From brett@sr.hp.com Thu Mar 17 16:48:45 1994
Date: Thu, 17 Mar 94 12:34:34 PST
>From chroma@deeptht.santa-cruz.ca.us Fri Sep 27 02:09:02 1991
Relay-Version:
version Notes 2.8.4.1 1990/09/24; site hpnmdla.sr.hp.com
Date: Fri, 27 Sep 1991 09:09:02
GMT
Date-Received: Sun, 29 Sep 1991 16:10:22 GMT
Subject: Tennis Ball Cannon (approx 14K
long)
References: <1991Sep22.140610.33746@kuhub.cc.ukans.edu>
<22810230@hpcvaac.cv.hp.com> <1991Sep25.083913.17778@minyos.xx.rmit.oz.au>
The following posting is a design for a hydrogen/oxygen fueled
tennis ball cannon. The
posting is 14K characters long.
Dr. Explodo regrets having to publish under an alias;
he does so
in order to avoid difficulties with University and other
authorities who
might not share his view of tennis ball cannons
as marvelous and society-enriching devices.
Dr. Guy F. Explodo
Ph D, FRS, emeritus professor at the Yeovil Academy of
Theological Detonations
{Dr. Explodo made some refinements to the gas handling
procedures
which improved performance considerably. Here is the revised
paper, which
should be posted.}
Please note that any messages that are posted to me will be
posted
to the mysterious and inventive Dr. Guy F. Explodo. I have a secret
email link to
the Yeovil Academy of Theological Detonations, of which
I head the department of Photographic
Exploration.
chroma@deeptht.santa-cruz.ca.us
A SERIOUS TENNIS BALL
CANNON
Version 1.2 9/21/91 Dr. Guy F. Explodo
1.0 Introduction
3 goals in mind:
If used correctly and with proper respect, this cannon should not
be a danger to those who stand other than in front of the muzzle.
1.2 Use of Commonly
Available Materials
The cannon, its projectiles, and its propellant should be easily
1.3 Reliability and Ease of Use
The cannon should perform reliably and be easy to load and fire.
2.0 THE CANNON
2.1 Bill of materials
A 18" of 2.5" diam sched 40 PVC pipe
(a
tennis ball is a press fit into this pipe)
B 2.5" PVC slip fitting connector, female slip
fit both ends
C PVC bushing; 2" internal pipe thread one end, male slip fit
other
end
D 6" of 2" steel pipe, external thread both ends
E Steel T; 2",
2", 1.25"
F 2" external thread 1/2" internal thread steel bushing
G
9/16" fine thread steel jam nut
H 1.25" external thread ~1" internal thread
brass bushing
J a 1/32" copper sheet, about 2" x 2"
K brass tubing -
1/16" OD, 1/32" ID
L brass tubing - 1/8" OD
M clear vinyl tubing -
1/4"
N spark plug
P Scripto Tokai Electra electric cigarette lighter
2.2 Supplier Suggestions
A - J: any large hardware or do-it-yourself store with a
reasonable plumbing supply department.
K - M: available at a model-airplane-type hobby
store.
N: auto supply store
P: drug/supermarket/hardware store
Acetone
Blowtorch
Electric drill
Epoxy cement, high-strength filled
Hot glue gun
Pipe wrench
Pliers
PVC pipe
cement
Sand paper, coarse
Soft solder
Tin snips
2.4 Fabrication
Instructions
Exploded views of the cannon are shown in Figures 1 and 2.
—- J
+–+
( ) H
+–+
A B C D +–+ E F
+—————-+ +—+ +—][ +=====+ +==| |==+ +==+ G, M, N
| | | | | ][ | | | | | >
Figure 1
Exploded View of Cannon (small scale)
+———+
| |
| |
| |
| |
| |
| |
| | A
| |
| |
| |
|
|
| |
| |
| |
| |
| |
| |
| |
|/////////| <- PVC
cement
+———+
+———–+
| |
| |
|- - - - - -| B
| |
| |
+———–+
+———+
|/////////| <- PVC cement
| |
| | C
| |
_| |_
| XXXXXXXXX | <- internal 2" thread
————-
+=====+
XXXXXXX <- external 2" thread
I I
I I
D
I I
XXXXXXX <- external 2" thread
+=====+
internal
+=======+
2" thread -> IXXXXXXXI H J
I I
I +==+ I=I [
I XI +X=+ I
[
E I XI IX I I [
I XI IX I I [
I XI +X=+ I [
I +==+ \ I=I [
internal
I I \ \
2" thread -> IXXXXXXXI \ \—- external 1.25" thread
+=======+ \
\——- internal 1.25" thread
external
2" thread ->
IXXXXXXXI
I I F, G, N
+- -+
\ /
\ /
U
Figure 2
Exploded View of Cannon (large scale)
2.4.1 Barrel Assembly
Using PVC cement, attach A and B. Then attach B and C. Wait for
XX hours for cement to come to
full strength, then screw D into
C.
