Where can we find good pneumatic wheels?

[Chris is me]

Originally Posted by EricH

I don't know about the MBS wheels in terms of traction and wear; mountainboards aren't exactly designed for light use, though. (And they're not designed to be self-powered...)

For what it's worth, neither are the McMaster wheels... They're for casters, no?

Mountain board wheels are high traction, but that's partly because they're designed for dirt and grass. Thus the wheels are pneumatic to increase their contact patch, since on loose non-carpet surfaces your surface area comes into play (dynamic friction due to deforming surface). So how they perform on carpet remains to be seen.

Do keep in mind traction for non driven wheels may not be the #1 priority. Scooter and inline racing wheels are a perfect size for first (90-125mm) but have a polyurethane tread with a hard 80-95A durometer to decrease wear and to allow for controlled skids.

[Ian Curtis]

Originally Posted by EricH

The McMaster ones are high-traction. Give us 2 of those as our center wheels, and we'll able to hold our own in a pushing match if needed. 4, and we'rr a bit better. They wear well, too; when you see the red, pull out the spares, but you've got a few more matches. One set could last an entire event, eliminations included, and be usable in practice later. The cost is about the same, $20 US/wheel, but McMaster is known for fast shipping if they're near your area (and willing to deal with you).

I don't know about the MBS wheels in terms of traction and wear; mountainboards aren't exactly designed for light use, though. (And they're not designed to be self-powered...)

1276 used pneumatic wheels and hubs intended for mountainboards in 2005 for our two powered rear wheels. The front two were omniwheel casters. We played in the vicinity of 10 matches (qualifying plus 3 elimination rounds), had a week of driver practice and two more years of abuse driving it on just about everything as a defender for driver practice and demo bot. They stood up just fine. I don't remember the vendor, it was just some mountainboard shop we found online.

You can barely see the top of one in the lower right.

One of the reasons we gave up on pneumatic wheels was they make driving straight (especially in autonomous) a really big pain in the butt. We found how straight we drove could be impacted hugely by a relatively small difference in tire pressure. We found it much simpler to drive in a relatively straight line once we made the switch to solid wheels. YMMV, or you might actually finish on time so you have time to test better code!

[akoscielski3]

Originally Posted by ChrisH

Major bumping, several inches in the air bumping. Pneumatic tires bounce really well once you get them started, and if you keep going they bounce higher. If we're using 6 wheel drive we'll probably have plaction wheels on the corners. They slide sideways pretty well without giving up much in the way of fore-aft traction.

If everyone was havng problems with 6WD why was 1114 moving so easily with 8WD (2010).

[AustinSchuh]

Originally Posted by akoscielski3

If everyone was havng problems with 6WD why was 1114 moving so easily with 8WD (2010).

I would be very surprised if 1114 had all 8 wheels in the same plane. I bet that the center four wheels were dropped slightly, on the order of 1/8".

[EricH]

Originally Posted by AustinSchuh

I would be very surprised if 1114 had all 8 wheels in the same plane. I bet that the center four wheels were dropped slightly, on the order of 1/8".

And that made the wheelbase shorter than ours in 2006, where we had very little drop and 6 wheels. Long wheelbase=tougher turning, in general. This is why most 6WD robots have a dropped center wheel or omnis (or other low-friction wheels) on the corners. We didn't have nearly as much trouble after putting Skyways on the front corners.

Link to the McMaster wheels: go to the McMaster site and enter the part number into the search box. You'll get the page; the wheels are near the bottom. We used the gray treaded ones.

[Karthik]

Originally Posted by akoscielski3

If everyone was havng problems with 6WD why was 1114 moving so easily with 8WD (2010).

There's considerably less "bounce" in the 8WD we had compared to the 6WD that 330 employed with the same wheels. If construct a polygon between the centres of our wheels this year (or any standard 8WD) so get an upside down trapezoid. If you do the same with a 6WD you get a triangle resting on a vertex. Looking at these shapes, it's easy to see why one would have more rock, and thus more bounce.

Originally Posted by AustinSchuh

I would be very surprised if 1114 had all 8 wheels in the same plane. I bet that the center four wheels were dropped slightly, on the order of 1/8".

Austin is correct. Here's a picture where our drop is depicted pretty clearly.

http://www.simbotics.org/resources/g...l/_3260103.jpg

[Chris is me]

Originally Posted by EricH

Oh, and using 6 of these wheels on a 6WD is asking for turning problems, even with a dropped center wheel.

Tell that to 70, 494, 469, 1114, and 2370 last year. 2370 actually used four pneumatic wheels in the long configuration - and turned just fine, somehow! I'll never understand that.

[EricH]

Chris, I said 6 of those wheels in a 6WD drop, in 2006. We had trouble turning. I don't know if there is any video of the Arizona practice rounds around, but we bounced around a bit.

Solution: the front wheels, which were the primary off-ground wheels (6WD drop drives rock a bit, but can be weighted so one set or the other is mainly on the ground), were replaced with 6" Skyways. No more problems. In 2005 we used 6" Skyways on the corners; in 2007 we broke quite a few AM hubs on our rear wheels, but not so many on the front wheels. (We also caught a hub that had partially failed. Mark Koors happened to be the FTA at the event, so he got a wheel in the process of failing for analysis.) 2008 saw the revised AM 6" wheels on the corners.

[XaulZan11]

Originally Posted by Chris is me

Tell that to 70, 494, 469, 1114, and 2370 last year. 2370 actually used four pneumatic wheels in the long configuration - and turned just fine, somehow! I'll never understand that.

Didn't 70/494 have a crab drive in the wide direction?

[Wayne TenBrink]

Originally Posted by XaulZan11

Didn't 70/494 have a crab drive in the wide direction?

Yes.

[Jay TenBrink]

Originally Posted by XaulZan11

Didn't 70/494 have a crab drive in the wide direction?

When we were in skid steer mode we had a wide aspect ratio. Traction was a consideration. As the tires wore down and got stickier it was harder to turn. In the off season we put tape on the front tires to reduce traction to make turning easier.

In the past we had long aspect ration bots with skid steer. In 2004,5 our tires were about 10-12" OD. They took lots of power to turn and were not " precise". On a high center of gravity machine there was quite a bit of bucking/tipping. We started out this way in 2006 and ended up with 2 omni wheels before we shipped.

On a low CG bot the long aspect ratio configuration was OK. In the future we'd most likely go with the 6 or 8 wheel design.

Jay

[Wayne TenBrink]

Related thread about mounting sprockets, etc.

http://www.chiefdelphi.com/forums/sh...ad.php?t=88066

[Kevin Ray]

We've used pneumatic tires in 2002 and several other years but those were the best tires/wheels yet. They were small so there was little bounce, yet great traction. The fact that they were pneumatic also lent itself to correct for leaning and imperfections in the carpeted surface--four wheels were always gripping. That was the year when 71 Hammond Beatty had the crawler which dragged the two goals with the opponents kicking and fighting to the other side of the field--so traction was paramount.

Here's a link. At the time everyone made their own hub mounting plates. The following year, FIRST came out with hubs in the KOP. Two large fender washers with the holes bored out with the use of standoffs sandwiched in between worked well for many teams.

http://www.skywaywheels.com/products/caster/index.html

[Yalib]

Originally Posted by Joe Ross

50% of the time that 330 used mcmaster 2717T51, we went to Einstein. Your mileage may vary.

I'm also a member of 2630,
We checked out the mcmaster wheel and it looks really good, Do you know if this wheel has a tenon slot?

[EricH]

You mean a keyway? Not stock--you'll have to modify the hub. It's designed to be used as a caster (unpowered), so any powered use needs modification.