2-Ball Catapult vs 1-Ball Flywheel


Since balls seem to be a huge deal, deciding whether to use a 2-Ball Catapult vs a 1-Ball Flywheel depends on the teams objective.

  Both have their merits. A flywheel could shoot balls from long-range, providing more point-heavy autos, as well as staying outside of the battle in flag-area when scoring. However, a 2-ball catapult allows the robot to making more time-efficient scoring, meaning the teams can score numerous Hail-Marys before a match ends. 
  Both launchers also have their demerits. A flywheel assembly can be very touchy. If you forget about the numerous factors involved (e.g. Wheel Grip, RPM, ball Compression, assembly friction, etc), the launcher may fail in aim consistency. However, a 2-ball catapult will only be able to perform close-range shots, oppents just need to block off your "functioning distance" during the match, and ball may not hit flags with enough force to toggle them.

From what I have seen in recent years, these subsystem have maintained basic norms. Flywheels will be fast enough to provide high muzzle velocities required to shoot the ball long-range, but can be extremely touchy. Catapults can be consistent is the rubber-band tension is high enough, but testing for two-ball shooting and tensioning the assembly correctly is very tedious.

What is your opinion on this debate?



Think it is a myth to say that 2-ball catapult can only shoot at short range.

But you are right to say that in general, all catapults will have limited firing positions.
Without a range-changer mechanism, catapults will have up to 4 firing positions:

  1. 2 balls are on the upwards path (of the projectile motion)
  2. 2 balls are on the downward path
  3. 1 ball on the upward path
  4. 1 ball on the downward path

Personally I think it is enough firing positions to make it unpredictable for the opponents.

As for flywheel, as I always says - theoretically there can be unlimited number of firing positions. But practically, how many positions can you fine-tune?
During nbn, discobots only have 2 main firing distances.




And while we’re on the subject of shooting positions, how many shooting positions do most flywheels have outside of auton? 1. A flywheel also requires an indexer or amazing driving and the feeder system tends to be slower (though this isn’t a hard and fast rule.) The main disadvantage of a catapult is if you align incorrectly or get defended, you will miss both shots, but a lot of driver practice or vision sensors (or a combination) can definitely solve this issue. With the right optimization, I see no scenario in which a flywheel outcycles a double catapult.



I’d argue that a flywheel can almost match the double-shot capability of a catapult. If you tune things right you can shoot your first ball at the top flag, then since the flywheel will have lost speed, shoot your second ball at the middle flag. Not quite as fast as a catapult, but with a fast intake the difference can be minimal.



You don’t always want to shoot both balls though, so unless you also make an indexer for your double catapult the flywheel wins that category.

Pretty much if you are trying to shoot two top flags quickly, the flywheel will outperform the catapult. You could make a catapult to shoot two top flags at once, but then the flywheel is better at shooting a top then middle flag.



Something that I don’t quite understand - what’s the disadvantage of releasing both balls at the same time?

Even if one of the flags are already turned to your alliance’s colour, there is still no harm in releasing both balls at the same time.

As for shooting 2 top flags consecutively, i admit, most likely flywheel will win in this category.
The flywheel will need to use it’s indexer, and then spin up to speed again and aim.
The double-ball catapult will need to reload and aim.
Guess the real difference will depends on how fast can the catapult reload (or intake).



The disadvantage would be the wasted ball. If your intake is a bit slow, then you wouldn’t want to launch a ball for no reason. While I’m not sure this can have a large enough impact to be the sole reason for switching, it’s a strategic aspect that should have an impact.
Although, I’m not sure teams who can effectively use a double catapult will have intake problems, though.



Looking at the speed of my teams’ intake, I don’t think it matters to me if I am “wasting” one ball here and there.
In any case, we will just pick up the balls even as we are travelling to the next position easily.



I think there are some misconceptions on loading and releasing a double catapult.

If your team only wants to shoot one flag, it is easy to simply load one ball into the catapult. Your positions might be a little different, but this actually feels like an advantage. Shooting a single ball from multiple positions is the benefit of flywheels that double catapults lack. Giving double catapults this advantage makes them at least as good as flywheels.

