Andrew,
I hope this helps a little.

In 2002 the belting material that we applied was cut by hand from part number 5994K854 in the McMaster-Carr catalog. We glued the tread to our aluminum wheels, and then used small screws to hold the edges in place. The belting never came off, and wore down a fair amount over 2 FIRST events and an off-season event. We probably should have changed the tread out for new pieces somewhere along the line.

In 2003 the belting material that we applied and used at Silicon Valley was cut by hand from part number 60155K113 in the McMaster-Carr catalog. We glued the tread to our aluminum wheels, and used a few small screws to hold the ends in place. During the regional we ditched the screws because although we didn’t think they’d make contact with the surface (they were pretty well recessed), we wanted to be within the rules as much as possible (regarding no metallic items touching the ground). We used zipties in place of screws to hold the edges of the belting in place. We changed tread Thursday and Friday nights before the pits closed at the competition (the grating on the ramp tore our tread up pretty well). It was a long process which would have been made a lot easier if we had built an extra set of wheels. Oh well.. that’s next year, I guess.

The belting material that we applied for Cal Games was cut by hand from part number 5994K854 in the McMaster-Carr catalog. We applied this tread with glue, and held the edges in place with zipties. This material was a lot more resilient in the face of the grating on the ramp, and not that much of a difference in CoF on the HDPE (it was a little less, but we didn’t drive like we were on ice). We had to change one tread (along with many other drivetrain problems that weren’t tread related), and we were forced to secure it with only zipties. We replaced old zipties with new ones after each match down the stretch. After about 12-15 matches in one day, the tread wasn’t as worn as the tread we used at Silicon Valley after only 4-6 matches.


Adam Y,
A parent on our team who works at Northrop-Grumman is going to look into getting us a sample wheel with neoprene casted around it as tread material. I’m really excited to see how that compares to the belting materials that so many FIRST teams currently use.

These wheels look really cool. Where did you get the gum rubber? How much did it cost? Were there any problems of tearing at the bolt holes?

Thanks

We got the Gum Rubber from MSC Industrial Supply.

I don't know the cost but the rubber is 1 inch thick and each wheel has 2 6'' round tires. They did not tear.

They didnt even really wear down after 10 competitions!!

Thanks guys for the information. Gives me a lot to think about in what remains of the pre-season.

Now it just remains to be seen what the rules this year will allow or not allow!

Re: What do you use for wheels?
 

... the material that we think would best serve the purpose of the competition... :D

Re: What do you use for wheels?
 

My, wasnt that enlightening... :rolleyes:

Re: What do you use for wheels?
 

8" Mongoose MountainBoard Pneumatic wheels and tires worked incredably well for us during 2003 season. If the new game warrents it, we will use them again. Or if we need too, we will switch to tank tread if the new game requires a lot of climbing.

Oooooh Pretty.
 

I found the tires you were refferring to...
I'm just wondering:
What kind of Coeff. of Friction did you get with those on carpet?
Somewhere in the 1.2-1.5 range?

Or... what kind of linear pushing force was your robot able to exert on the carpet?

Inquiring minds want to know!
(We're looking at better tire options for 2004)

Thanks,
John

casting tread material
 

Some of the coolest wheels that I saw last year were on (I think) Team 74's robot. They had machined center hubs with some form of urethane or other soft material cast onto the hub. They either had the mold or pictures of the mold at Motorola Midwest. They appeared to work pretty well too.

We used double-sided cogged belt glued to aluminum sprocket-type wheels. While this ensured great hookup with the wire mesh, it was also very poor durability. Our pit crew got very good at swapping in new sets of wheels. I'm hoping that our team will try something like the cast wheels this year.

Ken

Re: casting tread material
 

This seems like the thing to do from a cost, flexibility, and coolness stand point. The molds probably don't have to be too high tolerance to work and can therefore be made fairly inexpensively.

I'd be very interested to hear how this turns out. In particular, what material you end up using and where you get it, what material you use for molds, etc.

Re: casting tread material
 

Actually, cast molding so few parts could be pretty expensive. Though they don't need too high of tolerances, you've gotta cut a die set most likely from a solid block of a special steel alloy, spend the time to CNC it, plus the cost of the material you're making the wheels from... that's not TOO cheap, especially since you'd need to charge that all of that out at true hourly cost on the bill of materials because high school students probably won't be able to watch the whole process through...

