Four Bars are all the rage because they are relatively bulletproof, but what’s the most complicated (or coolest) linkage to ever see use on an FRC robot?
I know 148 was proud of their double 4 bar in 2011, and 842 had a pretty neat chain run as well, but that can’t be the extent of super cool mechanisms. A friend suggested 217 in 2007, but there must be a whole host of mechanisms out there.
Go! 
Check out Wildstang 2007…
217-2007 is BY FAR the winner of “coolest linkage.” Your friend is correct.
67’s arm linkage in 2005 was also great, and very inspiring to me. While it is just a 4-bar linkage, it is a really cool 4-bar linkage!
See attached. I highlighted the 4 different links to help understand it.
The yellow link was stationary (the chassis of the robot), the blue link was the output, and they drove the red link.
-John
Didnt quite of few teams have the same arm linkage as 217? From that pic of 67 you can see 217 in the background and I know atleast 1902 had the same arm linkage.
217-2005 had a “perfect” 4-bar.
217-2007 had… something else. I think it was technically an 8-bar linkage… with a cross-over link.
Pics:
http://www.chiefdelphi.com/media/photos/28207
http://www.chiefdelphi.com/media/photos/27487
http://www.chiefdelphi.com/media/photos/27238
I recall team 67’s 2008 robot as having one of my favorite linkage mechanisms (at least conceptually… implementation looked painful 
). Spring loaded extending member in a single DOF mechanism to achieve a very unique path and stay within size constraints, very cool!
Also a big fan of 1625’s over-center launching mechansim, though I’ve yet to use it on a robot. I’m sure a time will come.
The Thunderchickens arm from 2007 is very unique, and another favorite of mine. I used it as one of my “pick any mechanism and do a report on it” style of exams for free-body analysis in college. I wish I remember more details of my analysis, but I wasn’t very good at documenting things back then.
67: http://www.chiefdelphi.com/media/photos/30680
1625: http://www.chiefdelphi.com/media/photos/31538
Short analysis on 217’s arm attached as well.
217_FBA.doc (617 KB)
217_FBA.doc (617 KB)
190 used a 6-ish-bar mechanism to obtain a “not-quite-rotational” motion to deploy the minibot ramp in 2011. (One of only two minibot ramps to “ship” with a robot in 2011, I believe, even though they were all the rage at champs. The other original ramp belonged to 233.)
Not an arm, but a linkage nontheless, and definitely complicated.
If I find a good video or picture that shows the linkage I’ll edit my post to add it, at the moment I haven’t found one. It was removed from the robot for the promo video so that we wouldn’t give away the ramp idea before our first regional.
I generally don’t toot our own horn but our Overdrive linkage was pretty cool.
I’ve attached a picture of the linkage Steph is referring to. It’s a 6-bar (4-bar with a driver dyad) that lifts the ramp from its storage down low in the robot up and over the tower base. The virtual center (the point in space that the entire mechanism is rotating about at any given time) is always somewhere around the rear edge of the robot frame.
Another great linkage in FRC was 67’s 2008 adjustable 4-bar. The operation was seamless, and very clever.
Stephanie
That is really cool! How did your team design/develop this linkage? Did they model it in CAD and articulate it on screen or did they prototype it to get the lengths and pivot points right?
Thanks.
Phil
Looks like you went through and picked all my favorites.
I’d add 148’s 2011 four-bar, because of the clever use of the cylinder as part of the upper link.
I guess I could mention that lame 842 arm from 2011 (and its predecessors mentioned in the below thread): http://www.chiefdelphi.com/forums/showthread.php?t=90284
That was one of my favorite mechanisms for a week or two, right up until we tried to build the darn thing.
Another cool linkage system that I’ve only ever seen used once: 1565’s linkage drivetrain from 2008: http://www.youtube.com/watch?v=RvN4K2ieR5g
DING DING DING, I think we have a winner. I have never seen that video before or any video of 1565’s 2008 robot and I say that takes the prize. That is actually very innovative. Not to sound demeaning to the team, as I am giving them tons of praise, this seems like a poor-man’s swerve; all be it it is only bi-directional, it still works on the same concept. I wonder if you could use mechanum wheels in the same setup.
