1915

Item 1915

DESIGN: Electrotor-SloMo ~ Motor - Radial Flux - Rotor - Outrunner Project

Objectives:

Cooling:

The rotor losses in PM synchronous motors are small so most PM machines employ passive cooling of their rotors.

See; DESIGN ~ Electrotor-SloMo ~ Motor - Radial Flux - Stator - Cooling

See OTHER: Electrical - Motor - Cooling. See Cooling of Stator on Outrunner:

Aluminum transfers heat to air 250/43 = 5.8 times faster than steel does? See; http://www.engineeringtoolbox.com/overall-heat-transfer-coefficient-d_434.html

Also see program on computer 'Engineering Power Tools' ~ 'Thermal Properties of; Metals, Non-metallic, and Gases'

Drawing:
Do not consider this idea

The rain will go into the scoop and then drain out the trailing edge of the blade through small holes.

At high forward speeds there must be some way of stooping the air from exiting on the retreating blade.

Forced Air Through Root of Blade and Rotor Hub:

At a rotor speed of 600 RPM and no forward speed the blade at all azimuths will experience an airflow of 88 ft/sec at 1.4 ft R
At a rotor speed of 600 RPM and a forward speed of 60 mph the blade at 270 azimuth will experience no airflow at 1.4 ft R
At a rotor speed of 600 RPM and a forward speed of 60 mph the blade at 90 azimuth will experience an airflow of 176 ft/sec at 1.4 ft R

Therefore the mean air speed of all apertures will remain the same irrespective of forward speed. However this airflow must be equally distributed around the circumference of the stator.

Coefficient of Thermal Expansion:

See; OTHER: Electrical - Motor - Rotor - Permanent Magnet ~ Coefficient of Thermal Expansion

For consideration re reduction at air gap.

Initial Consideration:

If it is decided not to go with Halbach then consider that the steel that carries the flux between magnets can serve 'double duty' by being the anchor for the pitch pins. This assume that lament steel is not required for flux path.

Components:

Magnet:

Halbach: How are the magnets that have circumferencial flux to be fitted in between the pole magnets that have radial flux?

Frame: Yoke ??

Potential Concerns:

"The major faults of electrical machines can be broadly clasified as follows:

Broken rotor bar or cracked rotor end-rings

Static and dynamic air-gap irregularities

Dynamic eccentricity

Winding short

When a turn to turn failure occurs, the shorted turn acts like the secondary of an autotransformer. If for example, a coil has 60 turns per phase and the shorted turn has one turn, the current in the short will be 60 times larger than the normal current. The heating effect is current squared times resistance (I2R). This example would result in (60)2 or 3600 times the normal heating effect. It doesn’t take very long for this heat to start melting copper and insulation. The resulting loss of insulation manifests into a phase to ground fault, usually within seconds. Typically this type of fault is recognized by a lot of melted copper.

Bearing failure

Magnets and Safety:

Bandage:

A band (fiberglass and epoxy) used to hold the permanent magnets to the rotor.

For this outrunner, the unidirectional fiberglass tape or tow should probably be wound around the circumference around the rotor toroid. The fiberglass might then be used to mount the torque/pitch device.

This may work to the detriment of cooling, however the heat generated by the rotor will be quit low, particularly if it is a Halbach Array. The fiberglass may isolate the rotor somewhat from the higher heat generated by the stator.

The corrosion of the permanent magnets [PMMT section 8.5.6 will probably be eliminated by this fiberglass and epoxy

The bandage can be steel. [PMMT p.131]

For more information see [PMMT fig. 8.11, p.370 & 373]

Perhaps pinned horseshoe magnets will negate the need for an overrunning clutch.

More:

If a magnet should come loose it MUST have the ability to drop out of the motor by gravity; whole or in pieces.
Ideas for consideration:

A non-conductive (flux) ring that is stationary that has a low-friction surface and presents a slightly smaller airgap then the stator's shoes.
A low-friction coating of the shoes.
Teeth in the stator that will grind up the loose magnet.
Others must have considered this concern.
How is this concern routinely inspected?

Buried Magnet:

Safety: The chance of having a magnet break and/or come loose is eliminated.

"While the interior permanent magnet rotors support the use of rectangular magnets, the presence of ferromagnetic material at the rotor surface dramatically increases the air gap inductance. Furthermore, it adds a reluctance component to the torque produced." [Source ~ BPMMD p.118]

Weight:

See: BUY ~ Motor ~ Fullsize - Radial Flux - Stock Fisher & Paykel ~ Weight

Magnet:

The dimensions of current (bought) rotor are approximately 35mm (1.375") x 13mm (0.5 ") x ???

Halving the width of the magnets and doubling their count will result in a more consistent airgap around the circumference. However this mean that the narrow magnets will be butted together in pairs and this edge between them does not provide for bonding to the housing. Is this a concern?

Flux Ring (Item 1933):

This iron ring has the permanent magnets bonded to it. It transfers the flux between permanent magnets and it holds the 3 pins, which are connected to the torque arms (drawing 1934.dwg)

It has been mentioned that if a remote part of the yoke (ie. at the greatest radius) can magnetically hold a paperclip then the x-sectional area of the yoke is too small.

Associated Pages:

Initially displayed: April 10, 2010 ~ Last Revised: September 6, 2011

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.