Team 3489's Catapult Prototype

[Kevin Thorp]

Inspired by Team Titanium, Category 5 decided to try a catapult, scavenging parts from our 2011 'bot:

http://youtu.be/cyMTlgvDjZM

It works pretty well propelled by both pneumatics and surgical tubing, but we need to control the distance. And to auto-load balls.

[Mk.32]

Looks pretty good, how do you plan to auto load the balls?

[Tom I]

Looks pretty good! As long as you can a) control distance and b) aim somehow (via turret or turning the robot), you should have a pretty solid thrower, good job with thinking outside the box and using a catapult.

[Austin2046]

i like it a lot. even if u can't score consistently, if you were doing that from the far end of the field you'll be getting lots of shots off, and getting balls to your side of the field. The four basket arrangement might also help with the variability of the shots. you might not always hit the 3 pt shots but they could bounce off and land in one of the 2 pointers.

[billbo911]

If you can control the distance and alignment, that will be a really killer half court(+) shooter. What a great start and good luck on refining it!

I'm thinking a robot name of "MJ" for that bot.

[Tuba4]

What kind of distance were you getting with your mock-up?

[Kevin Thorp]

Originally Posted by Tuba4

What kind of distance were you getting with your mock-up?

I think the trash can was about 25' away.

We haven't figured out auto-loading yet. A belt-type ball elevator is pretty simple. The tricky part is getting it from the top of the elevator to the "cup", one at a time.

Controlling distance is another challenge. We might preload the rubber tubing by winding it up around a spool with a revolution counter. And/or adjusting the air pressure. I wonder if we're allowed to use electronically-controlled pressure regulators?

This is getting complicated. A spinning wheel launcher is pretty simple.

[Tom I]

If you're throwing that reliably from 25 feet, maybe you could consider specializing in throwing from the other side of the court, say like in your protected alley. This would allow you access to balls automatically from your alliance inbound area, and maybe you'll just always throw from x- distance away. sure it would limit your range of throwing, but hey "The Jack of all Trades is the Master of None." Being amazingly consistent at one thing is better than being somewhat consistent at a lot of things.

[Ninja_Bait]

Get it to throw full field. I think it would be easier to make something for the inbounder to feed into than to make a ground-to-arm ball collector. I'm not totally convinced that it can't be done, since I haven't actually tried to design it, though.

[RedLeader342]

Originally Posted by Tom I

If you're throwing that reliably from 25 feet, maybe you could consider specializing in throwing from the other side of the court, say like in your protected alley. This would allow you access to balls automatically from your alliance inbound area, and maybe you'll just always throw from x- distance away. sure it would limit your range of throwing, but hey "The Jack of all Trades is the Master of None." Being amazingly consistent at one thing is better than being somewhat consistent at a lot of things.

unfortunately, this alley isnt protected. its purely decorational. its in the rules ;D

[HumblePie]

Originally Posted by RedLeader342

unfortunately, this alley isnt protected. its purely decorational. its in the rules ;D

[G28]



Robots may not touch an opponent Robot in contact with its Key, Alley, or Bridge.
Violation: Foul; Technical-Foul for purposeful, consequential contact.


You're right about one thing..... it is in the rules

[Phyrxes]

Neat!

Are you venting the cylinder to atmosphere or which fittings are you using to make it double action. Last time we tried to make one like that we had issues getting it to work as a double acting cylinder due to the volume of air we were trying to move through a fitting.

[Kevin Thorp]

Originally Posted by Phyrxes

Neat!

Are you venting the cylinder to atmosphere or which fittings are you using to make it double action. Last time we tried to make one like that we had issues getting it to work as a double acting cylinder due to the volume of air we were trying to move through a fitting.

We used standard 1/4" OD push-to-connect fittings.

But we sorta cheated on the valve, using one that has more flow than is allowed in the rules. Later when we installed a "legal" valve our range dropped about 15%. I think we can get that back if we go to two smaller cylinders, each controlled by it's own valve.

Larger cylinders = more power, but more time to fill & exhaust.

[martin417]

Originally Posted by Kevin342

We used standard 1/4" OD push-to-connect fittings.

But we sorta cheated on the valve, using one that has more flow than is allowed in the rules. Later when we installed a "legal" valve our range dropped about 15%. I think we can get that back if we go to two smaller cylinders, each controlled by it's own valve.

Larger cylinders = more power, but more time to fill & exhaust.

Multiple small cylinders, each connected to its own legal valve is an excellent way to achieve higher speed. Another trick:

(Assuming you want high speed and force on cylinder extend, and retract speed / force are not as important.) Use multiple small cylinders, each connected to its own valve. On all but one cylinder, do not put a fitting in the retract port, and plug the retract port on the valve. On the final cylinder, connect as normal. That will greatly reduce the amount of air you have to force through the exhaust ports on the valves during the extend motion, and eliminate much of the back pressure on the cylinders. We used this technique in 2008.

Third trick using multiple cylinders:

To vary speeds: Connect all cylinders to the valves in the normal fashion. High force kick, extend all cylinders.
Lower force, extend some cylinders, keep some in retract. A cylinder has more force in extend than it does in retract, so as long as you have as many or more cylinders extending than retracting, it will extend. If you use four cylinders, that will give you three different extend speeds / forces. We did this in 2010 (we also used surgical tubing to help extend, so we could actually extend with all but on cylinder in retract)

[Kevin Thorp]

While one group was working our a catapult prototype, another built a single wheel shooter:

http://youtu.be/LXIYwYKEA8Y

We knew this first iteration would not have a lot of range, but it'll be a good test bed for experimenting with aiming and speed control.