Re: Ramps
 

Wire or cable is not a good idea in my opinion since it has memory and won't want to lay flat.

As I said in a previous post I recommend Mason's line It is a strong string and is available in florescent colors so it is highly visible and it will lay flat so the entanglement hazard is low. http://www.homedepot.com/s/mason%27s%2520line?NCNI-5

Re: Ramps
 

We did some testing at GTR-C with a tethered ramp. Thin aircraft cable was less prone to getting caught in our wheels than 3/16 nylon rope. We made a ramp from pink panther insulation foam, it was not particularly durable but it only weighed a pound and worked just fine.

Re: Ramps
 

I can't find anything on those brands indicating their rated loads. Do you have any source that might list that? We found that we need higher than 80 lb rated load for an application, and I don't know whether or not I can trust Masons Line.

Re: Ramps
 

I suggest you try Braided Fishing line like http://www.amazon.com/Power-Pro-2110.../dp/B005ADORGK.

In my experience it's breaking point is well above its rated load. Just make sure you use the right knot, the "palomar knot" is recommended for braids.

Re: Ramps
 

I wouldn't.

Not for the breaking strength, but for the visibility factor. 35 thou or so isn't all that easy to see, particularly from the edge of the field. You'd want to make fishing-line rope with it just for visibility. Remember, if the refs can't see the tether, we may be doing some investigating after the match to make sure the tether is actually present and is actually in one piece. That's going to take a while... Particularly if for some reason we decide that we need to check after every match.


I've seen some nice elastic-y cord, as well as nylon webbing. I might--if I was y'all--look at some light kernmantle-type rope. Not climbing-weight, mind you, but something on the order of shoelace size. It can be a smidge on the heavy side, but it's plenty strong.

Re: Ramps
 

Did you notice the color linked too is High Vis yellow before you commented?

Also, assuming the "we" in your comment is the refs; that is your decision on whom to give additional scrutiny, just don't penalize them for your ridiculous decision. It should be pretty easy to determine if the tether is in place.

Re: Ramps
 

High Visibility Yellow, at .035" thick. On carpet. From a distance. Think about that for one moment.

Is it going to be visible? Yeah. Is it going to be easily visible at close range? Yeah. Is it going to be easily visible at 15 feet? 20 feet? 50 feet? How about 150 feet (somewhere in the audience)? Not so much.

And because it's not as easily visible as, say, mason's line, the refs--even if they can see it clearly--are going to have people asking "isn't that a penalty?" to which the response will have to be--every match--"No, because there's a tether there" (and a quick-thinking ref will hopefully check the tether after every match just to make sure it didn't snap). Remember, if you make something obvious, the refs are a lot less likely to have to take time to make a judgment call (BTW, we don't like making judgment calls if we don't have to). If you make it non-obvious... well, it could go either way. Chances are that you'll be asked nicely to see if there's any way to make it more visible.

For example, I think it would be a lot easier to see if someone were to apply a rope-making machine to the line and turn 1 strand into 6 or so strands all tightly woven together.

It is. Realize this: It should be easy to determine if the tether is in place. Yes, I agree. It may be LESS easy to determine that it is still in one piece! And if it is not in one piece, we'll probably start with a suggestion to use a stronger tether if possible (assuming that such multi-piece-ness was accidental), and only start going for stronger "suggestions" if it happens again.

Because remember: If you can "get away with not following" a rule (here I'm aiming at the perspective the rest of the teams may be seeing from, and giving us a hard time after or during the event from), there are other teams that may be, shall we say, a little "less accidental" about "not following" a rule, and then you're the "well, they got away with it" team used as an example by said teams. I don't like those kind of situations, as a spectator OR as a ref!

Re: Ramps
 

It is legal or not? Without clear rules to the contrary, if the refs decide to penalize a team because it inconveniences them because it makes them answer questions from the crowd (like that happens); then that is against the intent of Franks message here http://www.usfirst.org/roboticsprogr...hes-resolution

BTW, 80LB power pro, does not snap unless you have a serious fish on the line, a 120 LB robot doesn't stand a chance.

Re: Ramps
 

I agree.

But let me ask one simple question. Let's assume that you see a ramp, on the far side of the field from your team, with no apparent tether to its parent robot. What is your assumption, and how does that affect your experience?

Now, I know in FRC, many people (like you and me) will go "Oh, they found something hard to see as a tether" and go ask the team questions, and learn something new. But others (I make no assumptions on actual involvement level) will probably assume that the team is being allowed to slide past the rules, and the logical conclusion from that (flawed) assumption is that teams are getting away with cheating (I'm assuming, that they don't go talk to the team in question, or the officials, for some reason). Does that help their team experience?

I submit that it doesn't help that individual's team's experience, partly due to "one sour apple". And there's nothing the officials can do about it if the team doesn't ask questions to clarify. That's a shame.

So by making a somewhat visible tether even more visible, you actually improve the team experience, without the various officials getting involved at all. Just a thought. (And it helps the refs out--see tether, know that tether is/isn't wrapped around tote/robot/container, makes it easier to score--and makes it much easier to avoid getting snagged after the match if it's misbehaving.)



Just out of curiosity, how well does it do when run over by mecanum wheels or inadvertently snagged in a drivetrain? Tensile strength and shear strength aren't entirely the same... I'm guessing you've run a couple of tests? I highly recommend doing a quick strength/snag test if one isn't sure of how a tether will hold up, if there's a robot available.

It not getting tangled is a big deal. Because if it gets tangled it has the potential to ruin a wheel, and render our robot and our partners robot useless for the match.

Re: Ramps
 

EricH,

Your reaching really hard now; one mythical team (alliance) that doesn't ask any questions about a possible infraction of the rules (which could easily be answered by the refs or other teams), instead of the dreaded unicorn crowd question before?

Now your also asking the merits of the braided line? Can it be cut? Yes, anything that will cut the lines you suggested will also cut braided fishing line.

How does the tether being wrapped around anything make a difference in the score? How does the line that is wrapped around anything impact the score or the game? If a rope is around the stacks is ok, does it change the score if a braided fishing line is wrapped around instead?

Your preference is a thicker line that you perceive as more visible, the rules allow for other options.

It may be time to think logically...

Re: Ramps
 

If I were making the call, I would find a robot without the basic control system to be in violation of (emphasis mine):
There are a couple of other details about connections and license plates, but at a minimum, the part would have to have the minimal control and communication system and the signal light working. I did not find anything about a minimum number of sensors or actuators.

Re: Ramps
 

The ability to withstand a pull without breaking is not an issue for something like a passive tether/leash. Getting cut is what I'd worry about. A piece of material that's less than a millimeter thick seems likely to be easily damaged by robot wheels and gearboxes.

Eric's caution appears sound to me. I agree with the basic idea that you should also avoid making it difficult for people to see that you are following the rules, and a .035 wide line is going to be difficult to see.

For one thing, a tote stack in autonomous only counts if it is not in contact with a robot.

Re: Ramps
 

Check out Team Driven 1730's robot. https://www.youtube.com/watch?v=I9ceoJls16s It has a ramp and is a rear-loader. It uses the Human-Player Station. It can make stacks of 6 with container and noodle very fast. The ramp is made entirely out of lexan.

Re: Ramps
 

Mason's line is pretty strong but I don't know of it having a specific load rating. A roll is cheap enough tht you could test it yourself.

If you want a line with a load rating I'd go with "Paracord", the stuff Home Depot sells has either a 130lb or 160lb rated working load in the 1/8" version. Lots of teams are successfully using it for their lifts this year.