pic: 57's frame is coming along

We’ve solved the high centering problem, so that’s good. Electronics might have some difficulties, however.

What are the dimensions of those pneumatic wheels?


7.65" (200mm) diameter. They are Andymark hubs with the black version of the same tires used by AndyMark.

Those are 8" wheels. To head off the inevitable next question, that bit of framing is about 13" wide and 15" long.

Just wondering (we have been working through our first year of a riveted WCD), how are you planning to run chain with those 2in tall cross members in the space between axles? Are you going to use extra large sprockets, outer chain, or individual wheel motors? Or are you dreaming up some fancy chain routing?

Also, if you are going to be running chain, are you planning on #25? We learned the hard way that it might not be strong enough for flying over defenses, flat out shattering a few links. We know “flying” over them is probably not best for any drivetrain, it’ll inevitably happen a few times even if drivers are careful, but if a drivetrain can’t handle that, there’s going to be failures.

I can’t speak for Kevin, but I’d probably be giving chain-in-tube a look for this configuration.

We’ve done the WCD, riveted chassis, and chain-in-tube before. With this, I’d probably just resign to putting the chains on the wheel side. Big sprockets means chain will be dragging on the defenses, which is definitely not what you want. However, with chain-in-tube, if something goes wrong, it’s a nightmare to fix.

Aww drat, a serious question. I was hoping to string people along for a bit longer. This is actually the frame for our ball intake, with 8" pneumatics outside instead of 4" colsons inside.

In answer to your actual question, our chassis is also 6wd west coast pneumatics., still on 1x2. Our usual solution is wheels outside belts inside. Any inner cross pieces are bolted to the top of the wheel rails. A belt on a 30 tooth pulley will just barely sneak underneath the top of a 1x2. With smaller wheels, we’d run a smaller pulley, but a 24 tooth on 8" wheels would be trouble. I’m mildly concerned about 9mm wide belts on the 30s as it is. We’re going to seriously exercise things and see if we need to move up to 15mm wide.

I know other options are to make a belly pan and run belts just above that, or square up your frame with cross pieces fore and aft of the belt paths.

If you drastically over size your belts, you could probably get away with running them around cross pieces that would need removing to replace the belts if I did that, I’d also leave 2 spares also trapped around the cross pieces and ready to slide over and replace a broken belt. And make sure the cross piece is removable over a lunch break.

As for chain, it’s been a while since we’ve had a chain drive. Maintenance on chain drives was trying and failures were costly. We switched to belts a few years back and haven’t looked back.

Looks eerily similar to ours.

Can I ask where you got the black version of the andymark pneumatic wheels?

The interwebs. (Amazon, specifically)

Have you found any issues in initial testing that shows a scuffing problem with carpet?


Hi Kevin,

I would be interested to know how “bouncy” they are at different psi

ROFL ::ouch:: ::ouch::

we’re getting our actual chassis together with those wheels weds and should be doing some driving on saturday. (This week’s build schedule is interrupted by my dad retiring on Thursday)

So I can have answers to performance questions around then.

I would be careful using the plastic clamping bearing blocks we broke a few on the ri3d chassis going over the obstacles with speed.

Ours as well…I had to take a second look. Realized that the idler wheels in the middle were different.

Cooper, that is a fascinating insight. Like I said, this isn’t our actual chassis. We’re using the aluminum VersaBlocks for the outside wheels on our chassis, but we’re using a plastic bearing block for the middle wheel to get the 96 tooth spacing from two simple clamping gearboxes. I’ll definitely have the students abuse the chassis a bit to see if we need to do something about the plastic block for the middle wheel. If it’s too fragile, I’ll have to mill down a versablock to get the same spacing.

I think the block would be fine if it didn’t take so much load from wheels being cantilevered. We had the issue on the outer wheels of a wcd and not so much the middle wheel because at that point the middle wheel was in the air, or didn’t hit the defense/obstacle first/last.