Velcro tread

[Brandon Zalinsky]

To clear up the facts about 1058's drop-down velcro drivetrain. (you can see it in this video at 1:23 and 1:43):

It is two piston-actuated, drop-down wheels driven off the same axle that drives the rear mecanum wheels. They pivot on swing arms and lift the rear mecanums off the ground. The wheels are 6" Andymark Plaction wheels treaded with commercial-grade (I don't know which product exactly) Velcro. We planned to have the drop-drive on for our first competition, the UNH District Event, but we only ended up bringing a whole bunch of pieces that never made it on the machine. It is an auxiliary drive, and by no means has to be on for the robot to drive well. At UNH, we talked to one of the inspectors about the legality of the wheels and showed him our Velcro-treaded wheels. He got a good laugh and said he was OK with putting it on if we had time at the competition. The same thing happened at Northeastern University District Event, with the same results. We then had the system on for the New England Championship event, and made it a point to show the inspectors that we had the Velcro-treaded wheels. They were ruled legal. The inspectors even called us back to re-measure our bumpers, as there was a question regarding to when the wheels were activated. When the robot tilted forward, the inspectors made sure that the front of the bumper did not dip below 2" from the floor. They passed without modification, and we continued competing.

I hope this cleared up any questions you may have had regarding 1058's use of Velcro in 2014.

[Roger]

I have no definitive opinion either way about using Velcro wheels for FRC, but as soon as I saw the question I was thinking of a game (with much lighter robots) that involved a carpeted floor curving up a wall that the robots would have to drive up and around.

[FrankJ]

The LRI is the final judge of what the rules say & if a robot is legal as for as the teams are concerned. (OK it might really be the head referee, FTA or some combination of that). You can search CD & find examples of this. You can find examples of robots legal in one competition & not legal in another. So if I thought velcro was legal & wanted to use them in competition, I would have a plan B ready just in case.

Please note I am not criticizing or judging the LRIs or the system. You have to have a final judge & there are times where reasonable people can reach different decisions.

[MamaSpoldi]

Team 230 started out this season with 2 feet covered with velcro that we could push down on pistons to prevent being pushed. We used them at the Suffield Scrimmage but they did not pass inspection at our first district event in Groton. In fact, we replaced the velcro with rubber and they were still not allowed. It was believed that they would damage the carpet so based on both R6 and G10 the feet had to be removed. (In the end it was all good... as we won the event so I guess we didn't really need them. )

I recognize that feet are not the same as wheels, but when being pushed in a direction orthogonal to the way the wheels spin, they provide essentially the same traction and forces on/risk of damage to the carpet.

My point is be careful in what you believe to be legal based on one event or one inspector. I definitely agree that it is probably better to try to get a ruling from GDC on the Q&A... and if they respond with a "cannot comment on a specific design" then definitely be prepared to remove or replace the possibly offending wheels (or feet in our case).

[nuclearnerd]

A question for those condemning velcro treads (from someone who's never used them): Are you sure velcro will damage the carpet? I am under the impression that velcro releases by uncoiling the plastic hooks not tearing the loops (if it tore the loops, it wouldn't be very reusable would it?) Even if the velcro tore away some of the loose fuzz, I can't imagine it would be much worse than the reams of carpet remnants we dug out of our (KOP-wheeled) bot this year!

MamaSpoldi - that's incredible! I don't understand how any thoughtful judge could rule that a rubber pad were any different than a stationary rubber wheel.

[Jon Stratis]

No, I'm not sure it would, but the concern is that it would. I had an old rain jacket with velcro straps that let you tighten the wrists, and over time the velcro really tore up the wrist part where there wasn't any loop side.

The point isn't whether it's legal or not... no one here can say definitively either way. It's questionable enough that a team could get different rulings at different events if they don't ask on the Q&A.

[EricH]

Originally Posted by Jon Stratis

No, I'm not sure it would, but the concern is that it would. I had an old rain jacket with velcro straps that let you tighten the wrists, and over time the velcro really tore up the wrist part where there wasn't any loop side.

Same here, jacket and all.

Sure, the loops won't necessarily give way right away (same for surrounding fabric. But it doesn't take long (say, a few years for a jacket)--call it a few hundred attach/detach cycles--for wear to show up, even under normal use like that. Now consider a robot with industrial-strength Velcro as its tread material. It's "attaching" for at least a few cycles a match, and if it's slipping in a pushing match, you're dealing with a very, very fast cycle--might hit several hundred in one spot in a couple of matches if you push in the same area. There goes the carpet. (For other similar items, see "HiGrip in powerful drivetrain slams wall in auto and keeps going". That automode ended with a hole clear through the carpet!)

