Re: FRC3005 High Shooter
 

The 1/2" hex shaft runs thru two versa blocks. In order from the side with the large gear to the back side we have:

10-32 pan head
washer
large gear
spacer (not ideal, but it sets the large gear far enough out to clear our harbor freight ratchet)
hex bearing
hex bearing
cam that hits a limit switch at "fire-ready" position
spacer
hitch pin

On the large gear, we milled off the shoulder on the side of the choochoo linkages, as well as countersunk the gear roughly an 1/8" by the washer diameter (such that the pan head is flush with the face of the gear). We intentionally cut the shaft ~1/32"-1/16" short, so when we tighten the pan head screw down, we compress the shaft and take out any slop.

Re: FRC3005 High Shooter
 

This looks great, looking forward to playing with you guys in Dallas this year.

Re: FRC3005 High Shooter
 

Nice work guys. It's great to see a team pull this off. We ran into a lot of troubles with it but we're still testing so it may or may not be on our robot in Dallas. Good luck to you guys and see you in a few weeks!!!

Re: FRC3005 High Shooter
 

I'd like to echo this and add our thanks to team JVN for sharing the choo-choo design. The concept of using cam actuation to tension the catapult was not something we would have explored without seeing how "easily" it could be done. This opened up new opportunities for learning. I know some fear that the Build Blitz and Ri3D may limit teams' creativity, but I feel it's just the opposite. Without seeing it done, we would have been stuck in our comfort zone (pneumatics). Now, we'll be able file this away as another option and hopefully continue to innovate on it in the future. To all of the Build Blitz and Ri3D teams, and the FRC teams who share their new and creative implementations, thank you. You are truly the giants on whose shoulders we are privileged to stand.

Katie
Head Mentor, FRC 2052 KnightKrawler

Re: FRC3005 High Shooter
 

Thanks for these details. Can you also describe the bolt and or bearing detail between the short link and the large gear? We are having trouble with that attachment. Any help or details of your design would be greatly appreciated.

Re: FRC3005 High Shooter
 

The short link is attached to the large gear (as well as the long link to the short link) using these binding posts. We machined out a clearance hole (next drill bit size up from the nominal, maybe 5-10 thousandths clearance) for the post to fit through, as well as countersunk the heads. The linkage arms are 5/16"x3/4" 6061 aluminum.

For the binding posts, your ideal fit is such that you can fully crank the binding post together, but it is not pinching the linkage. Too loose, and the linkage slides laterally, too tight, and you cause extra friction. You can get close by countersinking, leaving just a hair of the female post sticking up, then use a sander to get more precise. We used JB weld inside the binding post to ensure it doesn't come loose, and heavy duty grease under the binding post heads for free movement.

As a follow up to prior posts, we did end up having an issue after a dry fire with the versa block slipping, resulting in an incomplete mesh and gear failure. I remounted the versa block with aluminum strap bolted into the 2x1, between the upper clamping screws on the block, to prevent any movement. This is similar in principle to the Versa Cams, which would probably work just fine. I also made a 1/4" x 2" Delrin spacer to put between the big gear and the Versa block face to reduce movement of the 84T gear out of plane, due to the high loads the gear is imparting on a slightly cantilevered shaft. It was resulting in ~5-10deg of angular misalignment between it and the 18T gear. The spacer cut this down to 2-5 deg, which still isn't great... but is better.

Thanks,

Steven