Mechanical PWM Timed via Rotary Moment

[evolvingape]

I have been thinking about the possibilities for Mechanical PWM using slip rings and I came up with this:

The first image shows a slip ring with 4 conducting surfaces and 4 insulating surfaces. Each of the 8 segments would occupy 45 degrees. The shaft is in the center (White). Around the shaft is an insulating tube (Green) that the slip ring is mounted on. There are 4 slide fit holes to transmit and 4 oversized holes to isolate all with center bore on the same radius.

Two of these rings mounted 45 degrees out of phase to each other would allow DC+ and DC- output to the brushes with a pulse of 50% Duty Cycle every 90 degrees. Effectively multiplying our rotational frequency by 4.

The second image shows a Trapezoid that would be a perfect shape to have the plastic surface insulators laser cut. The Phosphor Bronze PB2 slip rings would have to be designed to accept them as an interference fit. (It was too difficult to draw a Trapezoid on the slip ring hence this note).

The third image shows a PWM Slip Ring Air Cooled Assembly. The entire assembly is mounted in compression for stability with the drive being transmitted via the hub and taper bush.

A Tesla Pump has been sandwiched between the end hub and the slip rings at each end. Air is sucked in through a passive intake in the centre and expelled at 90 degrees to the shaft by the pump. The PB2 is acting as both the conductor of electricity and heat.

Once assembled the assembly needs mounting in a lathe and turned to a true surface for the brushes to run on. As there are two different materials at the surface they will wear at different rates and the entire assembly may need to be trued up on the lathe from time to time. How long a period before this will need doing, if at all, I do not know.

A potential plastic for use as an insulating surface could be Celazole PBI:

http://www.theplasticshop.co.uk/celazole-pbi-2260-0.html

It seems to have a good balance of properties for what we require. See what you think ?

The PWM slip rings can either be mounted straight to the secondary shaft of the HELP/HELT or they can be used in the air cooled assembly.

The air cooled assembly is for PWM of Solid State Dry Cell Resistors such as used in the FESA. With the 90 degree pulse rings mounted 45 degrees out of phase to each other the Dry Cell will be pulsed 180 degrees out of phase at a frequency of 4 Hz per 60 RPM.

So what do you all think ? A viable idea ?

[CompuTutor]

The second image shows a Trapezoid that would be a perfect shape...

I get what your postulating,
but perhaps there is an easier way.

Make a mold the cone shape Desired,
line it with pre-cut copper triangles,
steady a center shaft in the mold,
pour full of two part epoxy,
polish finshed item in a drill.

Would work for prototype's
to try variations to ideas.

Also,
have you considered the standard
centrifugal RPM governor design ?

It may lend an easier ways to approach
to the sensing and responding aspect of this.

[evolvingape]

Hi CompuTutor,

Thankyou for your input.

I did not mention in the thread but the point of the Trapezoid was that the base was wider than the top so that when epoxy glued and tapped in with a mallet and compressed in the stack it would be impossible for the insulator to "fly out" under centrifugal force when spinning. I am sure you understand that but this note is for those wondering what we are talking about.

No I have not considered the standard centrifugal RPM governor design, could you please elaborate on how we could build a device like that and what the advantages in sensing and responding would be ?

As people have probably noticed the designs for mechanical PWM i have posted are very similar to my designs for my turbines. After so many years of thinking about my turbines with out of phase discs I find it very difficult now to think about anything else as a solution to similar problems.

The PWM of the Dry Cell is an "add on" that was not considered until recently by me. I actually never thought of it until a few weeks ago when I finished releasing all my work.

I should also point out that if anyone does want to go the route of the design I have put up make sure you carefully think about where all the phase holes in every component are going to be. The airflow holes and the Hub support holes are not for example on the slip ring diagram. Build a prototype out of thick cardboard and use a pencil to push through and check the alignment of every hole is the easiest way.

A DC Motor with a potentiometer and laser tachometer (for speed readings) will tell you the RPM and you can calculate the Frequency from that. The Dry Cell power source from a Battery. This will help in the prototyping and finding the best design for the cell you are using.

Any thoughts and suggestions welcome