Does a polyurethane wheel have enough of a tacky feel to get some grip ?

Polyurethane can be cast to have a variety of hardnesses. It can be rock hard, or cushiony soft. You need to get the durometer value of the material to know for sure. The lower the number the softer. Durometer is usually defined as a "Shore" value.

Without an additive polyurethane is not normally tacky or gummy, unless it was mixed wrong (i.e. never cures). There are some additives that can be used to prevent full curing of the polyurethane, but you don't want it for something going over a dirty surface. If you need a replaceable tack surface there are brush-on and spray-on materials that will provide for this. The tack can usually be removed with alcohol or acetone, and reapplied. Check out art supply stores for starters.

-- Gordon

pogo wrote:

hardwood floor ? Or is it hard & slick more like Delrin

get some polyurethane paint, IE tool handle paint.

you dip your wheels into it, and have a nice, good grip "rubber" coating on it.

Rich

Alcohol will actually melt polyurethane. I use rubbing alcohol to clean the polyurethane wheels on my minisumos and they get a slight tack to them.

This quickly disappears as dust is picked up by the wheels. I've discovered that the 99% alochol makes the wheels too clean, and they pick up dust faster than when I clean them with rubbing alcohol (which is 70% alcohol and has some mineral oil).

This is correct. Alcohol may swell or attack polyurethane, as the material is made from alcohol. But I was thinking drugstore isopropyl alcohol, which is one third water. (I prefer the kind without mineral oil.) Most polyurethanes shouldn't be too attacked by this solution, though these days there are different polyurethane mixes (some even water-based) so it's always a good idea to test any possible solvents.

-- Gordon

hardwood floor ? Or is it hard & slick more like Delrin

Friction, or perhaps starting friction. Perhaps you can google to find tables of the coeficients of friction between the materials of interest.

Would be nice if it were so. Ever try to get polyurethane off of aircraft parts? If alcohol would do the job a lot of people would be very happy. The strippers that they have to use are _nasty_ stuff. Alcohol doesn't touch it.

The slight tack was there to begin with--what you're doing is getting off all the crud that it picked up.

Huh? The molecular structure of the urethane monomer is like that of alcohol only in that both contain carbon, hydrogen, and oxygen. It is not in any sense "made from alcohol".

The water is just a carrier, it's not the "base".

hardwood floor ? Or is it hard & slick more like Delrin

I've just been out looking at wheels today - for the purpose of running on a fibreglass pultrusion (smooth...shiny) to turn an encoder

I found;

Nylon is slippery Poly wheels are ok - not 'tacky' but much better than nylon Poly boat rollers are good Rubber wheels are better Natural rubber is best of all

I'm not sure of the hardness you need, but you want a wheel that will not deform too much under the weight of the robot. It has to be large enough in diameter and wide enough at the cross section so that with the hardness of the rubber tire, there is enough surface area to move the robot without slipping "under normal conditions," and not so much that turning becomes impossible or too power intensive.

The "tacky" feel is typically "molecular friction."

"Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives." - Alliance of The Polyurethane Industry

Irrelevent. The point is there is no single type of "polyurethane," or single method of casting or applying polyurethane. "Water based polyurethane" is precisely the definition of a Minwax product: " Water Based Polyurethane for Floors." I'm not going to argue what the definition of "is" is.

Those in the medical field well know to be careful about the use of alcohol as a cleaner or disinfectant with some types of polyurethane-based components, such as catheters. Companies specifically tout the additives they use to provide alcohol-resistance.

-- Gordon

OK, technically you're correct. But it's not alcohol like when cured.

So? Try to remove _any_ of them post cure by applying alcohol and you'll find that you are wasting your time and your alcohol.

Some time you might want to visit an aircraft plant and show them how to dissolve cured polyurethane with alcohol since you are so absolutely certain that it is alcohol soluble.

As for the medical warnings, that seems to be the only field in which such degradation is known and I find myself wondering why that is.

Hi John,

It probably depends on the additives that are in the polyurethane. You can get polyurethane coated wire to make coils for earphones and whatnot. If you read the directions for the wire, after you've made your coil, you brush on some alcohol. This cause the polyurethane coating to melt slightly and fixes the wire in place.

Depends on the state of cure. The polyurethane that we used on propeller blades, after curing for a month in the shop (which "by the book" meant it was completely cured) would clean right off of fiberglass with a selective stripper. When the blade came back from five years in the field that stuff wouldn't touch it.

Well ... that settles it. No polyurethane wheels for me! I will be using tetra-hydra-free-for-all, instead!

Huh? Why would not being alcohol soluble be a disadvantage in a wheel?

It was my attempt at a joke to lighten the mood ...