Technical Information
A major problem for common conventional motors
is the presence of brushes, which limit the motor life and also create friction
and noise. Brushless motors eliminate these disadvantages but in most cases they
are more expensive and too complicated. The simple and inexpensive brushless
motors shown on this site have quite good parameters even when they are compared
to industrial motors.
The most impressive result was achieved in the
no-load efficiency test: one of the reed switch motors built from the kit worked
non-stop over 50 hours on one 1.5 Volts AA size battery. This result is better
than most industrial motors with comparable power can provide. To achieve this
result the reed switch was moved slightly away from the rotor. The motor axles
were lubricated with WD-40. The motor torque in this experiment was too low to
do any real work.
Stan's science project included over 3000
measurements comparing the speed of the motors. All of the motors worked
quite fast. Some of these speed measurements in rpm (revolutions per minute) are
shown in the table below:
| Motor type | RPM(1.5V) | RPM(3V) | RPM(4.5V) | RPM(6V) |
|---|---|---|---|---|
| Build-it yourself motor (2 magnets) | 1000 | 1500 | 1900 | 2200 |
| Reed switch motor (2 magnets) | 1200 | 1900 | 2300 | 2500 |
| Reed switch motor (4 magnets) | 1500 | 2600 | 2800 | 3000 |
| Reed switch motor with transistor | 0-900 | 1800 | 2200 | 2500 |
| Motor on a Hall effect switch | X | 0-1200 | 2500 | 3000 |
| Motor with optical control | X | 0-700 | 1400 | 2200 |
Project CD available at the
ordering page contains full information about
Stan's experiments including all graphs, tables, etc.
Your results may vary significantly as they
depend on the accuracy of assembly, position of the sensor etc.
The last two motors in the table do not work on
1.5V and may not even start on 3V. If you want the motor with optical control to
start on 3V or even less you need to make the blades of the disk wider. However,
the motor will be less efficient and the transistor may become hot.
Different load tests showed that the motors
have quite large torque. With a string attached directly to the motor's axle
most of the motors lifted 75g on 6V. When the motors were connected to a speed
reducer some of them were able to lift up to 4 kg (9 lbs) on 6V (the motor was
slow, though). More about this experiment is described in Experiments / Applications.
The motors may consume a significant current in
case the rotor is stalled. Since the resistance of the coil is about 6 Ohm, the
maximum current according to Ohm's Law is about 1A when 6V applied to the
circuit. This current is much smaller when the rotor spins at optimal speed.
Large current may overheat the transistors and the electromagnet itself. This is
why it is not recommended to exceed 6V in your experiments. However, if you have some experience
in electricity and electronics, you may try higher voltages - most of the motors showed great
results on voltages up to 12V. If you decide to do this, please, follow these
recommendations:
- The rotor should be spinning all the time when you apply this voltage to prevent parts overheating.
- The power transistor may need a heat sink.
- It is not recommended to use higher voltages for the reed switch motors unless you use the ZNR. Reed switches normally do not work long on higher voltages because of the spark generated between its contacts.
- The resistor connected to the LED in the motor with optical control should have a greater value.