Tesla's earthquake machine - was it just a practical joke? Answered
Nicola tesla, in his early years, was not shy when it came to use science through direct contact.
Most of it we would call today playing practical jokes on students and friends alike.
His harmonic balancer got the nick name earthquake machine.
I won't go into the story how all came together, you can read the story on Wikipedia or other sites to the fullest of your imagination.
Howver, I would like to go into some details of this invention.
Or better: I will try to explain my view on why this machine might have actually worked close to what the story tells....
Studying old paents and other documents is no fun and not always you can reach any valid conclusions from any of it.
I mean, if you coud then you wouldn't need a patent for it.
Some things however are so good, so special that they never get a patent, the company keeps it as an iternal secret.
Same way a brewery won't tell you the exact recipe for the beer they make ;)
The harmonic balancer has very little to go with except stories and some comments Tesla scattered here and there.
So let's start by some claims Tesla made about this machine:
1. It has a free swinging mass.
2. The mass is balanced using "air springs".
3. It usues very little energy.
4. It finds the harmonic frequency of the object attached to automatically.
If you think about the above you could say right away it is bogus.
But think about the terms and language of the old days ;)
Add the fact that Tesla never really gave any direct answers to how his inventions actually work and you see where I am going here.
Point 1 and 3 are easy to imagine in many ways.
Number 2 on the other hand contradicts itself at a first glance.
But, if you place a piston with a good mass and good seal into a cylinder nd close both ends while the piston is in the center....
A bit like these to shake emergency torches and flashlights.
With that idea in the back of a head one can imagine shock absorbers and more.
And a "mass" "swinging" in such a sealed tube would certainly be subject to the "spring" force of the air being compressed in front and the forming low pressure on the other end.
The last one however had me stumped for almost two years with me getting nowhere.
A mechanical system can't adjust itself to the harmonic frequency of anything....
Then I saw a collection of funny videos.
One of the clips had about 100 metronomes standing on a board.
The board was place on two rollers so it cold move freely from side to side.
All the metronomes wre set to about the same timing.
But of course you just can't start them all at once or even so they swing in sync.
After just a short while though, one by one found a matching partner on the board.
Faster ones slowed down, ones totally out of sync seemed to miss a beat here and there.
And then it hit me!
Hundret swinging masses on a board and the board moves together with them!
Once all were in sync and harmony the board moved basically exactly the same way sidewas as the single pendulums above.
Number four finally solved :)
How though could one try to replicate this impossible invention these days and without knowing any exact details anyway?
We know it used one or two electromagnets.
These moved the mass back and forth horizontally in the machine.
However, it was more formed like a T wih a fat base.
Tesla needed a dead simple way of doing with electricity what the metronome does just mechanically.
If you have a little mass on a spring and one contact on the spring plus another on a tube that is around the mass - what do you get?
No, not the trigger for something really nasty when you pick it up...
Right! You get a motion detecting switch.
A bit like our gyroscopic sensors do now in our phones....
And if you cut the tube lenghtwise you end with two opposing contact to switch two magnets on depending on what side of the tube is hit by the mass (contact) swining on the spring.
Try it out with a spring from old pen and a screw inside as a weight - quite sensitive if you get the weight right.
Some drawing suggest he height was about the same as the width of the machine.
This would suggest the contact was actually hanging upside down, so it could swing in the wider base.
A bit of fine and very flexible opper braid with a weight would make a nice pendulum here....
Do a little experiment first though ;)
Make a sturdy frame or if you have none try a truck. ;)
If you place the frame on wheels and a pendulum with just a string and some sinker at the end - what would happen if you move th frame sideways instead of swinging the weight?
Inertia keeps the weight in place while the top mount of the string moves away.
And if the weight stays in place for just a fraction of a second before starting to move with the frame?
Correct! since the angle of the string changes, the ball appeas to move up.
Not really by much but enough for an electrical contact to open....
We have some ideas now on how those electromagnets might have been triggered by Tesla, what about the mechanics of the moving mass that claimed to have created earthquake like results?
Precision is no problem these days, just check these toy kits to build your own Stirling engine or you trusty old Swiss Army Knife.
And even a second hand air cyclinder and piston can be modded to act like a free swinging air pump.
Only question that really remains would be how to match the mechanical system with the electircal?
We have two seemingly independent masses, one to make things move violently, the other to energise the part that make the first mass move - or to be precise to give it a tiny push in the right direction.
What does mean you wonder...
Let me try to simplify it down a bit.....
If you push someone on a swing you can have a very hard time by working against the mass of the person sitting and enjoying the ride.
Or you could give the person just a tiny push - right when the swing starts from the highest point to go back.
Could that mean it is really as simple to build as Tesla claimed?
If the top mass is limited by how far it can swing FREELY before the air pressure works against this movement then we would only have to set the length of the pendulum so the contact happens right at that point on the x-axis of the top mass.
Ok, and how would that make anything swing at all?
If the top mass is first energised there is nothing to stop or influence the movement, except the "air springs".
So it totally overshoots like those metronomes on the board.
It swings back and closes the contact on the other side of the movement way early as well.
Now the electromagnetic impulse from the second movement actually works against the moving top mass.
And this swinging of total non-control continues while whatever the thing is mounted to also starts to move, even if it is just fractional.
Over time both swings, from the machine and the object, will get to point where they influence each other in a "positive" way.
For Tesla's experiment one would say negative though as it was quite violent in the end.
Little by little both swing will get closer to being in sync and with that in resonance.
The electromagnetic push however continues....
Only that now the top mass of the machine is in sync with the thing it is mounted to.
The machine became you standing behind a big swing and trying push someone higher and higher....
It is all just a theory though and any minor earthquakes that might register around my area are pure coincidence ;)