LISTING 1. RC to H-bridge Conversion.
RPM of an RC plane’s propeller. The
obvious trick here is to make an
encoder disk and glue it to the motor
shaft, then mount the emitter/receiver
close to the surface so the lines can
be read. I drew up an encoder disk in
a drawing program, glued it to some
poster board with white glue, and
then used the same glue to mount it
on the shaft. Check out Photo 3.
TESTING THE MOTOR
■ PHOTO 4. ‘Run’ profiles for testing.
So that’s it. The
motor is mounted on
its own board with an
encoder disk and is ready to test.
The PC computer interface for the
Power Analyzer Pro allows the user
to create a ‘Run’ with which you
can specify a variety of test profiles,
as shown in Photo 4. On the
‘Waveform’ tab, you will notice that
I have chosen a simple linear ramp
with the following parameters: No
start delay, a peak value of 100%
(which is full speed), holding the
peak value for 10 seconds, and
specifying that the ramp will take 30
seconds. It is possible to choose
other waveforms, as in Photo 5.
When we execute this Run
profile, PWM will be fed to the
motor such that the PWM follows
the graph in Photo 4, gradually
increasing until the motor is
running at 100% and then holding
there for a period.
During the Run, in real-time, a
graph will be drawn of all the
measurements we have chosen.
Power Analyzer has a tool with
which you set your dials, gauges,
and graphs, but I won’t be going
into detail on that setup. However,
looking at Photo 6, you can see
the output I was getting.
Let’s try and do a brief analysis of the various lines in the graph.
The gray line represents the linear
throttle response, which is actually
a steady increase in PWM (and
consequently voltage) and, as you can
see, it follows the programmed profile.
The purple line is the actual
measured RPM from the encoder
disk. I should note that the analyzer
application has the ability to massage
the data coming in and, in this case,
the RPM in is automatically divided by
the number of lines on the encoder
disk, divided by two. This produces
as the analyzer believes it
is using a
thing to note
■ PHOTO 3.