View Full Version : 1212 pneumatic catapult prototype
http://www.youtube.com/watch?v=YDuA0Ed2JmU&feature=youtu.be
So we actually improved it after I took this video but I didn't record it. The metal bit in the middle is the height of the goal.
Very Nice!
Did you select that starting angle for the cylinder on purpose? It seems like a good way to get around flow restrictions without added mechanisms.
It seems that is is what is happening:
1. The cylinder has a very short lever arm at the starting stage
2. Because of this, pressure must be very high for the cylinder to start moving
3. Once the arm starts moving, the cylinder gains leverage (the lever arm is longer) and moves the ball very quickly.
Did you select that starting angle for the cylinder on purpose?
To be completely honest, we chose that angle because we didn't want to make it any taller or it'd be harder to herd the ball (and a bit of laziness on our part), it was really just a happy accident. And your comment actually enlightened me as to why our other attempts weren't working so well, thanks!
Looks nice, I've wondered how the pneumatic launchers that worked in 2008 got the pressure build up needed for a quick fire without any fancy mechanisms and that video gives a good view of it.
To be completely honest, we chose that angle because we didn't want to make it any taller or it'd be harder to herd the ball (and a bit of laziness on our part), it was really just a happy accident. And your comment actually enlightened me as to why our other attempts weren't working so well, thanks!
Glad I could help! Thanks to you for posting the video!
Hoffer5236
12-01-2014, 13:37
This is really impressive. My team is also using pneumatics, but we have two with long arms. We're still trying to figure out how to decrease the length while keeping the power. Currently we have two c-channels as arms and a stainless steal rod for the basket. You guys seem to have figured out and it's awesome.
Uncle Paul
12-01-2014, 16:12
Thanks for the video and information. Any chance you could provide the spec's on the cylinder you used? Stroke, bore, etc?
I'm in awe right now that was just fanstatic keep up the good work.
falconmaster
12-01-2014, 21:55
Here is our pneumatiuc shooter
http://www.youtube.com/watch?v=fljCPwHhnHw&feature=youtu.be
Any chance you could provide the spec's on the cylinder you used? Stroke, bore, etc?
Unfortunately, I'm at home now and we don't meet till Friday so I can't be terribly specific. Today we changed it so it's 2 11 inch pistons with 1.5 inch diameters, but that's all I remember, we actually hit the ceiling with that setup. The one in the video is pretty beefy, if I were to make a rough estimation, it's around 15-20 inches long with a 3 inch diameter, I don't know beyond that, we did this fairly haphazardly without any calculations or anything and just stumbled upon something that worked.
Here is our pneumatiuc shooter
http://www.youtube.com/watch?v=fljCPwHhnHw&feature=youtu.be
Wow! That's very impressive you guys got it to work so well so early, thanks for sharing
Hoffer5236
13-01-2014, 06:41
Here is our shooter: http://youtu.be/r-9v9loC2As. Right now we are trying to make it shorter, and we don't really have a way to do that. Currently the cylinders on there are bimba 1.5in's, but I'm not sure the stroke on them.
http://www.youtube.com/watch?v=YDuA0Ed2JmU&feature=youtu.be
So we actually improved it after I took this video but I didn't record it. The metal bit in the middle is the height of the goal.
What is your supply set-up like? What was your air pressure and what solenoids did you use for such quick air flow?
camalex3999
13-01-2014, 22:43
Glad to see that other teams are having success with the pneumatic catapults. Our team is doing something similar. We have a catapult made with two pieces of conduit and roughly 30 lbs of spring force on the end. We are planning to use a piston to pull it back. When we tried it today we only put air to one side and it extended too slow when releasing the pressure. Tomorrow we plan on hooking up both sides to see if we can get it to extend faster.
Without the piston we can shoot the ball about 7' high at 16' away.
What is your supply set-up like? What was your air pressure and what solenoids did you use for such quick air flow?
I don't know a whole lot of pneumatics stuff, we have a member that's super into it so we just kinda rely on him :p From what I remember though (and I may be wrong), we filled up a tank to 120 psi then used 60 psi to extend the piston. In the video we just opened a valve mechanically. We had better success with two separate pistons hooked up to two separate solenoids though, actually hit the ceiling and nearly doubled the distance, not sure what solenoids we used but we didn't buy anything new to do it and we don't meet till friday so I can't really give more info than that. Like Jeffy pointed out though, the orientation of the piston at the beginning likely allowed the pressure to build up.
When we tried it today we only put air to one side and it extended too slow
You may want to try something other than a piston. Seems like most teams are going with motors. Another idea is to use a nautilus cam gear like that robot in 3 days team that didn't finish, or to see a functioning one look at robowranglers from 2010 (http://youtu.be/_hTyXQUgYLE?t=1m48s)
Dave Otis
14-01-2014, 00:20
Wow, impressive, thanks for sharing. Question regarding the valve you used. We have been using a Festo VPLE18-M5H-4/2 - 1/4 with a 12" stroke, 0.75" bore BIMBA cylinder. We didn't get the launch distance we were expecting and so tried putting two of these valves in parallel, and also using 3 large pneumatic capacitors and keeping the pneumatic lines as short as possible. Any advice based on your successful launch? Thanks!
Any advice based on your successful launch?
I didn't do the pneumatics on the prototype, I just built it with some others, so I don't know a whole lot about pneumatics but from what you said, you may need to either use more pistons or a bigger piston. Your setup actually sounds pretty similar to our initial attempt, after which we got it shooting better with a larger piston, after which we got it shooting better with multiple smaller pistons. Sorry I can't help you much on the pneumatic side of things. On the mechanical side, however, I can help a bit more. If you need more speed, you can either attach the piston closer to the pivot point or make the catapult longer. If you move the piston half the distance closer, you will get twice the speed but it will require twice the force. Another idea is to make the angle between the catapult and piston smaller. As Jeffy said, it seems that the pressure builds before it shoots like this. I made a picture for you http://puu.sh/6kqsp.png
Hoffer5236
14-01-2014, 12:05
Here is our pneumatiuc shooter
http://www.youtube.com/watch?v=fljCPwHhnHw&feature=youtu.be
How did you get the varying pressure for the pistons to make them shoot different heights? We cannot figure out how to do that.
How did you get the varying pressure for the pistons to make them shoot different heights? We cannot figure out how to do that.
I wonder if you could treat the solenoid like a MOSFET and PWM it. Has anyone ever tried that?
Oldbikerider
14-01-2014, 16:52
I wonder if you could treat the solenoid like a MOSFET and PWM it. Has anyone ever tried that?
This is how the turbo boost control works on my Subaru. Or at least how it used to work before I built my own boost controller.
A quick test should show if the valve can respond quickly enough - listen for the chatter and find the frequency it stops chattering.
Another idea for catapult distance adjustment would be to open the valve for a varying time. A slower valve that cannot be pwm'd may still be fast enough for one opening and one closing within the filling time.
Graham.
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