Catapult vs Wheeled Shooter
 

I'm curious on what went through your heads when you were deciding between a catapult and a wheeled shooter when designing your robot. Team 3072 went with the wheeled shooter so that an opposing robot couldn't hit us hard enough, then dislodge our ball out of our shooter. I've noticed about an equal number of top level robots that have both designs.

Re: Catapult vs Wheeled Shooter
 

Our decision was based on past experience with rebound rumble - that year, there was so much variability with the balls that wheeled shooters had a real tough time being consistent. We assumed it would be the same with these balls!

Re: Catapult vs Wheeled Shooter
 

I think you mean Rebound Rumble :)
Breakaway was 2010 and used soccer balls!

edit:: and although I'm not on a team and don't have to build a bot, I would probably have gone towards a wheeled shooter design. Having seen both in competition that worked well, I think the wheeled design has more flexibility for shooting position, accuracy, and power.

Re: Catapult vs Wheeled Shooter
 

Catapults are more reliable and accurate, and are also amazing at batter shots. However, wheeled shooters can swivel on a turret (254 style) and have more angles of release. With catapults usually you can just get 2 different angles of release. Plus you have to worry about the ball falling out of a catapult. That being said, I have seen extremely successful robots with both types of shooters.

We went with a wheeled shooter this year, and it worked well, but as the balls got abused it lost some of its range. As most years it was a learning experience.

Re: Catapult vs Wheeled Shooter
 

My team went for a catapult, because

the loading time was not an issue, since we could only shoot one boulder at the time.
It is also faster to shoot, since you don't have to get a flywheel to a certain speed before shooting.
It is more precise, especially with worn off boulders

Re: Catapult vs Wheeled Shooter
 

I find it interesting how certain shooter designs this year seemed to vary heavily by region- for example, Texas has a bunch of amazing catapult robots (118, 148, 2848, 4587), but California, in contrast had no top-tier catapult bots (correct me if I'm wrong), with nearly all the top teams (254, 1678, 971, 973, etc) opting for flywheel shooters.

Re: Catapult vs Wheeled Shooter
 

We went with a two wheeled shoot because of our experience with catapults in Ariel Assist. By the end of the competitions, the catapult was struggling to maintain accuracy. We also figured we could integrate more systems into a wheeled shooter system such as a collection system and a scaling system.

Re: Catapult vs Wheeled Shooter
 

We had two main competing designs during the first week: a single wheel turreted shooter for batter/midrange shots, and a catapult for shots from the outerworks.

Initially the entire design team was leaning towards the turreted shooter, but we built prototypes of both concepts and weren't happy with the ball to ball variance of the wheeled shooter. We were worried about aiming accuracy for the outerworks concept as well, but the catapult prototype showed good repeatability and was able to hit the target at that distance, so we settled on the catapult.

Then we wasted half of our build season on a drivetrain.

Re: Catapult vs Wheeled Shooter
 

I would say 4 of the top 5 bots in MN are catapults, but the best robot, 5172, is a flywheel.

Re: Catapult vs Wheeled Shooter
 

A very good team, given enough iteration and development time, can make almost any design competitive.

However, I think it's pretty clear that catapults were the way to go this year, in retrospect, unless you really needed the packaging benefits of a wheeled shooter. Catapults could more easily shoot consistently and could more easily be built to shoot over a defender from the outer works.

Re: Catapult vs Wheeled Shooter
 

Yes you are correct about CA. I can't think of any consistent catapult shooters here. I think a big factor is the use of vision tracking (thanks to the assistance of 254 and 971). Wheeled shooters give a more consistent straight line shot that allows varying distance. Catapults appear to be more dependent on a set distance.

Re: Catapult vs Wheeled Shooter
 

We pretty early on leaned away from a wheeled shooter since we were worrying about ball consistency and we didn't think we would need very fast shooting times. We made a pretty consistent pneumatic catapult in 2014. We are pretty good with catapults so we decided to stay with it this year.

Re: Catapult vs Wheeled Shooter
 

I think 401's shooter was deadly, and pretty precise.

3072 had a couple positions of being able to shoot at different positions on the field, so we could make it from the outerworks, all the way to the batter. I'd be confident if we could shoot from the neutral zone on making it. Our prototypes for our shooter vs catapult were heavily on the shooter side. We just never got there with a catapult.

Re: Catapult vs Wheeled Shooter
 

We know how to build, tune, and debug a wheeled shooter, and they've been good to us in the past. We don't know how to build, tune, and debug a catapult. We could probably figure it out, but early prototyping showed that a wheeled shooter could get us the performance we wanted, so why do something else?

I am guessing that many of the Texas teams had the exact opposite experience.

Re: Catapult vs Wheeled Shooter
 

I feel like 401 can agree that if you wanted to add a fourth adjective to their shooter, it would be "temperamental". Wheeled shooters, unless nearly expertly honed in, can be temperamental. When they are on a roll though, watch out.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

A few things that wheeled shooters have over catapults:
-Ball protection
-Turrets
-Ability to be on an arm
-Familiar (2012)

Catapults definitely have consistency among other benefits, but I disagree that it's cut-and-dry catapults over wheels.

