1896

Item 1896

OTHER: Electrical - Motor - Rotor - Winding

Information:

The delta winding connects the 3 groups of windings to each other in a triangle-like circuit, and power is applied at each of the connections. This pattern is typical to low-speed, low-torque motors. The Wye ("Y"-shaped) winding, sometimes called a star winding, connects all of the windings to a central point and power is applied to the remaining end of each winding.
Although efficiency is greatly affected by the motor's construction, the Wye winding is normally more efficient. At any given time, two-thirds of the windings in a delta configuration are running at half the voltage of the other, which is an impact on efficiency. The Wye winding always powers only two windings in series, so higher voltages (or lower-resistance windings) can be used.
From a controller standpoint, the two styles of windings are treated exactly the same, although some less expensive controllers need to read voltage from the common center of the Wye winding.

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You can choose between "star" and "delta" winding. With "star-winding" the motor will have a higher torque, less RPMs and will pull less current (amps). "Delta" will result in a "hotter" engine with higher RPMs and more power, but will pull more amps and will produce more heat. The star is also more difficult to handle for the brushless controller.

More Information:

for less winds (and a faster spinning motor), use thicker wire.

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more winds = more inductance THUS drawing less amperage (longer runtime for me )
more winds = a slightly stronger magnetic field (i.e. torque) PER AMP because of the more efficient field, slower spinning armature and less tendancy to stall because of the lower rpm/volt (Kv) rating

less winds = a weaker magnetic field at higher rpm THUS faster spinning armature
less winds = less inductance and resistance THUS letting more amperage flow through.

keep in mind that when your amp draw goes down your power goes down too. but you can offset that by increasing the voltage.

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The best way to think of Kv is as an electrical gear ratio. Low Kv= low rpm and high torque. High Kv= low torque and high rpm. A prop that can be driven directly with a 400Kv motor would need a 10 to 1 gear reduction box if you were to use a 4000Kv motor, provided that both motors have the same safe maximum amp rating.

Kv is determined by the number of turns in the winding, more turns = lower Kv, and by the strength of the field magnets, stronger magnets = lower KV. On permanent magnet DC motors used in industrial applications, the first thing I check is the Kv. If the motor is supposed to run 1800 rpm with 180 volts but my tachometer is reading 2500 rpm at that voltage, the field magnets are shot.
There is also a Ka rating, which is torque per amp. It is complimentary to the Kv and if you know the Kv, you can calculate the Ka.

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Article on Winding density

Higher voltage = Higher speed

Increasing the number of turns will reduce RPM and increase torque.

More Information:

For 2-phase see; DESIGN: Electrotor-SloMo - Motor - Overview - 2-phase ~ Winding. The general info may be moved to this page.

For 3-phase see; DESIGN: Electrotor-SloMo - Motor - Overview - 3-phase ~ Winding. The general info may be moved to this page.

For 4-phase (or n-phase) see; DESIGN: Electrotor-SloMo - Motor - Overview - 4-phase ~ Winding. The general info may be moved to this page.

Converting:

Converting from Star to Delta hookup, the RPM/Volt value is multiplied by 1,73.

Converting from Delta to Star hookup, multiply the RMP/Volt value by 0,578.

Miscellaneous:
"As a guideline, here are some basic points to consider -

The higher the number of turns on a tooth, the greater the magnetic field produced for a given current. Stronger magnet field results in more torque and lowers the RPM/Volt number.

For higher RPM values, fewer turns are required but results in less torque being available. The lost torque can be recovered though by pushing more current through the motor to increase the field strength.

Thicker stator packs help reduce the RPM/Volt values while thinner ones do the opposite."

The Lucas, Retzbach and Kuhfuss Motor Winding: (LRK & DLRK)

Notes:

While they are not LRKs in the strictest sense, DPS motors are close cousins of the LRK. In a LRK stator, every other stator tooth is wound. Hence, LRKs are described as SPS (separated phase sector) motors. In the DPS variant, every single stator tooth is wound. Both the LRK and the DPS use special winding schemes. Diagrams of each are available on the Internet.

On the question of whether LRK or DPS or ABCx4 is the "best" scheme for a motor, I think Ralph (powerditto) and Ron van S have hit the mark: the winding scheme determines motor characterisitics, whereas maximum power and maximum efficiency are determined by motor dimensions and materials.
A motor of any type can be wound for (comparatively) high torque or high RPM, depending on the number of turns on each tooth. Some types may be more suited for one or the other. Magnet pole count has a similar effect.

A motor is also a generator, and under no load will accelerate until it produces as much voltage internally as it is recieving*. As it accelerates to this speed the current it draws will drop off. Adding a propeller or other load keeps the motor from reaching it's no-load speed, and it draws current such that the power (amps X volts) going in is equal to the power being produced*.

*(not considering inefficiency factors - bearing and air drag, wire resistance, etc.)

So if a motor is wound with 20 turns per tooth it will produce a certain RPM per volt (Kv) at no-load and a certain amount of torque per amp (Kt) under load. If you rewind the same motor with 10 turns per tooth using wire of twice the cross section area it will produce twice the Kv and half the Kt, approximately. It will need a smaller prop or the amperage will be much higher and possibly produce more heat than it can handle.

Reconfiguring magnet poles has a similar effect, voltage is generated by changing the magnetic field in the coils. So halving the pole count will roughly double the Kv and halve the Kt. There is an important relationship between magnet width and tooth width, so this is not as certain. Magnet strength and airgap also play into it.

Outside Information:

Torquemax The LRK Site
http://www.femm.info/wiki/LRKAnalysis : Finite Element Method Magnetics : LRKAnalysis
Torcman Assembly Procedure
Investigation on Pole-Slot Combinations for Permanent-Magnet Machines with Concentrated Windings ~ Have hard copy and saved on E: drive

http://www.gobrushless.com/kb/index.php?title=Brushless_101_-_Chapter_3

More on LRK & DLRK http://www.tcrconline.com/documents/Brushless/Brushless%20Motors.pdf

Last Revised: February 20, 2010