Just some thoughts,

Matt

Re: What do you use for wheels?
 

John, I didn't do any Co-efficeint of friction testing, but on carpeting we had plenty of traction to push other robots around and we were very difficult to push of of the ramp. We won Clevland, runnered up at Great lakes, Seeded #2 in Newton, wonRI, and Won Sweet Repeat. I would say the wheel combonation was very effective for us this year. Also, Teams 47 and 48 also used the Mongoose wheel combo and both teams seemed to have good traction. Sorry I don't have anymore technical info on the tires, I don't care why it works, it just does! LOL :p Now if we want to get into the finer points of the trans or chasis fabrication or technical data of a 700 HP Big Block Chevy, now were talking! ;)

Re: What do you use for wheels?
 

I am from team 74 and we did form urethane wheels. We used skyway 8" wheel chair wheels, tore off the rubber around the outside. This gave us our rim. We machined two molds out of some scrap blocks. Placed the hubs into the molds that had a center pin large enough for the center hub. Clamped it down with a plate to hold it tight to the bottom. Then we just hand poured the urethane around the outside. We waited 24 hours and pulled the wheels out of the molds. The urethane held up well. We had good traction on the
HDPE. We ran two regionals with the first set. We decided to put a brand new set of wheels on for nationals. We still could have ran the old ones.

Re: What do you use for wheels?
 

Custom omniwheels each year for one pair of wheels.

Search CD for pics of the ones we've used from the last two years, and also look at Patrick's whitepaper on omniwheel-drive systems. He challenged our team to find a more efficient drive system.

Re: What do you use for wheels?
 

There are good things to each type. OVer the past years, there were four types of wheels that I saw unique, each with its own downside.

First are omniwheels. These are good when you have a finite amount of space and want to go with a simple, two-wheel drive train. Omniwheels have more control than a castor would.

Next, think table saw. A team two years ago at the Philadelphia regional fabricated lexan wheels similar to a one-way saw blade. Advantage: Better traction so that one could not be pushed. Downside: The wheels tore up the carpet, a big problem last year. Robots have many a time been shut off because they are tearing up the carpet. So you have a 50/50 chance with those wheels. it really depends on the competition.

Next, tank treads. Our team used treads in 2002, and it helped us tremendously. Teh advantage: We used conveyor-type belts for our treads, and this gave us tremendous traction (think more surface area). Downside: We would get small nuts and bolts stuck in the treads and cause slippage. It did, however, lend itself to four-motor drive easier.

Lastly, pneumatic wheels. These are a good standby. Most of the time, they're effective. They come in the kit (cheap), the area touching the ground can be changed quickly, and, they provide a tiny bit of cushioning to the robot. Traction can be an issue if the pressure in the tire is off because of the rubber.

Our team had found that the other wheels do not work as well on inclines (usually a factor in the game), and on any smooth surfaces, like last year's lexan surfaces. You could try to add grooves, or modify the wheels however, but make sure your wheels are one solid piece. I would not recommend adding anythign to a wheel for traction, because whatever you add, if you spin your whells, can and will come off. Not pretty in-between rounds to scramble and change wheels.

Re: What do you use for wheels?
 

That’s a really bad idea. With an only omniwheel drive base you'll end up just getting pushed around with very little forwards/backwards traction.

I don't know what kit you're looking at, but for as long as I've participated they haven't put any pneumatic wheels in the kit. There were wheelchair wheels(2 6" and 2 9" in 2003/2002), but those are just solid rubber, not pneumatic.

The surface you're thinking of is HDPE. The ramp walls were lexan, but I don't think anyone was driving on them(at least not intentionally ;))

And now onto the actual thread topic...
Be careful when picking out wheels with a lot of traction. Its great when you're going straight, but unless you design carefully you may have trouble turning. For example, last year my team used really nice solid neoprene wheels. They provided great traction on both the carpet and the HDPE, but we had a lot of trouble turning since we used 6 wheels. We were using only 2 drill motors so we ended up tripping(or near tripping) the breakers any time we tried to turn.

To make sure you won't run into the same problems, try reading Chris Hibner's white paper on drive train basics. You'll be able to find it in the white papers section when it comes back.