UNDERSTANDING, DESIGNING & CONSTRUCTING ROBOTS & ROBOTIC SYSTEMS
■ BY PHIL DAVIS and KEN TAIT
THE SAGA OF THE SILVER
BOMBER — PART 2
WE APOLOGIZE FOR THE DELAY in getting Part 2 out to you — it couldn’t
be helped. As mentioned last month (in the Balancing Bot article), due to
the RoHS (Restriction of Hazardous Substance) Directive, we had a tough
time procuring parts and the needed PC boards, so this delayed being able to
actually build and test a controller.
In Part 1 of this article (two months
ago), we explored how finding some
surplus Silver Bombers led to the
development of a controller for the
motors they contained. We explained
what would be required to run various
motors of this size and came up with
a practical design.
Anyway, after much prodding and
re-selecting of parts, Ken was finally
was able to assemble a complete unit.
Photo 1 shows what it looks like with
a temporary heatsink installed, which
we reshaped on Jerry’s mill one night
to facilitate the testing process. The
final version will most likely have a
different heatsink arrangement.
requires only four basic signals to
make it run. These are:
• An enable signal to turn the whole
• A direction signal for forward and
• A fan enable signal, although this
could be set to run constantly.
• A PWM signal to control the speed.
This signal line, in conjunction with
the enable signal, also initiates a
braking action when the PWM signal
Basically, this controller is just
a high powered H-bridge, with
no onboard CPU or smarts.
Consequently, we have to be able to
drive it in some fashion. The controller
Since all these signals go through
opto-isolators, they require an active
low drive signal, which can easily be
provided by NPN transistors or a
microcontroller port pin.
Let me describe the function of
each signal in more detail. The enable
signal effectively kills the whole
controller by telling the HIP4081A
driver to turn off all of the outputs.
This effectively ‘floats’ the FETs and no
voltage is applied to the motor.
The direction signal (as the name
implies) causes the driver chip logic to
enable the appropriate FET set to
apply the correct polarity to the
motor. Note that there is really no
such thing as forward or reverse,
except in how you set up the motor
direction in your application.
This signal will cause current
reversal in a very short amount of time,
not necessarily a good thing when
powering large motors. Instantaneous
current reversal causes large current
spikes in the system and stresses on the
parts. Energy has to go somewhere. For
all practical purposes, you can’t reverse
a motor’s direction that fast anyway. It
takes a finite amount of time to arrest
the inertia and for the magnetic field to
collapse before an actual, physical
reversal can occur.
It’s important to
build some delay in
the driver software to
The fan enable
signal turns the fan
on or off. If using
■ PHOTO 1. A 50 amp