Re: 1726 Prototype Testing
 

kinda looks like what where going with. great job.

Re: 1726 Prototype Testing
 

Nice job. It appears that the ball develops a rearward spin with this design as it rolls off the catapult forks. This is elegant. It seemed to roll back towards the bot after the shot.

The mechanism illustration suggests an "over center" latching scheme where actuators initially pressurize with the force vector of the actuators aimed just below center of the mechnism fulcrum. As such it will not fire unless somthing bumps them above the fulcrum. Possibly the small gizmo at the far left of the illustration does this. Getting both actuators "over center" at the same time may be a challenge due to build tolerances and mechanism flex.

I wonder about the shot to shot repeatability in terms of height and trajectory. To be shooting on the move, the shot to shot repeatability would be important.

Re: 1726 Prototype Testing
 

What makes the "ball pick up" device go foward and back

Re: 1726 Prototype Testing
 

Actually, I'm just really bad at making drawings :) I believe this picture from our gallery demonstrates it best:

the point where the piston attaches is just above the line created by the front pivot point and the end of the flinging arm. When the cylinders are pressurized, the catapult "slowly" begins moving because of that slight height. The end pieces you see are just mechanical stops so the catapult arms are always under the point where the piston attaches.

As for the ball-picker-upper, we simply use a pneumatic piston right now, but may end up switching to a motor to conserve air for the catapult:

Re: 1726 Prototype Testing
 

Thanks of the clarification and the details. Your design is a real inspiration to others that are looking at catapults.

How is shot to shot repeatability in terms of height and trajectory?

Regards
Frank

Re: 1726 Prototype Testing
 

We won't know how repeatable it is until we build the last part, which is an arm that sits on top of the ball to hold it down, and is raised when we want to fire the ball. The idea is to use the downward force of this arm plus the weight of the ball to overcome the initial vertical upward force of the catapult...and then when the top arm is released, the vertical force of the catpult is greater than the weight of the ball, so the ball fires. In our initial tests using my arm as the ball holder downer, this seems to work ok, but we need to do some fabrication soon (ie today) to get that arm built and on the robot, so we can answer your question more accurately :)

Re: 1726 Prototype Testing
 

you're loader mechanism seems to work well but I'd hate to see what happens when you accidentally run into a wall at full speed

Re: 1726 Prototype Testing
 

heh...we already know what happens when we do that! and so we're working on other ways to build it to take more abuse.

Re: 1726 Prototype Testing
 

Funny you should mention that! We were working on a design today for a collapsible ball picker-upper:


The 1/4" strip of lexan acts as a slight spring. It takes just the right amount of force to push it, and the aluminum bracket prevents the arm from swinging out.

We realized we need to design this after we (I) accidentally test-crashed the manipulator into a wall and it was almost mangled beyond repair (but not quite, because we did repair it)

Re: 1726 Prototype Testing
 

Here is our version of your catapult!http://www.youtube.com/watch?v=LwmyQMlmaRY
Thanks for the help!

Re: 1726 Prototype Testing
 

Nice! see, it's not so hard to do :)

Re: 1726 Prototype Testing
 

Different configurations are likely to work, too. We've prototyped one arm of our two armed launcher and achieved heights of about 5' at a 45 degree angle using just two 1.5x8" cylinders and one clippard tank of air at 60 psi. We are building the second arm (two more cylinders, one more tank) and expecting to clear about 8' with both working together. We'll post some video when we get that happening.

As for picking up the ball... just try smashing it into the wall. If your front end is low the ball shoots up, and you drive right underneath it as it falls back down.

Not particularly elegant, and not much good in the open field, but I'm not quite sure how anyone is going to get a ball to sit still on the open field for them to grab anyways. Mind you, I may be wrong about that... I haven't played this game before, you see...

Jason

Re: 1726 Prototype Testing
 

actually, we have an automated system for picking up the ball that appears to work quite nicely ;) All we have to do is run into it...

Re: 1726 Prototype Testing
 

Was there any validity to the following comment that was posted on the YouTube video at
http://www.youtube.com/watch?v=G9y-L...eature=related

=================
dougji I hate to burst your guys bubble, but this is illegal. You're not allowed any "sudden stop" launching mechanisms.

frc1726 (2 days ago) Could you please cite a rule, Q&A response, or team update paragraph that says that? We haven't seen any such thing, and would like to know if you are correct.

=================

What is the definition of a "sudden stop" launching mechanism?

Regards
Frank

Re: 1726 Prototype Testing
 

I have not found anything that gives it any validity, and I think the person who posted that might not understand how our robot works.