I have no preference. I just get what I need as long it will get the job done to my requirements and standards (As high as the sky)!
The plates were bent all out of shape and the bolt “axles” that we had bent and broke. Most of them were fixable, but with more resources than those that are available to teams at a competition, such as a large finger brake.
We switched from AM 6" to VEXPro 6" last year, and here’s what we found:
VEXPro wheels are lighter, every bit as durable, and drive pretty much the same.
Silly question: do VEXPro and AndyMark have the same mounting configurations? That is to say, can we use AndyMark hubs with VEXPro wheels without modifying either?
The mount pattern is the same. (6 Size 8 holes on a 1.875” circle). I don’t know how well they work together though.
Thanks everyone for your input so far. It seems like many of you claim that not only 6" wheels just as durable and effective, but in some cases even more so. This sort of surprises me a little bit, but I guess my viewing experience is limited to only a couple regionals and some YouTube videos. I do have one additional question to ask. I have heard (and seen) that a four wheel configuration does not turn very well in a long drive base. I am curious as to how the wheel diameter would affect this capability in a long mecanum setup. Watching this video, it seems like AndyMark has a setup that turns admirably well in a long configuration on 8" wheels.
As a team that used these wheels this year they are great as long as you don’t misuse them. Ie. Drive them on black top or other non-smooth surfaces. They are much lighter, drive the same and are worth using.
You can use the Andymark hubs if you modify the wheels slightly. In order to make the hub butt up against the wheel side plate you will need to sand off the little nubs that are designed to connect to the Vex Versahubs.
As mentioned above the mounting pattern is the same (6 holes spaced evenly on a 1.875" circle) however the pattern on VexPro products are designed for a #8 bolt while the pattern on AndyMark products are for a #10 bolt. So an AM hub on a VexPro wheel might not be completely centered, unless the wheel is bored out for a #10 bolt.
If the mecs are designed, manufactured, assembled, and mounted properly, and the vehicle allows each of the 4 wheels to touch the floor with sufficient force to prevent slipping, a long drive base should work fine.
We are switching vex because it is lighter, as previously mentioned. They are mask of abs (mostly), so they are strong.while staying light
Can you show me where you got this data?
It didn’t sound right to me so I checked the websites:
Vex 6": 1.33 lbs
http://www.vexrobotics.com/vexpro/wheels-and-hubs/mecanum-wheels.html
AM 6": 1.3 lbs
http://www.andymark.com/product-p/am-0136L.htm
Thanks!
That didn’t seem right, so we threw some on the scale:
6" VEXpro Mecanum Wheel: 1.25 lb
8" VEXpro Mecanum Wheel: 1.90 lb
Note, this includes the internal threaded standoffs used for mounting a sprocket or hub onto the wheel.
I’ll have our guys update the website.
We really liked the 6 inch VEX Pro mecanums this year for the most part. However, after 2 regionals and championships and several demos, they decided to eat themselves. Within two weeks of each other rollers started breaking off of 3 of the wheels. During one demo, 10 of the 12 rollers broke off of one of the wheels in rapid succession. It made for a clunky performance, but we gave the rollers to the kids we were demoing for as souvenirs. Since our robot looks like a rabbit, we just called the rollers “droppings.”
We had to replace all 4 wheels before Cowtown Throwdown. It would have been devastating if it had happened during competition though.
That said, I have generally been very impressed with the products that VEX Pro puts out and I plan to continue usung their products regularly.
Were these demos on a non-flat non-carpeted area?
It’d be nice if all wheels are great on all surfaces, but with something as funky as mecanums I’d certainly be happy with merely lasting great on flat, carpeted surfaces.
? Where did the 12 number come from
This particular demo was on a flat gym floor. No carpet, but once one fell off the rest were doomed because of the additional strain on the rollers.
I dont have one of the wheels in my hand right now, but I believe there are either 10 or 12 of the diagonal rollers on each of the wheels. All but two broke off.
As for where the number twelve came from, that goes back to some ancient paleolithic people that had one more than eleven of something and had to come up with a name for it. Just a guess. 
We use 6in AM just because they’re cheaper then the 8in and we were tight when we got them. Haven’t had any issues
So, we are debating about 6 inch or 8 inch mecanums, I think! I really think 8 inch wheels are ideal. They aren’t massive, nor are they small. You wan’t a balance. That will allow you to get the best out of both worlds! If you have too big of a wheel, it will be heavy, and wouldn’t have as high of a torque. If you had too small of a wheel, you would have a high torque, low speed drivetrain. This can all be compensated for within the transmission! If you have a smaller wheel, it would need to turn faster. Wouldn’t that mean that the rollers would be turning faster, meaning more maintenance would be needed? If the rollers are turning faster, doesn’t that mean that a greater consistency between wheels would be needed to keep the robot from strafing?
AndyMark should make 7 inch wheels 
What constitutes “too big?” What constitutes “too small?” Do you have any actual data or experience on the performance of different wheel size that indicates that 8’’ is the “proper size?” Your mention of 8’’ as being a “balance” in the absence of any empirical justification seems more like anchoring than anything else, and your anchor here seems fairly arbitrary.
The first effect you mentioned (roller speed resulting in more wheel maintenance) is completely marginal; most of the wear on your wheel is most certainly not going to be wear from the rollers rolling, and besides I can attest that haven’t had to do any serious maintenance on a mecanum wheel of any size since AndyMark’s thin-plate 2008 6’’ models. The second effect doesn’t, in general, match my observations - 6’’ have always seemed to strafe far better for me than 8’', though I admit this is likely confounded by center-of-mass placement on the robots I’ve worked with. Perhaps someone could actually test this, if they’ve got a practice frame and some time on their hands?