Rules on metal casters

[stevo2k]

Section 5 of First Robotics Competition Documents on page 12(here) states "Traction devices may not have surface features such as metal, sandpaper, or hard plastic studs, cleats, or other attachments. Anchors, i.e. devices that are deployed/used to keep one’s robot in one place and prevent if from being moved by another robot, cannot use metal in contact with the carpet or other playing surfaces to 'stay put.'"

Does this mean we cannot use metal casters?

[Cory]

I think the part where it said you cannot have metal touching the carpet was pretty clear... So don't have metal touching the carpet.

The rule is not just for devices intended to let you hold your ground. metal cannot be touching carpet

[Don Wright]

Actually, I believe the rule is

just for devices intended to let you hold your ground

Hence, if you read the entire sentence instead of just reading part of it to get full understanding of the rule:

Anchors, i.e. devices that are deployed/used to keep one’s robot in one place and prevent if from being moved by another robot, cannot use metal in contact with the carpet or other playing surfaces to 'stay put.

A metal caster which does exactly opposite of this would not be illegal. If I Made The Call anyway...

[sanddrag]

What about a metal roller? Completely round and smooth no sharp or rough edges on the carpet. It seems as if some rubber tires could damage the carpet easier than this. What about a polished metal ball? Would that be disallowed? I think the "no metal or hard plastic" rule is being over-restrictive, just as is the "teams must use the provided copper lugs" rule, but thats another discussion for another day.

[russell]

Anything that creates friction with the carpet, and is intended to support your robot doesnt seem to be allowed. I think it is so teams do not put nail type things on the bottom of their robot so they cannot be moved.

[Cory]

This rule was created after 2002 when teams discovered those nifty little filecards and used them for traction purposes. There were also many teams with metal treads, or traction devices on their wheels. 45, 188,810, etc.

FIRST got tired of the carpet getting destroyed and put this rule into effect. The idea is no metal touching the carpet... no matter how smooth.

[Wayne Doenges]

Here is the whole rule:

<R27> Robot wheels, tracks, and other parts intended to provide traction on the playing field (“traction devices”) may be purchased or fabricated. In no case will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices may not have surface features such as metal, sandpaper, or hard plastic studs, cleats, or other attachments. Anchors, i.e. devices that are deployed/used to keep one’s robot in one place and prevent if from being moved by another robot, cannot use metal in contact with the carpet or other playing surfaces to “stay put.” Gaining traction by using adhesives or Velcro-like fastener material is not allowed.

It specifically mentions "Traction Devices". My opinion is that if you are using metal casters to support your robot, not driving, it should be OK. YMMV

Wayne Doenges
CAD Mentor

[jgannon]

Originally Posted by Cory

The idea is no metal touching the carpet... no matter how smooth.

I wouldn't doubt your word, but I don't think that's accurate. You say that the rule was created after 2002, which would mean that it was in effect last year, too. Our robot last year had two wheels and two metal ball transfers, all of which touched the ground. We were inspected in Sacramento, and twice in Atlanta. It's hard for me to believe that they would have missed something like that all three times, so I can only assume that the interpretation that the other folks (2000vfr800 and Wayne Doenges) have provided is correct. Feel free to prove me wrong.

[Cory]

Originally Posted by jgannon

I wouldn't doubt your word, but I don't think that's accurate. You say that the rule was created after 2002, which would mean that it was in effect last year, too. Our robot last year had two wheels and two metal ball transfers, all of which touched the ground. We were inspected in Sacramento, and twice in Atlanta. It's hard for me to believe that they would have missed something like that all three times, so I can only assume that the interpretation that the other folks (2000vfr800 and Wayne Doenges) have provided is correct. Feel free to prove me wrong.

Ok, I agree with what you say. I think it should be legal for a smooth metal wheel to be touching the ground. I'm not sure that's what FIRST thinks though.

There should be no way for it to damage the carpet, which is what the intent of the rule is. I would ask FIRST for an official answer though.

[jgannon]

Originally Posted by Cory

I'm not sure that's what FIRST thinks though.

