Robot Rule R08 - what does it mean, and what should it mean?
 

In another thread, we have a good discussion regarding the "metal on carpet" rule, R08 (page 12).

There seems to be some disagreement with how this rule should be interpreted. Some people think that this means "no metal on carpet". Others think that it means "no additive traction devices which gain traction".

I'll make a case for the latter:

The intent of this rule, if I understand it correctly, is to not allow metal treads, as on TechnoKats and Wildstang robots in 2002. Also, it is aimed at not allowing file cards, which were also made famous by Team Hammond in 2002, and then copied by many teams that same year. Also, there have been teams who put metal or plastic cleats or even sandpaper on wheels to give them a traction advantage. These additions were legal, back in 2002 and before, but FIRST created a rule (R08) due to too much damage being done to the carpet and field (heck, carpet would even buckle up in some places). Maybe this rule can be scrutinized to death so that no metal can ever touch the carpet, but I seriously think that is not the intent.

What surprises me is that well-meaning people look at this rule and automatically think that it's a "no metal on carpet rule". They are doing their best to interpret the rule, but possibly missing the intent.

I welcome everyone to discuss this topic here, and maybe we can come up with some sort of consensus, one way or the other. Then, whatever the consensus is, we might be able to effectively write a rule explaining this more clearly so that everyone can work within clear boundaries.

Sincerely,
Andy

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

I think you already said it best.

1. Don't damage the field.
2. Don't have metal intentionally on/or frequently contacting the playing surface so number 1 doesn't happen.
3. to mean the "traction advantage" part is secondary to the above two items. If I want a traction/friction advantage there are plenty of materials you can turn to anyway.

In fact, I don't think I'd even bother stating anything about metal on the playing surface if I were to write the rule (in many games it's almost entirely unenforceable anyway). I'd simply go for - "don't damage the playing field ... you may be asked to modify/change stuff if what you have is found to be a potential hazard to the field." (or something like that.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

I was a little confused by the rule. It prohibited drive chains under the rationale that metal even touching the ground was tractive force, but that didn't apply to smooth chassis rails like 254 and 1868. That particular Q&A threw me off.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

I hear ya. In this case our team tried to think about the common sense part of it only - so we added skids with a polycarb shield so the chains couldn't contact the bump at all with the idea "yeah, chains on carpet bump edges = bad." However, when some folks started worrying about every possible smooth rail that could hit the field it got a little unnecessary.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

In looking at the rule...

<R08> ROBOT wheels, tracks, and other parts intended to provide traction on the carpet may be purchased or fabricated (“traction devices” include all parts of the ROBOT that are designed to transmit any propulsive and/or braking forces between the ROBOT and the FIELD). In no case will traction devices that damage the carpet or other playing surfaces be permitted. Traction devices shall not have surface features such as metal, sandpaper, 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) shall not use metal in contact with the carpet to “stay put.” Gaining traction by using adhesives or Velcro-like fastener material is not allowed.

The interpretation should be applied to "traction devices" and devices used to transmit power to those devices. I believe the intent is to prevent damage to the carpet surface and to prevent damage to the underlying floor. In some cases, the arena is setting up the field over basketball court, or composition rubber running surfaces. Robots that have moving metal in contact with the field can penetrate the carpet and the sub surface. In addition, robot parts that damage the carpet require repair between matches. This year has been one of those years that carpet became so damaged that many events played more on colored gaffer's tape repairs than on actual carpet. Many teams were surprised when refs and/or inspectors informed them of problems with their robot structure damaging carpet and the possibility of DQ should they fail to fix the problem. The need for low CG combined with the extreme angle of the bumps and ramps caused significant carpet damage throughout the season.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

I think the widespread allowance of teams to use rivits in attaching wheel treads disallows the interpretation of a ban on metal touching the carpet. While I conceed that some teams may recess the rivits to avoid this situation I doubt most do.

Al does a nice job with his interpretation tying back the the letter of the rule. Of course, I wouldn't expect any less of Al.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Thanks, Mark. Teams that use rivets to attach tread to wheels get extra scrutiny from inspectors. If the rivets are small, buried in the tread material and between tread extrusions, they are usually allowed. Haphazard installation of rivets get suggestions on how to replace/repair in order to pass inspection. At least that is the theory.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Really? We used rivets in 2008 and 2010 (and 07, but I wasn't on the team then), and I don't remember the inspectors looking incredibly closely at them, if at all.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Al, if this is the case do you happen to have pictures teams could use as guides in the future? (Knowing that this rule may change in said future.)