2.4.2 Combustion Chamber Assembly
Cut a 3 " piece of tubing K. Drill a
clearance hole for this
tubing into copper sheet J. Insert the tubing about 1/2" into
of the tubing is parallel
to and in contact with the copper
sheet. Make sure the bore of the tube is not pinched
closed.
Soft solder the tube to the copper sheet so that hole is sealed.
Cut a
1" piece of tubing L. Slip this piece on the end of the
smaller tube, crimp it with the
pliers (again, make sure the bore
of either tube is not pinched closed), and soft solder it
in
place. This tube should be a press fit into the 1/4" clear vinyl
tubing M.
2.4.2.2 Safety Bushing
Soft solder the assembly of 2.4.2.1 to the end of H
without
external threads. Do this so there are no voids. Trim the edges
of J as close to
the edges of H as possible. Screw H tightly
into the 1.25" port of E; the only passage
for gas into E should
be through the brass tube.
The idea of the safety bushing
is the same as that of a boiler
safety valve; it is designed to be the weakest part of the
cannon
combustion chamber. If for any reason the pressure in the
combustion chamber
rises to a point where it might rupture
explosively, one of two things will happen: the safety
diaphragm
will rupture or the soft solder joint will fail. In either case
combustion
chamber pressure will be safely vented.
2.4.2.3 Screw D tightly into E, then screw the
other end of D
tightly into C.
2.4.3 Igniter Assembly
2.4.3.1
Roughen the inside surface of F and the outside surface
of G with coarse sand paper. Clean the
inside surface of F and G
with acetone. Using high-strength filled epoxy cement, attach G
bushing and the hole in
G are coincident. Allow cement to set
until it reaches full strength. Screw N tightly into G;
the
threads will not match exactly, but it should be possible to
engage enough threads
so that N is secure.
2.4.3.2 Disassemble P, carefully removing the piezo electric
piezo device electrodes;
one is on the bottom and one on the
side. Use high voltage insulation wire if possible. Care
must
be taken in this operation; the electrodes on the piezo device
are made of a
low-temperature alloy, and the plastic body must
not be melted.
Attach the piezo
device firmly to the outside of F in such a way
that it will not interfere with screwing F
into E. The best
technique for doing this is left as an exercise for the builder;
when
the prototype was built acrylic tubing and hot glue was
used.
Soft solder the
ends of the wires to the base and tip of the
spark plug. When the igniter is taken into a dark
room and the
plunger of the piezo device pressed, a spark should appear at the
electrodes of N.
Screw the igniter tightly into E. The cannon is now complete.
A mount or carriage for the cannon is left as an exercise for the
builder.
3.0 THE PROPELLANT GENERATOR
The recommended propellant for the cannon is a mixture
of
hydrogen and oxygen; this can be produced by the electrolytic
dissolution of tap
water. Other mixtures such as oxygen or air
and acetylene could be used but are not
recommended because no
experiments were done with them and cannon safety properties are
unknown if they are used.
A generator for the recommended propellant can be built as
3.1 Bill of materials
A 4 carbon blocks 4.5" x 1" x
0.25" *
B An automobile battery, or:
C A transformer with a 120 VAC primary and a
secondary whose
voltage will produce a DC voltage in the range of 12 - 15
when applied
to D. The secondary should be capable of
supplying 2 amps without undue heating.
D 2 amp
bridge rectifier.
E A plastic bucket of about 4 liter capacity
F A large funnel
whose small end fits inside the neck of a 2
liter soda bottle.
G Several 2 liter soda
bottles
H Several 2 liter soda bottle caps
* - this is the one item that does not
meet the "easily
obtainable" criterion of 1.2 above. The carbon blocks used in
the Model 2.0 prototype generator were obtained from a
metals-and-materials surplus yard.
Large carbon electric motor
brushes probably could be used. A Model 1.0 prototype was built
electrolysis corroded them
very quickly.
3.2 Fabrication Instructions
3.2.1 Electrode Array
Wire the carbon blocks as shown in Figures 3 and 4. Wires can be
attached to the blocks
by drilling holes in them and holding the
stripped ends of the wires in place with 6-32 nuts
and screws.
Coat the parts of the screws protruding aboce the carbon with hot
glue or
epoxy to protect them from corrosion.
Assemble the carbon blocks into the array shown
in Figures 3 and
4; note that the blocks are staggered to provide clearance for
the nuts
and screws. Assembly can be done by using short
sections of tubing E as spacers between
blocks, and holding the
blocks together with rubber bands.
