Chief Delphi - Potential Energy stored in a pneumatic ram

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Re: Potential Energy stored in a pneumatic ram

Quote:

Originally Posted by squirrel (Post 898966)

Several teams used this concept in 2008 to launch the track ball. Also consider using an "over center" linkage design...so you don't need to use a lot of force to release it.

what is a over the center ,linkage system?

Re: Potential Energy stored in a pneumatic ram

Quote:

Originally Posted by Al Skierkiewicz (Post 899211)

As a reminder to all teams and those that are reading this thread...
R01> Energy used by FRC ROBOTS, (i.e., stored at the start of a MATCH), shall come only from the following sources:
A. Electrical energy derived from the onboard 12V battery (see Rule <R40> for specifications and further details).
B. Compressed air stored in the pneumatic system, stored at a maximum pressure of 120 PSI in no more than four Clippard Instruments tanks. Extraneous lengths of pneumatic tubing shall not be used to increase the storage capacity of the air storage system.
C. A change in the altitude of the ROBOT center of gravity.
D. Storage achieved by deformation of ROBOT parts.

I'm kinda wondering - maybe this should be put on the FIRST Q&A. If we were to use a system that had the ability to use a pre-charged kicker cylinder it seems we would have to demonstrate to inspection that there is NO pre-charge condition prior to match start. I suppose putting a gauge on the cylinder circuit downstream of the valve could demonstrate there is NO pre-charge while the robot is in the fielded 'disable' mode.

What say you Al ? Should I put it to the Q&A ? We want to use something like this.

Ed

Re: Potential Energy stored in a pneumatic ram

You could, but be sure to word it carefully.

As I see it, what you want to do is this (correct me where I am wrong):

Start the match with only the clippard tanks at pressure (allowed per <R01a>. Or don't, and let them pressurize during autonomous)
After start, open a valve to extend a piston.
Mechanically limit the extension of that piston to something like 1/2 its stroke.
Allow the back end of the piston to completely pressurize to 60 PSI or so.

So far, are we OK? If not, I'd need to see a rule.

Using some mechanism, release the mechanical limit, allowing the piston to extend the rest of its stroke.

Still OK, right? Assuming you follow the rest of the rules (e.g, perimeter and safety), it still looks OK to me. (My opinion is worthless at any competition though)

Re: Potential Energy stored in a pneumatic ram

We had the same idea actually. Although, we had the idea of using something like a trigger mechanism off of a control group on a firearm.

Quote:

Originally Posted by ChrisH (Post 899272)

It depends on how it is used. You could apply force to the rod of a pneumatic cylinder that had air trapped behind the piston by a closed valve. This could cause the air in the cylinder to exceed 60psi, which would be a rule violation. There are various ways to both do this sort of thing and prevent it, depending on what you are trying to accomplish

In our implementation, the air wouldn't be trapped, only the piston would be trapped (somewhere) midway along it's stroke. If there were a force applied to the pneumatic cylinder, it would back-pressure into the system and still be regulated to 60 psi. If I remember correctly from accidently putting the regulator backwards on the 'high pressure side', the pressure releases if it's above 60. One of the first things we do every year is hook the regulator backwards and have our entire system never go past 60 psi, then someone remembers what happened the year before.

Quote:

Originally Posted by ebarker (Post 899291)

You could also prove that it is not pre-charged before a match by unlocking the triggering system, and the cylinder at this point wouldn't fire.

Edit: Don's question should cover the Q&A question that I'd even like to ask. Could someone submit that?

Re: Potential Energy stored in a pneumatic ram

You got it perfect.

I just noticed that the FIRST website has not yet posted the pneumatics manual for this year so for the moment we are falling back on the 2009 manual even though that isn't 'official'.

And the KOP checklist doesn't have the part number of the FESTO valve used in this years rookie kit and I'd like to know what that p/n is.

la dee da

Re: Potential Energy stored in a pneumatic ram

Our catapult was powered by 2 8" stroke 2" diameter pistons. at the begining of the match the latch would engage and the accumulators on the cylinders were charged to 60 psi. We had a third cylinder (our latch) which was i think 3" stroke and 1" bored. we machined 5/8" shaft to thread onto the end of the piston. The latch worked by extending into a bracket on our catapult which was really just a ball bearing supported by 2 plates. When we fired we just applied a small amount of pressure to the latch and the catapult launched. the only damage we had was that the 28 mm extrusion we used for the catapult had quite a bow in it at the end of the season due to all the pressure.
Its hard to see but it is vissible in the 3rd and 3rd last pics.
http://team781.com/gallery/2008/2008waterloo/