the circuit

the motor

video

schematic

This is an extremely preliminary circuit design. A few chips could easily be designed away, and some startup logic would definitely help. It has evolved from an original idea which ended up being not quite right. A redesign of some of the timing components would help.

Circuit Description:

The 555 timer is setup to generate a clock pulse as a voltage controlled oscillator. My original idea was to adjust the control voltage based on the back EMF in order to correct the commutation but in the end the circuit doesn’t function that way. For now I left the timing circuit as is but it would function much better if setup as an astable oscillator instead of a voltage controlled oscillator. Since I’m not actually using the voltage control, pin 5 of the 555 is setup with a neutral voltage (1/2 Vcc) using a pair of 10k resistors.

When setup as a voltage controlled oscillator, the 555 generates spikes instead of a nice square wave with 50% duty cycle. In order to get a good clock pulse with 50% duty cycle, the 555 output is fed into the 4013 D flip flop which is wired to toggle it’s output. In this way the Q output can be used as a 50% duty cycle clock pulse for the rest of the circuit.
I wasn’t sure how many parts of the circuit were going to need a clock pulse but it turns out only the 4017 receives it, which means the 4013 can be eliminated entirely.
The 4017 decade counter is setup to enable 6 lines in sequence which are used to hardwire the 6 step commutation. Each of the six lines are fed through rectifiers so that they are isolated during the commutation sequence. From the rectifiers the commutation is wired to the H-bridge setup with 3 NPN and 3 PNP transistors with free wheeling diodes setup to eat the HV that may come off the motor EMF. Since the PNP transistors need inverted signals, all lines that run to the PNP side are fed through inverters first. I used a single chip hex inverter for the job. Running the clock at this point is enough to make the motor spin, but it has zero torque since any interruption will break the commutation.
From this point the back EMF zero crossing point is read off the motor using 3 op amps, one for each motor wire, which are setup to compare to the neutral motor wire. Since HV may come of the motor, a resistor stack built using 75k resistors is used to isolate the signal going to the op amps.
When the motor is running, only two wires are ever energized, leaving the third for back EMF detection. The output of the three op amps is fed to the 4066 (4 channel analog switch) which is wired as a multiplexer to enable the motor wire EMF which is not energized. The switching is done by wiring the enable lines to the appropriate output of the 4017.
At this point the output of the 4066 shows the zero crossing point of the back EMF of the motor. This zero crossing point is in turn fed to 1/4 of an LM339 comparator which is compared to a reference voltage (determined by scoping the back EMF). The output of the comparator is now an on/off tick of when the zero crossing point happens. This output is fed into an NPN transistor to invert the signal which is then used to hold the reset line of the 555 timer. This causes the clock tick to adjust based on the back emf detection, giving the motor torque.

A *lot* of improvements could be made. Mosfets would help for power output. The clock circuit is garbage. A PIC microcontroller would eliminate a lot of the complexity. Still, I wanted to put this out there so others could see it.

Before starting this project this room was empty. It’s taken a long time to start from nothing.

A spool of 21AWG high temp magnet wire:

Winding the coils after they’ve been cut:

Some wound coils:

A prototype ring:

Copper stand offs:

Going for the dodec:

DO-DECA-FAIL-DRON Wiring it together will NOT work. It must be welded. Additionally, the way I wound the coils almost guarantees a short, as attempting to powerup the prototype proved.

Try again, this time for the cube shape, brazed together:

FAIL. Straight propane is simply not hot enough to melt the bronze brazing rods. There were mixed posts on the internet on whether it would work, so now I now for sure.

This is what you need, oxygen + rocket fuel:

My fireplace setup to do some torch welding:

A welded/brazed half ring:

OH NOES! TOO HOT

Needs some more love and cleaning up:

Things are starting to take shape:

Out of oxygen I tried to keep going but it just blew burnt fuel all over everything:

Why a polywell?  Because they are new (to me),  awesome, and because all the other amateur/hobbyists seem to be doing are fusors and tesla coils.  I wanted to create something different, and if Dr Bussard could make one “in the garage on a shoestring budget” then it seems anybody could if so motivated.  The device is relatively simple, barring vacuum chambers and high voltage requirements.  It should be possible to build one.

Constructing the hardware will take some time as the vast majority of my experience is in software.   I’m knowledgeable but inexperienced in working with hardware, electronics, and metal work.

Here is my first attempt at a ring.

As you can see, it’s not so good.  I cut the length exact, but then the ends were impossible to bend. Here is a later attempt:

Using a hammer definitely isn’t the way to go. I hammered it round, but I hammered it to a dented worthless death.

You need to use a tubing bender:

Using a tubing bender, you can bend the entire length of tubing into a giant spiral/spring shape, then cut along the length, cutting all rings at once, and bend the slight bit of warp out of it once they are cut. It’s much easier to get the warp out than trying to bend the very ends into a circle.