R06

[Joe Johnson]

[R06] Traction devices may not have surface features such as metal, sandpaper, hard plastic studs, cleats, or other attachments. Traction devices include all parts of the Robot that are designed to transmit any propulsive and/or braking forces between the Robot and the Court.

Would a metal wheeled caster (http://www.mcmaster.com/#standard-casters-with-steel-wheels/=gjsson) or a steel balled ball transfer (http://www.mcmaster.com/#standard-caster-ball-transfers/=gjsrn4) violate this rule?

It seem not since the purpose of the device is not to provide propulsive or braking forces. But I sort of had an idea in my head that the rule was "only plastic touches the floor" but as I read it now, that is far from the rule.

Joe J.

[remulasce]

Should be OK. I've seen casters on bots before, which were presumably metal. Don't transmit torque/slash up the carpet? Legal.

[Kevin Sevcik]

Ditto. Many casters on robots are made out of hard plastic and they're legal. Not to mention skids. That's not to say that casters on a robot are all that great an idea, as you well know.

[Joe Johnson]

... That's not to say that casters on a robot are all that great an idea, as you well know.

Everything is a trade off. In general batteries belong in the middle of your robot, unless you want to move your CG an extra inch or so to give you the margin you need hang off a bridge... ...so you move 10% of your robot forward 10 inches and you take your inch and get over the ickyness of a battery at the edge of your robot.

And so it is with casters. For 99% of the time in FRC, they suck pretty bad, but that 1% they offer something that overcomes the suckiness.

Now that folks think steel Ball Transfers are legal, has anyone used them on a FIRST robot? Tips please?

FYI, in my case the are competing with feet that are currently Delrin but if I don't go with these ball transfers, I am probably going to use UHMWPE -- the best thing I can think of for a slippery foot if I don't go with moving parts...

Joe J.

[Wayne TenBrink]

I believe that Team 2771 is using ball transfers this year.

[Lil' Lavery]

Now that folks think steel Ball Transfers are legal, has anyone used them on a FIRST robot? Tips please?

341 has a pair of them on the bottom of their ball collection/bridge manipulating appendage.

[GilaMonsterAlex]

Wait? Is adding tread against the rules then?

[Al Skierkiewicz]

Joe,
The basis for this rule is twofold. One involves damaging the carpet, so most of the rule addresses that. The second is intended to protect the floor beneath the carpet. In some venues, this is a basketball court or some other non-concrete surface. In general, this is interpreted as no metal touches the carpet. Each design and part are inspected at the time of inspection. If the part chosen poses no threat to the field or floor, it generally allowed.

[Mike Marandola]

We are using a metal ball roller for our robot (http://www.youtube.com/watch?v=f5xym48mykQ) this year.

[JamesCH95]

Some food for thought:

It certainly wouldn't be as sturdy as a metal one, but a plastic ball caster (http://www.robotshop.com/search/search.aspx?locale=en_us&keywords=plastic%20ball%20caster) would give you the best of both worlds.

A small un-powered omni wheel (http://www.andymark.com/product-p/am-0349.htm) would also get you the same effect, but I don't know enough about your application to know if that is a good solution.

[Jared Russell]

As Sean said, we have a pair of metal ball transfers on the corners of our intake device. They are only there to protect the field. Under normal circumstances (e.g. we are on level ground), they don't touch the carpet. They only touch the bridges.

I don't see why they would be a problem. A caster is not really a traction device. We looked a plastic ball casters, but the problem was finding one that we felt confident would hold up when we whack the bridges.

[GilaMonsterAlex]

Thanks Al, that's how I've always interpreted the rule. Just got me worried for a second after re-reading it.