In a message dated 23/07/2005, dcrice@............ writes:

Doug  Crice          http://www.geostuff.com

To  remind folks of the specifications, I would like to repeat and expand  
them.

1) A person ought to be able to carry it  around.
    Lets widen this out a bit to say three people max,  each carrying 
component parts? 210 lbs? 

2) It  needs reasonably high frequency output (ping instead of  thunk)
    This implies that the impact velocity needs to be  high.

3) Build  it for $1000-$2000 (cost, not sales price) in lots of 10 units,
using  commercially available and machined parts and normal labour  rates.
    Sure costs need to be considered, but mass  production does not 
necessarily mean producing high volumes at any one time,  just the ability to produce 
the article rapidly with a very low batch start up  cost and low overheads. 

4) It  should be safe, even when used by students
    We used to define three degrees of 'proof' for the  undergraduate 
laboratories. Fool proof, idiot proof and student proof. If you  insist on student 
proof, you won't even have a pedal cycle, never mind a car....  The power of an 
inquisitive mind to thoroughly louse things up must not be  underestimated.

5) There  should be no significant regulatory issues (a problem with 
dynamite, the  perfect source)
    What sort of charges / energy output is involved  here? What do we 
actually need for the surveying operations were are  considering? Does the source 
have to be generated deep underground? 
    We need to design machines for the  jobs, NOT a universal machine. 

6)  Operating supplies available in third world countries.
    And in the developed world.

7) It  needs to work better than a sledgehammer used with a seismograph that
can  stack multiple impacts.
    We could also try designing a better / different  type of sledge hammer / 
impactor?

8)  Because the source will probably be used in a repetitive fashion, it
needs  a reasonably fast cycle time (many seconds, not many  minutes).
    We need to be careful here. If we specify too  rapid a pulse rate, or too 
high an energy per pulse, we will automatically  be specifying very powerful 
and expensive equipment.

9) The  seismic signature should approximate a zero phase wavelet, which as  a
practical matter; means the energy prior to impact should be  comparatively
modest.
10) Good ground coupling is needed. In the case of  a sledgehammer, a metal
plate is placed on the ground as a target. In the  in-hole shotgun, a hole is
augured just big enough to hold the device below  the soft topsoil and
preferably watered.
    Is there any published work on the optimal shapes  of ground coupling 
plates, flat or conical, resonant modes, mass etc?

The  crossbow idea is equivalent to the "elastic wave generator", powered by
the  large rubber band. Existing units weigh a couple of hundred pounds,  but
it's got me thinking about a portable version.
    The reason that I suggested some sort of metal  spring, is that the 
properties of most elastomers are very time dependant. The  properties of metal 
springs are not, apart from the physical mass / inertia of  the spring. The 
cross-bow form allows you to continuously accelerate the  projectile to a high 
velocity, without giving it a shock impulse. There are  other mechanical linkages 
/ principles which could be used. The larger  Roman ballistas used to fire a 
bolt over about 500 m max.

The  variations on exploding bottles don't seem to meet the requirements for  
reasonably safe operation.
    Lets not rule out the principle. I am thinking  of an analogy with a 
petrol driven rock drill, which has a linear piston  striking an anvil. That is 
optimised for rapidly repeating blows. Here we need  to redesign it for optimum 
performance with either a single stroke, or at most  two strokes in a 
sequence. Maybe we could power it with bottled gas?

An  earlier variation was the "vacuum assisted weight drop". It had a 6 ft  (2
meter) long tube about 6 inches (15 cm) in diameter with a 100 pound  steel
bullet inside. The bullet was pushed up with air pressure, then  evacuated.
When the tube was full of vacuum, it was released and  accelerated by its
weight and by atmospheric air pressure. At the bottom  was a 100 pound anvil
and plate combination pressed on the ground by the  weight of the whole
mechanism. With equal weights for the piston and anvil,  it didn't bounce
(think of that ball bearing toy). The VAWD worked  reasonably well, but
weighed 1000 pounds and cost over $10K 20 years ago.  Using air pressure as
the accelerant provided a nice signature, since the  force was external to
the system, though when you released the piston, it  instantly lost 100
pounds of weight, providing the equivalent of a negative  sledgehammer blow.
     If it is 6" dia, the force from air pressure  will be 3^2xPix14.7 lbs = 
416 lbs.
 
    Maybe they should have concentrated on the energy  available from the air 
pressure and increased the impact velocity? 
 
    It is possible to crank this force with a 10:1  chain winch. Maybe a 
hydraulic system? Anything much greater or several cycles  per minute and you need 
an engine / power source to do it. 1 man gives  about 0.1 HP, continuous 
exercise. There is an alternative operating mode, in  which you extend the plunger 
/ piston or whatever and then pump out the air  from behind it?
 
    The long tube design does give a high power  stroke, but a relatively low 
final velocity. It would be difficult to use the  tube design for very high 
velocities, but it could be developed considerably  from a 100 lb mass + a 400 
lb air push ---> 44 ft / sec. 
 
    Maybe one of these somewhat random ideas can  developed, or will generate 
other ideas?
 
    Regards,
 
    Chris Chapman








In a message dated 23/07/2005, dcrice@............ writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Doug=20
  Crice          http://www.geostuff.com

To=20
  remind folks of the specifications, I would like to repeat and expand=20
  them.

