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

billbo911 13-01-2014 23:31
2073 Pneumatic Catapult
 
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.

pfreivald 13-01-2014 23:35
Re: 2073 Pneumatic Catapult
 
Lookin' good!

buildmaster5000 14-01-2014 09:47
Re: 2073 Pneumatic Catapult
 
What are the specs on the cylinder? Specifically bore and stroke length...

billbo911 14-01-2014 12:16
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by buildmaster5000 (Post 1326922)
What are the specs on the cylinder? Specifically bore and stroke length...
Really good question!
After trying a Bimba 178 (1.5"dia. X 10" stroke) we found we just didn't have enough height or distance out of our system. We run it at 60 psi which produces 106 Lb. of force.

So, our next thought was that the force was sufficient, but we needed more speed out of the cylinders. So, to maintain the force, we substituted in two Bimba 0910 (1 1/16"dia X 10" stroke). This yields the same 106 Lb. of force at 60 psi, and moves a lot faster.

An additional note here is that we are using low pressure storage tanks between the valve and cylinder. One per cylinder. This is done to maximize air flow to the cylinder by not restricting it as it flows through the valve.

Birdie048 14-01-2014 12:33
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1326996)
An additional note here is that we are using low pressure storage tanks between the valve and cylinder. One per cylinder. This is done to maximize air flow to the cylinder by not restricting it as it flows through the valve.
Great addition. We were running into the same problem.
Thanks!

JohnFogarty 14-01-2014 13:20
Re: 2073 Pneumatic Catapult
 
What valve are you using on there?

billbo911 14-01-2014 13:36
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by JohnFogarty (Post 1327050)
What valve are you using on there?
Honestly, I do not have the specific part number. The best way to describe it is The standard double solenoid valve from the KOP from previous years. You can also purchase them from VexPro right here. Their part # is 217-2948.

That said, in the configuration we are using it, it really doesn't matter what specific solenoid valve is being used. While the cylinders are extending, very little air is actually flowing through the valve.

wilsonmw04 14-01-2014 14:11
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1326996)
Really good question!
An additional note here is that we are using low pressure storage tanks between the valve and cylinder. One per cylinder. This is done to maximize air flow to the cylinder by not restricting it as it flows through the valve.
Does this really work? Isn't the valve restricting the flow for everything "downstream" regardless of the volume?

billbo911 14-01-2014 14:26
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by wilsonmw04 (Post 1327075)
Does this really work? Isn't the valve restricting the flow for everything "downstream" regardless of the volume?
Here are some additional details to help explain why it works.

Each cylinder (1 1/16" dia X 10") has a displacement volume of 8.87 in.^3. Each cylinder also has an accumulator tank (2"dia X 6"lng.) in line between it and the valve. The accumulator tanks have a capacity of 18.87 in.^3.

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.

So, as you can see, the air through the valves really doesn't move the cylinders during launching, it's the air in the accumulators that does.

BTW, this is not our original idea. We learned it in 2008. We have just modified it to our needs in this game. I wish I knew which team used this back then so we could give credit where it is due.

pfreivald 14-01-2014 14:35
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by wilsonmw04 (Post 1327075)
Does this really work? Isn't the valve restricting the flow for everything "downstream" regardless of the volume?
We didn't get to really test it yesterday, but plan to test exactly that today--we built a pneumatic test board with that in mind. If I haven't posted something by tomorrow afternoon, somebody please bug me and I'll post up our results.

wilsonmw04 14-01-2014 14:43
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1327082)

So, as you can see, the air through the valves really doesn't move the cylinders during launching, it's the air in the accumulators that does.
We get a similar effect with a different mechanic. I'll throw a collector in line with it tonight and take a before and after video so we can compare. I'm rather interested to see if it works.

JohnFogarty 14-01-2014 16:37
Re: 2073 Pneumatic Catapult
 
I'm no master with Pneumatics, but could you draw a small diagram, OR take a picture of how you have it tubed together once you've tested it successfully? This could really prove useful to a couple of teams down here in South Carolina.

seg9585 14-01-2014 16:37
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1327082)
Here are some additional details to help explain why it works.