As the picture in Nuttyman54’s post shows, we designed the linkage in Solidworks before fabrication. There are plenty of calculations for linkages like this, and it is a very popular thing to learn/do at WPI. One of the professors has written a few books on machine design and is an expert on these types of linkages (among other things, of course). If you search “design of machinery” in google, his book and his website are the first few hits. This linkage was relatively simple in that context, though complicated for a FIRST robot.
The idea that Nuttyman54 referred to with the linkage was that we basically wanted to mount the ramp as low as possible in the robot, but have the center of rotation above the bumpers and land the top of the ramp at the highest legal point on the pole. Having a linkage like this allowed us to accomplish all of those goals as well as keep the minibot secure and protected during the match, prior to deployment. The mechanism was quite robust considering its complexity, only having a couple of minibot failures all season.
A few more, since this thread has so many potentials. Both of my favorite linkages of 2012 happened to be on the same robot (the beautifully designed D’Penguineer robot, you may have heard of it).
The first is a locking mechanism for deploying a bridge wedge. A single cylinder is used to first drive down the wedge, then move the pin into locking position via well placed grooves. A very clever solution to a problem that just about every team using a drop-down wedge had to face.
http://i.imgur.com/l6N33l.jpg](http://i.imgur.com/l6N33.jpg)
The next is about as simple as a linkage gets; one cylinder and one pivoting part. Great way to package the mechanism into such a small space. D’Penguineers used this to get their 2-speed 4 wheel independently steered swerve drive to transition smoothly over the barricade.
http://i.imgur.com/01E1kl.jpg](http://imgur.com/01E1k.jpg) http://i.imgur.com/KJZ7Jl.jpg](http://imgur.com/KJZ7J.jpg)
We built this during one of our Summers of Robot Fun for Drive trains we built a “twitch drive”, like 1565’s linkage. (See the Power Point on the page) One of our VEX teams then built one a year later for competition It had all the features of wide and short bases, and worked well for them. With the grippy wheels it was a winner in any pushing contest. Downside was the huge force on the upper part of the pivot and the shaft. The force applied by the wheels on the standard VEX shaft was the weak point. If I had to do it today, (and I might since this has triggered the thought) I’d use the VEX small turntable as the pivot point.
More on topic for the linkage was a team at “Overdrive” that could pick the ball up off the floor and swivel it up and over the bridge, either placing it or tossing it over. I want to say it was Rolling Thunder 1511, or Moe 365 since they are awash in engineering coolness, but I’m not 100% sure.
190 in 2008 had a crane like appendage. If i can find a picture i’ll post it later.
Unfortunately, that linkage never made it past the build season. We had some major controls issues dealing with the transition between when the link was compressed and when it started to expand. We ended up removing the adjustable link and creating a new lower link with a different pivot point that provided the same motion, at our first event of the season. I think it ended up being a lot more robust too. I am not sure the adjustable link would have held up to the abuse.
It was a decent idea, but the execution was lacking a little bit.
148’s 2011 adjustable 4-bar linkage had much better execution.
While this was a very unique system, the crane was essentially a very long version of 233’s famous arm, mounted vertically. It wasn’t a linkage by any sense of the word, so I don’t think it qualifies for this discussion.
190’s 2007 championship winning robot did have a 7-bar linkage on it, in the gripper:
Open position, closed position
It was operated by a single piston which when extended would first actuate the “finger” linkage, gripping a tube and pulling it back into the claw. Once 13 lbs of grip force is achieved, the continued extension of the piston would lift the entire arm up to a 45 degree angle (all while maintaining a constant grip force on the tube).
Video here, best shots are from 0:30 to 1:00
Might be a bit of a minority opinion here, but I actually think the replacement for 67-2008’s adjustable link made for a really cool linkage. The required placement for the link was in the middle of where the arm had to go through, so HOT used a unique combination of shapes and materials to make a “hollow” pivot point that was really cool. http://frcteam67.dyndns.org/HOTPhotoAlbum/2008/2008-03-6-8%20FingerLakes/P1010001.JPG
I’ve always been envious of some designers’ abilities to seemingly pull cool, complex linkages out of their heads and onto a robot. Does anybody have neat resources to learn more about synthesizing and designing linkages for various tasks? I’d love to learn more as that’s essentially the most fascinating part of mechanical design for me right now.
