Building a better caster.
 

Yay, more questions :)

Okay, we all know what casters are, I'd imagine. But, today has taught me that I don't really know too much about how they're assembled.

Specifically, what sort of bearing is used at the top of the caster? Y'know, the part that swivels?

What keeps the vertical shaft in place? Why doesn't it just fall out? :)

Like always, I'm plotting something.

A Caster+ of sorts. But, conventional casters aren't adequate, so I'm looking into building my own. But, umm, I don't know the answers to those questions, so I'm kind of stuck.

I suppose this could be germane to other applications where you've got stuff spinning around a vertical axis.

Help me :) Please.

My idea for a new caster would be to have the wheel attached to a stationary disk in a chamber. The disk will glide over small ball berrings. That would be my idea, but there are problems and such with that.

177 used "mouseball" casters last year.... i think they are available through small parts. They are MUCH lighter and smaller.... They act pretty mcuh like a mouseball, there is a small metal ball in the middle of an aluminum casing - the small ones probably weigh a quarter of a pound.

Tom

I'd like to avoid building my own bearings at all costs.

Existing casters won't work for my application.

The last two years we, along with a lot of other teams, used Omni Wheels. Basically, omin wheels act as "powered casters." Imagine a wheel that can be powered like any other, and yet has almost zero lateral friction.

I wish I had a picture handy, but I don't. Take this example, however: one team uses a round object with washers all around it. You can use this as a drive wheel, with the washers digging into the carpet for traction, and since the washers are circular, they will spin when you move them laterally, and create very small amounts of friction.

Is that helpful, or were you looking for a better concept for a non-powered caster?

Stephen

Omni-wheels offer the unique distinction of being able to be driven, and while that has its advantages, it's a design that's readily accessible to teams that might want it.

What I've been trying to do is develop unique solutions to problems that may or may not arise in this year's game. Some of my solutions are overkill, but it keeps me thinking outside of the box.

This year, for the first time, omniwheels are within the capacity of my team to create. However, they offer some disadvantages which I'm trying to overcome. Namely, they still rely on skid steering and they don't resist being pushed from the side.

Any sort of caster has no resistance from being pushed from the side...omni-wheels can also function as non-drive wheels.

Omni-Wheels from our bot last year


http://www.chiefdelphi.com/forums/at...=&postid=18427

what are you looking to do that may help us with a direction to go. I take it you want to make a caster that locks so if you get pushed you don't slide sideways?? I maybe able to help if you can fill me in on what you are looking to do.

It sounds to me like you are trying to build a sort of crab drive system. I tried to push one of those systems on my team last year, they shot it down. Such a system is very diffuclt to construct and code (though I know I could have done the code part).

Anyway, you are looking for a thrust bearing to support the load on the caster. (a thrust load on an axle means the load goes down the axis of the axle) You will also need to use standard bearings to prevent the axle from twisting, even more so if the axle is not directly over the wheel.

Hope that helps.

Thanks everyone :)

I wound up all but eliminating the bearing entirely. Instead, I designed my own which ought to be as equally effective as something commercially available, and it's probably lighter (though not cheaper, I'm sure.)

The entire thing needs to be manufactured from raw materials, and I probably just reinvented the wheel, but it meets all of the criteria I wanted from it.

We'll see if we decide to use it in just a few weeks. In either case, I'll be more willing to discuss it later on in the season. It's nothing I've seen done before in my reasonably limited experience.

If you watch Full Metal Challenge on The Learning Channel they had a little lawnmower-like car with some giant casters. They looked pretty tough. Also, Harbor Freight Tools sells industrial casters if that's any help.

Omni Wheel construction questions
 

Now those wheels are pretty cool! :D

I assume the knurled pieces have pins extending from each side, and fit into grooves (or bearings) in the frame plates somehow, with a cover plate screwed on like a sandwich, right?

What're you using for a spin bearing surface, a bronze sleeve, or commercial roller bearing? Is that a fixed pin with the bearing hidden inside the knurled piece, or a spinning pin with the bearing surface within the plate area?

Gee... It seems like a LOT of force on a LITTLE pin. What are the support pins made of, and how big are they to support that much weight? Did they bend on you?

- Keith

why no castors
 

I hate casters! we had bad experiences with them our rookie year two years ago, they were unreliable to get th e robot going in the direction you told it to, because the would swivel into place before driving, causing the robot to swerve uncontrollably, so I would be against any casters, unless their lateral friction in smoother than glass, because they will effect the turning performance of your robot!