I will have to give credit to Dr. Tesla for the design of the oscillator. I will however submit a crude representation of his his work. Keep in mind the diagram is not to scale, the actual piston in the oscillator moved a distance of [ 1/ " up to 3/8"]. You may notice the lower part of the fraction under the one is missing. I have not seen a book with the actual number printed so this is somewhat of a mystery to be solved. It could be as little as 1/ 1000 and the printer could not print the number.
One of the major features of the oscillator is that it could move massive weights (coils) with little energy input. This was due to the small movement of the piston combined with the spring effect produced by the piston slamming into a closed chamber. The air inside the chamber compressed and acted as a spring, forcing the piston to travel the opposite direction. At the same time this occurs the slot on the piston aligns with the inlet to allow high pressure working to propel the piston like a rocket toward the other end where it once again slams into an "air spring".
The diagram does not show the electromagnetic coil system that also controls the frequency of the piston. I will submit an additional diagram soon as I can.
Two electromagnets positioned on either side of the shaft. In the drawing the coils appear to be about one foot in diameter. The shaft has two coil pairs attached to either end which are on either side of the electromagnet fields when the shaft is at rest. When the shaft is given a slight tap, the coils are forced into the electromagnetic field. When one coil enters the field, it energizes a coil on the opposite side of the shaft producing an oscillation in the coils, somewhat similar to the oscillation produced in (oddly enough) a Tesla coil. Also similar to the Tesla coil, a capacitor arrangement is mentioned that provides electricity for the field coils.
Here is an actual picture of the electro-mechanical oscillator. Note the size of the field magnets. They were constructed of numerous flat sheets of iron. Using flat sheets of iron, as opposed to a single piece of iron, increases the magnetic field. Recent research with permanent magnets and permanent magnet, electromagnetic combinations could greatly increase the work done by the oscillator. In Dr. Tesla's machine, current is provided for the field coils by the generator. By using a permanent or combination magnet arrangement current for the field coils could be reduced, resulting in a greater output.
Motion of the piston was controlled in three different methods. Connecting the coil pairs on either end of the shaft, forces the coil on the opposite end into the field when it is at full charge, resulting in the coil being repelled from the field at the same speed it enters the field. The motion of the shaft is also reversed mechanically by both the air spring and pressure from the working fluid. Either steam or air can be used to drive the piston. If steam is used, a vacuum is created when the steam enters the jacket and condenses. The vacuum created at the outlet pulls the piston in addition to the steam push on the other end. The most important part of the picture cannot be illustrated but can demonstrated. The resonant frequency of the machine could be adjusted to match the resonant frequency of any object.
Dr. Tesla was able to match the resonant frequency of objects in the room by adjusting either the electrical or mechanical movement of the piston. He was able to identify different objects in a circuit by matching their resonant frequency. The mechanical oscillator had to be mounted on wooden blocks to help damp vibration. Dr. Tesla also showed parts of a steel arbor that had been torn apart with one of his oscillators.