FRC 3357 shooter arm

[first_newbie]

How does the 3357 arm work, and what mechanisms do they use?

[chapman1]

In order to save other members of the Chief Delphi community from having to Google, here is a link to 3357's youtube channel:

https://www.youtube.com/user/cometsrobotics

[The other Gabe]

I certainly can't tell you any specifics, but I'm darned sure that's a 4-bar linkage they're using

[IamBuild]

It's pretty complicated. The whole shooting deck and pickup mechanism is all on 3 pivoting arms, one in the front and two in the back. When it is all the way down everything lays flat locking it in place. To lift it up from there we have a piston that hits the front of the main deck unlocking it in a sence. From there we have 2 pulling points on the front arm of the structure that 2 bungee assisted pistons pull on to lift it into place. In all we have 6 large speargun bungies and 3 pistons to raise and lower it. The pistons are pulling on a cord that goes through a 2-1 pully system on each side to get the extra distance required to pull it up, the other two bungies work to pull it back down when we release the pressure from the pistons to keep tension on the cord.

[wilsonmw04]

It looks and acts like a linkage that we tried to use for Ulimate Ascent.

https://www.youtube.com/watch?v=ZuvmSLGaNTw

[IamBuild]

Yeah that's pretty similar! Love that video by the way, looks so professional!

[jdunston94]

To fill in a few more of the numbers, yes it is a modified 4-bar linkage. The front arm has roughly 120 degrees of rotation and we have it tuned right now so at the peak, the shooting deck is at about 43 degrees above flat. To initiate the upward movement we are exerting over 100lbs to "break" the linkage from the locked position. After the first 15 degrees of rotation by the front arm it gets much easier. I will see about getting our design manual loaded online for people to look at as we have the math behind our robot design there.