Catapult vs Wheeled Shooter

[Moskowapplepi]

Team 2067 went wheeled shooter even though we did prototype a catapult half way through build season but found more consistently accurate shots from a wheeled

[fargus111111111]

343 opted for a catapult design for several reasons,
1. We have seen a drastic decrease in shot power from our 2012 bot as we wear out the wheels and balls
2. A catapult can fold flat and with height being a severely limiting factor this year we saw this as a huge package benefit
3.The catapult was simple and required less time for us to assemble and test
4.It shoots as soon as the trigger is pulled, there is no spin up time.

Ours, after a few revisions, finally was capable of clearing a full height defender from the outerworks and ducking under the low bar *as long as they weren't reaching over our bot*
We also found that our design gave us a pretty wide range of good distances to shoot from

[GeeTwo]

The memory foam ball changed its performance drastically in the first few hours of use, which we knew would make a wheeled shooter problematic.

More importantly, we decided to go low bar and high goal. The trajectory to get over a tall blocker required slow and arched over fast and straight, preferably launched from the "back" of the robot. That's what catapults do.

[Chris is me]

Originally Posted by Jared Russell

Citation needed?

If you look at the top 20 teleop high goal OPR teams, only 5 of them (195, 1024, 118, 148, 230) are catapults.

If anything, side-by-side dual wheel shooters a la 971, 987, and countless others were the way to go this year.

It's pretty clear multiple designs can be optimized this year to a level of effectiveness good enough for high level play, and it's kind of hard to just go with the most popular design as the best one. After all (and I know I will get flak for this) mecanum drive was almost strictly better than traction drive last year, particularly for landfill robots, yet lots of top teams stayed away from it. This wasn't necessarily because they made the wrong choice - in a lot of cases, they decided they could more easily optimize the type of system they know better.

We have had a LOT of games with wheeled shooters in the last decade for foam balls - it's a known problem with lots of examples of great designs. We have had relatively few catapult games, and the catapult games featured much larger balls being thrown farther than the small balls, so the catapult design was more exotic.

Maybe it would have been more accurate to say "I think a catapult would have been better for my team", than the general case.

[mathking]

I think other posters are correct to point out that no choice is inherently better. The right choice is the one that works best on your robot. We prototyped some catapults and wheeled shooters. Initially we shied away from a catapult because the initial designs we tested uses pneumatics and we wanted to avoid the loss of space. Then the kids made some good motor powered catapults and we had two choices for fairly accurate, consistent shooting. Ultimately it was our design criteria that made the decision for us. The team decided that quick, consistent scoring was more important than necessarily high scoring. Wanting a robot that could score both low and high was easier on our chassis (our number one design priority was a robust, consistent drive train) with a two wheeled shooter than with a catapult because the two wheeled shooter was also able to gather and manipulate the portcullis and cheval. This made the overall robot less complicated and made it easier to fit under the low bar. The best catapult design we had would certainly have been a good choice. It just wasn't the best choice given our overall design and the priorities we set at the start of the build season.

I will also say I am glad that we create a design hierarchy at the start of each season. It made the (often passionate) debate over shooter design choices easier to make. And the kids who developed the catapult were left not with a "our design wasn't good enough" feeling but the realization that the two wheeled shooter design simply worked better with the rest of our robot.

[Drakxii]

Originally Posted by happyWobot

Someone mentioned Aerial Assist. Thats a great example. That game piece was very elastic, it needed lots of time in contact with the energy being transferred so it could retain it. That's a really good example where a catapult is better.

Actually it's a bad example as nearly no one did wheeled shooters with Aerial Assist because the ball were so large. A wheeled shooter needs go around at least 2 side of a ball, that's hard to do safely when the ball barely fit in the frame perimeter and anything outside of the frame perimeter is fair game to hit.

[backdrive]

Originally Posted by Mark Sheridan

Cause we so fly in Cali


There are two really good catapults going to champs from California: 1836 and 5124.

