Recently watched a fascinating video on compliant mechanism, i.e. single component mechanisms that achieve complex translational motion, and have been thinking of potential applications in FRC. What are your thoughts? Do you know of any examples of such mechanism currently or in years past? If so, how have they performed?
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Just this year, our team’s mentors were able to convince our students that making mechanisms (specifically ones that will stick out of our frame perimeter) can be made out of polycarb rather than aluminium. They never quite trusted it, but we’d continually run into issues of our grabber/intake being bent beyond repair.
So this year we’ve got a polycarb dual-grabber and a mostly polycarb intake (which we also climb on), and not only are they more than strong enough, but if we get rammed, they just bend back into place (unless it is a truly catastrophic hit) and we’re unaffected. Granted, this isn’t the same kind of “compliance” that the video shows, where you have pivot points based around bendy material.
This is earlier in the build season, we’ve since made some sizable changes, but this is a picture with both of our polycarb mechanisms in it. So far they’ve been working great!
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Sure, there are a tone of examples of compliance in FRC to achieve proper mechanism function. From 2767 this year: the “trident” (100% student lead & designed, it is an awesome piece of engineering):
Prototype: https://www.chiefdelphi.com/uploads/default/original/3X/e/8/e8147fe9630508754749bd62fe067387ec1b1084.mp4
Final(ish) version: https://www.chiefdelphi.com/uploads/default/original/3X/8/e/8e6e4d65d769e3ceb17662ffb5cd39032350c0e5.mp4
There is +/- 30degrees of compliance for taking up any misalignment.
The “coconut” that the ball sits in also has some compliance for securing a good seal on the cargo with the suction cups.
Polycarb is easily one of if not the most used complaint material in FRC.
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I’ve never seen it used in FRC, but I’d love to see someone do a series elastic actuator for compliance to help protect motors from sharp jerk forces being applied when smacking manipulators into field elements for scoring. But that’d be a little more complicated than polycarbonate or just “bendy material”.
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What width polycarb are you using? I saw your bot up close, but I guess I didn’t look close enough.
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971’s cube intake last year utilized series elastics.
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Mostly quarter inch, with 1/8th inch in a few places that are less structural and more about containing the cargo. We even have our piston-powered rack-and-pinion-actuated four-bar grabber made out of polycarb. Works great.
Really the only downside of polycarb is that the clear stuff photographs terribly, it’s hard to tell what is going on with a static photo.
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If you’re not putoff from it, they do sell “smoked” polycarbonate which comes in dark shades. It looks pretty cool, no structural affects from my observation.
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Smoked polycarb makes the robot go faster. Proven fact.
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Oh yeah, we have definitely wanted smoked polycarb or stuff in our team colors, but it’s more expensive for us, and we tend to make a lot of revisions (see: mistakes) and have large pieces.
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Oh, yeah. That intake was my favorite part of their robot last year. It was such a great way to add compliance to a highly structured mechanism. Having well-controlled elasticity is tough, and they nailed it.
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Just saw this and thought I would add this industrial complient gripper systerm to this thread.
Polycarb intakes that can flex under impact are pretty common, as mentioned.
On a smaller scale, we had a lot of fun designing flexures into 3D prints for our DIN Rail mount system.
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If this thread has been revived, I’ll add our experience this year. Our first many versions of our hatch gripper were all 3D printed from TPU. This gave them the elasticity needed to be able to crash into the driver station wall without shattering, and accept game piece misalignment without snapping. Unfortunately, the system was a bit too elastic and would sometimes only grab the hatch by one “petal” and then drop it once it pulled out of the loading station.
Here are the only pictures I could find:
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Hey, I have that guy’s book! I can’t believe I missed this thread the first time around…
Last year, we designed a compliant claw to grab claws at our second event, made from polycarbonate: https://imgur.com/qciH7d1h.jpg
We used the generative tool in inventor 2019 to get a starting point for the design, and went through a few iterations until we found one with the right balance of torsional stiffness and lateral flex. We were driven to a compliant design by limits on carry-on weight and space, and concerns about robustness.
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It looks like your link is broken, if you remove the “i.” it should work.
I’m not sure I see the claw you are referring to, do you have a more focused picture?
Thanks, edited the link. It’s the polycarbonate mechanism on the front of the robot (the end facing away from the driver station). Unfortunately, I don’t have a huge amount of pictures from last year.
Interestingly enough we found that our .25" smoked polycarbonate was noticibly more flexible than our clear polycarbonate. It didn’t make a difference in our case but it’s defintely something to keep in mind.
And speaking of polycarb, it’s great! Super fast to cut on our CNC router and absorbs shock really well. Our elevator gearboxes this year were actually cut out of .25" polycarb plate as our aluminum ones didn’t get back from anodizing in time (oops), and we didn’t have any issues thoughout the entire season. Our arm was also connected by polycarbonate struts (see attached photo) which gave us some compliance when placing and absorbed any shock that would have gone to our turret plate.
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1684 has used polycarb for our intake the last two years and it’s served us well. Laser cut by one of our students at the company he works for. (a sponsor)
Both had flex to them which helped absorb shock. When we’d find stress points, they’d be addressed.
2018 - top & bottom flex wheel rollers for the cube:
2019 - horizontal flex wheel intake for hacthes & cargo
Edit: meant to reply to the OP, not just @juju_beans Whoops!
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