Durability of tetras

[tkwetzel]

Seeing all the pictures of the robots come together, I have noticed that those tetras really will be extended pretty high into the air. It is also a good chance that many will fall from great heights also. It seems that they may break easily after being dropped from 10'+ a few times. Has anyone dropped a tetra from a height as such and noticed any damage? Or has anyone noticed any damage at all to tetras that you have built and tested with?

[Greg Marra]

Originally Posted by tkwetzel

Seeing all the pictures of the robots come together, I have noticed that those tetras really will be extended pretty high into the air. It is also a good chance that many will fall from great heights also. It seems that they may break easily after being dropped from 10'+ a few times. Has anyone dropped a tetra from a height as such and noticed any damage? Or has anyone noticed any damage at all to tetras that you have built and tested with?

Umm, we scratched them up really good. Not structural damage, but they're not pretty to look at anymore.

And due to some mishaps with testing, our vision tetra has some scratches in its vision panels. I'm afraid the vision tetras are going to get beat up on the most...

[MattK]

ours have been breaking like crazy. Our Advisor goes to pick them up and they just fall apart... although maybe that is just due to his super strength

[Ashley_05]

Our tetras have been falling apart too. Last night, we were engaged in a tetra, it was lifted above the larger tetra and it simply fell apart. I think that several tetras will be replaced this season, but hey, it's part of the game.

[Marc P.]

I think it depends on the properties of the clovers used to assemble the tetras. The real field tetras at the kickoff seemed pretty sturdy, and didn't look like they would come apart too easily. See here.

[katkana]

Our tetras have been holding up.... eh, decently. We haven't really put them through their paces completely (the robot's in pieces at the moment, so it can't do anything... ) but none of the tetras we were using have shattered beyond repair.

Also... here's a question: are the tetras y'all are using PVC? 'Cause the USF specs on the tetras say they're to be made of aluminum and I'd figure they would hold up better than the PVC has been...

[Mike]

Originally Posted by MattK

ours have been breaking like crazy. Our Advisor goes to pick them up and they just fall apart... although maybe that is just due to his super strength

Lol, same here

[Swampdude]

All I can say is I hope they stock a lot of extras at the competitions. Our cap system is tearing them up. It's not as much the bot's fault as it is the fact that these things are heavy with a rather weak joint. I don't think they were designed with rapid play in mind. Then to compound that with a couple bots fighting over one, there's going to be a big pile of dead tets after each competition. Or at least those clover things. They need to make metal ones.

[Wetzel]

Originally Posted by Swampdude

All I can say is I hope they stock a lot of extras at the competitions. Our cap system is tearing them up. It's not as much the bot's fault as it is the fact that these things are heavy with a rather weak joint. I don't think they were designed with rapid play in mind. Then to compound that with a couple bots fighting over one, there's going to be a big pile of dead tets after each competition. Or at least those clover things. They need to make metal ones.

Perhaps you need to rethink your robot design. You have a system that you like, but is "tearing them up." Because your design was breaking the official tetras, you made stronger ones to practice with. However, the tetras are as they are. With the Sterlite bins in Stack Attack, FIRST intentionally chose a weaker container as part of the challenge. Having custom injection molded parts, and lots of them, made it is unlikely for FIRST to spend a lot of money to redesign the major game piece now.

You don't get to engineer how strong a human chest is, you need to engineer your car to not exceed the loads a chest can take in a car accident. A foot can only take so much energy, you need to design the boot to keep the energy below that threshold.

In FIRST as in life, there are design criteria that can not be changed.

Wetzel

[Tim Arnold]

Originally Posted by Swampdude

All I can say is I hope they stock a lot of extras at the competitions. Our cap system is tearing them up. It's not as much the bot's fault as it is the fact that these things are heavy with a rather weak joint. I don't think they were designed with rapid play in mind. Then to compound that with a couple bots fighting over one, there's going to be a big pile of dead tets after each competition. Or at least those clover things. They need to make metal ones.

Yeah, expecially when your throwing them across the field...

[tkwetzel]

Those of you that are saying that your tetras are falling apart like crazy...have you glued the end caps on to the PVC pipe like the competition tetras will be? And how have the tetras been breaking? Like have the clovers been breaking or falling off or are the end caps falling off?

Originally Posted by katkana

Also... here's a question: are the tetras y'all are using PVC? 'Cause the USF specs on the tetras say they're to be made of aluminum and I'd figure they would hold up better than the PVC has been...

The scoring tetras will be made of PVC. The tetra goals will be made of aluminum.

[Daniel Brim]

Also, keep in mind that the ends are going to be injection molded, as opposed to a thin piece of lexan (or something similar) that most teams are using. I think they'll hold up.

[Swampdude]

The plastic clovers started shearing very early on in our testing. So we quit on those early. The glued end caps entombed the hardware inside the PVC once the clover tore the pipe was no good. So the whole thing quickly became trash. The ones we practice with are duct-taped end caps, then used the conduit strapping in a triangle pattern like someone suggested on here (I'll look for that picture and link it here). That holds up for a while, but the strapping isn't thick enough gage. Maybe if we doubled them up it would stay. But like you said, just dropping them busts em open. The plastic clovers were the easiest to break. That metal flange they made to hold the magnet would work good.
The stress concentration in the folded corners of that plastic will never hold up. But the bolted points tore out also. It's just not a capable material. I originally was worried we would get penalized for breaking these things, but I later convinced myself they were going to be breaking all over the place by design issues within.
http://www.chiefdelphi.com/forums/at...achmentid=2807

[Jeff Rodriguez]

Our tetras have steel clovers and the end caps are not glued. They come apart all the time, but it's not a big deal to stick it back together.
Our tetras do not like to be thrown. They don't even like to be slid along the ground. I have broken too many just tossing them while resetting our field.

[SURVIVORfan44]

One of our tetras broke yesterday, it was accidentally dropped from way up in the air. It just snapped...but it could be fixed!