Before Tesla devised beautifully simple rotary machinery, he explored other methods of generating alternating current. One of those was the mechanical oscillator, and [Integza] had a go at replicating the device himself. (Video, embedded below the break.)
Initial attempts to reproduce the technology using 3D-printed parts were a failure. The round cylinder had issues sealing, and using O-ring seals introduced too much friction to allow the device to oscillate properly. A redesign that used external valving and a square cylinder proved more successful.
Once the oscillator was complete, the output shaft was fitted with magnets and a coil to generate electricity. After generating a disappointing 0.14 volts, [Integza] went back and had a look at the Maxwell-Faraday equations. Using this to guide the design, a new coil was produced with more turns, and the magnetic flux was maximised. With this done, the setup could generate seven volts, enough to light several LEDs.
While it’s not a particularly efficient generator, it’s a great proof-of-concept. Yes, Tesla’s invention worked, but it’s easy to see why he moved on to rotary designs when it came to real-world applications. We’ve seen [Integza] take on other builds too, like the ever-popular Tesla turbine.
Connect it to a steel beam and very slowly vary the oscillation frequency. Profit once the building starts to shake :)
A building I worked in had the steel beams magnetized by a lightning strike.
It caused distortion in CRT monitors placed near them.
Fascinating! I would have never thought of that as a possibility, though it makes perfect sense considering the huge currents that lightning can carry. Must have been one heck of a hit!
I was a tech in charge of moving into lab space once occupied by large NMR magnets (physics research, not medical). Got things set up and the CRTs degaussed no problems. Then a grad student shifted his monitor slightly- pretty colors! I punched the degauss button and the screen returned to normal. Turns out the rebar in that area of the floor had been magnetized to a significant degree… I switched out the CRT’s for LCD displays shortly after.
There are antique mechanical alternators that generate a high enough frequency to be used as a source for LF radio. I believe that HackaDay has had at least one article about one of them that is still in working order (but only used on special occasions).
Yep, here it is: https://hackaday.com/2016/06/26/get-set-for-saq-on-alexanderson-day-with-these-active-antennas/
Back in the days of tube radios in cars, there used to be devices that used mechanically oscillating metal fingers and an array of coils to generate high voltages for the tubes from the 12V battery supply. They didn’t generate much current, but it was enough to make a radio work.
In low power applications they were apparently cheaper than the motor-generator alternatives. IIRC they were called vibratons or something similar, and looked like an olde-style metal capacitor can.
https://en.wikipedia.org/wiki/Vibrator_(electronic)
Yup, I’ve seen those before. Interesting tech.
I also used to have a mechanical oscillator made by Hewlett-Packard back in the days when they made the very best test equipment on the market. It resembled a metal can, slightly smaller than a 12 ounce soda can, but with an electrical connector on one side. Not sure who I ended up giving/selling it to, as that was a few years ago.
The shaking-building background story in the video reminded me of my dorm prank — I noticed that every room in the building was identical in size, and it was easy to estimate the acoustic resonant frequency of them.
At the time I had, let’s say, non trivial woofers and a decent amplifier, so I borrowed a wavetek signal generator from a lab one evening to see if I could excite that resonance (something like 15 Hz). It turned out to be reasonably high Q, and was pretty dramatic when you hit the right frequency.
So, naturally, I cranked it to 11. The whole building of a hundred identically resonant rooms ended up singing in sympathy, but nobody could figure out where the humming was coming from.
It was annoying as fsck, so I quit after a couple of minutes, but it was a pretty neat demo. Too bad most of the rest of the building were psychology or english or other artsie types and didn’t appreciate the science in it.
I used to work in transportation simulation, using what amounted to hydraulic woofers (electrohydraulic cylinders) with a 600 hp hydraulic pump for that extra “oomf”, all sitting on a giant seismic mass – a huge cube of concrete set into the ground. It’s intended purpose was to simulate road conditions under whole truck mockups etc.
And “oomf” it did – we could make the bathroom fixtures shake anywhere in the building and it was long enough ago that some of the system could run on analog tapes. Led Zepplin never sounded so good…at least up to about 100 Hz or so…all on our own time, of course.
Instead of cobbling up a crazy new valve, why didn’t he just put more mass on the reciprocating shaft, and stick some return springs on there? Ol’ NT got the mass for free bcs materials, and the spring air piston was probably chosen over plain old coil springs for durability reasons, but the mass and the spring essentially give you your ‘tank circuit’. To be a good oscillator, you need high Q, so you need mass and spring enough to dominate the friction. afaict, video guy hasn’t got a resonator so much as he has an astable multivibrator. I.e. whereas NT got sine waves, video guy gets triangle waves. What he did with the new valve is more akin to how you make an oscillator from a 555 – push one way then the other then repeat.
I’ve got to wonder given I can’t find the data anywhere, what would the efficiency of one built to tesla’s exact design be? would it be close to that of a steam turbine, >90%?