View Single Post
  #18   Spotlight this post!  
Unread 12-02-2014, 02:08
Travis Hoffman's Avatar Unsung FIRST Hero
Travis Hoffman Travis Hoffman is offline
O-H
FRC #0048 (Delphi E.L.I.T.E.)
Team Role: Engineer
 
Join Date: Sep 2001
Rookie Year: 2001
Location: Warren, Ohio USA
Posts: 4,047
Travis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond reputeTravis Hoffman has a reputation beyond repute
Re: pic: Team 48 - Lock n' Load

Quote:
Originally Posted by DampRobot View Post
Is that shots from 16' into the goal, 16' to hit the ground, or something else?
That would be 16' to the bottom of the goal as indicated on the white FRP target in our shop. We'll have access to a *real* practice goal once we gain access to the auxiliary gym, where we have the room to set it up.

Quote:
Originally Posted by johnr View Post
I know nothing is going to happen but i sure would like to see a steel cable thru the center of that spring. I just don't see a way to hook one up in this picture. Maybe once it is mounted. I worked on garage doors for 30 years. Please be careful.
We planned on running some "anti-explosion" means through the springs at some point. I can suggest sooner rather than later. They really appear to be contained well by our delrin spacers, but if the springs fail due to internal defect in unexpected fashion (we do not stretch them beyond their recommended max deflection), we'll want something to prevent them from being launched into orbit.

I hope the catapult folks (and safety inspectors) are equally as concerned with the high velocity tips of catapult arms weakening, breaking, and launching into space at some point. ;-)

Quote:
Originally Posted by ekapalka View Post
I can almost wrap my head around how it works, but not quite.... How are you selecting the high or low shots? I think I understand, but am not positive... So... for the low power shot you pull back the spring 3" (using only the pneumatic cylinders) and for the high power shot you use the motor to pull the spring? Or both? Can you switch between powers on the fly (i.e transition from low to high or high to low without firing in-between)?

I can't believe how compact it is. I thought it was huge until I recognized that it was in a vice, and then everything else started coming into perspective. It's definitely one of the coolest things I've seen so far
Thanks - we were aiming for a compact design. Here's another video of our shot with an appended closeup look of the launcher firing - http://youtu.be/v_7ZfDrzMA0.

The cylinders only affect the setting for the shot power. They are fully independent from the motor/gearbox-driven rack/pinion mechanism that cocks and fires the ram.

There are two shot power settings:

Low power setting - cylinders are retracted. Motorized rack and pinion stretches the springs about 6" total from a barely-stretched starting point.

Higher power setting - cylinders are extended to 3" stroke, Pre-stretching the springs 3". Motorized rack and pinion stretches the springs 6 additional inches for a total deflection of 9".

A carriage rides on round bearings inside the 4" x 4" shell. This carriage is driven by the two shot power cylinders - it moves the steel shoulder bolts to which the front spring loops are attached - these shoulder bolts travel inside slots milled into the sides of the 4" x 4" (this is the part that looks like a cocking lever on a machine gun). The rear spring loops are attached to a steel crossbar running through the back of the 1" aluminum ram. The shot select system can be actuated independently from the motor/gearbox cocking mechanism. I will try to get closeup video of this actuation tomorrow.

The motor/gearbox drives a 20 DP 56T steel pinion gear with about 6 linear inches of teeth on it - the rest of the teeth are cut off, creating a "flat" on the gear. The pinion teeth engage with the steel rack gear attached to the 1" aluminum ram, stretching the springs and cocking the launcher back. To fire, we simply run the pinion into the "flat" zone, permitting the springs to release their energy and the ram to fire forward. We run the pinion from the flat zone to the mesh zone to re-$@#$@#$@#$@# [<-- HAHAHAHA re-"male chicken"] the launcher and repeat the process. We only run the motor/gearbox in one direction - there is a ratchet integrated into the gearbox for anti backdrive.
__________________

Travis Hoffman, Enginerd, FRC Team 48 Delphi E.L.I.T.E.
Encouraging Learning in Technology and Engineering - www.delphielite.com
NEOFRA - Northeast Ohio FIRST Robotics Alliance - www.neofra.com
NEOFRA / Delphi E.L.I.T.E. FLL Regional Partner

Last edited by Travis Hoffman : 12-02-2014 at 03:15.
Reply With Quote