2363 Triple Helix "pre-release" video of Genome Eta

[ToddF]

So, 4-5 inches of snow fell the night before bag day, canceling school. A small band of mentors and students braved the hazardous roads and fair weather drivers to spend one last day of testing before putting the robot in the bag. The parking lot to the school was unplowed, so some of us parked at a nearby park and hiked to the school, carrying gear on our backs. Since school was closed, we had no access to our normal test space in the auditorium. We had to make due with a tiny carpeted foyer. Our skeleton crew didn't include any members of the multimedia team, so I had to fill in. They will be putting out a more polished release video, but here is a quick and dirty "pre-release" video of Genome Eta.

[dougwilliams]

Amazing robot with lots of capabilities! We're looking forward to playing with you in Virginia this year!

[Lil' Lavery]

Curious about how you ended up designing the recycling container grabbing arm. Why opt for the "passive" chain rotation of the second joint over, say, a 4-bar linkage? Chain failure seems like a higher risk than linkage failure, to me.

[JDGallagher]

Originally Posted by Lil' Lavery

Curious about how you ended up designing the recycling container grabbing arm. Why opt for the "passive" chain rotation of the second joint over, say, a 4-bar linkage? Chain failure seems like a higher risk than linkage failure, to me.

It seems to me that their design would be lighter, more compact, and simpler than a 4-bar linkage of equal length and strength, but I may be wrong.

[wilsonmw04]

Awesome job as always! can't wait to see it in action @ VCU.

[EricLeifermann]

Love the RC holder mechanism. Super sleek and elegant.

[Lil' Lavery]

Originally Posted by JDGallagher

It seems to me that their design would be lighter, more compact, and simpler than a 4-bar linkage of equal length and strength, but I may be wrong.

Given the range of motion required, you're almost certainly correct about the more compact aspect. However, with the larger size and transport configuration rules, compactness is less important than most years.

[ToddF]

Originally Posted by Lil' Lavery

Why opt for the "passive" chain rotation of the second joint over, say, a 4-bar linkage?

Like this one?


We tossed around the pros and cons of the two concepts. There were a few main points that made us lean towards using chain as a virtual 4-bar:
- That design plays to our fabrication strengths. The central tube is the only fabricated item, and the only precision dimension on it is the center to center distance between the holes. Minimizing fabricated parts count was big for us this year, as most of our mechanical team are rookies. For the 4 bar, we'd need to make 4 tubes and 8 end plugs for each arm. Before we ran out of money and weight budget, we planned to have two arms. Throw in a practice bot, and you're looking at 48 fabricated parts. For the chain arm, that drops to 4.
- Mechanical play. In my experience, for linkages to work well, they need to have bearings with absolutely zero play. In this case, that would probably mean good quality rod ends. For 4 arms that's 48 rod ends. Expensive.
- Actuation. Although the prototype had pneumatic actuation, we suspected you'd need more complex control than a bang-bang cylinder to do the things we want to do with the arm. Actuating the chain style arm is as simple as connecting a COTS gearbox to the tube. Driving the 4 bar arm isn't nearly as straightforward.

The nice thing is that the arm ended up with a weight of about 14 pounds. If we come up with a better way (cheaper and lighter), we can swap it out at our first regional.

Originally Posted by Lil' Lavery

Chain failure seems like a higher risk than linkage failure, to me.

Well, that's simple engineering design. If the tension on the chain exceeds its rated strength it may fail. The links, on the other hand, have lots of failure modes, tensile stress, buckling, thread pullout, etc. Used properly, both links and chain will work fine. Used improperly, they will both fail. As I say to the students, "Engineers don't need to guess. You can run the numbers and KNOW. That's what all that math you guys are learning in class is actually used for in the real world."

[Lil' Lavery]

That's exactly the type of response I was hoping for when I made the inquiry.

However, with regards to the failure, I was more concerned with the chain potentially jumping/skipping or external forces on the chain than actually overloading the chain.

[ToddF]

Originally Posted by Lil' Lavery

However, with regards to the failure, I was more concerned with the chain potentially jumping/skipping or external forces on the chain than actually overloading the chain.

Gotcha. That doesn't seem to be a problem. When lowered very quickly against an immovable object, the arm support structure disintegrates before the upper arm chain skips. Unfortunately.

Myself, I prefer a nice mechanical fuse, rather than destroying structure.

[Jean Tenca]

That is the coolest can manipulator I've seen so far. Another awesome robot from you guys. I really hope I get to take a closer look at it in St. Louis!

[1629GaCo]

Great robot!!! See ya at Chesapeake!

[Nathan Streeter]

Absolutely loving this! I expect this to definitely be the best 2363 robot to date!

Way to just keep iterating and adding functionality... love the arms!

[Addison4300]

WOW! I LOVE that container claw! Very unique design! Great Work!

[PowerfulKitty]

I love seeing this robot completed. When I first saw your feeder station loading video weeks ago, I was amazed. And the systems you've added are very nice looking. I love the nifty design that picks up the RC.