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-   -   2073 Pneumatic Catapult (http://www.chiefdelphi.com/forums/showthread.php?t=124610)

WaterClaw 14-01-2014 17:36
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1326793)
Height, distance, check. It scores!

Through various modifications and experiments, we have found a shooter design we are confident in. Minor adjustments here and there can be made to achieve extra distance or height.

http://www.youtube.com/watch?v=I9KXe...ature=youtu.be

When weighted to the floor, with a pair of size 12 feet, it transfers even more energy into the ball.
Well done. It seems reasonably accurate.

Ether 14-01-2014 17:56
Re: 2073 Pneumatic Catapult
 
1 Attachment(s)
Quote:
Originally Posted by billbo911 (Post 1327082)
Here are some additional details to help explain why it works...

The cylinders are actually only retracted to 2/3 of their total length when the catapult is in the load position. The valve is then opened to allow the accumulators and cylinders to precharge up to 60 psi. The catapult is actually in a below top dead center (TDC) position, thus causing the arms to be forced against the stops and not allowing the arms to move. (There is the secret).
To launch, we just use a small dia. cylinder, or our hands during testing and in the video, to lift the catapult arms into an above TDC position, the rest is history.
Is the attached sketch a correct representation of what you are describing?

The blue line represents the launcher, the brown block represents the stops in the loaded position. The black circles are the pivot points.

In the loaded position (as shown), the launcher is being pressed against the stops. An upward force at the green arrow will move pivot2 above the line connecting pivot1 and pivot3, and the rest, as you said, is history.

billbo911 14-01-2014 18:13
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by Ether (Post 1327180)
Is the attached sketch a correct representation of what you are describing?

The blue line represents the launcher, the brown block represents the stops in the loaded position. The black circles are the pivot points.

In the loaded position (as shown), the launcher is being pressed against the stops. An upward force at the green arrow will move pivot2 above the line connecting pivot1 and pivot3, and the rest, as you said, is history.
Although the positions of the pivots aren't exactly where ours are, because of mechanical mounting options, functionally your picture and description are correct.

SenorZ 14-01-2014 18:13
Re: 2073 Pneumatic Catapult
 
How are you reloading this? Once the cylinders are retracted don't they need to be forced into a locked position again?

Ether 14-01-2014 18:17
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by SenorZ (Post 1327196)
How are you reloading this? Once the cylinders are retracted don't they need to be forced into a locked position again?
If the launcher is heavy enough gravity could pull it over-center into the locked position. Once it's over-center, then you charge the cylinder to arm it.

Just guessing here.

billbo911 14-01-2014 18:19
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by SenorZ (Post 1327196)
How are you reloading this? Once the cylinders are retracted don't they need to be forced into a locked position again?
We use Pixie Dust!




Sorry, it just seemed like the right answer at the moment.

Because of the mechanical mounting offset provided by the mounting hardware, and the wonderful force of gravity, the arms cause the system to fall below TDC when the system is retracted and then recharged. This causes the system to be locked once again, waiting to be fired.


EDIT: Ether beat me to it.

pfreivald 14-01-2014 20:58
Re: 2073 Pneumatic Catapult
 
Clever. Our pneumatapult failed quite well this evening. I'll have to try this when we meet on Thursday!

wilsonmw04 14-01-2014 21:07
Re: 2073 Pneumatic Catapult
 
ours is ALMOST there. We have a range of 4-13ft mostly... at 9-10 ft, our shot is just a tad too high. We need to flatten out the trajectory just a bit and we have it set.

I tried the collector and I didn't notice a difference. Then I read the thread and saw we needed one on each side of the piston. We will try that Thursday.

pfreivald 14-01-2014 21:42
Re: 2073 Pneumatic Catapult
 
Mr. Bill, am I correct, then, in deducing that you have to recharge the cylinder and the accumulator entirely after every shot?

billbo911 14-01-2014 21:52
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by pfreivald (Post 1327280)
Mr. Bill, am I correct, then, in deducing that you have to recharge the cylinder and the accumulator entirely after every shot?
Yes, this is true.

Honestly, the cycle time between shots may be a bit long. Although, if our estimation is correct, the amount of time between shots in this game "should" be enough to recharge.
Although, you could add a large high pressure storage volume to help compensate for that, too.

pfreivald 14-01-2014 22:18
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1327290)
Yes, this is true.

Honestly, the cycle time between shots may be a bit long. Although, if our estimation is correct, the amount of time between shots in this game "should" be enough to recharge.
Although, you could add a large high pressure storage volume to help compensate for that, too.
I'm thinking "maybe three shots in autonomous = two second or less reload time required". At least that once.... Lots of air tanks may be in our future!

Justin Shelley 14-01-2014 22:33
Re: 2073 Pneumatic Catapult
 
The thing that I worry about with piston launching is that shots may become unreliable with varying air pressure and the possible need for tanks to hold enough air for multiple fires. What benefit is there of this method versus piston to pull catapult to fire position and surgical tubing acting as the force that throws?

bEdhEd 14-01-2014 22:43
Re: 2073 Pneumatic Catapult
 
Nice! Glad to see one of our favorite teams doing well! I do worry about losing too much air pressure, but realistically the majority of this game isn't even launching the ball.

Mike Marandola 15-01-2014 02:10
Re: 2073 Pneumatic Catapult
 
Will you be able to vary the distance of your shot? We prototyped something similar but ultimately decided against it due to the lack of variability.

pfreivald 15-01-2014 08:32
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by marandola316 (Post 1327440)
Will you be able to vary the distance of your shot? We prototyped something similar but ultimately decided against it due to the lack of variability.
Couldn't you put in at least one retractable stop to get different shots?


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