Development of 1678's Can Grabber

[hionwind]

Having been intimately involved with all phases of development and testing of 1678's can grabber, I thought the FIRST community might be interested in seeing how things progressed throughout the season.

After kick-off, our team agreed to implement a "chokehold" strategy of acquiring all four cans from the step in autonomous. Our belief was that, if we accomplished this, it would be impossible for our opponents to match our score. This topic has already been well debated in other threads so I won't go into the details.

Our original design involved a foldable wing that could deploy in under a second. We prototyped it using two windsurfing masts (I'm an avid windsurfer) and the following videos show how that went:

https://www.youtube.com/watch?v=vexSNAX_FPY
https://www.youtube.com/watch?v=F0qQm_RG1tI

After a lot of discussion and consultation with engineers who knew a lot more than us about light wingspans (think airplanes) we decided to design the wing using thin sheet folded into a rectangular section and articulated with 4 hinges. The design was completely fabricated and assembled a few weeks before the Central Valley Regional. Here are a couple of videos of testing:

https://www.youtube.com/watch?v=STkH0Xh9Vok
https://www.youtube.com/watch?v=bbwh8DBykYw

We were getting pretty excited at this point. We had a design that was within transport configuration, could be set up in less than a minute, reached the cans in about a second and released cleanly. We were working on the pulley system to reel the entire contraption back in when we saw the reveal videos showing 118's and 3310's can grabbers. We thought, "what is the point in going for all four cans when someone is going to beat us to at least 2 and possibly all 4?" We immediately abandoned this design and began working on our own 2-can grabber with just a couple of weeks to go before the Central Valley Regional. We decided on a motor-driven system using extendable hooks similar to 118's. Here are a couple of videos of us testing the hook and pull back:

https://www.youtube.com/watch?v=C1V0eBOVy0Y
https://www.youtube.com/watch?v=QdI3Xl1XARI

Here's video of one of the first tests on the full system:

https://www.youtube.com/watch?v=P8t-SM8cK0E

One of the things we worked on quite a bit was preventing bounce-back and also the addition of a shield to prevent opponents getting their hooks into the can. Here's a video of the shield testing:

https://www.youtube.com/watch?v=hegki23HHFY

We ran this system at the Central Valley Regional, Sacramento Regional and Silicon Valley Regional. At CVR, we built a cheesecake version from scratch and mounted it on 1323's robot. At Sacramento, we mounted the same cheesecake on 5458's robot. At SVR we mounted it on 5027's robot and then gave it to them to take to CMP. 5027 was very successful in the can war on Newton, including a great battle with 3310.

Even though our 2-can grabber was fast (around 250 ms) we knew that teams would be faster at champs so, even before SVR, we started working on a lighter, faster version. We decided we needed to power the system with surgical tubing to make it faster so we came up with a four-bar linkage that allowed us to develop a lot of power with a system that could be placed behind the arms. The design team came up with a super light triangular frame design for the arms made out of 1/2 - inch carbon tubing but it just seemed to weak to me. I got my windsuring masts out again and we prototyped the four bar linkage hammering the mast onto the can. It was super fast and almost destroyed the top of the can. We were convinced we should just use a single carbon tube. This was about a week and a half before champs. We hastily ordered some 1-inch carbon tubes and began designing a new hook using 1-inch aluminum tubing for the prototyping. The biggest problem we were having was bounce back. The hook would bounce more than a foot above the lid before settling back in and we knew we could lose the can in that instant. The solution came by accident when we were testing cushioning materials to soften the impact and reduce bounce back. During one test we saw the cushioning material push the can forward, locking the hook in which resulted in minimal bounce back. Here's a video of that revelation:

https://www.youtube.com/watch?v=2VdM73rIgKU

We quickly modified our hooks to incorporate a wedge behind the hook to push the can forward. This turned out to be the crucial piece of the puzzle that made our can grabbers so effective. We felt that it accomplished three different objectives: (1) it locked in the hook so there was no bounce-back, (2) it moved the target for our opponents grabber making us think we didn't need the shield anymore, and (3) it absorbed the direct impact of the arm reducing the risk of breaking the carbon tube under the extreme force we were exerting on the arms. We tested our final arms with 12 wraps of surgical tubing per arm and achieved times or around 130-150 ms. in the shop but decided to go with just 8 wraps at champs to reduce the strain on the system. We feel good about that decision:

https://www.youtube.com/watch?v=M8C9qQC6fXE
https://www.youtube.com/watch?v=7VtND14eEno

Throughout this entire process, our students worked relentlessly and never stopped pushing to make our can grabber faster and more reliable. I am so proud of what they accomplished.