What's the coolest (or most complicated) linkage ever used in FRC?

[Ian Curtis]

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!

[JB987]

Check out Wildstang 2007...

[Stephi Rae]

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.

[IndySam]

I generally don't toot our own horn but our Overdrive linkage was pretty cool.

Here is a pick on CD

The Blue Alliance has some good videos of it in action.

[Nuttyman54]

Originally Posted by Stephi Rae

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'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.

[philso]

Originally Posted by Nuttyman54

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.

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

[Stephi Rae]

Originally Posted by philso

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

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.

[s_forbes]

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.



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.

[Adam Freeman]

Originally Posted by Nuttyman54

Another great linkage in FRC was 67's 2008 adjustable 4-bar. The operation was seamless, and very clever.

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.

[JVN]

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

[dodar]

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.

[JVN]

Originally Posted by dodar

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

[s_forbes]

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.

[RogerR]

Originally Posted by s_forbes

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.

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/sh...ad.php?t=90284

[s_forbes]

Originally Posted by RogerR

I guess I could mention that lame 842 arm from 2011 (and its predecessors mentioned in the below thread): http://www.chiefdelphi.com/forums/sh...ad.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