Each cylinder (1 1/16" dia X 10") has a displacement volume of 8.87 in.^3. Each cylinder also has an accumulator tank (2"dia X 6"lng.) in line between it and the valve. The accumulator tanks have a capacity of 18.87 in.^3.

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.

So, as you can see, the air through the valves really doesn't move the cylinders during launching, it's the air in the accumulators that does.

BTW, this is not our original idea. We learned it in 2008. We have just modified it to our needs in this game. I wish I knew which team used this back then so we could give credit where it is due.
Fascinating, I never thought of doing it this way. I want to try this now (I'll give you credit, hah).

I assume the tubing diagram would look like this:

Compressor --> Upstream Accumulator (115 psi) --> Regulator --> Valve --> Downstream Accumulator (60 psi) --> Cylinder
T-junction connecting both the downstream accumulator and cylinder to the valve.

Mechanism it's supporting is against a hard stop with a pivot latch, and a second piston on its own valve connected to extend, retract the latch

billbo911 14-01-2014 16:49
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by seg9585 (Post 1327145)
Fascinating, I never thought of doing it this way. I want to try this now (I'll give you credit, hah).

I assume the tubing diagram would look like this:

Compressor --> Upstream Accumulator (115 psi) --> Regulator --> Valve --> Downstream Accumulator (60 psi) --> Cylinder
T-junction connecting both the downstream accumulator and cylinder to the valve......
Absolutely correct!

One note:
To maximize the air flow from the downstream accumulators to the cylinders, use double ended accumulators and feed into one end, putting the "T" between the valves and accumulators, then run the hose from a straight fitting on the other end of the accumulator into the cylinder, also with a straight fitting. Avoid using the 90deg fittings if possible.

chrisfl 14-01-2014 16:57
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1326996)
Really good question!
After trying a Bimba 178 (1.5"dia. X 10" stroke) we found we just didn't have enough height or distance out of our system. We run it at 60 psi which produces 106 Lb. of force.

So, our next thought was that the force was sufficient, but we needed more speed out of the cylinders. So, to maintain the force, we substituted in two Bimba 0910 (1 1/16"dia X 10" stroke). This yields the same 106 Lb. of force at 60 psi, and moves a lot faster.

An additional note here is that we are using low pressure storage tanks between the valve and cylinder. One per cylinder. This is done to maximize air flow to the cylinder by not restricting it as it flows through the valve.
Funny, we had almost the same setup for prototyping and we were able to get it with the one piston(1.5in bore and 10 in stroke)

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?

DavisDad 16-01-2014 21:51
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...
WOW! That is an elegant solution to the FRC pneumatics flow limitations. Your TDC latch is brilliant. Thank you for sharing the design. We made a copy today (no accumulator) and it worked beautifully. As my son said: "those guys rock!"

pfreivald 16-01-2014 22:04
Re: 2073 Pneumatic Catapult
 
We couldn't get the shot we want out of ours, so we scrapped it and are working on other designs. But thanks so much for sharing the general idea!

DavisDad 16-01-2014 23:08
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by pfreivald (Post 1328334)
We couldn't get the shot we want out of ours, so we scrapped it and are working on other designs. But thanks so much for sharing the general idea!
Have you tried making or buying a proportional control valve (AKA I/P)? We made one that worked pretty well but was a modified regulator, so illegal. You could turn knob w/ gearmotor & multi-turn POT.

One of the students said today that a "Quick Exhaust Valve" or "Dump Valve" is legal this year. This is a shuttle valve on the exhaust port that charges from solenoid and dumps to atmosphere. Anybody know about this?