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Kara,
I am not surprised, inspectors can do some serious looking when you think they are looking at something else. You would be surprised how much I can check out while a team is hooking up their driver's station and powering the robot.

Andrew,
Many teams use commercially available belting for tread. This belting is available through McMaster and has 'teeth' that are 3/16-1/4 long. If a small diameter rivet is used, the head can easily fit between these 'teeth' without danger to the floor. On other material it is possible to counter sink the belt since the substrate is as thick as the teeth. Again the rivet would never touch the carpet, even if the teeth were worn off. Many (most) teams also compress the substrate while inserting the rivet which is akin to counter sinking. All of these methods prevent 'traction' contact with the carpet and the possibility for damage is minimal. We are seeing less custom wheels now that there is commercially available wheels that are easy to obtain and designed specifically for driving on carpet.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

(emphasis mine)

I'm a referee, not an inspector. I would only be called upon to assist in interpreting the rule, not enforcing it. But in my opinion, the letter of the rule says no.

The spirit of the rule, as explained by Andy, is that these laces would not be expected to damage the carpet. They are somewhat recessed, and if they do touch the carpet they do so with a smooth surface. Hopefully the letter of the rule can be changed to match the spirit of the rule. Especially given that sometimes rivets that hold on treads do touch the carpet, but without damage.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Andy, I agree with your interpretation of the intent. However, relying upon the eight-year-old intent of the rule writers isn't a sustainable way to codify the rules for the FIRST teams of today. (Indeed, as Gary notes, a plain reading of the rules seems to be pretty clear.)

188 also used metal treads in 2002. In Woburn's case, they were made from slices of thin-section aluminum C-channel extrusions, screwed to a turned plywood core. Having played with those wheels, I think it's fair to say that with attention to detail, they're not going to automatically ruin the carpet. Rounded corners are a must—not just for the sake of the carpet, but also so that you don't dig in when turning.

In fact, they've got the unusual feature of slipping very little on carpet in the direction of motion. This means that you can't spin your drivetrain so fast that you melt the patch of carpet below you when immobilized—compare that to conveyor belt treads which have been known to do exactly that (e.g. 188 in 2004 with some sort of wedgetop and a 6-motor drivetrain in high gear). It's not so good for your motors and your gearboxes, but it's actually better for the surface of the carpet in that circumstance. Also, because the screw heads are deeply recessed in the channels, it's harder to snag a loop of carpet and drag it with you.

However, because the carpet isn't particularly well secured, all of that traction can stretch or detach the carpet from field elements. But this isn't a feature of metal wheels—it's a feature of high-traction wheels.

I have many comments about this rule (and the similar ones from 2009 and other previous years):

1. The 2009 rule (which was less precise) and ruling was that devices that created thrust (e.g. a fan) with a component normal to the playing surface were traction devices. That is a bit arbitrary and inconsistent—any normal force (weight, change in momentum, buoyancy, etc.) contributes to the traction of the robot. The key is the traction at the wheel—nothing else even bears consideration in the traction device rule.
   
   Under the (better) 2010 rule, there is still the possibility that someone could rule that a propulsion fan—which disturbs the air impinging upon the field and exerts a measurable force upon (for example) the alliance station wall—is a "traction device" under the definition presented. (That is, unless "directly transmit" was the intended meaning—in which case, the rule should have said so, especially given the confusion about the meaning of the 2009 rule.)
   
   
2. "In no case will traction devices that damage the carpet or other playing surfaces be permitted." This implies a mandatory consequence of damaging the field, but not necessarily a prohibition of devices that are likely to damage the field (but haven't yet done so). There are other rules (like <G24> and <G26>) that specify in-match penalties for field damage, but again, they happen after the fact.
   
   This isn't a bad thing—it makes sense to know whether an item is going to damage the field, before banning it and inconveniencing the team. But when enforcing that provision in this way, it would be helpful to know that FIRST has the same understanding of the rule—and that they'll put up with one match or practice match worth of field damage, in order to prove a violation.
   
   
3. The sharp edge rule (<R05>) should also include potential field/venue damage—that would pre-emptively deal with most obviously deficient designs, without actually risking damage.
   