1) A person ought to be able to carry it=20
around.
    Lets widen this out a bit to say three people m=
ax,=20
each carrying component parts? 210 lbs? 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>2) It=20
  needs reasonably high frequency output (ping instead of=20
thunk)
    This implies that the impact velocity needs to=20=
be=20
high.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>3) Build=20
  it for $1000-$2000 (cost, not sales price) in lots of 10 units,
using=20
  commercially available and machined parts and normal labour=20
rates.
    Sure costs need to be considered, but mass=20
production does not necessarily mean producing high volumes at any one time,=
=20
just the ability to produce the article rapidly with a very low batch start=20=
up=20
cost and low overheads. 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>4) It=20
  should be safe, even when used by students
    We used to define three degrees of 'proof' for=20=
the=20
undergraduate laboratories. Fool proof, idiot proof and student proof. If yo=
u=20
insist on student proof, you won't even have a pedal cycle, never mind a car=
.....=20
The power of an inquisitive mind to thoroughly louse things up must not be=20
underestimated.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>5) There=20
  should be no significant regulatory issues (a problem with dynamite, the=20
  perfect source)
    What sort of charges / energy output is involve=
d=20
here? What do we actually need for the surveying operations were are=20
considering? Does the source have to be generated deep underground? 
    We need to design machines for the=20
jobs, NOT a universal machine. 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>6)=20
  Operating supplies available in third world countries.
    And in the developed world.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>7) It=20
  needs to work better than a sledgehammer used with a seismograph that
c=
an=20
  stack multiple impacts.
    We could also try designing a better / differen=
t=20
type of sledge hammer / impactor?
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>8)=20
  Because the source will probably be used in a repetitive fashion, it
ne=
eds=20
  a reasonably fast cycle time (many seconds, not many=20
minutes).
    We need to be careful here. If we specify =
too=20
rapid a pulse rate, or too high an energy per pulse, we will automatica=
lly=20
be specifying very powerful and expensive equipment.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>9) The=20
  seismic signature should approximate a zero phase wavelet, which as=20
  a
practical matter; means the energy prior to impact should be=20
  comparatively
modest.
10) Good ground coupling is needed. In the cas=
e of=20
  a sledgehammer, a metal
plate is placed on the ground as a target. In t=
he=20
  in-hole shotgun, a hole is
augured just big enough to hold the device b=
elow=20
  the soft topsoil and
preferably watered.
    Is there any published work on the optimal shap=
es=20
of ground coupling plates, flat or conical, resonant modes, mass etc?
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>The=20
  crossbow idea is equivalent to the "elastic wave generator", powered bythe=20
  large rubber band. Existing units weigh a couple of hundred pounds,=20
  but
it's got me thinking about a portable version.
    The reason that I suggested some sort of metal=20
spring, is that the properties of most elastomers are very time dependant. T=
he=20
properties of metal springs are not, apart from the physical mass / inertia=20=
of=20
the spring. The cross-bow form allows you to continuously accelerate the=20
projectile to a high velocity, without giving it a shock impulse. There are=20
other mechanical linkages / principles which could be used. The larger=20
Roman ballistas used to fire a bolt over about 500 m max.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>The=20
  variations on exploding bottles don't seem to meet the requirements for=20
  reasonably safe operation.
    Lets not rule out the principle. I am thin=
king=20
of an analogy with a petrol driven rock drill, which has a linear piston=20
striking an anvil. That is optimised for rapidly repeating blows. Here we ne=
ed=20
to redesign it for optimum performance with either a single stroke, or at mo=
st=20
two strokes in a sequence. Maybe we could power it with bottled gas?
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>An=20
  earlier variation was the "vacuum assisted weight drop". It had a 6 ft=20
  (2
meter) long tube about 6 inches (15 cm) in diameter with a 100 pound=
=20
  steel
bullet inside. The bullet was pushed up with air pressure, then=20
  evacuated.
When the tube was full of vacuum, it was released and=20
  accelerated by its
weight and by atmospheric air pressure. At the botto=
m=20
  was a 100 pound anvil
and plate combination pressed on the ground by th=
e=20
  weight of the whole
mechanism. With equal weights for the piston and an=
vil,=20
  it didn't bounce
(think of that ball bearing toy). The VAWD worked=20
  reasonably well, but
weighed 1000 pounds and cost over $10K 20 years ag=
o.=20
  Using air pressure as
the accelerant provided a nice signature, since t=
he=20
  force was external to
the system, though when you released the piston,=20=
it=20
  instantly lost 100
pounds of weight, providing the equivalent of a nega=
tive=20
  sledgehammer blow.
     If it is 6" dia, the force from air press=
ure=20
will be 3^2xPix14.7 lbs =3D 416 lbs.
 
    Maybe they should have concentrated on the ener=
gy=20
available from the air pressure and increased the impact velocity? 
 
    It is possible to crank this force with a 1=
0:1=20
chain winch. Maybe a hydraulic system? Anything much greater or several cycl=
es=20
per minute and you need an engine / power source to do it. 1 man gives=20
about 0.1 HP, continuous exercise. There is an alternative operating mode, i=
n=20
which you extend the plunger / piston or whatever and then pump out the=
 air=20
from behind it?
 
    The long tube design does give a high power=
=20
stroke, but a relatively low final velocity. It would be difficult to use th=
e=20
tube design for very high velocities, but it could be developed considerably=
=20
from a 100 lb mass + a 400 lb air push ---> 44 ft / sec. 

 
    Maybe one of these somewhat random ideas can=20
developed, or will generate other ideas?
 
    Regards,
 
    Chris Chapman