Caster Wheels

[Al Skierkiewicz]

Mk,
Casters are perfectly acceptable but have drawbacks. When moving from a forward to reverse direction the cater must rotate about it's vertical axis which requires some side to side motion to accomplish. If the robot is in a position that it cannot move sideways, the casters will actually fight your commands. Other robots can direct your robot actions by pushing on the side of the robot where the casters are located. Omni wheels react the same way.
On tilted surfaces, they have a mind of their own. While they may work this year, in a year where climbing, ramps, or bumps are part of the game, casters are by far from the best choice.

[IndySam]

We have a few rules on team 829.
Drive train rule number 1. No casters.

[thefro526]

Originally Posted by IndySam

We have a few rules on team 829.
Drive train rule number 1. No casters.

816 has the same rule.

MK.32, have you looked into using a simple omni-directional wheel in place of a caster? Here's a link: http://www.andymark.com/searchresults.asp?cat=69

A pair of Omni wheels should give you similar turning ability but they will be much more predictable and have a slightly higher resistance to pushing than a caster, and you can power them if you wanted to.

[Nick Lawrence]

From experience, casters are flat out terrible for FRC.

Omni wheels are the way to go for what you want to do.

-Nick

[Alan Anderson]

Slippery skid plates might even be preferable to caster wheels. At least they don't put up a fight when you want to change direction.

[pfreivald]

A well designed ball caster might vaguely be acceptable, but not really. Casters are NOT your friend.

Also, if you choose to ignore the general advice given here about not using casters, put your drive wheels in front if you at all can -- it makes it a lot easier to line up on things properly if the front of the robot isn't pivoting around the back.

[Mk.32]

Thanks for feedback.
We will be switching to something else for sure.
Are the plastic omni-directional wheel fine or are the steel ones that much better?

[EricH]

Originally Posted by Mk.32

Thanks for feedback.
We will be switching to something else for sure.
Are the plastic omni-directional wheel fine or are the steel ones that much better?

Either one should work.

Also, consider adding a chain run to power the omniwheels. You get more forward power, without affecting sideways motion of the omnis.

[zbanks]

Not to hijack this thread, but...

Our team was planning on using ball casters with CWD. We have a drive platform and its incredibly maneuverable.

3 years ago, we used omniwheels on a 4-wheeled robot for slippage, and it worked pretty well. However, it was a huge pain when they broke, considering how expensive they were.

Apparently, (before my time, and there's not a whole lot of recollection about them, which could be good or bad) about 5-6 years ago we used a similar design to now. It was claimed to have great maneuverability, but if you dropped the robot or anything, the casters could dent, which would prevent them from rolling correctly. However, they're cheap enough where you can easily have extras on hand.


This year, when we designed the robot, we chose ball casters based mostly on these experiences. We assume that omnis would not provide any significant prevention from being pushed and rotated around our center. We were also being cost-conscious, being a pretty low-budget team. Plastic omnis would have been about 4x as much as a heavy-duty ball casters, which are also readily available at a hardware store.

Since we're using direct drive, powering omnis wouldn't be worth the hassle, either.


Basically, I want to make sure that our decision was sound. Based on our pretty limited test, it seems to work pretty well, but that means nothing in FIRST Has anyone had any trouble with ball casters?

[EricH]

If you must use a caster, ball casters are about the best to use. As long as they aren't acting like swivel casters, that is.

I believe the AM omnis have had a strengthening redesign since about 3 years ago, too.

[Chris is me]

Use AM Plastic omnis if possible. Coolie Dualies are wheels I've never seen used successfully, unfortunately.

[Mk.32]

What about ball caster, how well do they work?
If they don't really work i think we probably just go with a 6 wheel drive system.