(+)——-+———–+
| | >| |<- - - -0.25"
+-|-+ +—+ +-|-+ +—+ —
| | | | | | | | | | |
| o | | | | o | | | 1.0"
| | |
| | | | | |
| | | | | | | | V
+—+ +—+ +—+ +—+ —
| |
(-)————-+———–+
Electrode Array - Side View
Figure 3
(+)——-+———–+
| | >| |<- - - -0.25"
+-o-+ +-o-+ —
|
| | | ^
| | +—+ | | +—+ |
| | | | | | | |
0.125"- - - ->| |< | | |
| | |
| | | | | | | |
| | | | | | | | |
| | | | | | | |
| | | | | | | |
4.5"
| | | | | | | |
| | | | | | | | |
| | | | | | | |
| | | | | | |
| |
| | | | | | | |
| | | | | | | | |
+—+ | | +—+ | |
| | | | V
+-o-+ +-o-+ —
| |
(-)————-+———–+
Electrode Array - Top
View
Figure 4
3.2.3 Gas Collection
3.2.3.1 Cut a 2" piece of
brass tubing L (see 2.1 above). Drill
a press fit hole for this tubing into the center of one
of the
bottle caps of H. Press the tubing into the hole so that 1.5"
projects from
the top of the hole; secure the tubing in the hole
with hot glue to seal the joint between
tubing and cap.
3.2.3.2 Put the electrode assembly into the bottom of E with F
arranged over it so that any gas bubbles rising from the
electrode assembly will be caught by
F. Fill E with tap water so
that the level is slightly above the top (small end) of F. Fill
neck to prevent leakage,
invert it into the water in E. Maneuver
it so that the neck is under water and over the small
end of F.
3.2.3.3 Electrical Connection
Either the battery B or
the transformer C and rectifier D can be
used as the power source. Connect the (+) and (-)
leads from the
electrode array to the appropriate DC outputs of the power
source.
When the power is applied as shown in Figures 3 and 4 bubbles
should form on the
electrodes, rising through F into the bottle.
14.5 VDC across (-) and (+) should put about 2
A through the
circuit and produce 0.5 to 1 liter of H2, O2 mixture per hour,
using tap
water with a resistance of approximately 15 K ohms. If
water resistance is larger than this,
add a small quantity
(approximately 0.1 gm/liter) of NaOH to the water to increase
conductivity.
The two liter bottle of 3.2.3.2 should fill with the gas mixture
in
2 - 4 hours, displacing the water in the bottle. It may be
necessary to siphon water out of
the bucket to prevent over-flow.
When all the water is out of the bottle, put an
unmodified cap H
on it to retain the gas mixture. Place the bottle vertically for
at
least 1 hour, so the hydrogen will rise to the top. A bottle
of gas should not be stored for
more than about 72 hours; with
time the hydrogen can and will diffuse through the walls of
the
bottle, lowering the power of the propellant.
4.0 LOADING AND FIRING THE
CANNON
It is recommended that eye protection by worn by the operator and
by
observers of the cannon. No open flames or other sources of
ignition should be within 50′ of
the cannon during steps 4.4 to
4.7.
Have a tennis ball and a 24" ram rod
ready (a piece of 1.5"
schedule 40 PVC pipe makes a good ram rod).
4.1 Make
sure the safety bushing of 2.4.2.2 faces away from the
operator and any observers.
spherical wad, and push it into
the muzzle of the cannon to PVC
bushing C. This wad will prevent the gas from dissipating
All people except the
operator firing the cannon should be at
least 20′ from the cannon, on the opposite side from
the safety
bushing of 2.4.2.2.
4.4 Losing as little gas as possible, rapidly
replace the cap H
on the mixture-filled bottle from 3.2.3.3 with the cap of
3.2.3.1.
4.5 Connect the brass tube on the cap of 3.2.3.1 to the brass
tube on the soldered
to the safety diaphragm of 2.4.2.1 with an 8
- 10" length of tubing F. Holding the bottle
vertically with
neck up, squeeze it to force the gas mixture into the cannon.
When as
much as possible of the gas mixture has been squeezed out
of the bottle, remove the bottle and
plastic tube and push the
tennis ball into the muzzle of the cannon. Use the ram rod to
push it down the barrel until it seats against PVC bushing C.
4.6 All the operations of
4.5 must be done without delays or
pauses so that a minimum amount of propellant gas is lost
through
the wad and out the barrel of the cannon.
4.7 Aim the cannon; press the
plunger of the piezo device on the
igniter to fire it.
reply to:
chroma@deeptht.santa-cruz.ca.us <—This is preferable
or !path uunet!sco!deeptht!chroma
<—–This is "oh well"
"Dr. Rock doesn’t advocate drugs, he just
prescribes them!"
.—- From an Old Dr. Demento …thanks Keeper… 
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