Here is an update PIC on our rail gun ball puncher, which has been shrunk to a total of 29" length with a stroke that is now 8" in length. We have opted to go with a pneumatic retractor-loader & surgical tubing ram power hybrid design for greater simplicity.
The pictured setup retains the 2"x1" slotted framing backbone and uses dual slider blocks - one for the retractor/trigger assembly and one for carrying the ram.
A 2" diameter by 8" stroke cylinder pneumatically retracts the rear slider block carrying the gate latch trigger mechanism, pulling the ram with at as it further stretches the surgical tubing. Then, when fired, only the mass of the ram and ram slider block are being accelerated by the tubing.
Weaker surgical tubing, after shot is fired, pulls the retractor/trigger slider block forward to reengage the back end of the ram slider into to the gate latch. Then the cylinder initiates a reload sequence to prepare for the next shot.
The bilateral symmetry keeps forces on both slide blocks well balanced for minimum drag.
We were intending to mount the shooter high in the robot, but with all the tip overs in the week one competitions, we may need to rethink this.
-Dick Ledford