FRC3005 High Shooter
 

FRC3005 tested our competition robot's high shooter last night, and we were pleased with the initial results (turns out... math works!) We had calculated a release angle for an 18' shot and made a few estimates on the bundle tension to achieve that. We are adjusting our release strap to be closer to the choo-choo full extension point (without shock loading the choo-choo), which should flatten our trajectory and give us our preferred shot.

Check out the video, our Facebook page and Twitter feed (to keep our PR team happy), and feel free to ask any questions on our implementation of the BuildBlitz JVN shooter. We appreciate the great starting point, and we feel we were able to iterate on the design several times to fix some potential failure points (and learn a lot in the process). We're looking forward to competing at the Dallas Regional March 13th-15th.

Re: FRC3005 High Shooter
 

Looks good, what is your full range of makability? It looks like the highest point of your ball's trajectory goes above the top of the goal. If this is true are you worried about having a dead zone in the middle of your range at all?

Re: FRC3005 High Shooter
 

I love the sound the strap makes when it comes under tension.

Re: FRC3005 High Shooter
 

Eventually, it will be from 12' to 20' or so. You are correct, the trajectory is currently a little too steep. We'd like to be hitting our 18' shot on the fall from peak trajectory.

Our strap limits us roughly 4-6 deg from our final flatter shot angle. We didn't want to get too close during initial testing to the flattest angle we can shoot, because if we go too far, we'll shock load the choo choo. Our next stage of testing will hard mount the currently tied off restraint strap, which should flatten our angle. If it doesn't, we might have to lower our power slightly.

Steven

Re: FRC3005 High Shooter
 

You're right the highest point in the arc is above the top of the middle goal in this shot. This was our initial test shot based on a calculated angle and guesstimated force but we were surprised how close we got to the shot we wanted. We will be modifying the release angle tonight to lower the peak so we don't' have a dead zone. With the stop-strap it makes launch angle adjustment a pretty simple affair.

We also tested with a fully inflated and under inflated ball and were working out how much that variable was going to affect our shots. Our automatic stop when fully cocked wasn't dialed in yet so we need to repeat that process again now that we have a consistently cockable system done.

Re: FRC3005 High Shooter
 

Very cool. Looks good.

Re: FRC3005 High Shooter
 

And that, kids, is very bad (tm)

Re: FRC3005 High Shooter
 

Yep. Here was a piece from our first iteration. We had left it slotted for flexibility in determining final geometry. The shock load on the choochoo from about 25% of our final bundle tension was enough to pull a 1/8" or so offset into our 1x2 VersaTube.

Pic

Steven

Re: FRC3005 High Shooter
 

Just uploaded another version of the video with some more in-depth views of our shooter mechanism! Check it out!!

LINK

Re: FRC3005 High Shooter
 

Please never have a student reach over the launcher to do that again.. That part of the video made me very very nervous.

Re: FRC3005 High Shooter
 

It looks like there is no tubing attached in that portion of the video.

Re: FRC3005 High Shooter
 

Ok, good... I can relax. It's something We've had to drill into our students' heads repeatedly. I generally treat every stored energy system the same way I treat a gun and assume it's loaded.

Re: FRC3005 High Shooter
 

Andrew,

Appreciate your concern for my arm. (I have kid arms?) The shooter was only loaded with about 5lbs of force (the minimum to make the choo-choo turn over properly) in that shot since we were aligning some sensors and I reached over the top so the camera could see what was happening, I assure you that's not a habit... ::safety::

We were aware from the beginning of the design that we would need to have a safe procedure for releasing/resetting the system to get it on and off the field. Even while we are testing we don't want to rely on dry firing the system to release our shooter.

We tried several unpowered methods to release the shooter safely and ultimately given that our arm can be held cocked with ~40lbs of force and I don't want to be transporting the robot in a cocked state we will use a similar approach to release the shooter at the end of the match (minus the arm through the top obviously). We have a cheater bar that we stick in the end of the shooter to hold it down and then reaching under the shooter where the choochoo can be manually released and the shooter eased up. We are still working out if it's better to put a safety ratchet strap on the arm before we release, or if the process of putting that strap on puts more human bits in danger than it would be protecting. Of course we're also happy to hear suggestions for a better release method.

Re: FRC3005 High Shooter
 

I applaud your choo choo gear implementation (Versablock mount), and wish I'd have thought of it during build blitz to save me from making those two custom plates, Bravo.

-Aren

Re: FRC3005 High Shooter
 

If I may, how are y'all constraining the large gear axially on the shaft?

-Madison

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