Re: Catapult vs Wheeled Shooter
 

Catapults can definitely be on an arm ;)

Re: Catapult vs Wheeled Shooter
 

Cause we so fly in Cali


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

Re: Catapult vs Wheeled Shooter
 

Our team went with flywheels because of a couple of reasons. 1: We had looked at previous games and saw how effective flywheels were. 2: We thought the balls were durable enough that there wouldn't be variance. 3: Even if the balls were going to start breaking our compression would trump any damage. 4: One of our new mentors that has been with FRC for a while said that no matter what we would get to a fixed angle, fixed shot speed, and fixed shooting spot. I think those words along with previous game footage really gave us tunnel vision. 5: We wanted to figure out how to use flywheels. Those alone kicked our butts last year on Carver and we wanted to learn how to use them effectively. Lastly 6: We imagined that by Championships defense bots were going to become less of a problem. Plus as an added bonus our drive train is so strong we can push any bot that gets in front of us and (although we haven't tested it) we could probably shoot from our batter and still hit the target.

^
Just to point out, in case no one saw, 2848's shooter did start out as Flywheels. It was only at Dallas did they build and implement a catapult into their robot. Again not poking at them, just stating how catapults seem to be really good at this game.

Re: Catapult vs Wheeled Shooter
 

Re: Catapult vs Wheeled Shooter
 

Our prototype phase took way too long this year parly because we were trying to decide between the two. We ended up using a wheeled shooter because it was more consistent than our catapult prototype and it let us build a 2 axis shooter that fit under the low bar.
Definitely the coolest shooting mechanism our team has ever built!!

Re: Catapult vs Wheeled Shooter
 

I guess I stand corrected. :D
I completely forgot about your bots, despite seeing videos of 3360 at least.

Re: Catapult vs Wheeled Shooter
 

We had tried a wheeled shooter and didn't like the space requirement. Not much experience with either.

Re: Catapult vs Wheeled Shooter
 

That's actually a more complex question than it might seem. Several things first:

Cons - catapult

Catapults take up a lot of space.
Energy transfer and release can be problematic without the right equipment
Dependent upon the stored energy you use, it can take time to replenish
Release angle can be limited without extra articulation or features
Need extra systems to load it

Pro-catapult
Energy transfer is more consistent because the game piece is in contact with the catapult longer.
Simple and reliable if built right

Cons -wheeled
The need to understand the relationship between wheels, game piece, compression, energy loss variability, damage to game piece, flywheel effect, flywheel size, flywheel weight, speed, and loading.
The need to understand the difference between speed, torque, motor kickback, and density of game piece
Outside the robot they are vulnerable to damage
Enormous amount of energy required to articulate if on an arm
Harder to set at precision angle
Harder to design especially if outside perimeter

Pros - wheeled
Instantly reset for use
Can perform both ingress and egress with same design
Variable control over power
Variable control over angle if on a pivot (can batter shoot or long shoot for example)



Someone mentioned Aerial Assist. Thats agreat 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

But you have to consider other things. In this game particular chassis comes first, not the shooter. We used large wheels with a high chassis floor. A narrow frame so it would not get trapped going through a defense at angle. After that it would not been difficult to make a catapult but would have been difficult to load it. Tall wheels take a lot of space. Point is the wheeled shooter was the best choice in this game for us based upon how we wanted to play the game and the kind of chassis we used. The bumper rules also drove that decision as well forcing the shooter outside the frame.

But as for how difficult it is to make a wheeled shooter I wouldn't say it's that hard. Several things though.

Small wheels are harder than large ones. Weight on outer perimeter of wheel is more important than its diameter. Rpms is not enough. You can pair a mini cim direct with a heavy 6-8 inch wheel or a high rpm 775pro at 4:1 with a light 4 inch wheel. Either will work. But a mini cim with a light 4 inch isn't going to shoot far. The heavy wheel reduces kickback. And the amount of compression on the ball and the contact material between wheel and ball matter significantly. A lot of energy loss can be taken there if it's the wrong contact material. And no matter how much math you throw at it, you can never be prepared for the variability in the balls surface, density and elasticity characteristics. You have to adjust everything to take that into account but it's more gut, intuition, and feel than science. In that regard I recommend you listen to what your bot is telling you. Literally. Listen for the kickback, the smoothness of egress, grinding, etc. Dust and marks on the ball tell you a lot too.

Finally some one mentioned 401. They were loading in at one event and their students brought the bot in to the pit. I asked one of the students about it and he looked at me with this serious look and said "this thing is scary". Was he not joking. Thats a wheeled shooter that doubles as a Howitzer. They overcome a lot of the game piece variability by shooting in a straight line but they need high precision control over angle to do that and hit the mark. Their design is really quite remarkable. Ballistic trajectory is what most people including us use, 401 is shooting laser beams.

