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Unread 06-01-2014, 16:25
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Launching the ball

Thought some of you might like this, dug out of archives, team 39 's robot was great at this and we have partnered up with them again this year. This is there 2008 robot launching this years ball.
https://www.youtube.com/watch?v=fsGUgaVG2ho
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Unread 06-01-2014, 16:27
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Re: Launching the ball

Wasn't there something special about their pneumatic setup that year? They found a way around the air flow issue somehow, but I don't remember.
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Unread 06-01-2014, 16:43
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Re: Launching the ball

We found video of 39 early on on Kickoff day, with the 2008 ball. I too would like to know if they did anything special.
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Unread 06-01-2014, 18:34
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Re: Launching the ball

Ahh, now I remember. Unfortunately, <R90> prohibits that specific setup. However it may not be necessary this year, given that this ball is ~1/3 the weight.
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Unread 07-01-2014, 07:49
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Re: Launching the ball

The pneumatic trick is called blocking the cylinder. You essentially use two pistons, one large and one small whereas the smaller cylinder acts as a release mechanism. The larger cylinder is activated, but it cannot move because the smaller cylinder is blocking its movement. When the smaller cylinder is moved it unblocks the large cylinder. The resultant force of the large cylinder is tremendous.
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Unread 07-01-2014, 07:53
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Re: Launching the ball

I don't think they used that trick. It's kind of dangerous.
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Unread 07-01-2014, 08:24
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Re: Launching the ball

Yeah. What if some metal snaps? There will be so much force built into the mechanism, the bot would be too dangerous for students to be around while active! I think it may be a good idea to work a little more on the design? Why not just use many small-diameter pistons, to retract quickly, and act as a team to generate a ginormous force?
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Unread 07-01-2014, 08:56
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Re: Launching the ball

We're not talking about a punching design. We're talking about an arm design. If you watch the video, you'll see....
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Unread 07-01-2014, 10:51
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Re: Launching the ball

Quote:
Originally Posted by yash101 View Post
Yeah. What if some metal snaps? There will be so much force built into the mechanism, the bot would be too dangerous for students to be around while active!
Actually the force involved is no more than the cylinder has normally when it has reached its final position. Anything not built properly can be dangerous, cylinders no more than spinning motors.

The key advantage to this arrangement is that the air has already evacuated the other half of the cylinder leading to a faster extension. Instead of having to push 60psi air out of the chamber, that volume of air has already gone. As the cylinder extends, the remaining normal pressure air will have to leave too, slowing the cylinder perhaps as it extends.

In previous years our team has used quick exhaust valves, but I believe that those are not longer permitted. Instead the return air has to pass out the solenoid valve. Haven't read the rules in that detail yet. Pity, we used it on our 2008 catapult.
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Unread 07-01-2014, 11:48
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Re: Launching the ball

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Originally Posted by MrForbes View Post
I don't think they used that trick. It's kind of dangerous.
It's definitely not for the faint of heart, and getting that small cylinder to smoothly catch and release a pre-charged large cylinder is mechanically difficult... But it's a tempting way to make a linear punch, I must say.

The actual pushing force of the piston may be the same, but it's dishonest to say it is "just as dangerous as a normal piston". The piston is moving several times as fast and releasing the force all at once. (Yup, contradicting myself)
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Unread 07-01-2014, 12:02
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Re: Launching the ball

Team 39's robot (as shown in the video, modified for prototyping purposes) does not violate any of this year's pneumatic rules that I can tell. The original design used several solenoids to feed one cylinder, but this is prohibited in the 2014 rule set.

The partially filled catapult cylinders + latch approach from 2008 was very dangerous, I cringed a lot when seeing these robots used at competitions.

Here is a shot of the NERDS (team 1726) catapult from that year. Due to the geometry, the weight of the ball allowed pressure to build up in the cylinders before they had enough force to get the ball moving. This is similar to the latch approach, but if it is dry fired there is not a massive amount of stored energy being released instantaneously.

Catapults are dangerous! Make your system as safe as possible if you take this approach.
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Unread 07-01-2014, 12:27
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Re: Launching the ball

Not sure what "blocking the cylinder" actually is, but to have most of the air ahead of the retracted piston be gone when you want to fire the piston with max. peak velocity, you either need to evacuate it with a vacuum pump, or seal the exhaust port when the piston is full extended and then pull the piston back into the cylinder, creating a vacuum inside the cylinder as it retracts.

This demands some kind of retraction mechanism combined with a trigger hold/release mechanism strong enough to retain the piston with 120 psi behind it. Venting pressure during retraction and reapplying it after retraction allows for the retraction mechanism to be weaker. The key factor is to have a cycle that maintains as little air in the cylinder as possible when piston is retracted and ready to fire.

Having to push out almost no air from the cylinder, ahead of the piston disk as it accelerates gives a serious boost to peak velocity, and lengthens time in contact with the ball.

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Unread 07-01-2014, 12:54
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Re: Launching the ball

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Originally Posted by RRLedford View Post
This demands some kind of retraction mechanism combined with a trigger hold/release mechanism strong enough to retain the piston with 120 psi behind it.
you mean 60 psi?

It works fine without evacuating the other end of the cylinder.
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Unread 07-01-2014, 15:46
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Re: Launching the ball

Ah, I see. The Poofs had a similar setup for the actual launch in '08.
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Unread 07-01-2014, 17:21
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Re: Launching the ball

Maybe the piston doesn't have to apply force directly. Maybe it can be used to apply centripetal velocity to the ball or pull the ball during launch. Food for thought.
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