Be careful with extensions/appendages

[mrwright]

We have a JVN style collector on our robot and last night it was broken in an instant. We knew that it was a big risk to have anything sticking outside of the frame perimeter so our drivers have been training to keep the arm up until the last possible moment.

One quick turn by the defensive robot and our nice sheet metal arm along with the air cylinder was destroyed. Luckily we have lots of time to practice and to redesign our collector arm. We just wanted to let everyone with these style of collectors to be warned and be prepared to have them bent or broken. I foresee this happening to a lot of teams. If we wouldn't have had this happen to us we would have been in very big trouble had it happened at a regional.

We are really beefing up our design and we will be much smarter about exposing that arm. Hopefully this helps others out as well!

[Electronica1]

What thickness sheet metal is that?

[mrwright]

.080 aluminum.

[Whippet]

This is why we decided to make our robot out of wood. It's no less likely to break, but when it does we can have replacements made and ready to go in ~1 minute.

[Zebra_Fact_Man]

We're using 1/16" square Al tubing. Not the flashiest stuff, but you'll be hard pressed to find a way to break it on the field.

[DonRotolo]

I think many teams will suffer a similar fate. It's just too easy for the ball collector, sticking way out there, to get pushed from the side (accidentally or on purpose, as this is not contact "within the frame perimeter").

Be sure it is stiff when struck from the side, have the drivers pull it in when not being used, and maybe design some way to protect that cylinder, like a break-away pin.

[wireties]

We used .125 wall 1x2 and a linkage from a motor (instead of pneumatics) to raise/lower a JVN-style pickup. And we put a "fender" over the pickup wheels. After reading this I hope it lasts!

[mrnoble]

I was going to ask, "what's a JVN?", but then I remembered my Build Blitz history. This year's game and build season will go down as a major adder to FRC lingo, I think.

Relating to the problem at hand, we've made our collector/shooter out of the strongest materials and construction methods on the entire robot this time around. Much more concerned about cantilevered parts than about a well-protected drive base.

[Adam Freeman]

This is a good design lesson!

If you can't design it to be robust enough to survive a hard impact (because of weight, material, etc), then make sure you design in some flexibilty or a known weak link that can be replaced easily when damaged.

In 2012 we over designed our arm to survive extensive impact, using 2"x3"x1/8" square tubing. Even then we collapsed our arm in the elims at Champs and had to spend valuable time fixing it instead of planning for our next match.

Other years we have used lexan or other materials to create a flexible joint that can survive competition play.

Always try to understand the environment your part is going to have to function in.

[mrwright]

We ended up rebuilding another arm that is using rectangle tubing and it is already much more robust. Using a polycarbonate arm sounds really appealing though. We may look more into that.

[CalTran]

Originally Posted by mrwright

We ended up rebuilding another arm that is using rectangle tubing and it is already much more robust. Using a polycarbonate arm sounds really appealing though. We may look more into that.

16 did that polycarb back in 2008.

[Alan Anderson]

Originally Posted by CalTran

16 did that polycarb back in 2008.

The TechnoKats 2003 "ball drive" robot used a polycarbonate bin-stacking arm, intended to survive being hit by other robots (or ballistic storage totes). Flex can be a good thing.

[Boe]

This is one of the ways we are protecting our roller bar http://www.fightingcalculators.org/b...r-frustration/