Self accelerating reed switch magnet spinner.

[synchro1]

@TK,


       Sheer genius! That could mount on the top of a Coanda lift body and fly around like a new spy drone.

[TinselKoala]

Actually I think we have just about invented the brushless DC "outrunner" motor and its op-amp pwm controller.

[MileHigh]

It looks like a 3-wire interface to the coil array.  Two power signal wires and a fat common ground return wire.  A few basic tests with a D-cell and a compass/small magnet and you could figure out what energizes what and with what polarity.  It would be a fun project to make a motor controller for that.  An Arduino software project or go analog.  The design of the timing circuit opens up a lot of possibilities.

I think of the power booster circuit for the driver.  If you make a voltage servo amplifier like the power booster in theory there is no need for any recirculating diodes or back-EMF collection system.  The power booster circuit would literally suck up any kick-back from the coils.

In my mind it would be fun to go in "blind" without knowing what the real controller does.  You can see how the motor could be made to act like a sort-of stepper motor at low speeds.  But with sophisticated electronics, could you make it turn smoothly at low speed?  What about torque?  Only the mad scientist knows.

P.S.:  I just noticed that the circuit is AC-coupled.  There must also be a DC-coupled version of a power booster.

[synchro1]

@TK,


       Bust your old VCR open and you should find an "Outrunner" motor just like that one already attached to the bottom of the bearing! I tried to wire mine "Imhotep" style, but failed to get it to work. I think you and Milehigh may be re-inventing the wheel!

[TinselKoala]

I haven't yet looked at the motor in a VCR head.

The brushless outrunner and other brushless DC motors that use three wires: all three wires are "equal". They can be hooked to the controller's 3 wire output arbitrarily. If the motor turns in the wrong direction, any two of the wires can be reversed and then the motor will turn in the other direction.

Here's some info from a very complete app note that describes just about everything you need to know about these brushless DC motors and their drive circuits.

Sensorless Motor Control
It is possible to determine when to commutate the
motor drive voltages by sensing the back EMF voltage
on an undriven motor terminal during one of the drive
phases. The obvious cost advantage of sensorless
control is the elimination of the Hall position sensors.
There are several disadvantages to sensorless control:
• The motor must be moving at a minimum rate to
generate sufficient back EMF to be sensed
• Abrupt changes to the motor load can cause the
BEMF drive loop to go out of lock
• The BEMF voltage can be measured only when
the motor speed is within a limited range of the
ideal commutation rate for the applied voltage
• Commutation at rates faster than the ideal rate
will result in a discontinuous motor response
If low cost is a primary concern and low speed motor
operation is not a requirement and the motor load is not
expected to change rapidly then sensorless control
may be the better choice for your application.

So for the sensorless system, the motor is driven by energizing the phases cyclicly, and using the non-energised phase's BEMF as the "sensor" to tell the controller what's up.

This is a long but very interesting document (48 pages). I recommend it for anyone working with brushless motors. There are schematics and program code for both sensored and sensorless drivers.