1904

1904.html

DESIGN: Electrotor-SloMo - Motor - Axial Flux - Overview - Homopolar Motor for Coaxial (phaseless)

Objective:

To evaluate the viability of a phaseless BLDC motor with counter-rotating rotors for a MicroLite Coaxial helicopter.:

Drawing:

The large diameter thin bearing is to be replaced by 'Gap - CW Rotor to CCW Rotor', illustrated below.

The central gimbal is to be elevated so as to be closer to the vertical center of the rotors.

Perceived Advantages:

All wires are active, unlike phased motors where one coil is always off.

However, a multiphase motor will have a higher percentage of active coils than a 3-phase motor.

Picture:

Perhaps Relevant Note:

ForAFPT machines with slotless windings the air gap is much larger and equal to the mechanical clearance plus the thickness of all the non-magnetic materials (winding, insulation, potting, supporting structure) that is passed by the main magnetic flux Since there are no slots, Carter coefficient k_C = 1. [Source ~ AFPM p.9]

Specifications:

Prototype in the Above Pictures:

The windings consist of 3 segments of 120º each. For parallel or serial connection. For redundancy.

Wire 19 AWG. ~ 0.0359 " dia. ~ Resistance mΩ/m or Ω/km @ 105Ί = 35.1 Ω ~ Maximum amps for chassis wiring = 19

Actual turns per 120º + 46 * 2 = 92. For first. Second and third may be 90 to 92. Does this mean that the voltage will be 3 * 90 = 270 V if the 3 windings were wired in series?

Measured resistances: (1) = 0.4Ω, (200 = 0.4Ω, (3) = xx.

Calculator: http://www.ifigure.com/engineer/electric/electric.htm

Power Source: From homemade ASC computer:

+12.19 Volts ~ Black to VΩ, ~ Yellow to common ~ Black to 10A ~ 0.72 Amps

+5.13 Volts ~ White to VΩ, Black to common ~ White to 10 A ~ 2.06 Amps

+17.33 Volts ~ White to VΩ, Yellow to common ~ White 10A - ~ 0.12 Amps

Assembly:

Stator:

Flux and Ball Bearing:

Will passing flux through a ball bearing result in excessive heat, or other problem?

Segment the stator ring for;

Ease of winding of wire.
Redundancy of power circuits.
Access of cooling air into and out of the center of the coil.

Use Thinner Wire????;

Winding of Coils;

Consider winding the coils on rotor segments of 90º or 45º and then bolting them together.
These segments, particularly if there are multiple of 2 or 3 could server as redundancy for the event of an electrical failure.
The core, about which the copper wires are wound, should be non-ferromagnetic material But must it be a lamination and can the lamination be a wound coil from a single strip?.
It should contribute to the transfer of heat from the transfer heat from the copper windings.

3 Circuits for Redundancy. Is there any advantage by wrapping the coil wires of the three circuits at the same time and around all 360º, since this might result in the active wires assisting in .......

Joining Coils assembly to hub: Concern

Consider using spokes just like a bicycle wheel.

Cooling of Coils: Concern

The stator may be subjected to excessive heat due to an inability to extract it.

Pass a coolant into the center of the coil torus via the odd numbered spokes and remove it via the even numbered spokes.

Or, insert pressurized air into the center of the coil torus and allow it to escape via numerous gaps.

Or both. Keep the heat down

Rigid Supporting of Stator: Concern

How to firmly hold the stator in the magnetic forces while not taking up much of the space that is needed for the coils on the inside radius.

Could the copper windings on the inner radius of the 'flattened torus" and at an ID that is less than the ID of the ring of permanent magnets be bonded to by some material that will not be detrimental to the electrical, magnetic and cooling etc. of the coils. This "structure" will attach the stator to the "mast". The copper wires will carry this structural strength on out to the OD of the stator.

Theoretically the stator should not be subjected to any torque due to the CW torque and the CCW opposing each other.

What will the axial forces from the magnets be?

Rotors: ~ electrical one on the motor. How to distinguish between the two?

Lamination Ring to Hold Magnets and Transfer Flux between the Rings:

Is there any reason to believe that a pair of solid steel rings win not be just as good as a ring of laminations?

Bearing Between the Two Counterrotating Rotors:

The intention is to place a Thin Section ball bearing between the lamination frames that are holding the permanent magnets of the CW and CCW turning magnets.

The flux density of air is approximately 1000 times less than that of 1% silicon iron [see ~ EMDPS p.27-29]. This means that if a bearing cannot be used between the lamination frames then the gap must be as small as possible.

Perhaps a bushing type of material, which might also be ferromagnetic could be attached to both of the lamination frames. This may allow for a smaller air gap and reduce the friction should the gap be closed. Note that magnetic attraction may be attempting to close this gap.

The bearing on the drawing should be a thrust bearing. This will be particularly true if there is a magnetic attraction between the two lamination frames.

