Catapult, Flywheel, or Other?

Who’s using what? Is anyone using more than one? If you’re using “Other,” what is this “Other” that you are using (unless, of course, it’s secret)?

It seems like the catapult launcher that team 62 build is the most consistent and has the fastest reload time of any of the launchers, but I would assume that if it was build sloppily, a double flywheel would be superior. A single flywheel has a huge potential because of the power conserved, but it needs some way to get less backspin and more distance. I was thinking of some sort of second, smaller flywheel, or maybe just a spacer, that spins freely above the first one, so that some of the power used to give the ball backspin is converted to making the ball go farther. However, using one of the flywheels to indirectly spin the other one might be less efficient than just powering up the second flywheel, and that launcher might also have problems with consistency given the varied ball specs. And the fact that baseball batting cages around the world, almost every team that succeeded in Singapore, and literally every team that did well in the 2006 FIRST competition used a flywheel speaks for itself… In any case, after I prototype all of the designs, I’ll post something, but it seems like the quality of the design is more important than the design itself, at least this early in the season. Hope this helps. :slight_smile:

Double flywheel, two geared/chained together.

My opinion on launcher choice is that, flywheel is something pretty hard to control. It’s a challenge, a challenge bigger than rubber band catapult.

I love challenge and if I were competing, I would just go straight into flywheel, gearing design, trajectory calculation, ball feeding, velocity regulation, TBH as posted by Mr. Pearman, ratchet, everything involving a speed that has not been safely achieved in VEX before.

But a rubber band catapult, with some nice design work, can in theory match up the firing rate and maneuverability of flywheels. We all saw that. And of course a lot more stable, meaning a lot less realistic hassle, like bearing wearing off, shaft twisting, friction, encoder being destroyed, motors overheating, motors being damaged, and so on. I mean, given that GDC ruled that you can’t use a tube to pour balls into your robot to achieve 10 ball per sec firing rate only possible with flywheel, how fast can firing rate be anyway?

But still, if I were still the irresponsible technician of my team, I would lead them down the road of flywheels full of danger and obstacle just for the excitement of it…

However realistically speaking, I would rather see my team spending more time with designing and come up with a rubber band shooter that’s perhaps 1 ball per 2 seconds that works reliably, than building a flywheel launcher that theoretically shoots 2 balls per sec and being troubled by all of its realistic issues. However this is only for the sake of winning competitions easier. Which choice is better for learning more robotics and engineering? That’s another topic.

Originally I expected the single flywheel to be the most popular because, like what Infinity Minus 1 said, a single flywheel has a huge potential because of the power conserved (even though it has its flaws). Having worked with a double flywheel before, I feel that a single flywheel design will be faster (but not necessarily more consistent) than the double flywheel design.

As for the catapult, I’ve felt that Cameron’s Robot in 3 Days build is the best design. Shooting balls straight into the net, in my opinion, is still the best way to score. Having the trajectory shaped like an arc, like BNS’s design, would be more inconsistent.

Very curious to see what the teams who marked “other” would do for their shooter.

Based on the design team 62 revealed it seems a piston style shooter has an inherently faster rate of fire than a flywheel. The only flywheel with a similar rate i have seen was team 8059a who used 4 motors. Haha im also kinda curious what you were you thinking for a 10 ball per second rate of fire. And how does not being able to use a tube to pour balls into the robot affect that? Also a single flywheel’s ability to save energy was mentioned. Was wondering if someone could explain the theory behind that. Cause it seems like it would waste alot of energy due to the friction of being rolled off a guide. Thanks

Has anyone considered using two launchers, say a pair of single flywheels to launch two balls at once? Or maybe dual (or triple) catapults that all launch at the same time?

I haven’t see anyone trying this yet. It would likely be a waste of motors, but I like the idea. If anyone tries it, I think it’ll be like the tether-bots from Skyrise. A few pop up late in the season, they perform impressively, but the idea doesn’t really catch on.

Our team has designed two launchers so far, a two wheel flywheel for our robot that mainly goes after possession of bonus balls and a single wheel flywheel for our lifting robot that just stays in the corner and goes through all the driver control loads.

With testing each design we discovered that each launcher had its pros and weaknesses as with anything in vex.

For example the singular flywheel can shoot with a very fast fire rate and is slightly more accurate due to the balls having a huge amount of backspin. With the dual flywheels the fire rate is slightly slowed but we have the ability to alter the flight patterns of the balls by slowing down one of the wheels. For example if we slow down the top wheel just slightly we can lob the ball higher for close up shots. If the wheels spin at the exact same rate we can get full field shots really well.

A video of the field robot and it shooting can be found here:

we should have a video testing the single wheel launcher soon hopefully:D

To be honest I don’t feel that it will be a feasible idea. The balls are relatively big as compared to the opening of the net, which makes it harder to score multiple balls at once. Also, unless you have a super accurate shooter which shoots accurate 100% of the time, the balls will most likely hit each other and set each other off-course during their trajectory.

Doing multiple balls at once is sort of like a gamble; if 1 ball goes off, the other ball will also go off. But, if both balls travels in the desired trajectory, both will go in. If your launcher messes up during the whole of a match (happened before, which costed the team its tournament champion trophy), you are basically disabled for the match.

Having a 1 ball shooter is more reliable because other balls won’t disturb the 1 ball. The shooter will be able to have better control over the 1 ball, as compared to shooting 2 balls.

Yeah, I do agree with you that the most feasible idea for the 2 balls shooter is a tether-bot idea, but it causes unnecessary risk of entanglement (especially expanding out of 18x18 in this years’ game). Even in skyrise, the top teams do not want to do tether-bots because they sacrifice a lot of advanced functions (for example, scoring high, scoring skyrises etc.) to double the simpler functions (2 6-bar 1-cube scorers), which, in my opinion, is not really worth.

But, I am curious to see what teams would come up with if they decide to go this route. It will definitely be interesting and it will definitely require thinking out of the box.

May I ask what gear ratio did you use for your shooter?

Also, please post a video of your elevation! It seems really interesting!

Now, what if there was a dual launcher that alternated shots; one from the left, and then one from the right?

I love the idea, but you’re still not saving all that much time, since the reset time is only about 1 second per ball with a well-designed launcher. Also, scoring pre-loads from the starting tile would be a bit tricky since you would have to feed the balls into 2 different launchers at almost the same time, so the risk of doing it too early (and not shooting the ball all the way to the goal) or too late (and losing precious time) is much higher than with a single launcher. Again, its a clever idea, its just not practical given the motor constraints we are given. Hope this helps.

Why are you posting all this random information on a robotics forum? If you feel the need to tell someone about your sweating issues and your analysis of artistic anecdotes, then kindly spam some other forum related to those topics.

EDIT: The posts I were referring to have since been removed. Thank you to whichever moderator/admin removed the posts.

I actually considered this idea friday night of worlds, and quickly threw it out. You’re making each ball’s target less that half the size it already is. That it itself would be extremely tough to make accurate, not to mention the extra power, etc. you’d need.

Actually, I feel like a linear launcher like 62’s may be able to pull off an alternating shooting style. Since their launcher is either winding up or firing, an alternating style is most likely easier for them to achieve. I do agree that it’d be pretty tricky to fire preloads from the tile since the ball delivery would have to be insanely optimized to make use of both launchers.

Not exactly. The location of each ball as it passes through the opening is essentially a random variable, but the two locations aren’t *independent *random variables. When aiming one ball you don’t have to assume that you have no knowledge of where the other ball will end up. For example, if one ball is a little too far to the left then the other ball is probably also a little too far to the left.

Even so, alternating shots are almost certainly better than simultaneous ones.