Design Process: 2012 Shooters

[Adam Freeman]

We used a process very similar to what Jared described for 341 and came to very similar conclusions on the style of shooter. Single axle, double wheel, non-turretted, and fixed angle.

Because we were concerned with building too much complexity into our shooting system (ala 2006), we quickly decided that if we could shoot from the key, then we would not need an adjustable hood or a turrett.

Our decision point between key / fender shooting was determining how possible it was to shoot from the key. If we could achieve 90% or greater, the protection of the key was well worth it. If not, we would have to risk being defended getting to the fender.

We did not specifically determine any set requirements for how quickly we could shoot. Although, we obviously wanted to shoot as quickly and accurately as possible.

Prototype / Development:

I don't have any pictures of our prototype available right now. Our website is down...hopefully I can link to them in the future. We quickly designed a sheet metal single axle prototype shooter to test our shooting accuracy. We didn't really do any testing with double axle shooters. Just playing with the balls and knowing we wanted backspin pointed us towards a single axle shooter. We had a pretty decent approximation of a shooter for a prototype. It was mounted on a piece of plywood, so shooter testing could be conducted independantly of the rest of the robot development. It was powered by a CIM hooked up to a power source, so we could regulate the speed. It had 6" KOP wheels and was adjustable for the amount of compression we wanted. I believe we started with 1" of compression, but that resulted in quite a bit of slip when shooting at the speeds required for a key shot.

Using our prototype shooter, we tested for accuracy at different positions on the key, backboard v. "swish", as well as different shooting angles. We found that at 45 degrees banking off the backboard, we had a rather large sweet spot on the key. Meaning we could be positioned within a couple of feet and still shoot a high percentage. We ended up proving that at ~4000 RPM, 45 degree shoot angle, and ~ 2" of compression, we could shoot at or above 90%. This gave us confidence that we were going down the right path.

One of the major findings we saw from our prototype shooter was that it was very sensitive to how the ball was feed/presented to the shooter wheels. Fed quickly, it would shoot too far. Fed slowly or if there was any resistance holding the ball, it would shoot short. Using this information, we were planning to design a paddle feed system (similar to FRC25-2006), but we could not get it to package without a significant amount of complexity. To design around the variation in the balls and allow for a consistent feeding method, we added in a short section of "gravity feed" between when the feed rollers release the ball and when the ball contact the shooter wheels. I believe that this was the key to our shooter being able to consistently shoot a high percentage.

Competition Shooter:

To develop the competition shooter, we needed to ensure that we could switch from the CIM on the prototype, to the FP or AndyMark motors that we had available from the kit. We wanted to use the FP673 motors, but we did not have enough to build two robots w/spares. So we opted for the AM-0912 motors. Based on the information from our prototype shooter, we selected a 2.52:1 gear ratio that resulted in the quickest spin up rate to 4000RPM and also gave us enough of a top speed RPM to shoot from the top of the key. We briefly discussed changing to a 4" wheel for packaging, but we decided against it based on too much change, complexity, and unknowns with a wheel that small.

The competition shooter used the provided 6" KOP wheels, with the nubs turned down, to eliminate ball damage. There was no real testing or decision making process for selecting these wheels. We had them, they were available, and they worked.

Outside of the gearing, we designed the shooter with as much shooter engagement as possible given the packaging space we had. The shooter mounting was incorporated into the frame to provide a rigid base. There wasn't lot of iteration to the competition shooter design. We were pretty much stuck trying to fit the shooter in the space available between the hopper and the arm.

Competition Learnings / Results:

We made no changes to the shooter throughout the competition season. Between Waterford and Northville, we briefly talked about switching to a different KOP wheel and played around with shooting at a slightly higher angle. Our testing between competitions showed no improvement with a different wheel or the change in angle, so we made no changes to the competition robot.

At Waterford we shot 58% in Hybrid and 71% during Teleop.
At Northville we shot 69% in Hybrid and 79% during Telop.
At Troy we shot 71% in Hybrid and 82% during Teleop.

Unfortunately, I can't find any data for MSC or Champs. I believe we leveled out around 80-85% for both Hybrid and Teleop shooting percentages.

We had on the fly speed adjustment for any ball variation or changes. But we did not make very many adjustments at all throughout the season for Teleop. Majority of the shooter speed changes were made for Hybrid. But once we moved from the top of key to the bottom/middle, our Hybrid performance became much more consistant.

We ditched camera aiming about 1/3 of the way through the Troy event. 217 loaded on some crosshairs for us, we gave control to the driver to line up, and off we went. Prior to this change it really felt like there was un-tapped potential left in the machine. I couldn't figure out why we were not shooting more balls. Then we removed the camera aim. That significantly increased the volume of balls we could shoot (2-3 balls/match). Basically, camera aiming was taking to long to line up, was not providing any increase in shooting percentage, and not allowing us to interact with more balls.

Overall I am happy with our shooter performance for this season. It was a simple solution to a complex problem and allowed our team to play the game exactly how we wanted too.