First CAD of a WCD, how did I do?

254 Lockdown had a question on this here:

1 Like

I might just be being dumb, but even based on their explanation, I’m not sure why they had to go with omnis. The reasoning they provide is wanting the robot to ride on the traction wheels and not get beached.

These are drive bases from 254 in 2018 and 2019. The support bars and the bumper rail are flush to each other, and it seems to also have some space so the wheels don’t rub against the back of the bumpers.

1 Like

I read that many teams had issues turning with 6 pneumatic wheels with the 1/8" drop in the versablocks, so I added some omnis, will turning be okay with 6 pneumatics?

I put the mounts above the wheels because of the suggestion from GalactechGoat above.

This is what I was planning on doing, good to know that this mostly mitigates the issue. Thanks

1 Like

This looks great, thank you

Can’t say on pneumatics, but we used 6 Colsons with 1/8" drop. No problems turning.

The thread I was reading specifically mentioned it being an issue with pneumatic wheels because of their compliance. I’ll see if i can find the post

1 Like

Pneumatics and omnis is an interesting combination. If you don’t think drop center pneumatic will cut it, I would probably do plain (drop center) traction wheels instead.

Good point about the squishiness of pneumatic tires.

What are the factors that lead people to choose pneumatics? We’ve been using Colsons but perhaps we’re missing something? I must admit the nitrile wheels on SDS’s latest swerve offering look very interesting.

I’ll typically suggest Pneumatic tires when we want to play the pushing/defensive game.

Pneumatic tires typically have better CoF.

So I’d set up a 4 wheel drive pneumatic tire drive with the robot as heavy as possible (120+heavy bumpers) driving wide (wheeltrack wider than wheel base) as this makes it easier to turn.

1 Like

Normally people use pneumatic tires for traversing obstacles, the squish of the tire helps the robot carry speed over bumps and acts like suspension that reduces the impact on the rest of the robot. Blue nitrile treads are awesome and super grippy, we used them in 2020 on AndyMark performance wheels and the robot drove better than any of our past robots.


I chose pneumatics because of the 1" bumps in the center of the field

This year, we used six 6" pneumatic wheels. The total drop of the center wheel was 1/4" since the tires are more squishy than colsons, but we actually achieved this drop by raising the front & back wheels by 1/8" and dropping the center wheel (and the gearbox) by 1/8". We had a tall, heavy robot and had no trouble turning.

The reason we chose pneumatic wheels over colsons was to reduce the intensity of the impact with the 1" steel beams on the field. When we tested driving over the beams with 6" colsons, it was very jerky and we were worried it would cause other issues over time. Since the reason for using pneumatic wheels was for hitting the bumps more safely, I agree that it seems counterproductive to use omnis in the front.

1 Like

We’ve had a strange love affair with pneumatic tires. Specifically red ones. They’re super snazzy, but I’m not all that convinced that were necessary in any year other than 2016.

Agreed, exaggerate the drop for pneumatic -quarter inch doesn’t sound unreasonable. You can also cheat by over-inflating the center wheel, and under-inflating the outside ones.


254 is using 6, 6" pneumatic wheels for the same reasons Brandon brought up. We have a short but heavy robot and are getting away with 3/16" of drop.

In 2018, we ended up with both center-drop and omnis largely by accident. We had originally planned on 6 Colsons, but our we found adding the omnis helped with turning, especially during the super-long 4-cube and 3-cube autons.

Also note that the render there show a Colson in the middle, when we ended up using blue-nitrile by the end of season because of increased reliability in encoder count tracking independent of the direction of the carpet weave.


Is this a C-C drop of the bearing bores, or measured off the full weight robot? Pneumatic tyres like to play tricks with this stuff.

1 Like

3/16" vertical center-center distance as milled on the frame rail.