The point? Can't shoot "laser beams" with a catapult. Only ballistic. If you store enough energy to catapult in a straight line its probably pushing the limit of legal. Besides even if you do it would be crazy difficult to control angle for threading the needle the way 401 does it.You use catapult or wheeled shooter depending on what you are trying to accomplish. Neither is better than the other until you define what it is you want to do. But that has to take into account all aspects of your design including chassis and navigation.

Re: Catapult vs Wheeled Shooter
 

Originally we were thinking about making some kind of catapult of pneumatic puncher because we thought it would be more consistent than a wheeled shooter. However, we weren't really getting anywhere with our prototypes, and we had done a two-wheeled shooter in 2012, so that's what we went with.

I'm happy with the way our shooter turned out. We debuted in Alamo shooting an average of four high goals a game and only missing two during the regional, including one in a practice match. We've been able to tweak it a lot throughout the season (adding encoders, adjusting the ranges for our close and far shots, etc.) This was largely due to the fact that we designed in a lot of adjustability for the angle and speed of our shots.

Re: Catapult vs Wheeled Shooter
 

Each type of shooter has its own set of Pros and Cons.

Whichever one you choose should be based on which fits best with your design and what else you are trying to do.

I would always suggest that anyone interested in learning how best to utilize each type of shooter is spend time with them in the off season.

Re: Catapult vs Wheeled Shooter
 

Neither. 4469 decided to use the same type of pneumatic setup as they did in 2014.

I definitely agree with this, after looking at how few dual wheel shooters were competitive in 2012 and 254 in 2014 we thought hooded shooters were surely the way to go. Due to the low mass of the ball backspin seems to hurt more than it helps especially for close up shots. It was definitely a humbling experience to see the effectiveness of designs like 971.

Sent from my Nexus 6P using Tapatalk

Re: Catapult vs Wheeled Shooter
 

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

Re: Catapult vs Wheeled Shooter
 

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

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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

Re: Catapult vs Wheeled Shooter
 

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).

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

How this thread makes me feel



Let's just agree it be shooting season.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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.

Re: Catapult vs Wheeled Shooter
 

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

Re: Catapult vs Wheeled Shooter
 

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 :rolleyes:, of course we came up with the same solution. :p

Re: Catapult vs Wheeled Shooter
 

Catapults had one big advantage this year that my team discussed in the early build season: typically, the vast majority of a catapult's variance is up-down (largely because of small inaccuracies in distance reading) while they are incredibly consistent left-right. The shape of this years goal allows for a little up-down inconsistency, since that's the longer dimension. I remember a lot of the catapult's I've seen hit a little lower than dead center from the outerworks (for example, 359's balls in tech valley seemed to touch the lower lip of the goal fairly often) but they still went in fine. For this reason, I think catapults were a lot more viable this year than they have been in previous years, and I would applaud any team that built one for making a sound strategic choice.

That being said, the packaging of a wheeled shooter and the flat linear trajectory (at least when you shoot as hard as we do) seemed to offer enough advantages that we decided to go with that. We didn't think defense would be too much of an issue because we planned for a fast release, and we'd already began work on a swerve drive that would make us much harder to pin and block.

The catapult is definitely a good choice this year, more so than I think it was in rebound rumble, but I think there are still advantages to having a wheeled shooter that make the decision nontrivial.

Re: Catapult vs Wheeled Shooter
 

At team 230, we were concerned about the variability of the ball as it impacts either a spinning wheel or linear punching style shooter. In addition, we were inspired by the extremely accurate catapult used by our friends at team 177 in 2014, that was not only accurate, but extremely hard to block.

We got around the lack of adaptability of a traditional catapult by going electric, with 2 mini CIMS and a 28:1 reduction (or something like that). We found we could adapt the command profile to get pretty much any trajectory we wanted. If we went spring or bungee powered it would have been far less adaptable.

We had a lot of people comment that they couldn't believe we could shoot with a fully electric catapult. We did a fair amount of simulation to optimize the gear ratio to maximize energy delivered to the ball. A lot of teams don't do this and as a result don't get the most energy out of their device.

We lean pretty heavily on simulation written in Octave (a MATLAB like language) running on a Linux OS. It's all open source, so if anyone want's some more info please stop by our pit in champs and ask for Henry (or the drive team coach if he's off somewhere).

Cheers,
Steve S.

Re: Catapult vs Wheeled Shooter
 

Can you provide a little more information:

1) About your command profile adjustments

2) What your simulation revealed about getting the most energy out of your device (speed?).

Re: Catapult vs Wheeled Shooter
 

Puncher, catapult, or wheels. Many teams had actuate launchers. Auto aim seamed to be what separated the good from the great.

Re: Catapult vs Wheeled Shooter
 

I agree with Citrus, wheedle shooters are better to track and there is better control of speed and trajectory. Catapults are cool but, they easy to use because you have to think about the speed or rotation of the motor. Then after dealing with that, then you about vision tracking which is a problem because it will be 100 percent so there is a lot to deal with. But, at the end of the day, it's down to which one you are familiar with or comfortable with.