Oh, awesome! I guess I haven't been paying enough attention to orange county!

[backdrive]

Originally Posted by Drakxii

Actually it's a bad example as nearly no one did wheeled shooters with Aerial Assist because the ball were so large. A wheeled shooter needs go around at least 2 side of a ball, that's hard to do safely when the ball barely fit in the frame perimeter and anything outside of the frame perimeter is fair game to hit.

It's not true that nearly no one did flywheel shooters, though they were definitely not the most common design; in fact, the winning and finalist alliance on Einstein both had a flywheel shooter on them (254 and 1114).

[pandamonium]

Originally Posted by Mark Sheridan

There are two really good catapults going to champs from California: 1836 and 5124.

Thanks! Yes the consistency was a major reason for us going catapult. We also liked the appeal of being unblock-able from the outer works while still being low bar capable. Yes several teams have accomplished this other ways with tall arms. The catapult seemed like a more simple approach for our team. The range issue is a bit of a misconception in my opinion. Our catapult has a pretty large sweet spot all the way from outer works to a little before the batter.
We have also added a ball clamp to keep the ball from bouncing out when going over obstacles.

[RoboChair]

How this thread makes me feel



Let's just agree it be shooting season.

[evoluti1]

For game pieces like this year's boulders, Aerial Assist balls, and even the balls from 2012, I think the notion that catapults inherently shoot more repeatably than wheeled shooters is a myth. If you're trying to launch a Lunacy moon rock or one of last year's recycle containers, then yes, a catapult is probably your best bet. But without more data directly comparing the catapults and wheeled shooters teams have actually built, I don't think anyone should be making confident claims to this effect.

Here's some slow-motion footage of one of the shots we took with our shooter prototype to test repeatability: https://youtu.be/lQUPcOZiL3c (one-wheeled shooter with a curved hood and 2" of compression. The hood on this prototype went through about 60 degrees of arc I think.)

The blue dots on the board represent where previous shots landed. As you can see, the consistency is as good or better than what we needed to make the shot from the outer works, and this was without even running closed-loop control on the wheel speed.

[Eric Scheuing]

We spent the better part of 3 weeks honing the design of our wheeled shooter to get it to perform consistently. Many tweaks were made in terms of wheel spacing, compression, and delivery mechanisms, but we manged to come up with something that seems fairly resilient to variations in boulders. Of course, no wheeled shooter is going to be 100% perfect, and occasionally we do get issues with a boulder pulling to the left or right a little, but we've got a pretty high accuracy all things considered.

If I had to do it all over again, I would definitely make a catapult though. It has benefits aside from accuracy. Most notably, they don't have to wait for their shooter wheels to spool up.

[Ari423]

I think this question is missing a category of shooter completely (or combining two where they shouldn't necessarily be combined). The category I am referring to is linear punch shooters. There is a big difference between a catapult (which throws the ball) and a linear punch (which punches the ball). I can't speak to the whole world, but I know a number of MAR teams successfully pulled off a linear punch (see 1089, 272). I'm not saying that that's necessarily the best shooter type, but I don't think it should be overlooked.

[jspatz1]

Originally Posted by Jared Russell

Citation needed?

If you look at the top 20 teleop high goal OPR teams, only 5 of them (195, 1024, 118, 148, 230) are catapults.

This is probably a much higher percentage of catapults than in the general robot population.

[GeeTwo]

Originally Posted by RoboChair

How this thread makes me feel



Let's just agree it be shooting season.

ELMER SEASON!

More seriously, though: most of the posters have said why they went one way or the other, and the reasons appear make sense for where each is coming from. As with nearly any FRC engineering decision, it comes down to two questions:

• What are your priorities? (For us this translates mostly into what is your game strategy?; YMMV)
• What are your capabilities/resources/experiences?

Since every team has the same core values and the same resources , of course we came up with the same solution.