Re: make vs. buy wheels
 

Metal doesn't give you splinters if it's worn down too much or beaten up... but wood is cheaper. Anyone try plastic at all?

Lots of teams use blue nitrile tread (I think McMaster carries it), though others prefer roughtop or wedgetop tread (not sure on where to get those). A little suggestion: use CD's search feature, looking for "blue nitrile tread", and you should find some websites.

Re: make vs. buy wheels
 

The common tread people use on custom wheels (and on IFI and some andymark wheels) is sold as "incline conveyor belting" from mcmaster. There are two surface types, wedgetop and roughtop.

The wedgetop is just offered from mcmaster in gum rubber (but I've seen some teams, 188 in 2007, with black SBR rubber).

The roughtop is offered in many types, but is most commonly used in natural rubber (tan), SBR rubber (black) and Nitrile (blue). Nitrile seems to wear the best by far, although offering reduced friction. The natural rubber seems to be commonly used, but can wear very fast. I've seen very few teams use the black SBR roughtop, but it seems to be closer to the natural rubber in performance and wear.

Re: make vs. buy wheels
 

We used the 'Wedge Top' belting in 2006 and it seemed to wear out pretty quick. I think in total we were forced to re-tread our wheels at least once a competition. Also, we've noticed that it dries out after 6-8 months which will end up reducing your traction.

We have used the black 'Rough Top' the past two years. It seems to hold up much better than the 'Wedge Top' does. Both years we were able to put about 15 hours of drive time, or roughly 415 matches, before the tread had to be changed on our practice robots. I don't recommend letting your tread get to this point in competition. We change ours about once every competition.

Also, the 'Rough Top' doesn't seem to dry out like the 'Wedge Top' does. Our 2007 competition robot has had the same tread on for the last 10+ months and it feels that same as when we cut it.

Re: make vs. buy wheels
 

My favorite wheels have got to be the colson wheels (found here and a billion other places). They have lots of traction, they're very thick, so as the tread wears down nothing needs to be replaced, they're light, and they're dirt cheap to boot. We used the 7/8" wide variety and they had plenty of traction.

Many people will say that the conveyor belting material offers more traction. I am dubious of this.

Although the conveyor belting material does have a higher coefficient of friction than the colsons, you must remember that it was designed to move food.... Food usually isn’t dirty (I hope), and it also doesn't offer much wear.

Colsons on the other hand were designed to be used as castors for heavy equipment. They are meant to work in dirty environments. As a result, Colson designed them to be resistant to dirt and wear slowly (they brag about this on their site).

We never had to change the wheels all season.... But we did replace two of them with omnis since they offered too much traction :D

Re: make vs. buy wheels
 

Some teams buy pneumatic wheels and modify them to interface with AndyMark or IFI sprockets. 330 goes through several sets a season, just because they drive them so much. Figure 2 sets of pneumatic caster tires per season, for competition only, and a third set in the offseason. And that's only the competition robot! Then again, that's better than blue nitrile, which may have to be replaced once a competition at minimum.

Re: make vs. buy wheels
 

In the past we have used Wedgetop (Gum Rubber) and Roughtop (Gum Rubber and SBR). We like the SBR roughtop, we got really good traction and it didn't wear too bad. When we used the Gum Rubber Roughtop it wore really quickly and it seemed like we had to replace it every couple of matches. And then there's the wedgetop. Like Jon Jack said, it dried out so now the traction has dropped off a lot.

Re: make vs. buy wheels
 

To cut down on maintenance time, we retread our practice robot wheels before every competition. This way when it comes time to replace a wheel we can simply take off a wheel and put a practice robot wheel on with the new tread. This way the time can be taken to remove the old tread and attach the new tread properly, without the pressure of getting it done before our next match.

After making custom wheels the past three seasons, I've got to say that outside of the potential weight savings it's not worth it. In 2007, I think I calculated it to have taken us almost 40 man hours to make 18 wheels. This year it took us just as long to make 28 wheels. All the while there are the machines and the students and mentors operating those machines that are tied up. That's a lot of time allocated to wheels just to save a few ounces and a few dollars.

