pic: 6CIM WCD

[Chris is me]

Originally Posted by Andrew Lawrence

3" wheels aren't really that small. I've gotten some decent clearance from 3" colsons on some CAD models on WCDs and other drive variations. If it weren't for colsons being the only source of 3" wheels, I'm sure we'd see a lot more of them in competition.

I would call 3" wheels "really that small". On a 2x1 frame, that leaves you with a large span to high center on, as well as at most .625 inches of ground clearance right at the center wheel. We've run 4" wheels on 3" tube in 2011 and while it did clear the bumps in the field, anything other than almost perfectly flat would not have worked for that drive.

Basically - there's a reason they aren't a super viable product. The teams that can handle and wish to use sub 4 inch wheels on their robots are the teams already making their own wheels. I wouldn't assume they'll work in the general FRC case just because it looks nice in CAD.

Originally Posted by Chris is me

I would call 3" wheels "really that small". On a 2x1 frame, that leaves you with a large span to high center on, as well as at most .625 inches of ground clearance right at the center wheel. We've run 4" wheels on 3" tube in 2011 and while it did clear the bumps in the field, anything other than almost perfectly flat would not have worked for that drive.

Basically - there's a reason they aren't a super viable product. The teams that can handle and wish to use sub 4 inch wheels on their robots are the teams already making their own wheels. I wouldn't assume they'll work in the general FRC case just because it looks nice in CAD.

In my models every wheel was moved down around 1/2" on the 2x2 to provide enough clearance, and it was sufficient.

[Gregor]

Originally Posted by Andrew Lawrence

In my models every wheel was moved down around 1/2" on the 2x2 to provide enough clearance, and it was sufficient.

Sufficient to what standard?

Originally Posted by Gregor

Sufficient to what standard?

1" of ground clearance is sufficient for most flat games.

[KrazyCarl92]

Originally Posted by Andrew Lawrence

1" of ground clearance is sufficient for most flat games.

Andrew, If you are using 2" tall tube with 1/8th" of wall and live axles in a WCD setup, then you don't have an extra half inch to drop the wheels.

The height of the tube that is actually usable in this case is 1.75" because you do not want to machine away the top or bottom walls of the tube for the bearing to fit. Then if you are using 1/2" hex like this design calls for, the bearings would be 1.125" diameter. This means that the lowest you can drop down the bearings from center without taking away top or bottom wall material is 0.3125". Assuming you already had a 0.125" drop center to begin with, this means that you would only actually be dropping the bearings (and therefore the shafts) by 0.1875". That means you have 0.6875" ground clearance with 3" wheels, not 1".

[Chinmay]

Maybe he's using steel

Originally Posted by Chinmay

Maybe he's using steel

Not anymore.

Originally Posted by KrazyCarl92

Andrew, If you are using 2" tall tube with 1/8th" of wall and live axles in a WCD setup, then you don't have an extra half inch to drop the wheels.

The height of the tube that is actually usable in this case is 1.75" because you do not want to machine away the top or bottom walls of the tube for the bearing to fit. Then if you are using 1/2" hex like this design calls for, the bearings would be 1.125" diameter. This means that the lowest you can drop down the bearings from center without taking away top or bottom wall material is 0.3125". Assuming you already had a 0.125" drop center to begin with, this means that you would only actually be dropping the bearings (and therefore the shafts) by 0.1875". That means you have 0.6875" ground clearance with 3" wheels, not 1".

My model uses 3/8" ID round bearings with .875" diameter.