2017 adjustable hood (shooter)

HI does anybody have any design idea to make an pneumatic adjustable hood for our shooter bot?

Check out 254s hood in 2014 or 3476s hood from 2016. 3476 released their cad from last year and it has the hood in it. A much more basic hood is 1986s from this year.

I also recommend looking at team 4976’s turret from this year. They had a really compact little multi-position hood that used an electric linear actuator to adjust the hood angle.

1986 Team Titanium used a cylinder to do close and long range shooting, you can see it really well in their reveal here:

Apparently 4976 uses an off the shelf FRC legal actuator, which is nice since you dont have to modify it to use a different motor, I can’t remember which one it was though.

OK, I’m curious. A pneumatic-selectable hood would presumably only have two positions (otherwise you’d use an electric actuator). There’s only one goal that anyone* used. This means you still have to move the robot to a specific range in order to launch balls at the goal, but now you have two specific ranges. What were/are the cases that justify the complexity of a two-position hood?

*OK, there were a few teams that dumped in the low goal, but AFAIK, none of them also shot the high goal with the same mechanism, and that case (unless it was a fallback in case high goal was less than 33% effective) would be even more curious than the one I asked about above. If you did THAT, same question!

1986 showed that the complexity is worth it. Use the hopper position for auton and the boiler position for teleop to save line up time/protect against defense. Same deal for 254s hood in 2014, farther out shooting position for auton and against the lowgoal for teleop for defense and presumably lining up purposes. Being able to maximize how you go about the task in big auton and teleop makes the added complexity worth it at least in my eyes.

I assume 3476 will release their cad at some point this year, but maybe just by zooming in on high res robot pictures (I’m guilty of this too) you can check out their adjustable hood for 2017. It uses a linear actuator that plugs into the roborio and slides along a slot for infinite variability within a wide range of shooting locations (even above our robot as we ran our center and side gear autos on their practice field). That setup worked well for them, and I thought it was a really effective way of achieving infinite shot variability rather than the two, or later three shot positions they had in 2016.

Definetly worth a look at some pictures or asking one of their design/engineering mentors for more specs,


The first two iterations of our shooter had a pneumatically adjustable hood.

Our original plan was to have a hopper shot (for the 40kpa in auto) and a fender shot (for general use in teleop). We quite quickly realized that we would not be able to meet our shooting speed goal if we did the fender shot, and tossed around the idea of using the adjustable shot for the hopper and one for a distance further away from the boiler. However, we ended up deciding that it was going to be hard enough to develop a shooter that worked with a fixed hood, let alone an adjustable one, so we ditched the idea for our third iteration.

It is more complex than a single position, yes, but it is relatively easy to do, and if you mess it up, then you just have a normal 1 position hood. So the opportunity cost is really low.

The primary benefit for a two position hood in this game was for teams who shot into the goal by driving into the boiler wall. You needed a nearly vertical release angle in order to get the shot right for the goal at this distance, but at other distances you needed a different angle.

The main reason you’d want to shoot from both places is because, in autonomous it is much better to shoot from the hopper in order to get the kPa auton, but in teleop it is faster for many teams to just drive into the wall and shoot rather than trying to line up a fixed distance away. Particularly with no protected zone to guard against shooter defense, a close shot was one of the only ways to resist defenders.

Your team must not be as good at messing up as mine - there are several times we tried to add adjustability or a second function and lost what we already had working.

Thanks, everyone, for the look into your decision processes!

You do want to be careful how you design features like this - it is very easy to design them in such a way that is worse than if you didn’t! But with this particular subsystem there are simple solutions for a second position that are basically retrofits onto existing shooters. 1986’s is a great example - you can see they essentially build a very solid 1 position hood, then added a little flap onto it, such that if the flap were removed you’d be back to square 1 like nothing happened. Just something to think about in the design phase.

I think it might be more correct to say that “1986 showed that the complexity can be worth it if that shooting strategy is the one you pick and you can pull off an adjustable shooter hood”.

1986 was an incredible shooter, but a lot of great shooters this year did it with fixed hoods. I think 33, 125, 195, 254, 971, 1678, and 2767 all had fixed hoods. Vision tracking used to vary flywheel speed is great ability to have for shooting from different ranges, and fixed speeds from known locations are really reliable.

I’m biased, because we had a single shot from up against the Boiler this year, a single shot from on the Batter in 2016, a single shot with a big sweet spot in 2014, and a fixed angle with different flywheel speed presets in 2013. We haven’t had an adjustable hood since 2012, and even then we mostly shot from up against the Fender with one speed. This off-season we might pursue vision tracking for varying flywheel speeds, and possibly a turret. We’re getting pretty comfortable with fixed-position shooters from known locations, though, and I would need a decent amount of convincing to do something else, given our design and fabrication resources.

We built a 2 position hood, but ended up locking it in one position to save weight. Varying the flywheel speed only got us about 4 ft of range adjustability. After that, fuel would hit the boiler from too low or too high. That was enough though that we could shoot from the hopper, and anywhere within about a robot length of the key line.

If you wanted to shoot from more locations, like the face of the boiler, or from a peg, you’d need an adjustable hood. But getting one shot this year was hard enough!

Here are a few photos of the hood, I can try to find video of it in action.

Google Photos

Google Photos

Google Photos

Google Photos

1 Like

Just for full disclosure, the adjustable hood device (and in fact much of the shooter) shown in the reveal video is not what we ended up competing with, although it was a similar idea.

It would be a stretch to call it “complexity.” Our two position shot was a very simple movement of the hood exit. Compared to the developement that went into the rest of the shooter, it was trivial.

A two-shot strategy seemed like a clear necessity to us. The hopper was the right place to shoot from in auto, and pressing the boiler was, in our view, the right place to shoot from in teleop. (FRC Commandment #5: If the rules/layout offer a protected place to shoot from, SHOOT FROM THERE.)

We used an adjustable hood for our shooter this year, but used a NeveRest instead of pneumatics.

You can see the gears on the back of our hood in this picture.

It allowed us to fine tune our arc based on the distance and, with our vision system, allowed us to shoot from almost anywhere on the boiler side of the launchpad, including the hopper in auto, as well as (albeit more slowly) from the boiler wall when were defended against.

It worked for us most of the time and I think it was definitely worth it, even though we did have a few cases where it wouldn’t zero correctly (from my understanding) and we would shoot too low.

This was our experience too. For a given release angle, there was a sweet spot of a few feet where we could get the vast majority of shots to go in by tuning flywheel speed. Too much closer or further away and even though we could make the median shot hit the center of the goal by tweaking speed (using auto-aiming vision code), the entry angle was either too shallow (misses because the effective size of the target is reduced, exacerbated by our 2-wide shooter) or too steep (starbursts of collisions from rebounds and weird spin effects from longer ball paths).

We decided to go fully adjustable this year and designed a servo driven shroud to control release angle. This allowed us to shoot from the hoppers as well as the center gear peg. If you would like to see the CAD, it is available on “TheBlueAlliance” or on GrabCAD under Team 2451. We utilized dual REV Robotics servos that had 330 degrees of rotation so that we didn’t need an external encoder to control position. The design was inspired by 254’s adjustable shroud from last year.

195 had an adjustable hood this year that worked via a rack and pinion like system

Andrew, Kevin, how did you calculate the amount of torque the rack and pinion would have to hold to keep the hood from moving? It seems to me that the reaction forces from accelerating the fuel would be fairly significant, no?

1 Like