[nuclearnerd]

Originally Posted by EricH

(For other similar items, see "HiGrip in powerful drivetrain slams wall in auto and keeps going". That automode ended with a hole clear through the carpet!)

OK, so then we are already explicitly allowing wheels that damage carpet. (they practically all do). I frankly can't imagine that "industrial strength velcro" will do any additional damage to "industrial strength carpet"

Perhaps I can suggest, any team wanting to experiment with velcro treads should do a controlled experiment. Find a way to measure carpet damage, and measure the difference between velcro and HiGrip (or other treads) under identical circumstances. Bring the results to competition to show the judges. Use the power of science!

[Al Skierkiewicz]

How about we look at this in a practical light. The velcro has a distinct adhesive property based on matching a particular type of "male" and "female" material. The strength of that adhesion is proportional to the mated area of the material. When mated with material other than that for which it is designed, bad things occur for both materials. Additionally, when it does produce friction with the floor, the force needed to pull it along the carpet is also very high. While everyone has admitted that the "male" velcro does pick up fluff, remember that it does not give up that fluff readily. At some point, (within minutes I suspect) the contaminant will have reached a point where the material is filled and all friction is lost.
In the case of wheels, the mated surface area is quite small, less than 1 in^2. in most cases. I would suspect that the coefficient of friction to be quite small.
What would determine carpet damage in my mind is watching the robot drive across the carpet. If it leaves a visible trail, I would say it is damaging the carpet. If it picks up a considerable amount of fluff in a short driving session (say one match), it is also damaging the carpet. In this case you will have a harder time with the FTA and Field Supervisor than with the LRI. They can prevent you from playing until you correct the problem.

[EricH]

Originally Posted by nuclearnerd

OK, so then we are already explicitly allowing wheels that damage carpet. (they practically all do). I frankly can't imagine that "industrial strength velcro" will do any additional damage to "industrial strength carpet"

The HiGrips in question were immediately removed from "damage-causing" condition. As I recall, they started by adjusting their automode, and maybe had some other tweaks. This would probably be a little more difficult with Velcro, partly because it would involve removal of the adhesive as well as the Velcro itself.


For the rest, see Al's post. I can see where damage would be coming from, having helped with field teardown (and thus the field anchor velcro) on more than one occasion.

[Michael Hill]

I'm confused, so have teams used it successfully? If so, and it didn't cause damage tithe field, why is this even an issue. Please stop speculating on whether damage will occur or not. Let teams try it, and if it causes damage, then it's a problem, but don't stifle innovation in the name of it potentially causing damage. It could work perfectly fine, but without testing, we won't know.

[EricH]

Originally Posted by Michael Hill

I'm confused, so have teams used it successfully? If so, and it didn't cause damage tithe field, why is this even an issue.

Team(s) used it--but, we haven't heard from the FTA(s) involved, or the head refs, that it did or did not damage the field. Various LRIs have stated (Al in particular, pay attention when Al talks about legality on robots) that it would not be allowed through inspection due to the high risk of carpet damage. And, as it violates the rule against attaching to the field, the referees can shut it down regardless of whether it damages the field--it merely needs to attach to be in violation. (Velcro, as I'm sure you're aware, is very good at attaching. And detaching under sufficient force, but that's not under consideration here.)


Remember: It's not all that uncommon for something to slip past the officials and only be caught later, when another set of eyes looks at the problem. Should it be highly unusual? Yep. Is it? Not really.

[Michael Hill]

Originally Posted by EricH

Team(s) used it--but, we haven't heard from the FTA(s) involved, or the head refs, that it did or did not damage the field. Various LRIs have stated (Al in particular, pay attention when Al talks about legality on robots) that it would not be allowed through inspection due to the high risk of carpet damage. And, as it violates the rule against attaching to the field, the referees can shut it down regardless of whether it damages the field--it merely needs to attach to be in violation. (Velcro, as I'm sure you're aware, is very good at attaching. And detaching under sufficient force, but that's not under consideration here.)


Remember: It's not all that uncommon for something to slip past the officials and only be caught later, when another set of eyes looks at the problem. Should it be highly unusual? Yep. Is it? Not really.

My issue is that it would be disqualified by LRIs for being a "risk". That is purely their baseless judgement call. Let's see some actual evidence that it's a problem before shooting from the hip and killing it before it even has a chance.

[cgmv123]

Originally Posted by Michael Hill

My issue is that it would be disqualified by LRIs for being a "risk". That is purely their baseless judgement call.

It's their job to make those kinds of calls. Are they supposed to pass every mechanism that looks unsafe because it hasn't hurt anyone yet?

[Michael Hill]

Originally Posted by cgmv123

It's their job to make those kinds of calls. Are they supposed to pass every mechanism that looks unsafe because it hasn't hurt anyone yet?

This isn't an issue of safety though...it's a completely different thing.