Then why would we have passed inspection three times if we weren't allowed to have metal on the carpet? We certainly weren't trying to sneak it past.

[dlavery]

Originally Posted by jgannon

I wouldn't doubt your word, but I don't think that's accurate. You say that the rule was created after 2002, which would mean that it was in effect last year, too. Our robot last year had two wheels and two metal ball transfers, all of which touched the ground. We were inspected in Sacramento, and twice in Atlanta. It's hard for me to believe that they would have missed something like that all three times, so I can only assume that the interpretation that the other folks (2000vfr800 and Wayne Doenges) have provided is correct. Feel free to prove me wrong.

It has been said before, and it will be said again: "Rules from prior years DO NOT APPLY to this year!" Just because a team was able to do something in prior years, they should not assume that they will be able to do the same thing this year. There will be new inspectors, new inspection procedures, new rules, and new controversies. I know that FIRST has tried to simplify and clarify the rules as much as possible without having them lose all meaning. But it is an imperfect science, and there are sure to be areas of contention (both during the inspections and during the matches) that result.

That said, my own take on <R27> is the same as Cory's first post - no metal touching the carpet, anywhere, anytime. If I take a conservative approach (frequently the best approach to interpreting the rules) to the reading of <R27>, then any metal part touching the carpet will cause a violation. Every object - metal or otherwise - will provide some traction when in contact with the carpet. The only time this would not be true would be if the carpet were a true frictionless surface, which it obviously is not. Also, the rule does not state that the "traction devices" have to be driven devices, it just says that the device has to provide traction on the playing field. Every object will do this, even if it is just being dragged around the field by the robot (or an opposing robot). The fact that a small metal caster provides only a very minute amount of traction is immaterial - the only thing that matters is that it is providing SOME traction. As soon as we accept that fact, then <R27> kicks in.

Yes, that would appear to be a restrictive rule, but "dem's da rules!" You might choose to argue past precedent and extreme interpretations of the wording with the inspectors. And you might or might not win the arguments (care to guess how it would come out if I were the inspector?). But rather than risk it, why not just use a different, non-metallic, caster? Plastic, acetal, phenolic, and even wood, casters are available, so why not just use one of those?

-dave

[Leav]

I can see what Dave is saying, and frankly, I agree - just because no one wants their robot to be disqualified because they chose metal wheels....

my team was thinking about using big metal bearings.... I'll try and describe them, because i don't know their name:

imagine a normal ball bearing ring, but imagine that the balls inside protrude inward, so that when a large metal ball is placed inside the bearing, it is seated on top of the balls, and can move effortlessly.

kind of like a (computer) mouse...

do these things have a name?
do you think we could find them in plastic?

Thanks,
-Leav

[ChrisH]

Originally Posted by Leav

I can see what Dave is saying, and frankly, I agree - just because no one wants their robot to be disqualified because they chose metal wheels....

my team was thinking about using big metal bearings.... I'll try and describe them, because i don't know their name:

imagine a normal ball bearing ring, but imagine that the balls inside protrude inward, so that when a large metal ball is placed inside the bearing, it is seated on top of the balls, and can move effortlessly.

kind of like a (computer) mouse...

do these things have a name?
do you think we could find them in plastic?

Thanks,
-Leav

I believe that is the "ball transfer" mentioned in jgannon's 01/25 post. Since they are generaly used for fairly heavy loads, I've never seen one made of plastic. That doesn't mean they don't exist, I've just never looked for one. In previous years we used fiberglass skids the serve the same purpose. We just found a nice shiny cup and laid up fiberglass around a bolt sticking up. These were then bolted to the bottom of the robot.

They worked pretty well, except for the massive static build up. I think we fried something that way.

[Jeff Pahl]

I've seen plastic / nylon ball casters, so I know they exist. However, we have not been able to find any place that we can order some from quickly.

Sure do wish FIRST would hurry up and answer the Q&A question on this subject.

Otherwise we are going to try and find some place we can order 1" plastic balls and then try and refit some of our metal casters with them.