Wasting a ball is never good, but if there are no sets of 2 flags turned towards your opponent’s color, your team is probably already winning. Even if you are determined to load 2 balls into the catapult and never waste a ball, you could simply flip some ground caps or play some defense until there is a set of 2 flags that can be targeted with the catapult.

The fact is a catapult has a cycling advantage because it’s so much faster to shoot two flags at once. Additionally, a catapult does not need an indexer, and back loading double catapult feeders are significantly faster than front loading flywheels. (A front loaded catapult would probably be about the same speed, I’m prototyping one right now so I’ll upload something once I get it working.)

At the end of the day, I don’t think any of this matters until our optimization ability catches up to our designs. A good flywheel beats a bad catapult any day (and vice versa), none of this really matters until much later in the season. But when late season arrives, I’m predicting catapults :slight_smile:



Some very valid points.

And for the upper level teams, intake speed is insane. Teams like yours won’t have any trouble cycling.
But one main problem I see for lower level teams (inspired by their coaches, mostly) is that they try to imitate the best teams, without having their experience or skill.

I still come down firmly on the side of catapults winning, but like to explore for argument’s sake. :slight_smile:



Personally I think, just like many decisions like this, the answer is take the advantages of both by allying with the opposite shooter. Both flywheels and catapults have advantages and disadvantages, but I think the two complement each other pretty well. For example, the d catapult could play a close range flag game while the flywheel stays st long range abd hsngs caps on posts (since flywheels are generally more compact and allow more room for a 1 mtr lift).
I think shooter type depends a little bit on your control system, too. With v5 the motors are built to handle loads over longer periods of time, allowing for a better fast reloading flywheel. However if you’re using edr you would have to dump at least half of your motors into a flywheel, making a d catapult the better choice.



First of all I give you gratitude for actually calling the catapult its appropriate name. People call it “Double Catapult” which means that there is two catapults located on the robot, either by one or two gearboxes, but people actually mean a single catapult that shoots two balls. This term is incorrect because it’s used as an adjective word to describe the noun after it, not an object that’s nonexistent in the name. Thus calling it a “Two-Ball Catapult” is both Correct and Accurate.

As someone who built many catapults, punchers, and flywheels, I can say that both have their pros and cons. But I would personally recommend a 2-Ball Catapult more than a flywheel if possible. If you make sure the tensioning is correct, a mechanism that shoots two balls at once could far outweigh a flywheel in shooting speed as well as when it comes to accuracy. Another thing is that a flywheel would require almost the same location as catapults in order to shoot the flags. In fact, many catapults can full-field similarly to a flywheel with one ball. With a flywheel in close It’s not as simple as lowering speed primarily because the ball won’t be able to have the desired horizontal force to push the flags and it would be just so complex to code to perfection unless someone has experience with PID, bangbang, or other coding methods to check and maintain a speed. The only pro I see with a flywheel compared to a catapult is its ability to lower speed at further ranges in which coding can display a massive advantage at shooting both flags compared to a catapult that can only shoot one from full-court. Unless you have experience with coding, good build quality, and great driving skills, I’d prefer just doing a catapult because it’s simple to make and easy to maintain and code.

So far my predictions are rathermore correct up to the first TVACast for this season around a week after the game reveal when it was aired. I expect a robot with a “2-Ball Catapult” to far surpass a flywheel by far later on in the season, with the addition that focusing on one system would outperform robots that follow multiple systems. Gosh I love the feeling of saying an opinion, in which 90% of the people I said this too on the media turn to me as if I’m completely wrong! Glad people understand a bit more of what I think now.
EDIT//: Made some grammar changes



@briancole don’t forget about linear punchers. They have some merritt as well.



I think we’ve all agreed that the “Two-Ball Catapult” is the best choice. But, just for argument’s sake, let’s lay it out

Linear punchers are fairly easy to build and tune, as compared to flywheels and 2B Catapults. They take up about as much space as a 1B catapult, if a bit less, even.

I think it’s also important to mention that the “best” design won’t work the best for all teams. Not everyone has the experience to build an effective 2B catapult, and would be better off with a 1B linear puncher or something simpler.



