Re: Team 842,The Forbes Arm, Mach-1
 

speaking of competition, where is everybody going?

Re: Team 842,The Forbes Arm, Mach-1
 

I was talking to all the other mentors about how this arm will be used all of next season by tons of teams. They didn't believe me there could be such an arm design. So I shown them the video.

"Yeah...prototype that arm for next season."

We'll make sure to always call it The Forbes Arm.

Re: Team 842,The Forbes Arm, Mach-1
 

First time in FIRST? Maybe...

However, no offense to Steve -- this is just an example of a grounded link, or as some people might call them a "virtual 4-bar" linkage. It is pretty darn cool, but this technology has been around for a long time.

One of my hobbies is researching cool mechanisms and linkages from history. Back in "the day" when computer control was non-existent, engineers designed machines which turn constant rotary motion (from a stem engine, or water wheel, or whatever) into all sorts of different motions -- including linear motion.

In fact, I know a company in NY involved in a design which utilized something similar to this for an oscillating shower-head on a paper machine.

Call it the Forbes arm if you want, but to me this is similar to the people who used to say Paul Copioli invented the 4-bar linkage...

Again -- no offense intended to Steve Forbes on a beautiful design.
I love it when someone takes a cool linkage or mechanism and uses it with great success on an FRC robot. Now if only I can find an excuse for a Geneva Mechanism (I keep trying to find one).

-John

Re: Team 842,The Forbes Arm, Mach-1
 

These are definitely cool mechanisms....

To echo John's comments, this mechanisms has been deployed before.

Team RUSH used the same system in 1997 for the very first inner tube game.

I can't find a picture right now. :( We call it a passive arm.

Re: Team 842,The Forbes Arm, Mach-1
 

I thought you still had to be within 60" at the start of the match?

Re: Team 842,The Forbes Arm, Mach-1
 

You have to be within your frame perimeter at the start of the match. You used to have to be within a 60 inch cylinder after the start of the match. That cylinder is now 84 inches.

Re: Team 842,The Forbes Arm, Mach-1
 

I was talking about the 60" cylinder rule, which has since been expanded to 84" Height limit is and always has been 60"

Re: Team 842,The Forbes Arm, Mach-1
 

John, no offense taken at all. I'm fully aware of the linkage concepts involved and know they're nothing new. When we had it modeled up in solidworks we were talking about how we had never seen an arm mechanism with this geometry used before on a FIRST bot... the name was jokingly suggested by another team member. Seeing that it was already implemented by 1595 in 07 shows that we're not actually the first to use it, which comes as no surprise.

I'm also fascinated with linkages and rotational/linear power conversion systems (Selectric typewriter, anyone?). This mechanism actually came from a somewhat structured problem solving approach. Sometime on Saturday (kickoff) night I sketched something like this on a piece of paper:

...with the thought that the ideal* arm would be a single DOF mechanism that followed that path. Floor to top peg, passing through initial starting position. After that it was easier to narrow the motion down to possible mechanisms. Form follows function! :)


Sounds like it was first implemented ages ago, I'd love to see a photo if you happen to find one!


*no such thing in this competition, but you know what I mean

Re: Team 842,The Forbes Arm, Mach-1
 

Here is a model of the arm that was done in GeoGebra (free program). You can change all of the lengths of the members and the gear ratio of the sprockets between the shoulder and elbow.
http://concordrobotics.com/arm/

Happy modeling.
Mark

Re: Team 842,The Forbes Arm, Mach-1
 

I found an interesting video this morning

http://www.youtube.com/watch?v=icp1w9PYQYk

Re: Team 842,The Forbes Arm, Mach-1
 

Our team saw this idea and was really enthused about it, I spent hours in inventor planning it out with all of the ratios. It is finally complete though it looks much different than this we reach the top pegs with ease. We will be posting videos and pics after ship along with our deadly deployment.

Re: Team 842,The Forbes Arm, Mach-1
 

Good Job.

Does the robot have to be under 60 inches this year?

Re: Team 842,The Forbes Arm, Mach-1
 

I guess it works, eh?

:p :D ;)

Re: Team 842,The Forbes Arm, Mach-1
 

Congratulations!!! I was following the Arizona Regional from afar via FRC Spyder. I had you tagged for score notifications. It was really nice to see you do so well and ultimately win the regional!

Again, CONGRATULATIONS!!!

Re: Team 842,The Forbes Arm, Mach-1
 

I guess your super fancy linkage arm beats out our claw on a stick, huh. :)