High friction wheels for a sumo bot

[Maltaeron]

I am working on a sumo robot and I am looking for high-enough friction 2 inch diameter wheels to be driven by two modified HS-485HB servos (83.3 oz inches at 6v).

The problem I have is that it is hard to compare various wheels I find on the internet and some can be very expensive! The one shown here http://www.active-robots.com/products/motorsandwheels/easy-roller.shtml is $20 per wheel and a little too large. I believe the kind of wheels I should use are hard foam, because of their high traction properties, but I don't really know that. These ones http://www.robotcombat.com/products/0-DAV5520.html seem to fit what I need, but as they are advertised for aircraft, I am not really sure they would be suitable for a sumo bot.

So my questions are: What kind of material wheels should I be looking for? Does anyone have any recommendations for wheels for a robot like this? (regardless to any of my constraints) And, is there anything else I should know about this?

I have been dabbling in robotics for quite a while now, but I still feel very much like a newbie... Thank you all for your help!

[rbtying]

Use the aircraft wheels - they seem to be good for your purpose.  The only challenge will be mounting them to the servo horns, and that's not particularly hard. 

[Crunchy Theory]

From the look of the foam wheels, they might be very light. I suggest adding a significant amount of weight to your robot as that might make the most difference once you have a good amount of traction with the wheels.

[Soeren]

But... You need to select your wheels (especially with foam wheels) after the weight of the 'bot.

[Maltaeron]

Well, I ordered the wheels after rbtyping's reply and am still waiting for them to arrive. They will probably show up on Monday and then I will be able to see how well they should work, but my robot is still mostly in planning right now. The robot is allowed to weigh up to 2kg, so I should think that is heavy enough.

Soeron, considering a weight like that, do you think these wheels will suit me, or do you have another recommendation?

Thanks

[Soeren]

Hi,

Soeron, considering a weight like that, do you think these wheels will suit me, or do you have another recommendation?

I have no real idea of their carrying potential (the web site really ought to put that info on the page).
Only clue is the text
 "These are some of the lightest wheels you'll find for your antweight bot"
And the website Robotics-Society defines antweight as...
 "Robot Weight Range:  0-454 g (0-1 lbs)"

I don't know if that's a universal definition, but it probably mean that you shouldn't put 2 kg on the wheels in question.

With wheels in general and foam wheels in particular, you have to select wheels for a certain range of compression percentage. Too much weight and the tyres will compress too much, making it run on the rim and too little weight and you'll have too little traction.
That's why I mentioned finding the weight before selecting the wheels.

Did you consider making your own wheels?

[Maltaeron]

At all the places I saw selling foam wheels, I couldn't find information of carrying potential.

I have lightly considered making my own, but I really don't know if I would be able to do so reliably or to what specifications I should make them or what materials I should use. I just did some quick google searching for information on making them, but the main thing I found was a bunch of guys complaining they couldn't find information on making foam tires...

[Soeren]

Hi,

I have lightly considered making my own, but I really don't know if I would be able to do so reliably or to what specifications I should make them or what materials I should use.

You could try a hole saw/cup drill on MDF of a suitable thickness (or glue together a couple of thinner after cutting them.

Then use a bolt of the right diameter (same as the lead drill) and a nut to make it able to go in a drill and sand them with #80 to #120 to a plane surface.

Finally, add a layer of foam neoprene (perhaps try to get free leftover bits from a diving shop that makes suits), or some of the mat material that can be had for keeping stuff from sliding in a car trunk.
Contact cement should be good for bringing MDF and foam into wedlock.
Or, cover the MDF with RTV silicone (this will be hard to get to a smooth finish though).
It's cheap to experiment with such stuff.

Hubs can be made from brass tube with an inner diameter matching your motor shaft and the outer diameter matching the hole from the lead drill (use epoxy glue for mounting them in the MDF and either a set screw (either make a thread for it if you've got the tools, or braze a nut over a perpendicular hole), or slice the tube and use a clamp).

I have used MDF (and chipboard before MDF was a reality) that way for making wheels on many a toy car.

[nickc]

I have a friend who has made his own from castable urethane.  It comes in two parts like epoxy and various hardnesses.  Something at the soft end of the spectrum works well.  He used an aluminum hub and made a mold for the tire.  I know he had good success with the bots and won several sumo matches against opponents that far outweighed his.

[Rick Brooks]

Maltaeron,
Here is a link for molding high traction tires out of polyurethane:http://brooksbots.com/ExSpurt%20Tires.html
That may be a little more work than you were looking for.
Also see this page for testing traction: http://brooksbots.com/Exert-O'Meter.html  You might get some more ideas there.
I assume that you are doing this for Science Olympiad.  I so, you don't have much time left.

Rick Brooks

[Maltaeron]

Well I just got the wheels yesterday, and, after playing with them, they seem to be holding extremely well. They have great traction as I had hoped, and with just 2kg they do not compress anywhere near enough for their to be a problem. I think these will do just fine.

Thanks for all the information about making wheels and what the various considerations are!