Re: Highest traction wheels
 

Anecdotal evidence from this past season indicates that Colson wheels to not grip as well as wedge top on carpet, but are absolute beasts on smooth surfaces...

...rattin' smattin' octocanum redesign...

So on a related note, what's the smallest wheel you can find (say, 2" diameter) with excellent carpet grip?

Re: Highest traction wheels
 

A custom wheel with tread of your choice i prefer mcmasters blue nitrile tread personally

Re: Highest traction wheels
 

Cool. Do you have a part number?

Re: Highest traction wheels
 

can't tell if your making a comment about the custom wheel part number or asking for the tread part number, but either way the tread part number 5994K852

Re: Highest traction wheels
 

Tread! Thanks!

Re: Highest traction wheels
 

no problem its worked good for us for the last two years. Last years bots tread finaly started to show significant wear after the season during demos while we were driving on pavement and concrete

Re: Highest traction wheels
 

I've heard good things about cutting tread into Colsons like so: http://www.team228.org/gallery/125/b...3511-8f172.jpg

I have no concrete evidence that this increases traction, but I know 228, 125, and I think 1477 all cut their tread like this so perhaps someone from one of those teams can chime in here with some data.

In response to Pat's questions about extremely small traction wheels, the only COTS ones I can think of are Colsons and Banebots, and even the hardest (blue) Banebots wheels would have to be changed too often to be worth it. I would at least explore the possibility of cutting treads into Colsons, because the alternatives are machining intensive.

Re: Highest traction wheels
 

Physics teachers the world over repeat this simplification. It is not true in real life. Coefficient of friction is a function of contact pressure for every traction system I've seen, namely coefficient of friction increases as contact pressure decreases.

There have been a number of tests done by forum members/teams indicating the wider wheels provide more grip with the same normal force... however I haven't been able to find the posts mentioning this yet.

You're making a simplification here, heat is not the only reason to use a wider tire/wheel. Wider tires/wheels allow for the use of softer tread compounds that might wear too quickly on a narrower wheel by virtue of having more material available to wear away.

A wider wheel/tire will generally have a contact patch with a more uniform pressure distribution than a narrower wheel/tire due to the wheel's/tire's structure's effect on the contact patch. The wider wheel/tire can thus generate more grip because the coefficient of friction is a function of pressure, and the wider wheel/tire has a lower peak pressure in it's contact patch compared to a narrower wheel/tire.

I suspect that the analogy of car tires to typical rigid robot wheels fails at one important premise: rigid wheels do not maintain the same contact area vs width because they do not have a controlled contact pressure (i.e. tire pressure). Thus a wider robot wheel could very well have a larger contact pressure.

This is the theory I've learned and experienced with race car design/driving and some FRC teams have demonstrated through testing robot wheels.

Re: Highest traction wheels
 

Cool -- that's easy to do, and the Colsons we're using are cheap enough to ruin without feeling bad about it!

Re: Highest traction wheels
 

IIRC, I've heard numbers of 1.4-1.5 COF being thrown around when talking about Colsons with treads cut into them. Don't quote me on that, as I'm not 100% sure, but I will try to confirm when I get a chance.

This, all of this.

One thing that I'd like to add, is there's also a 'cleat-ing' effect (mechanical interaction) between some wheels and carpeted surface. Roughtop Tread (any form, though harder is better) and the 'W' tread on versawheels are both good examples of materials where this comes into play.

Think of something like a plastic carpet runner, the kind with little plastic spikes on one side and a textured surface on the other. If you applied traditional friction models to them, you'd see that the math just doesn't add up. (or shouldn't add up) If you dig into this a bit more, you'll start to see that the spikes dig into the carpet and make it seem like there's more friction between the two surfaces than there really is.

Re: Highest traction wheels
 

We used 6" x 1.5" Colsons this year in a 6 wheel system with about 1/4" centre drop (which was too much). The drive team loves them. It's pretty difficult to tell if they're better with or without tread but after reading other threads on Colsons, we cut a diamond pattern tread in them using a dividing head on a horizontal mill. A thin slit saw set to cut about 0.100" deep slot on 15 degree intervals and about 15 degrees of parallel seemed about right. After 3 regionals and championships they show little wear. We did experience some lateral shifting of the wheel on the hubs we used but only on one or two of the outer wheels. Next year, we'll cut a coarse thread in the hub before pushing them in and maybe use a bit of PL Premium to help.

Re: Highest traction wheels
 

Nice. Our traction wheels were 2" diameter x 3/4" width Colsons with no tread pattern of any kind cut in them -- we just broached the center hole to a hex and put them on the shaft with appropriate spacers, and they worked like a charm (except for not having quite the traction we wanted.)

Re: Highest traction wheels
 

http://teamwhyachi.com/wheels.htm

45a tread. 2.25" dia

priced in the lol price range at $41


you could also modify a pulley like mcmaster part #6235K72 to work as a wheel.

Re: Highest traction wheels
 

Sounds like "buy bar stock and use a lathe" to me!