Re: [CAD_CAM_EDM_DRO] Digest Number 4425

Dave,

The reason you are having such a difficult time finding information on hobby
motors is because there are no recognized industry standards. Prior to the
advant of brushless motors, most motors were relabeled Mabuchi motors (made
in the millions). After that there were only about 5 manufacturers who made
brushless motors for the hobby industry. each tried to control the market by
keeping the information secret.

A few years ago someone figured out that CD Rom motors could be rewound into
useful, light weight motors with high torque. After that cat was out of the
bag, the explosion occurred. The Japanese and Chinese began exporting
cheapbrushless hobby motors (turns out they are easier to make than brushed
motors and require less parts). The speed controls (ESC) are just beginning
to trickle in at a cheap price.

Here is some information about hobby brushless motors.

1. They are all 3 phase motors. This means that the stator or internal
stationary part (Only on outrunner motors - more later) has coil windings in
multiples of three. Common stators are available in 3, 6, 9 and 12 (rare).
What this means is that any sensorless R/C ESC can be used with any other
hobby brushless motor.

2. Outrunner motors have a stationary stator (coils or armature) and a
revolving permanent magnet rotor. The rotor revolves around the outside of
the stator and drives the load (prop or drill bit). Conventional brushed
motors have stationary magnets and a rotating armature which drives the
load.

3. Inrunner motors are similar to outrunner motors except for the following.
The stator is on the outside of the magnets. The magnets rotate (high RPM)
on the inside of the motor. In runners are often coreless motors as well but
let's not muddy the water. inrunners tend to be better at getting rid of
heat. The downside is that they are more difficult to build since the
magnets usually have to be secured with glue and kevlar (generalization).

4. To figure out what size motor you need we use several values.
Kv - RPM per volt. This is how many thousand RPM the motor spins at with no
load when 1 volt is applied. Generally we measre the motor at a higher
voltage and then divide to get this value. Example 40,000 RPM at 12V would
yield a Kv of 3333 (rounded to get rid of the 0.333333333333333333333).
(calculated)

I0 = Amps. How many amps the motor draws for a given voltage and load.
(measured)

Rm - Ohms (measured)

Kt = inch ounces/Amp. (measured)

4. Wesites for more information:
http://www.rcgroups.com/forums/forumdisplay.php?f=13
http://www.gobrushless.com/testing/motor_test_results.php
http://www.gobrushless.com/testing/brushless_calcutort.php
http://groups.yahoo.com/group/lrk-torquemax/
http://www.castlecreations.com/


6. FMA Direct Servo lab can provide a signal to drive an R/C ESC and a
brushless motor.
https://www.fmadirect.com/site/fma.htm?body=Products&cat=8

Hope this helps.

Bill



Message: 5
Date: Sat, 03 Sep 2005 17:28:58 -0000
From: "turbulatordude" <dave_mucha@...>
Subject: Brushless motors from models and such

Hi all,

I have been trying to find information on these small hobby motors and
have come up pretty empty.

It seems there is not listing or charts that show what sizes are
available, surprizing that I didn't find manufacturers with such data.

Also, I have not found the electronical link between the controllers
and the R/C receiver. One guy at tech suppport said he thought it was
0-5 volts, but was not sure.

Does anyone know of any hobby lists or other sources of information
were the guys would actually know how the parts work ? it seems the
whole hobby is orienteated towards using the toys and not engineering
them. (just opposite of this list)

Dave