   
4. The real problem with the rule is in the surface features clause. Put simply, rivets or screws holding the treads down are, by almost any definition, a surface feature. Some teams used to go to great pains to recess their screw heads into the tread, but this is rare now, given the acceptance of designs which simply use rivets or slightly-protruding screws to secure the tread. FIRST, the teams and the inspectors have all tacitly acknowledged that there's not really anything wrong with that approach, except for the fact that it violates the letter of the rule. I haven't seen this issue pressed in many years. So if that's the rough consensus, why isn't there an exception in the rules for fasteners like these? Shouldn't the same principle of no harm, no foul be in order here?
   
   
5. Similarly, "metal, sandpaper, hard plastic studs, cleats, or other attachments" are not necessarily going to cause damage. Are they therefore banned on account of providing too much traction? (Even then, the specifics of the design would seem critical to that determination.) A reason should be provided (even if it is "because we say so").
   
   
6. Isn't the anchor clause redundant? (Braking being retardation or inhibition of motion—like with an anchor.) Why even introduce the extra definition into the rules?
   
   
7. The adhesive and hook-and-loop fastener clause really belongs with the other prohibited surface features. And why (potentially) ban a dried adhesive that doesn't stick or leave residue (e.g. cast epoxy), or the loop side of the hook-and-loop fastener (pointless, but harmless)?
   
   
8. The definition of "traction device" relies upon what the device is designed to do, not what it does. That makes it much more difficult to call, in the case of mechanisms other than high-traction wheels. (Actually, it says "includes", which could mean that there are other, unspecified traction devices.) Consider the case of drive chains on bump-climbing kitbots from 2010: were those designed to aid in climbing the bump? Who do the inspectors ask—Andy & Mark, because it's their kit, or the team that put it together? And one might make the argument that an unmodified file card was designed by the engineer at the file card company—and he certainly didn't design it as a traction device.
   
   
9. The statement "may be purchased or fabricated" ought to be in a footnote or clarification box, if anywhere. (It's not really relevant for 2011, since the anomalous 2009 rover wheels are long forgotten.)

If I had my way, I'd probably phrase it something like this:

<G?> [Disablement and point penalties for field or venue damage during gameplay.]

TRACTION FEATURE – A ROBOT feature that, during GAMEPLAY, directly (or through any GAME PIECE(S)) exerts a substantial tractive or resistive force upon the PLAYING FIELD, even if not designed for that purpose.

Phrased as "feature" rather than "device", to emphasize that it's not necessarily the whole wheel that is the problem—probably just a part of it. "Substantial" is a carefully-chosen ambiguity—it could be defined with a force specification, or left to the officials' discretion; it also depends on the way that game pieces are held in that particular game. Game pieces are included here, because it's conceivable that a robot could use a game piece to enhance its traction.

PENETRATING FEATURE – A ROBOT feature that, during GAMEPLAY, penetrates the entire thickness of intact PLAYING FIELD carpet, and/or abrades or otherwise damages the substrate supporting the PLAYING FIELD, even if not designed for that purpose. Also, a ROBOT feature likely to accomplish same.

Note that traction feature defined only in terms of actual function; penetrating feature also defined in terms of likely effect, so as to make it effective at inspection (irrespective of whether the robot has been on the field).

<R?> [Sharp edges rule with PENETRATING FEATURE ban to filter out obvious problems at inspection.]

<R?> If, in the opinion of the head referee or lead robot inspector, a TRACTION FEATURE has repeatedly or severely damaged the PLAYING FIELD, any GAME PIECE or other ROBOT (either at this event or any past events), the robot must be modified to mitigate the risk of further damage, and the modifications approved by a robot inspector, before the robot is allowed to take the field.

You should avoid wheel treads that will quickly melt or wear away the field carpet when your robot spins its wheels in place. Robots with too much traction can cause the carpet to stretch or bunch up, damaging the field. Protrusions on your wheels can get caught in the loops of the field carpet, tearing it apart and entangling your robot. FIRST recommends that you test your design before arriving at the competition.

Note that this would apply to things that aren't designed for traction, but exert it anyway. Past events are included, so that if Redabot damages the field at the Magnolia regional (and it's not corrected, for whatever reason), the officials at the Championship can rely on that fact to impose the prohibition immediately.

Re: Robot Rule R08 - what does it mean, and what should it mean?
 

Yes - what he said!

Tristan, you are THE MAN when it comes to this stuff. I would vote for you to get the FRC rules one month before the rest of us, just so you can sniff these things out. Your detailed work would save thousands of hours of anguish for the FIRST community.

Sincerely,
Andy