Home-Built Brushless Models

Home Hot CD-ROM Delta Hydro-Fly FAQ Gadgets Gallery Links
 

Motor Building Info

Tips and "How -To"s are on the FAQ page

Some useful information & tools for
designing and building outrunner motors

 

Winding Diagrams

CD-ROM

The 'standard' Star diagram for
9-tooth stators & 12 magnets

Star (Wye) Connection

Similar to the Star diagram above
for 9-tooth stators & 12 magnets

Delta Connection

The winding leads connected together
in pairs to create a Delta connection

LRK

For 12-teeth stators
(10 or 14 magnets)

Distributed LRK

For 12-teeth stators
(10 or 14 magnets)

Winding Scheme Calculator

For other combinations of
stator teeth & magnets

Winding Scheme Table

A very handy table showing
winding schemes for teeth/pole
combinations

Calculators, Spreadsheets & Tables

Wire Size Calculator
(xls)


Airgap calculator for outrunner motors
(html)
Magnet Coverage Spreadsheet
(xls)
Wire Conversion Table
AWG to Metric
Wire XS (cross sectional) Areas

DELTA vs STAR (WYE)

F
or the same number of turns and wire thickness:

DELTA gives 1.73 higher power and amp draw than STAR

DELTA Kv (RPM)  = 1.73 higher than STAR Kv while the Kt (torque) = 1.73 lower

With a STAR connection, 1.732 less turns need to be wound to get the same power (and Kv) as with DELTA

In case you're wondering: 1.73 = sqrt(3)

Tutorials

How to wind a typical CD-ROM motor

This is the winding instructions for the
Apex Mini300 motor, but winding a
CD-ROM motor is exactly the same


ESC Max. RPM Limits

Brushless speed controllers (ESCís) have maximum RPM limits that they can drive motors at. See this PDF file.

 


How to determine the Kv of a motor

Method 1 (Power drill method) - quick and dirty method

1. Drive the motor with a power drill.

2. Measure RPM and voltage generated.

3. Kv = RPM / voltage   (also see Method 3)

- - - - - - - - -

Method 2 (Running the motor without a load)

This method is not very accurate with brushless motors, because different ESC's will give slightly different results. 

1. Run the motor without load at full throttle at various input
voltages and measure the RPM and controller input voltage.

2. You can measure the no-load RPM by marking two stripes

on the bell with an indelible pen. Then shine a torch on the
rotating bell and tach the reflected light.

3. To find Kv either:
a) Graph RPM vs Voltage, the slope of the line is Kv
b) For each voltage divide RPM by voltage, and
average your results. Theoretically, a) is more accurate.

- - - - - - - - -

Method 3 (Colin Dedman's formula) - this is my favourite method

1. Drive the motor with a drill press.

2. Measure RPM and voltage generated (by one phase).

3. Kv = RPM / (volts x 1.41 x 0.95)

- - - - - - - - -

Method 4 (Louis Fourdan's formula)

1. Run the motor no-load at full throttle at voltage V for a RPM in the good range.

2. Measure the no-load RPM and current (Io).

3. Find the internal resistance of the motor in ohms. It can be measured using the Kelvin (4-wire) method or taken from the specifications supplied by the manufacturer (some risk of error).

4. Kv = RPM / (volts - amps x resistance).

5. It's better to measure at 2 different voltages and average the results.

 

 

I post as Skylar on RCGroups.com
and also on
LRK-Torquemax

 

E-mail: Christo van der Merwe   ---   Skype name: Christo1636