Will the ball bearing or the bushing, due to their disruption of the laminations be detrimental to the eddy currents? [see ~ EMDPS section 2.29]. Perhaps not because their is not an alternating current. In fact do the two half frames even have to have laminations?

This bearing may also incapable of handling the speed. It would probably need caged balls.

Gap - CW Rotor to CCW Rotor:

Creating a thrust bearing by grooving and hardening of the rotor frames for balls. The magnet attraction will probably be creating an attraction between the two rotor frames.
The below is the preferred alternative to the use of a thin cross ball bearing, or the manufacturing a thrust bearing.

These are the steel backings and supporting for the magnets on the two rotors.

To allow the two rotors to rotate in opposite directions with the smallest possible air gap between them without contacting each other.

A vertical gap is preferred because the two rotors are liable to experience less horizontal differential change than vertical differential change.

This eliminates the difficulty (impossibility) of aligning three bearing.

Alternative 2: Consider having the vertical portion as a stationary ring. There will be two air gaps, one between the ring and the top disk and one between the ring and the bottom disk. The coils of wire are spaced further apart on the OD and it will therefore be easier to attach to the stator's inner core. The problem then becomes ~ what do we attach the stationary ring to?

Blade Count:

Consider 3 blades per rotor (w/ narrower chord or slower rotor) to reduce the moments on the bearings.

Magnet Support:

The material mentioned on one report was SAE 1010/1020 steel.

Miscellaneous:

Notes;

See Half-wave sinusoidal operation in [PMMT Section 6.2.1] regarding the possibility of pulsed DC current.

The initial drawing material came from DESIGN: Electrotor-SloMo ~ Motor - .......1527.dc, 1528.dc & 1529,dc.

Outside Information;

7.6.4 Counterrotating rotor ship propulsion system. [Source ~ PMMT p.336]

The above section references; [44] Caricchi F, Crescembini F, and E. Santini E. Basic principle and design criteria of axial-flux PM machines having counterrotating rotors. IEEE Trans on IA 31(5):1062-1068, 1995.

It is interesting but the magnets appear to indicate that it is not a phaseless one. It might be similar to http://www.unicopter.com/1740.html.

Voice Coils

Information on CNC Large Motor and Wiring:

BUY: Electrical - Servomotor

Concerns:

Related to Basic Idea: Limited or no control over each rotor's RPM, azimuth and torque, etc.

A problem appears to be related to Faraday's law of electromagnetic induction. For a generator; - "The value of the induced voltage is proportional to the rate of change of the flux". This phaseless motor concept has a constant voltage and a fairly constant flux around its circumference.

See 'Attempt to see if PWM using only the Positive can Drive the Two Rotors:' below for possible solution.

Notes;

Will the strong magnetic attraction of the 2 rotors make assembly and disassembly impossible or very difficult?

Will the idea even work. A/ or B/

This my concern and the reason for building the prototype. Some illustrations show the flux from the pole of the permanent magnet 'pulling' a portion of the coil into alignment with the PM; as you describe above. However, others show a portion of the coil of wires being in alignment with the permanent magnet and the rotation of the motor being created by the perpendicular interaction of the PM's flux and the magnetomotive force that is circulating around the near portion of the coil In other words, is the rotation of a motor caused by an alternating attraction and repulsion between the flux of the PMs and that of the coils; ~ or ~ is it caused by a right angle interaction between the flux lines of the PMs and the circulating flux lines produced by a bundle of nearby current-carrying wires.

[Source ~ EMDPS p.585]

[Source ~ EMDPS p.32]

Results of Test:

No go around and around:

Gave it 52.6 V, 11.2 A for 587 W and nothing happened. The air gaps between the magnet - coil -magnets may be too great and the air gap between magnet steel backing disk to magnet steel backing disk may be too great, however I think the problem is ~ 'dumb idea'.

Possible Reasons Why It Does Not Work:

The air gap is too great.
Do the portion of the coils on one side of the stator cancel the portion of the coils on the other side; due to opposite current flow directions and/or close proximity.
It is the coil that reacts with the PM generated flux, not just a portion of
Would a ferromagnetic core in the stator cause the motor to work?

Would it help if this core consisted of laminations? Perhaps a single coiled lamination?
Would it help if the lamination was divided into two halves by a material that was a very poor conductor of magnet fields?
Would it help if the DC electricity was pulsed into the coil(s)?

The problem appears to be related to Faraday's law of electromagnetic induction.
For a generator; - "The value of the induced voltage is proportional to the rate of change of the flux".
The phase less motor concept has a constant voltage and a fairly constant flux around it's circumference.

Perhaps one last attempt to make this motor idea work.

The idea is to supply high frequency pulses to the two motor windings. One winding will receive a voltage that changes from V to +V.max. and the other winding will receive a voltage that changes from V to -V.max.

It is assumed that this climb in the voltages from V to V.max. will react with the constant flux and thereby generate a rotational force on the two rotors.

What is unknown by me at this point in time is if the descent in the voltages back to V will generate a rotational force on the two rotors that is in the opposite direction to that produced by the climbing voltages.

