Quote:
|
Originally Posted by KenWittlief
understatement of the day! 183 joules could fire 13 balls all at once! what was all that talk about cycle times and being able to fire fast enough?  |
<SIGH> Hmmm... How do I put this?
What you're talking about is the theoretical
total energy contained
in that much
compressed air. That's a
lot different than what a
typical cylinder can provide in
output work, in a short time.
And YES, you are still ignoring
cycle time of the
system
(IOW, how fast it can get ready for the next shot).
Think about it... Well SURE, it sounds great! Yes, if you could
release
all of that theoretical energy in an
instant, you'd fire
a whole bunch of balls, and that would be pretty cool!
(You've then just "shot your wad". It'll take time to get
it charged up again.)
But that's not how
cylinders work. You can't just use the
raw air (that's "making your own cylinder", a no-no), and
you're STILL limited to whatever that darn thin tubing can
supply you.
Ya can't get
all of the work out, either. (Well, not in any
reasonable amount of time, anyway...
) Cylinder motion
is quite a bit like a capacitor charging in electronics.
The
difference between the load's back force and the
cylinder's force is
very important. If you actually tried to
get that full energy out of the cylinder by backloading it
heavily, it would take a very long time for the cylinder to
move to its final position (which in reality it wouldn't...
it'd stop from static friction first.)
The point is that cylinders work best when you
can vastly
overpower the load's back force, or else they slooooooow
dooooooown to a craaaaaawwwwwllllll. Not very useful
in contest.
OOC, Have you guys ever actually tried to USE a 2" cylinder
in a contest before? We have. It's SLOOOOOOW, and you
can cycle it
fully only a couple of times in a round. You just
simply don't have the
air, nor the
slew rate to drive it any
more than that!
Now I've used the 2", full length cylinders in several contests
with a couple of my teams. In fact, 1502 used one last year with
a multipositioning shoulder joint for our tetra arm. BUT, we
had to be
very careful in our design to not ask it to move
around
too much, or we'd risk running out of air. That's why
we used a motor for our arm's elbow joint. If need be, we could
use the "last gasps of air" to move the shoulder into a good
position, and leave it there. That happened a couple of times
in contest. No sweat. We could still keep lifting tetras from
the HP to the top of a goal via just the elbow joint, while the
air system slowly regenerated..
But what you're suggesting is to move it back and forth
repeatedly. Sorry to bust your bubble, but you just can't
do that more than a few cycles over several
minutes with
a 2" cylinder, or it stops. (I'm getting the impression some
people here have NEVER worked with the FIRST pneumatics
before...)
But don't take my word for it. Try it out for yourself when
you get the time! You don't have to build the catapult,
but you really need to know how the kit pneumatics behave,
or one of these days you may get yourselves caught by
expecting too much out of them.
Try this: Put together the basic kit pneumatics package.
Nothing fancy. Add ANY 2" dia cylinder. Point it downward
and attach a good sized weight to the clevis. (Let's say about
100 lbs.) Now try to run it continuously up and down full strokes,
and see what happens. Does it do it quickly? Does it slow down?
How many
total inches were you able to lift that 100 lb weight
up in 2:10?
Do that, and you'll gain some good insights into how much you
can get out of the kit's pneumatics. Good luck!
- Keith