popdown casters

[greencactus3]

im sure some teams have done popdown casters to help turn a 4wheel drive robot before. my question to them is... is there a easy way to make sure the casters hit the floor parallel to the floor. or does it not matter as lond as they aren't THAT angled to the floor... or does caster diameter matter?

[Kevin Sevcik]

Here's my suggestion. use a relatively long piece of aluminum with a piece of teflon on the bottom and just use one piston in the middle of the robot. I think it'll work better. You won't have to worry about getting two casters parallel. You don't have to worry about the casters coming down facing the wrong direction. I think it'll be easier over all.

[Ben Lauer]

Why do you need multiple castors? Just use one, and have a small cylinder pop it up and down. The cylinder could have less that an inch of travel, and therefore would be small, compact and lightweight. We were going to do this if our omni's fell though.

I am sure you can three wheel it for the turns. Plus, it should be down for long if you program it to pop down only when you turn past a certian angle.

[aaronbr28040]

Popdown casters are one of the best way to overcome the traction problems experienced when trying to turn doing skid steering. The easiest way to do a caster is to put it near the front of your robot with the center of mass preferably between your back two wheels to aid in turning although this is not neccessary. Casters take too long to turn and line up and continue allowing the robot to spin even after power is no longer applied. The best way to go is delrin, or teflon either in the stick or furniture slide variety. Be careful that your robot isnt going to be popping wheelies as ours is now .
-Aaron

[greencactus3]

Originally Posted by aaronbr28040

Be careful that your robot isnt going to be popping wheelies as ours is now .
-Aaron

oh no. we actually get air after hitting a piece of wood during a wheelie. VERY cool.. only makesure the landing area is clear of small balls. we kinda did a flip after we landed

on our design, we just wont be able to do it with just one caster. at the least we're going to need to use two. inlign for and back.
as in

.....................................
..............caster...............
.....................................
..............caster...............
.....................................
.....................................
drive........................drive
wheel......................wheel
.....................................

can't give out any more secrets...
but anyways, we might look into teflon or delrin.
but IS there a very easy way to make an omniwheel?
cheap and lightweight. it can be small. or actually, small is better.
we have a CNC mill, but its not exactly the fastest thing around.
will making one out of aluminum be too weak to support a robot?

[phrozen solyd]

Originally Posted by Ben Lauer

Why do you need multiple castors? Just use one, and have a small cylinder pop it up and down. The cylinder could have less that an inch of travel, and therefore would be small, compact and lightweight. We were going to do this if our omni's fell though.

I am sure you can three wheel it for the turns. Plus, it should be down for long if you program it to pop down only when you turn past a certian angle.

I agree with Ben on this one. In 2001 and 2003 we used a single popdown caster on our robot on the cylinder with 1" of travel. In both robots, the caster transferred most of the weight away from the back wheels, but not all. It allowed us to turn easily, yet maintain stability.

[Team1425]

We are using a pop down caster this year, ours has half an inch of travel (we added an internal stop to a 2" stroke cylinder, since thats what we had to use)


We made it just enough to pull the weight off the tires on our back end and to help from oversteer caused by the caster we plan on dragging the tires just slightly (this also helps our stability with one caster, although we have a really low center of gravity as it is)