TGA Reaper 17-01-2014 00:20
Re: 2073 Pneumatic Catapult
 
The day after we shot the first video we made another with some wider angles.
http://youtu.be/Zfx2kwGwvEg

bEdhEd 17-01-2014 02:56
Re: 2073 Pneumatic Catapult
 
Just had an idea you guys. Every time the video goes to slow motion, put in a different Dubstep drop, but no music on the regular speed parts. That would be funny to me for some reason.

wilsonmw04 17-01-2014 23:32
Re: 2073 Pneumatic Catapult
 
Sorry it took so long, but I finally had a chance to test out the collectors on our shooter. I made two videos. The first one had the collectors in line:

http://www.youtube.com/watch?v=hNUfE...BwU5QuFBVQGPyg

The second one has the collectors removed:

http://www.youtube.com/watch?v=4HNRL...re=c4-overview

Both videos were take with the front of the robot 9 feet away from the goal.

It looks like the shoot just gets higher. What that means for this shooter is that the arm is traveling though its arc faster. Is it something we are going to pursue? We aren't' sure yet. We like our shot the way it is without.

JB987 18-01-2014 10:36
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by DavisDad (Post 1328365)
Have you tried making or buying a proportional control valve (AKA I/P)? We made one that worked pretty well but was a modified regulator, so illegal. You could turn knob w/ gearmotor & multi-turn POT.

One of the students said today that a "Quick Exhaust Valve" or "Dump Valve" is legal this year. This is a shuttle valve on the exhaust port that charges from solenoid and dumps to atmosphere. Anybody know about this?
Quick exhaust valves are illegal according to recent Q and A...

http://www.chiefdelphi.com/forums/sh...hreadid=124806

billbo911 18-01-2014 11:13
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by JB987 (Post 1328808)
Quick exhaust valves are illegal according to recent Q and A...

http://www.chiefdelphi.com/forums/sh...hreadid=124806
This is specifically why we are experimenting with adding an accumulator on the exhaust side as well. It acts as a buffer to allow less restriction to the exhausting air, at least in principal.
Once our final catapult is built, we will test and see if it makes any measurable difference. But, so far, it appears it doesn't really make much difference at all. It may be that the air hoses are the biggest restrictions.

wilsonmw04 18-01-2014 13:04
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by billbo911 (Post 1328813)
This is specifically why we are experimenting with adding an accumulator on the exhaust side as well. It acts as a buffer to allow less restriction to the exhausting air, at least in principal.
Once our final catapult is built, we will test and see if it makes any measurable difference. But, so far, it appears it doesn't really make much difference at all. It may be that the air hoses are the biggest restrictions.
again, with our quick tests, we found of the difference to be noticeable. This is with the old metal 16in^3 tanks in line on both sides of the piston.

DavisDad 18-01-2014 15:26
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by JB987 (Post 1328808)
Quick exhaust valves are illegal according to recent Q and A...

http://www.chiefdelphi.com/forums/sh...hreadid=124806
Thanks Joe for the info, much appreciated. Maybe next year...

SenorZ 21-01-2014 11:12
Re: 2073 Pneumatic Catapult
 
We just rigged up a test of this set up.
Works OK. Just needs some tweaking... the rig was from an elastic catapult the kids were prototyping that we repurposed. Probably should build a new catapult.
http://youtu.be/W3DGCs-57xU

DavisDad 21-01-2014 12:52
Re: 2073 Pneumatic Catapult
 
Quote:
Originally Posted by SenorZ (Post 1330219)
We just rigged up a test of this set up.
Works OK. Just needs some tweaking... the rig was from an elastic catapult the kids were prototyping that we repurposed. Probably should build a new catapult.
http://youtu.be/W3DGCs-57xU
Have you looked into "rolling release" vs. your "cup" holding method? Here's a link to a paper: http://arxiv.org/ftp/arxiv/papers/1005/1005.0176.pdf

wilsonmw04 21-01-2014 16:53
Re: 2073 Pneumatic Catapult
 
While I was on the plane this morning, did some video analysis on those two videos I posted earlier.

our normal shot has a velocity of 6.1 m/s. With the 16in^3 collectors on both sides of the cylinders the velocity was 6.6 m/s.


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