On 11/22/2024 11:30 AM, bp@
www.zefox.net wrote:
Most "guns" just want to achieve a "maximum" (range,
load, etc.)
Not sure I understand what you're getting at here. On
the face of it that statement seems mistaken.
A gun (in the sense of handgun) tends not to have a "range control".
You can use "light loads" (bullets with less black powder than a
"normal load") but that's not really intended to decrease the
firing range.
Artillery is more along the lines of my goal -- where you
want to lob a shell at a particular distance from the gun.
There, however, the shells aren't altered to change the
range-from-launcher, just the elevation of the barrel
(though I don't know that for a fact; and, on battleships,
the explosive charge could be changed to adjust the range
to some extent)
Perhaps the most clever feature of the Giradoni mechanism
is pitting the momentum of the hammer _against_ the air pressure
bearing on the release valve. As the pressure goes down, the
valve opens farther, at least partially compensating for the
lower pressure.
I will have to see if I can find more detailed documentation
of the mechanism. We're only looking at onesy-twosy quantities
so spending much on engineering or manufacturing isn't a real
issue. OTOH, if it's an extra "hour with a file", that's acceptable.
Since you will have control of the exact pressure that particular
compensation isn't needed. Still, if the valve opens differently
on timescales comparable to the departure time of the projectile
repeatability will suffer and with it accuracy.
Yes. The same was true with the spring release mechanism I mentioned.
You want a "clean" transition from held (closed) to released (open)
Opening the valve
poppet before the projectile moves is one way to help repeatability.
For the velocities you envision that shouldn't be difficult.
I was hoping to capitalize on some "prior experience" with pneumatic
valves for real data before trying to build something as I indicated
in the initial post. My prior process control experience hasn't been
concerned with the details of the valves' opening or closing -- it's
always just been used as an electrically controllable "gate".
A pneumatic potato cannon seems like a good starting point.
Again, most "guns" try for maximum range. You don't see folks
bragging about the SHORTNESS of the range of their potato gun
or how repeatably it can achieve a given range (potatoes are
inconsistent projectiles). And, if the user wants to hit a
particular target, he has feedback from his prior attempts
to adjust the "charge", projectile and elevation. *We* have to
rely on that being baked into the design.
Even nerf guns want to aspire to having the longest range possible
(without risking injury).
My initial statement says it all:
We're trying to make a mechanism that will allow for the
REPEATABLE lobbing of small projectiles over short (0-20 ft)
distances.
putting only the /essential/ constraints in that statement.
I.e., you are free to define the characteristics of the projectile
and mechanism -- subject to the requirement for repeatability
and range (and the fact that it must travel over a high arc
to it's target -- as suggested by "lob" -- soas to avoid any
obstacles in the way)
But, I would imagine a potato gun would get the best range (for
a given "potato") with the "cleanest" valve transition!
[OTOH, with ammunition, you can control the burn timing as
well as total load to help propel the bullet down the barrel
with a slower/delayed burn. Maybe this "slowed release" impacts
the effectiveness of a potato moreso than a ping-pong ball or
other lightweight projectile?]