle... So my thought was maybe the wheels just aren't as smooth, but apparently other are having good luck with them.

Re: Problems with Vex Pro mecanum wheels
 

For a quick check, pick up on each corner of the robot and see if you can detect a difference. If the frame isn't square you should be able to tell.

Re: Problems with Vex Pro mecanum wheels
 

Oh sweet! I'll give that shot too. Thanks

Re: Problems with Vex Pro mecanum wheels
 

Also, your robot being 28"x28" doesn't necessarily mean your wheelbase is a square (but it may very well be or "close enough").

Re: Problems with Vex Pro mecanum wheels
 

We are also using these wheels. We used them to make us always be pointed at the target when we have vision solutions if we choose to be. I have noticed that strafeing is rather slow too...