Will the tetras spin?

[SteveO]

Does anyone know if the tetras will spin when they are grabbed? If I am gripping a pipe hard enough, will it slip/twist in its endcap? I know FIRST doesn't use endcaps, but will they do this?

[jgannon]

I think this was answered on the FIRST Q&A. The ends are going to be glued, so they shouldn't spin.

[Elgin Clock]

Originally Posted by jgannon

I think this was answered on the FIRST Q&A. The ends are going to be glued, so they shouldn't spin.

From the end caps to the pipes, probably no movement. But, we experienced that law knows as the weakest link, when we glued the caps to the pipes, and thus now the nuts and screws turn themselves loose inside the pipes..

Now what, should they make it a huge threaded rod from one end to the other to attach the clovers to the pipes now instead of a small screw and nut assembly?

Or, hey.. What about using Loc-tite on the nuts.. Maybe that would work. Then it may still twist, but not unthread itself??

I'm not sure.

[Max Lobovsky]

We've had bolts spinning in the clovers even with split washers. Anyone know if the real ones will have this problem?

[dlavery]

Yes, FIRST has said that the tetra pipes will be glued to the end caps. And in the part drawings, they indicate that the end caps will be attached to the LDPE tetra clovers with a bolt and t-nut (presumably, based on the drawing, a t-nut with spines that will grip the interior of the end cap to prevent rotation).

However, recognize that if you grip them by the lower horizontal edge pipe (as it is positioned when sitting on the floor) and lift it, you will be putting about 10 ft-lbs of torque on the connections at the ends of the pipe assembly. And if you bump into things and transmit shocks, the loading may be considerably higher. Given that the only thing that will prevent the entire end cap-pipe-end cap assembly from spinning around on the bolt will be the little spines on the t-nut, I am willing to put down a small wager (hey Dr. Joe! How about a case of Mt. Dew?!) that by the second weekend of competitions those pipes will be spinning like mad. I would recommend that you do not count on the pipes as rock-solid, we-will-never-spin, don't-play-me-like-a-LP structures. Devise a way to grip them so if the pipes does spin, it will not riun your day.

-dave

[Max Lobovsky]

I think the bolt heads/washers will be spinning in the clover long before the spines of the t-nut cut through the PVC, but regardless, would field staff try to fix this as best they can (Tighten or replace hardware and clovers, etc)?

[dlavery]

Originally Posted by Max Lobovsky

I think the bolt heads/washers will be spinning in the clover long before the spines of the t-nut cut through the PVC, but regardless, would field staff try to fix this as best they can (Tighten or replace hardware and clovers, etc)?

Unless the tetra actually comes apart, I doubt it. They make it pretty clear in the Q&A system that we can expect the tetra pipes to rotate:

Q 1180: We made a scoring tetra. When lifting by one of the legs the leg with the leg horizontal it rotates in spite of being tightened and glued. (we have rounded caps) Will the competition scoring tetra's legs rotate?
A: Yes, they may rotate depending on friction, etc.

Q 1182: PVC caps are glued to the PVC. Does the fastening of the cap to the tetra connector keep the PVC cap from rotating on the bolt?
A: No.

-dave

[SteveO]

Thanks for clarifying that. We're not sure how *exactly* we're going to be gripping the pipes, but this just adds to the team's desire to grab the tetra at two points for better control.

[russell]

Is there a rule against dismantling tetras? Like giving your robot a wrench or whatever and having it actually undo the bolts? I am not sure why one would want to do this, but some teams are talking about how many tetras they can fit on their bot, and if they could quickly assemble/dissassemble the tetras it would be a lot easier to store them.

[SteveO]

I'm guessing this wouldn't be allowed... I know its illegal to intentionally damage the field <S09> and probably the tetras too, though some tetras are bound to be accidentally damaged. Hats off to any team that is able to give their robot a wrench and dismantle and reassemble a tetra though

[Aignam]

Originally Posted by russell

Is there a rule against dismantling tetras? Like giving your robot a wrench or whatever and having it actually undo the bolts? I am not sure why one would want to do this, but some teams are talking about how many tetras they can fit on their bot, and if they could quickly assemble/dissassemble the tetras it would be a lot easier to store them.

That's definitely illegal. 100%. Maybe you weren't around for it last year, but FIRST stressed that when reading and interpreting the rules, we always let gracious professionalism and common sense prevail. This falls under common sense, I believe.

Basically, if something *seems* extremely illegal, but there is no specific rule against it, count on it being made indirectly illegal by some other rule (in this case the "no damaging the field or field components" rule), or just being so lacking in common sense that it is assumed to be illegal.

Know what is and is not illegal, but also know what is and is not in the spirit of the rules.

This isn't focused just on you---lots of other people should probably take notice. Here, have some positive reputation for thinking outside the box.

[Collmandoman]

oh my goodness =/ people need to be practical-- this is the downfall of many teams - Think of what is possible, and go with it.... taking apart tetras only to reassemble them(for space)... is .... you know.... not bright at all(NOT EFFICIENT or anything)~ Even with an EXTEMELY sophisticated robot.. you'll have time to do this once during a match. MAYBE TWICE..
I'm gonna get flamed

[Spikey]

After reading the first Q&A it does specify in one post that if one of the PVC pipes rotates thats okay, so even if they are glued rotation is something that is not out of the question.

[Digo]

I know now it´s done, but I would like to share my point of view. It´s not useful now, but may be for next year.

The tetra should be made to spin for sure or not to spin for sure. This doubt prevents you from thinking in many possibilities. You will not design a claw/arm counting that the tetra does/doesn´t spin knowing that this situation may change later, or that the tetras may be different from each other. So you need to give up thinking both ways and think about something that works both ways. I guess that limitation could have been avoided.

And I don´t think "that´s part of the challenge", because this way you don´t know what the challenge is.

[Max Lobovsky]

Our design definitley was affected by the tetras spinning, but I don't see how its different than any other "part of the challenge." Not knowing the exact parameters of the problem is definitley a common challenge in the real engineering world.