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)?
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.
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.*
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.
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.
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.
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
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.
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…
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?
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.)
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.
Hm… that lack of lateral grip might make Versa wheels a great choice for the outer 4 wheels in an 8 wheel tank drive.
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.
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.
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.
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?
A custom wheel with tread of your choice i prefer mcmasters blue nitrile tread personally
Cool. Do you have a part number?
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