New Vex Mecanum

[Gregor]

After extensive practice with the practice robot including running over the platforms many time at full speed, and 1 regional so far with the competition robot, we've had no issues at all with the 6" mecanums, other than 3 missing standoffs inside one wheel, but that was quickly corrected by VEXPro.

Absolutely love them.

[timytamy]

To add on a slightly different data-point:

We've been using the VEXpro 8in mecanum wheels which I believe have the same tabs as the OLD 6in and 4in.

The wheels have been holding up nicely, one set been through a regional and a few hours of practice, the other set seeing ~20 hours of usage. We're seeing wear in the roller bearing (bushing?) such that the rollers can now wiggle side-to-side. We're concerned that this may be the beginning of the failure mode that was seen on the OLD 6in and 4in wheels, can anyone who used the older wheels confirm or describe the failure?

We suspect that the wiggly bearings are allowing the rollers to rub against the tabs and lock up, but we don't have enough data/knowledge about mecanum to put any weight behind this claim.

One other thing, how do other teams fasten to these wheels? We're using #8-32 bolts into the tapped holes, but because of fear of shearing the plastic, these loosened over time and came out. We've added longer bolts, tightened them up more, and haven't seen any more of these failures yet, but we were wondering what is the recommended/common practice for attaching to these wheels. (We also saw similar failure in the bearing retention bolts, but these have just been removed).

I expect most of this post will be irrelevant once VEX have moved all of their 8in stock from last year, but more data is good right?

[lynca]

Last year we ran 4" VEXpro mecanums and it was a rough year. We eventually gave up on mecanums mid-way through the season of 2014. VEXpro admitted the failure and eventually sent us replacement rollers for all the wheels we ordered.

This year we switched to 6" VEXpro mecanums, we have yet to have a single failure. We struggled to find weight to add our h-drive so switching to mecanum really helped progress our robot capabilities without sacrificing weight.

The new VEXpro plastic clamping bearing blocks have been giving us a couple failures in normal drivetrain usage. We are looking at swapping to aluminium bearing blocks.

[s_forbes]

We had received two old wheels and two new wheels with our first order, and had unwittingly put all four on the robot without replacing the old rollers with the new ones that were included. The old rollers quickly wore out; the roller shaft was not rigidly held in place and allowed the rollers to bind up on the wheel body.

The new rollers seem to last really well. We did notice that they become a bit harder to turn by hand after a lot of use, but I'm not sure that it's enough to affect the driving. We may do an experiment at some point to see how a well worn wheel performs next to a brand new one.

Originally Posted by lynca

The new VEXpro plastic clamping bearing blocks have been giving us a couple failures in normal drivetrain usage. We are looking at swapping to aluminium bearing blocks.

A bit off topic, but can you elaborate on the failure mode? I think that we may be using more vexpro parts in the future, and I'm really digging all of the inexpensive plastic components they make.

[Ether]

Originally Posted by s_forbes

The new rollers seem to last really well. We did notice that they become a bit harder to turn by hand after a lot of use

Harder to turn?? The rollers should spin freely.

[s_forbes]

Originally Posted by Ether

Harder to turn?? The rollers should spin freely.

Yes, ideally they should spin with no resistance. New wheels have very little friction in the rollers. After lots of use they have a little bit more friction. I don't know how much more; this is a qualitative observation and I don't have any numbers. It may still be in the range of "negligible".

[lynca]

Originally Posted by s_forbes

A bit off topic, but can you elaborate on the failure mode? I think that we may be using more vexpro parts in the future, and I'm really digging all of the inexpensive plastic components they make.

I will just start another thread on the topic.
Plastic Clamping Blocks

[Monochron]

Originally Posted by timytamy

To add on a slightly different data-point:

We've been using the VEXpro 8in mecanum wheels which I believe have the same tabs as the OLD 6in and 4in.

The wheels have been holding up nicely, one set been through a regional and a few hours of practice, the other set seeing ~20 hours of usage. We're seeing wear in the roller bearing (bushing?) such that the rollers can now wiggle side-to-side. We're concerned that this may be the beginning of the failure mode that was seen on the OLD 6in and 4in wheels, can anyone who used the older wheels confirm or describe the failure?

The 8in. have had the "reinforced" design since last year. So the ones you bought this year have the same reinforcing that the 4's and 6's have. The wiggling is the same thing that we saw and we replaced the wheel before it got any further.

[Jaywalker1711]

We have been using the 6 inch wheels this season, no issues so far through practice and TWO districts.

Shouldn't have any issues at States or worlds *knocks on wood*

[Aren_Hill]

Originally Posted by Monochron

The 8in. have had the "reinforced" design since last year. So the ones you bought this year have the same reinforcing that the 4's and 6's have. The wiggling is the same thing that we saw and we replaced the wheel before it got any further.

This is incorrect, the 8" wheels do not have the new revision rollers yet, this is due to transition time of inventory (8" wheels are less popular).

The 8" wheels do hold up better than the older 6" and 4" counterparts though due to significantly less deflection when rolling at each roller tab.

As always, email me with any questions,

-Aren

[Nathan Streeter]

We're using the 6" Vex Mecanums, and have been very pleased with them!

If you have the old rollers on your 6" Vex Mecanums, definitely switch to the new ones! We had received the mecanums assembled with the old rollers assembled and a pack of new ones to put on... we put the mecanums with old rollers on when we made our practice bot (we make the practice bot first), and were generally underwhelmed with how it strafed slowly, but it was our first mecanum drive. When we made the competition robot we put new rollers on so that we'd never have to make the change... we were stunned how much more smoothly it performed, particularly when strafing (when the rollers are spinning fastest)! We didn't initially realize the difference was almost entirely the old vs new rollers, but eventually realized it...

Through two events with the comp bot and many hours on the practice bot, all our 6" Vex Mecanums with new rollers are holding up very well!

[Monochron]

Originally Posted by Aren_Hill

This is incorrect, the 8" wheels do not have the new revision rollers yet, this is due to transition time of inventory (8" wheels are less popular).

The 8" wheels do hold up better than the older 6" and 4" counterparts though due to significantly less deflection when rolling at each roller tab.

As always, email me with any questions,

-Aren

Thanks for letting me know. And so that you know, whichever representative I spoke to on the phone back in January assured me that the 8" wheels DO have the new revision rollers. This was months ago, so I assume the rep isn't giving that info anymore. We likely would have gone with the 6" had I known.

And it's important to mention, then, that the feedback I gave about the rollers becoming wobbly was about old version rollers, not new ones. I would edit my old post, but it has been too long.

[Aren_Hill]

Originally Posted by Monochron

Thanks for letting me know. And so that you know, whichever representative I spoke to on the phone back in January assured me that the 8" wheels DO have the new revision rollers. This was months ago, so I assume the rep isn't giving that info anymore. We likely would have gone with the 6" had I known.

And it's important to mention, then, that the feedback I gave about the rollers becoming wobbly was about old version rollers, not new ones. I would edit my old post, but it has been too long.

I was a little curious where you heard that, apparently I did not keep them completely up to date, apologies for that. If you have any similar questions in the future please email me.

-Aren