I think something people aren’t considering here is the use of the vision sensor. In theory if you can utilize the vision sensor correctly and manage to keep the color codes tuned (just using signatures definitely doesn’t work consistently enough, color codes kind of work, but everything seems to require re-tuning in any new lighting scenario), flywheel is infinitely better. Imagine sitting anywhere on the field and all you need to do is aim.

The real unseen design is double flywheel with individually powered sides. First, single flywheel loses a lot of energy to ball spin and double flywheel does not have that issue to nearly the same extent. Second, individually powering the sides allows you to curve the ball laterally and basically hit anywhere, so as an extension of flywheel + vision sensor, I think it’s quite possible to create an insane double flywheel configuration to hit anywhere on the field from anywhere else on the field.

From my experience it doesn’t seem to matter too heavily whether you have double catapult or flywheel so far. My double catapult seemed a bit faster than flywheel robots at recent competition, but considering how much time I needed to spend loading and aiming, it’s about equal in the end.



I thought about that early season and got really excited about it, but then decided against it becasue I hadn’t really played with the new coding format, and the beta vision sensor I got to play with seemed a bit difficult. But, I agree that it would be awesome, but then we’re back to the cycle time debate of two balls at once from one of two fixed positions, or one at a time with a lot of positions.

I think this would be awesome to see done, but for me at least, it’s an off-season project. (Assuming I don’t get to Worlds, which is pretty likely.)



We have managed to use the vision sensor to aim our double catapult for us very consistently.



You have some good points regarding the double flywheel, but I would like to mention some things after a season with a double flywheel:

The double flywheel has this major benefit with the design, in which…

But I simply must say that you are potentially over-estimating the precision of the vision sensor. The V5’s Vision Sensor, as what I’ve been hearing, has had some major accuracy problems, and even after filtering it probably would have problems too. Considering these inaccuracies, I am near certain that you would be better off knowing to shoot in close-mid range compared to far range if you do use the vision sensor. And in this range, I ought to believe that a simple flywheel design that is simplistic and straightforward would probably outweigh advanced-calculating programs that can alter the curve of a ball to hit the flag. Another heads up I can say is that having two gearboxes for a flywheel is outright heavy, bulky, and friction will not be equal on both sides. A double flywheel is much larger than a single flywheel and it leaves little-to-no room for a cap-scoring mechanism. Although I was a middle-schooler during that time, I regret having a double flywheel and I should have gone simpler and did a single flywheel.

Considering that you require the same compression and more distribution with motors, and because of motor distribution is having to be split 1/2 and 1/2 on both sides to share similar to the same exact wheel mass as a single flywheel on both sides but only with 1/2 the torque, I will almost guarantee you that a single flywheel would have a faster recovery time, less burnouts, and faster ball speed capabilities than a double flywheel.

Regarding the 2-Ball Catapult you have. According to what you’re saying about time spent loading and aiming, you simply need more driving practice.



All in all, regardless of what I say, the most important key element that makes a robot good is not what components the robot has, but the driver who is driving the robot. Practice, practice, practice, strategize, strategize, strategize. I will guarantee you that practicing and strategy is equally, and maybe even more important than a mechanism itself in competitions. I have known a team that was first seed in qualifications during Toss Up and only had a two-motor drivetrain and 1 motor two bar. And this is Texas we’re talking about during that time with Discobots, Robonauts, etc. What was the difference? Strategy and practice.



While I agree with this completely, this thread is all about design. A great driver can do leagues better with a great robot. at the end of the season, some random team from the middle of Ohio could have the best driver, but with a robot designed so badly they couldn’t do anything. :wink:

And I’ve never actually built a competitive flywheel, but a double flywheel would eliminate a lot of the issues about hood compression I’ve been hearing about. I disagree in theory, while in reality, you’re probably right. In theory, you can curve a ball anywhere you want and probably win a bunch of awards for it if you do it well. But, that would be very hard to build and code. And the vision sensor seems so inaccurate that you may actually be better off with complicated position tracking software using a bunch of encoders.