1726 Prototype Testing

[TheOtherGuy]

basically when the catapult is fully retracted, the cylinder sticks out 3 in. Before we shoot, we hold down the ball (from the top, we still have to make that part) and open the valve. Air from the tanks fills up that 3in. and we wait until it is time to fire. When we fire, we remove the top piece and the air inside the cylinders expands rapidly, launching the ball.

Maybe I should make a quick diagram...

[neoshaakti]

Originally Posted by TheOtherGuy

basically when the catapult is fully retracted, the cylinder sticks out 3 in. Before we shoot, we hold down the ball (from the top, we still have to make that part) and open the valve. Air from the tanks fills up that 3in. and we wait until it is time to fire. When we fire, we remove the top piece and the air inside the cylinders expands rapidly, launching the ball.

Maybe I should make a quick diagram...

so your bore starts 3 inches, and it fires out to 10? so basically you're using the potential energy of the bore that is protruding 3 inches?
yeah a diagram might help...

[MrJebus]

Think of it like a spring, but instead of energy being stored in the coils, its stored in the cylinder with the air. Only reason that it sticks out 3in is so the pressure can build, storing the energy.

[TheOtherGuy]

Originally Posted by neoshaakti

so your bore starts 3 inches, and it fires out to 10? so basically you're using the potential energy of the bore that is protruding 3 inches?
yeah a diagram might help...

Exactly!

Here's a diagram (out of proportion and not quite right, but what the hay):

[neoshaakti]

Originally Posted by TheOtherGuy

Exactly!

Here's a diagram (out of proportion and not quite right, but what the hay):

Oh that is pretty cool
do u have to program the bore to protrude 3 " out, or do u mechanically set block it from full retracting (Im guessing the 2nd...programming a bore doesnt seem probable)
haha

[=Martin=Taylor=]

Are you at all worried about running out of air?

I think you might hurdle too fast ( ) and drain your tanks.

[TheOtherGuy]

actually, yes, we are very worried about running out of air! Right now we lose about 35-40psi per shot, and it takes ~25-30 seconds to reload... Of course, you don't have to shoot it at 115psi, but we still plan on exploring different ways to conserve air.

[=Martin=Taylor=]

Well, you could start by removing all the other pistons.

Use servos to shift, and a motor to lift the loading forks. Pressurizing your tanks before every match might help maximize your air.

[Matt H.]

We hold the cylinders at 3in by using the weight of the ball combined with the piece (not yet built) which holds down the ball. Because of the geometry of the catapult it takes very little force to hold it down, but increases exponentially when released.

We are trying to cut down air usage and have been somewhat successful. Almost all of our cylinders are now single action instead of double action. By doing this we have cut air consumption for one shot from about 115-70 to 115-90 psi drop on four tanks (about 15 sec recharge time). If we start with the tanks precharged we should be able to get through a match without too much trouble.

On a side note does anyone know if it's possible to design a pressure readout display for the OI. I think that would be immensely helpful this year.

[dtengineering]

Originally Posted by Matt H.

On a side note does anyone know if it's possible to design a pressure readout display for the OI. I think that would be immensely helpful this year.

First of all... wow. We spent the first couple weeks planning to lift, until we got fed up with the 80" cylinder, then said "what the heck" and started putting together launch prototypes last week. We managed to get the ball onto the overpass using two 1.5 x 8" cylinders... but without any preload. The only catch was that we used the 120psi feed from the shop compressor, so it was back to the drawing board. This weekend involved sitting around with the calculator, spreadsheet, and a demo copy of Working Model to calculate what we'd need to do it with 1.5x8" cylinders as... for some reason... we have five of them kicking around the shop. Lo and behold, the calculations came out very close to your observations. Thanks!

Now, perhaps, I can return the favour, by suggesting that the device you are looking for is called a "pressure transducer" and that a quick search of the forums here brings up a link to here where you can see a picture of one that was apparently in the 2006 KOP. It's possible you have one sitting in your shop and don't know of it!

As for sending the data back and displaying it, I suspect your programming team is on top of how to send it, and perhaps someone is building a custom dashboard in labview?

Thanks again... I feel so much more confident with our design knowing that our calculations are not entirely off-base!

Jason

[MrForbes]

Thanks for the tip Jason, but I looked thru the 2006 KOP checklist and I do not see that transducer listed. I sure don't recall ever seeing it in my many diggings thru the pneumatic parts bin either. Maybe it is just something that was used the year before, and not in 2006, and got left in the manual? notice the page on your link shows that it's from 2005 and then relabeled 2006 at the very top

[dtengineering]

Originally Posted by squirrel

Thanks for the tip Jason, but I looked thru the 2006 KOP checklist and I do not see that transducer listed. I sure don't recall ever seeing it in my many diggings thru the pneumatic parts bin either. Maybe it is just something that was used the year before, and not in 2006, and got left in the manual? notice the page on your link shows that it's from 2005 and then relabeled 2006 at the very top

Hi Jim! I thought I'd seen that launcher design before... I never clued in to this being your team ! Great job.

You've got me looking around for the a place that sells the pressure transducer now, as I'm pretty sure we've got one in the shop, but if it isn't COTS any more, then I guess that is where it is going to be staying. A bit of a pain, as they seem to run about $100 or so, but here's one that I found at digikey that might do the trick.

http://search.digikey.com/scripts/Dk...e=MSP3251P1-ND

Note that I've never actually used the transducer before, so I can't say for sure that this is exactly what you need... I just remember one being in the KOP some years ago and having it sit around on the shelf and thinking hmmm.... we've got to use that one of these years.

Jason

[Matt H.]

Thank you very much for the help Jason. There has been a lively discussion of this on our team forum and the other option which has been considered is the use of several pressure switches to provide a general idea of where the pressure is (one at 20psi, one at 60psi etc.). Either way it's an interesting problem. Do you plan on using all five of your 1.5*8" cylinders?

[s_forbes]

Originally Posted by Hachiban VIII

Well, you could start by removing all the other pistons.

Use servos to shift, and a motor to lift the loading forks. Pressurizing your tanks before every match might help maximize your air.

Shift? what shift?

From what I understand they didn't optimize the shooting system at all; it really only needs to fill the initial 3", not all 10". That should save a ton of air for the other tasks.

[TheOtherGuy]

we also accidentally managed to land the trackball on the overpass:

http://www.youtube.com/watch?v=X3oHbSovZjA

it's actually pretty easy with a catapult!