In a message dated 2006/12/04, tchannel@.............. writes:

> What might be interesting, is to come up with a homemade "thumper" although 
> I have no idea how.  If I had one I would work my way around my house 
> thumping away and creating a map and corresponding signals.  I know they rent soil 
> compactors but I am not sure that would carry any distance.  I would guess it 
> would need to be something of considerable weight.  Has anyone done this on 
> a homemade scale?

Hi Ted,

       You can buy 12 V DC solenoid actuators which have a spring return. You 
can drive these unloaded or loaded, either from a switched DC source, or if 
you need more thump, from a high voltage capacitor. Beware of the huge 
transient voltages that  you can get on switching a high current solenoid. Check the 
max allowable capacitor current, maybe use several of lower capacity connected 
in parallel? You must not put a reverse voltage on a polarised electrolytic. 
       It may be an advantage to incorporate the solenoid into a SCR switched 
bridge circuit, so that energy stored in the solenoid is subsequently 
returned to the capacitor. 
       You have to mount these on a strong baseplate firmly attached to a 
building structure, or to the Earth. These may work at over 50 yard ranges.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/12/04, tchannel@.............. writes:



What might be interesting, is t=
o come up with a homemade "thumper" although I have no idea how.  If I=20=
had one I would work my way around my house thumping away and creating a map=
 and corresponding signals.  I know they rent soil compactors but I am=20=
not sure that would carry any distance.  I would guess it would need to=
 be something of considerable weight.  Has anyone done this on a homema=
de scale?




Hi Ted,



       You can buy 12 V DC solenoid actuators=20=
which have a spring return. You can drive these unloaded or loaded, either f=
rom a switched DC source, or if you need more thump, from a high voltage cap=
acitor. Beware of the huge transient voltages that  you can get on swit=
ching a high current solenoid. Check the max allowable capacitor current, ma=
ybe use several of lower capacity connected in parallel? You must not put a=20=
reverse voltage on a polarised electrolytic. 

       It may be an advantage to incorporate t=
he solenoid into a SCR switched bridge circuit, so that energy stored in the=
 solenoid is subsequently returned to the capacitor. 

       You have to mount these on a strong bas=
eplate firmly attached to a building structure, or to the Earth. These may w=
ork at over 50 yard ranges.



       Regards,



       Chris Chapman