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.

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