Highest traction wheels
 

Out of AM's HiGrip, Plaction, and Pneumatic Wheels, and these Colson wheels I've heard about. What definitively has the highest traction (on "smoother" surfaces)?

Re: Highest traction wheels
 

That is the key point in this question. Given that you're looking for traction on a smooth surface, rather than on carpet (which most teams are more used to dealing with) I can't give you a definitive answer, for that matter, there may be some debate on whether or not there is one, but that said I'll try my best.

There's really two things you want to be looking for to answer this question: Contact point surface area, and material types.


On a smooth surface, wheels with more surface area in contact with the surface (IE, a smooth wheel like a Colson wheel) should have better grip than one with less surface area in contact with the floor (like a Plaction wheel).

That said, material type is important too. As we saw in years past, if you put plastic wheels on a plastic floor, the result is very little traction. Taking that into consideration you may find that wheels with certain kinds of rubber (or other gripping material) grip better than others. I've not personally played around with Colson wheels on a smooth floor, but I do know that AM's HiGrip wheels have an extremely grippy rubber surface, meaning they may actually grip better even though they have less surface area in contact with the floor.

Of course if you REALLY want to grip the floor, there's simply no substitute for Tank Treads.



Disclaimer:
I don't claim to be an expert on traction, and I'm sure someone more knowledgeable will explain it better, these suggestions are based on my own personal observations over the past 8-ish years.

Re: Highest traction wheels
 

I believe some of your statements are incorrect. Usually, the only variables that affect traction are coefficient of friction and weight. Because wider wheels just mean that the same weight is spread over a larger area, you have the same amount of traction. This is different when roughtop tread and carpet interact, because the roughtop "locks" in witht he carpet and increses the amount of traction you have with wider wheels. This is also like drag racing, where they heat up the wheels so that they "stick" to the ground and wider wheels have more traction.

To answer the OP's question, I have heard that colsons have the most traction on flat surfaces.

Re: Highest traction wheels
 

Please elaborate on "smoother" surface.

Last year we found that there was a dramatic difference on the polycarbonate between the various wheel types. The Hi-Grip, when clean had a lot of traction where-as wedge top (usually a pretty good choisce for carpet) was quite poor.

Colsons were nice in that they had the least change (for us) surface to surface. If you are not worried about durability, in general the softer the durometer, the grippier the wheel.

There are also some really neat compounds out there that have exceptionally good grip.

Re: Highest traction wheels
 

This is also in effect on robots. The wheel will heat up during use and can gain traction because of this.


As stated above, softer wheels will do you better most of the time. However, when I built bots that drove on painted wood surfaces or stainless steel surfaces, a very soft foam wheel often had less traction than a harder rubber wheel.

One more thing,
When running a robot on a hard surface, the surface quality effects traction much more than on carpet. Sticky wheels will suck up dust and their CoF will quickly change.

If this were my project, I would first try a few different types of urethane wheels and test to see if I liked the results. I would also try a few different tread patterns.

Re: Highest traction wheels
 

RC carpet racers use foam wheels on carpet. Porous foam tends to grip really well on carpet but it would be impratical for frc use because of how quickly it wears

Re: Highest traction wheels
 

I think there are a couple of misconceptions here. There contact area will actually not be increased by that much with a wider wheel. It sounds odd, but the pressure that would be applied over a thinner wheel is now spread out over a wider one. That lower pressure doesn't allow the tread to expand as much along the wheel. However, because your width is greater, the contact area is roughly the same.

Second, drag racers have wide tires solely because of heat. You need big tires to dissipate it all. The stickyness that happens does, in fact, increase traction because it now brings in adhesion (your coefficient of friction is now >1). It literally is pulling the car down when this happens. However, in our situation, our wheels aren't producing near enough heat to do any of that.

Another thing to remember is that friction is very inexact. It's been seen in some circumstances that the coefficient of friction can change with respect to load (which goes against classical friction theory). There may be many other factors that come in to play as well.

Re: Highest traction wheels
 

There's simply no substitute for testing in this case-- as Michael said, friction is quite inexact, and this is especially true on FRC robots. If at all possible I would test you options on whatever surface you're thinking of driving on-- the calculation for coefficient of friction is quite simple.

You know, testing this on an actual robot would be an excellent summer project...

Re: Highest traction wheels
 

I've actually heard that Vexpro Versa Wheels have the most traction on FRC carpet. I have not used them and can't back this up. I think that 2337 did this year, maybe someone will read this and correct me?

Re: Highest traction wheels
 

They have good grip in the forward axis due to the "W" pattern, but horrendous grip in the sideways axis. This was confirmed for experimentally for us at Championships. (It wasn't our robot, mind you.)

Re: Highest traction wheels
 

You're not referring to team 1684, are you? Our pits were right next to each other, after all ;).

We did have diffuculties with being pushed sidealong with the VexPro tread on 8-inch wheels in a 6-wheel configuration.

Re: Highest traction wheels
 

Hm.... that lack of lateral grip might make Versa wheels a great choice for the outer 4 wheels in an 8 wheel tank drive.

Re: Highest traction wheels
 

I would personally prefer drop-center or omnis. They have some grip, enough to interfere with turning if you were to use them like omnis, but not enough to stop a robot with even a weak drivetrain to push you sideways into a wall with ease.

Re: Highest traction wheels
 

In pneumatic tires or equivalent, this is true. Widening the tire will not change the contact patch, the patch will grow wider but shorter. Thus the way to increase the contact patch is to make the wheel a bigger diameter. I need to dig around to find the book I referenced this from.

However, for solid wheels I do not think this is totally true. I think it behaves more like a rack and pinion. I think the contact patch is small, so to make it bigger is to make the wheel wider. As with gears, you can't make more teeth mesh, but you can make the teeth wider to hold more load (assuming the DP is constant). If your "teeth" on your wheel can hold more load, you have more traction. Of course this can't be totally true because the wheels sink in the carpet a bit.

Re: Highest traction wheels
 

We've done some static friction coefficient testing on both carpet and polycarbonate surfaces and found that the HiGrip wheels are excellent. We, however, did not test Colsons (even though we used them last year) or Versa wheels (yet - we have purchased a set for testing).

We test on two axes: the in-drive direction and perpendicular to this.

I agree that friction coefficient (between the wheel and driven surface) and the normal force applied between these two surfaces (generally the robot weight) are the key factors in determining traction.

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!