How do we launch this thing? 2014

[Maniac_Mechanic]

Ah, that glorious engineering question- how do we get this thing in the air?

I understand the ball is 24 inches wide and ~2.5 lbs. If anyone has more detailed numbers or tolerances, please add them.

Pyrotechnics are right out. They would totally set fire to the fabric. I'm sure the first thoughts everyone has are catapult arms. I was thinking about this and one of my sketches caused another problem appear. If arms are used to launch the ball, their own unladen weight will slow down acceleration of the ball or require a huge force to move.

I'm thinking broadly now. What if you used some much smaller arm that hits the ball and the impulse sends it flying? What can we come up with here?

Other things worth consideration:

The springs offered as part of the voucher http://info.vulcanspring.com/first-robotics-competition
They are constant force flat coil springs, not helical coil springs as you might picture.

How quickly will it be necessary to retract/ prime whatever launcher you have?

[Schnabel]

Welcome to the forum!

There's always this option.....

[AWB]

flywheel is out of the question due to the fabric ball. Our team is seriously considering the low goal.

[theCADguy]

I have considered some sort of pneumatic launcher. Team 1114 used one in '08(Overdrive). It actually works very well.

https://www.youtube.com/watch?v=NYNEAL_dK6I

[EricH]

Originally Posted by theCADguy

I have considered some sort of pneumatic launcher. Team 1114 used one in '08(Overdrive). It actually works very well.

https://www.youtube.com/watch?v=NYNEAL_dK6I

Wasn't pneumatic, though. I checked earlier today.

[audietron]

Originally Posted by EricH

Wasn't pneumatic, though. I checked earlier today.

To clarify on what Eric has said, a 3/4" aluminum rod is propelled forward by surgical tubing. The whole set is pulled back by a winch with a dog gear, when the dog gear is released the rod is launched at the ball.

here is exactly what they describe. http://simbotics.org/first/2008#robot

[RRLedford]

Originally Posted by audietron

To clarify on what Eric has said, a 3/4" aluminum rod is propelled forward by surgical tubing. The whole set is pulled back by a winch with a dog gear, when the dog gear is released the rod is launched at the ball.

here is exactly what they describe. http://simbotics.org/first/2008#robot

Does a pulley spin free on a shaft when dog gear is released?
If so, this lowers peak velocity of ram, since rotating winch pulley/drum stores energy as unwinding cord spins it up to peak rpm.

A better system, when triggered to shoot, will have the contracting surgical tubing be accelerating only the ram itself and whatever low mass tension element(s) are attached to the ram.

Plus, what happens to the winch cord as pulley/drum spins free when ram fires? Does it reverse wrap, such that the next wind gets done continuing in the reversed wrap direction. If the ram travel is small, not so many turns of winch will be needed, so less chance of cord getting tangled up during free spin.

If variable power shot is desired, reversing the rotation for alternating shots is useful, for when a multi-turn potentiometer is used to control cutoff point for desired amount of wind, since the pot only has a limited number of turns over its full range. Winding opposite ways for alternating shots keeps the pot from hitting its end of range.

-Dick Ledford

[Ian Curtis]

A big kick in the pants!

[cadandcookies]

Originally Posted by theCADguy

I have considered some sort of pneumatic launcher. Team 1114 used one in '08(Overdrive). It actually works very well.

https://www.youtube.com/watch?v=NYNEAL_dK6I

Looking at something very similar to this with adjustments for catching and making sure we can score in the 1 point goal.

[Coin3]

The flat coil springs could make for a good dampener when trying to catch the ball.

As for launching the ball, my first thought was a pneumatic impulse hit to get it going. That idea is now retracted from my head since I realized there will be a great need for power regulation when launching. There are a few more ideas I have but they still have to be realized on paper before I go shouting them out.

[Maniac_Mechanic]

Thanks for the welcome.

Yea, that is a question, how do you vary power for a shot vs a pass? I like a variable impulse system with different points of retraction for different range.

[Zeromonkey]

Originally Posted by Schnabel

Welcome to the forum!

There's always this option.....

Quick Question:
Upon analyzing this, I can't seem to find how they are rotating the arm. Do you happen to know how they accomplished this?

[BOSS]

Is it possible to use harvester similar to the ones used in rebound rumble. To take in the ball. Then raise up the harvester on an arm and reverse the motors shooting the ball up to make up the 2 feet into the goal. Plausible or is the fabric to big of a factor?

[thinker&planner]

I have contemplated most of these designs, in addition to a cam design. Our team plans to test a pneumatic shooter, but does not predict great success.

Personally, I believe that Simbotics' 2008 robot has a very nice design that would work extremely well this year.

I believe that the best designs are wither something similar to Simbotics' 2008 shooter or some sort of cam with a huge boot attached to the corresponding "hammer". (Google "da Vinci cam")

[RRLedford]

What you want to accomplish with your launches will dictate how you launch.

Aerial shots:
-Lower angle (<45º line drive) high goal shots?
-Arching (~45º+) high goal shots?
-Over truss 45º shots?
-Over truss near vertical shots (robot keeps rolling and catches ball on other side of truss -no catch points; posession maintained)
-Over truss shots


Low to floor shots:
-Passing only?
-Low goal shots across floor?
-Robot-to-robot transfer/assist passing?
-Passing to human "shots"?

Handling all these well would require both a variable energy launcher and a variable angle launcher spanning nearly a 90º arch in the vertical plane.
A turret for targeting some amount to left-right might also be useful.

Our team is starting out building a surgical tubing powered ram launcher.
The ram will have an infinitely variable retraction tension cord winder with a trigger system that only accelerates the ram itself and the tension cord - no stored energy wasted on anything else - like a crossbow, but without the bow.

We are prototyping now to see how compact and short travel of a ram we can have while still shooting fast enough for consistent accuracy and adequate trajectory & travel.

We are not yet clear now many degrees the shooting angle of ram will need to be made adjustable. We also want to load balls as high up on the bot as possible, so shots cannot be easily blocked, and less energy needed to clear truss and hit the high goal.

-Dick Ledford