I'm pretty sure we won't be making our own wheels again this year, as long as the new AndyMark wheels look like a viable option. By spending a couple hundred dollars we can have all the wheels we'll need, ready to go out of the box. Plus it frees up an extra 40 hours of machine and student/mentor time.

Re: make vs. buy wheels
 

Team 1251 have used UHMW for their wheels for 2 years and have had success with them. UHMW stands for Ultra High Molecular Weight plastic. Perhaps, Dave from 1251 will probably come across this post and post their experience with those wheels.

Re: make vs. buy wheels
 

UHMW or ABS plastic are both very dense plastics that work great for wheel applications. We used UHMW 2006-2007 and had very little problem with it, it is critical to remember you are working with a plastic when toleranceing these parts however that is where you run into trouble. http://www.chiefdelphi.com/forums/sh...ght=1251+wheel Here is the thread on our 06 wheels and the next year they were redesigned with a flange for the wedgetop to sit in. We reccomend sheet metal screws with a mushroom head to attach the tread and not rivits. I know the 07 was a 4 in dia wheel and the 06 I think was 6 in dia. When machining this plastic use coolant as the UHMW especially does not like excessive heat. 1251 has had custom wheels since 06 and dont ever regret making them. Making wheels is great if you have the time, resources money etc, if you don't buy them or modifiy the kit wheels with some high traction material as Arefin has showed us many times. The AndyMark FIRST kop wheel is a good product in the first place.

Re: make vs. buy wheels
 

Those look slick. And i assume you used the incline conveyor belting for traction. Ya, for us that little weight could matter a lot. About 300 holes later this year, our robot clocked in at 119.8, afterreplacing the sponsorship material :) And to mount the incline conveyor belting do you use rivets, screws, or something else? Thanks :D

Re: make vs. buy wheels
 

O, and how much did those wheels actually weigh?

Re: make vs. buy wheels
 

I think our 2006 wheels were like 0.28 lbs a piece, those are the ones drew posted. They were 5" in diameter and 2" wide.

Our 2007 wheels were 0.18 lbs a piece, 4" OD and 1" wide.

Since 2006 we have been making our own wheels and will probably continue to do so. For us, it is much cheaper to make them then to buy any of the ones that are in the market right now. They are also much lighter.

Overall UHMW worked good, but after some time the bearings began to get a little lose on the counter bores. The wheels were very tough, in fact in my opinion they handle impact better than our new aluminum wheels.

Best picture I could find of our 2007 wheels: http://www.chiefdelphi.com/media/photos/27927

For 2008 we decided to go with aluminum because we wanted to run them on live axles with a 1/8 key. There aren't any good pictures of them online. I will try to find one and upload it.

Re: make vs. buy wheels
 

We made our wheels have hex holes in them where the shaft goes, and they also looked really really nice.

Re: make vs. buy wheels
 

We have just been throwing conveyor thread onto the kit wheels for 3 years now, (8" Skyways?) and it works great. We never had a tread fall off or a wheel break, but if it did we could easily get another because the wheel was from the kit, and it only takes about a hour to put the tread on. (and a lathe)

Re: make vs. buy wheels
 

since we generally have a good idea of what our base is going to look like early on in the design process we know what size and style wheel to use early on, therefore we start machining our wheels and lightening our gearboxes early on in the season while the rest of the robot parts are being designed. that way we are already done with our wheels by the time it is time to get to machining other robot parts. a major part that goes into our decision on whether or not to machine our wheels is if they will be seen or not, b/c they do add an awsomeness to the robot as previously said. unfortunately there seems to be a curse around this decision b/c whenever we machine wheels they seem to be covered up by bumpers or something else, but if we decide to use purchased wheels they are always in plain sight. i guess ive kind of digressed but my main point is that as long as you plan your robot out early, you can machine your wheels without using up time that you could use to machine other parts.