Edit: Now, how to vary the voltage?

See [Source ~ EMDPS p.566] for possible answer.

And Or ask on Eng-Tips

Look Into:

Magnetostatics

Alternative Arraignment (w/ Transverse Flux?) that May Provide Greater Power:

If the PMs are in the rotors, then the upper lamination of steel teeth must be one piece with the lower lamination of steel teeth. In other words, the laminations will have a "U" shape.

If the coils are in the rotors, then a narrow airgap must probably be located between the back ends of the upper lamination of steel teeth and the lower lamination of steel teeth.

Test of Beaty's Drawing:

1/ From C. Beaty;

What you’re attempting to do, Dave, is to get a speaker voice coil to run in circles. I know of no way of physically implementing such a scheme.

2/ Build of Chuck's sketch and response;

The lower half of Chuck's sketch.

I agree with your statement on post #72, in that there should not be torque, since the effect of the downward axial flow of current in one vertical wire will be offset by the upward axial flow of current in the other vertical wire. [Fleming's left hand rule].

Surprisingly, there is a weak rotation of about 10-deg in one direction when current is applied and a weak rotation of about 10-deg in the other direction when the polarity of the current is reversed. Perhaps this is due to stray flux crossing the lower horizontal portion of the wire as it passes from the magnet to the ferromagnetic steel at the base of the assembly. Perhaps it's time to buy a small compass and find out what the flux is going on.

3/ From C. Beaty;

The wire is probably nearer to one pole than to the other.

4/ From DBJ

A third possible reason for the initial movement.

Perhaps a pulsed DC current might rotate the armature?

Eng-Tips Thread:

http://www.eng-tips.com/viewthread.cfm?qid=268004&page=1

Another thought is that if a CONSTANT dc current flowing through a wire cannot create a constant force; what about using PULSE Width Modulation to put a non-reversing current through the wire?

Might PWM be required anyway, since it might be the best means of varying the torque?

I hope that the electromagnetic activity at one side of the stator will not effect the activity at the other side of the stator.

___________________

March 25, 2010

waross

If Intermesher wants rotation with a steady DC current look here:
http://en.wikipedia.org/wiki/Homopolar_motor
and here
http://en.wikipedia.org/wiki/Homopolar_generator

March 27, 2010

Pursuing Bill's mentioning of the Homopolar motor, this web page came up 'Faraday Paradox' http://en.wikipedia.org/wiki/Faraday_paradox.

"The experiment proceeds in three steps:
1/ The magnet is held to prevent it from rotating, while the disc is spun on its axis. The result is that the galvanometer registers a direct current. The apparatus therefore acts as a generator, ....
2/ The disc is held stationary while the magnet is spun on its axis. The result is that the galvanometer registers no current.
3/ The disc and magnet are spun together. The galvanometer registers a current, as it did in step 1."

Further on it says; "There is no paradox or difficulty if one invokes the special theory of relativity."
Now it is really becoming confusing.

WHAT IF:

The previous sketch 1904_15 was changed to http://www.unicopter.com/1904_16.gif
In the sketch, the commutators (plural) are the stator and the magnets become the rotors. These two magnets are now composed of many thin sectors, which all have their polarity in the same direction.

Might the 'laminated' PMs cause experiment 2/ to now operate as experiment 1/?

Attempt to see if PWM using only the Positive can Drive the Two Rotors: This section is actually Control - Power

Low Power Side:

Perhaps similar to a DC ignition coil driver. See http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm

Perhaps the Hard copy of 'Speed Controllers' is the method of controlling the motor. It is no longer available at http://www.homepages.which.net/~paul.hills/SpeedControl/SpeedControllersBody.html, however there is a hard copy in the 3-ring binder 'Control Circuits'.

Locate opto-isolaters between the low power and the high power circuits.

High Power Side:

Power Circuit:

Initially try the idea with a single circuit (Q1)
Then try this if the above works.

Consider having the 3 solenoids fire at 120º from each other.

Proposed Modifications:

Wind a new stator using a coil of steel as the core.
Double up on the magnets.
Add more steel behind the magnets.
Reduce the size of the air gaps.
Build a simple timer controller with a rheostat to vary the timing.

Also Consider Pulse Amplitude Modulation.

Single Phase:

A three phase motor may be run from a single phase power source. (Figure below) However, it will not self-start. It may be hand started in either direction, coming up to speed in a few seconds. It will only develop 2/3 of the 3-φ power rating because one winding is not used. From http://www.allaboutcircuits.com/vol_2/chpt_13/9.html

For More Information See This Thread on Eng-Tips:

http://www.eng-tips.com/viewthread.cfm?qid=268004&page=1

Initially displayed: March 02 , 2006 ~ Posted to Rotary Wing Forum: March 02, 2010 ~ Posted on Eng-Tips: March 22, 2010 ~ Last Revised: March 28, 2010

The above utility invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use it. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.