So, the motor that this text is about is a 5-phase bipolar motor.
This is a high-end kind of stepper motor that requires relatively
complex drive circuitry and provides a lot of torque for its size and
a high step resolution.
A photo of the back side of this motor is shown in figure 1 below.
Figure 1. The back side of the motor.
The text and my comments are:
Maybe the batch number
The manufacturer logo, Berger Lahr seems to be owned by
Schneider Electric nowadays
Maybe the model number
The IP classification; 5 = dust protected, 4 =
splashing water protected
Is. Kl. B
Maybe the NEMA insulation class; B = maximum
130°C winding operating temperature; 80°C allowable
temperature rise at full load (at 40°C with 10°C hot spot
IW = 0,21 A
Rated winding current
RW = 32 Ω
α = 0.72°/0.36°
Step size, full step = 0.72°, half step = 0.36°
Figuring out the secrets
With 0.72° step size, the motor has 500 full steps per
revolution, which is quite impressive. Unfortunately, I have not been
able to find any information about this motor from the website of
Schneider Electric which now apparently owns Berger Lahr, so the
information necessary to use the motor (in addition to what can be
read from the plate) has to be found out by experimentation.
There are ten wires with different colors coming out of the motor and
it is easy to ohm them to figure out which ones connect to the same
winding. It is a little bit trickier however to figure out in what
order the windings are positioned inside the motor. The way I did find
out was to attach a long pointer to the motor shaft and to in turn
connect the various windings to a power supply. Often this would
produce a relatively large jump in the pointer, but sometimes the
motor took just a small step. When this happened I noted which two
windings were involved and the direction of current in the windings,
since the small step means that the windings are adjacent. The table
below shows the results of the experiment.
I wanted to know the holding torque of the motor, so I put the motor
with the shaft horizontal. Then I attached a horizontal lever at right
angle to the shaft and hanged a little bottle at the end of it (16 cm
from the center of the axis). I then ran current through one of the
windings and started to slowly fill the bottle with water until the
motor could no longer hold it. I then weighed the bottle and could
thereby calculate the holding torque. I repeated the experiment with
2, 3, 4 and 5 windings powered. The results can be seen in the table
# of powered windings
The data is visualized in figure 2 below.
Figure 2. The holding torque as a function of the
number of powered windings.
It seems like the torque increases almost linearly from 1 to four
windings, but powering also the fifth winding gives less of an increase
Driving the motor
Using H bridges I developed as described
in another article and a PICDEM FS USB
development board, I was able to run the motor. A short movie clip
showing the motor turning slowly is provided below.
There are lots of room for improvement and sophistication in the
motor drive. One thing that could be interesting to look into is to
use micro-stepping to reduce the vibrations when running the motor
(especially at low speeds).
Another thing is to build a more advanced drive that uses a higher
voltage when turning a winding on to increase the torque and maximum