The custom sonar bracket made from aluminum angle.
all the standard sonar modules. The HC-SR04 modules are
wider overall, have a wider spacing between the two metal
transducers, and also have some of the smallest mounting
holes I’ve ever seen. The most difficult part to deal with is
the tiny mounting holes.
There are at least a couple different flavors of the HC-
SR04 modules around. Some are green with four mounting
holes, and others are blue with two mounting holes. If you
are extremely careful, you can usually drill out a couple of
the mounting holes to accept a #2 screw. When mounting
them, you should add an insulating washer to help protect
the components placed right next to the mounting holes.
You can’t go any larger than #2. Otherwise, you will be
breaking through the edge of the PCB (printed circuit
board) or knocking off parts. During the build, I actually
had a small surface-mount cap come loose on the back of
one module. Luckily, I was able to resolder it. Instead of
using screws to mount the sensor, you could use some
double-sided tape or GOOP to avoid the mounting hole
Since these sensors are too wide to fit the standard
sonar brackets, I just made one to fit the module. Just pick
up some 1” aluminum angle from your local hardware store
and cut a length the size of the sensor or a little longer. On
the bottom side, you need to drill a set of five holes to
secure the bracket to the servo arm. The four outer holes
are smaller and accept the small self-tapping screws that go
into the servo arm. The center hole is larger to provide
clearance, so you can access the center screw in case you
ever need to remove the servo arm to replace the servo.
On the vertical portion facing the front, just drill two
more holes for the #2 screws (if you want to use screws to
52 SERVO 05.2013
The finished sonar bracket and sonar mounted on robot.
hold in the sensor). If you are going to use tape or glue,
then you don’t need to make these holes. When mounting
the sensor, the four-pin connector is facing up.
In order to get the cable to connect to the sonar
module, you can drill a hole on the lid about 1.5” behind
the hole where the panning servo comes through. Again, a
stepped drill works well for this. I added a rubber grommet
to protect the wire going to the sonar, but since the cover
is just plastic you should be okay without it. The only other
thing that is mounted to the head panel is a small normally
open pushbutton switch. This is good for user input. I put
this about 1.25” down from the edge of the opening for
the lid. You can use just about any style pushbutton switch,
or add extra switches if you prefer.
Adding Brains to the Beast
With most of the robot construction complete, it is
time to install a brain in our creation! You can really add
just about any controller that is your favorite since there is
quite a bit of room in these robots. The first robot is based
on the Propeller QuickStart #40000 board and can use the
#40010 P8X32A expansion board or similar to handle the
custom wiring specifically for the robot. The second robot
uses an Arduino board with a generic prototyping shield to
handle the custom wiring and connections for the robot.
Even though there are two different processors, there is a
lot in common with the way they are used. They each have
the processor, USB interface for programming, etc. Since
the processor boards are used as they are and don’t need
any customizing, they are attached to the body of the robot
using a small aluminum bracket. This way, the daughtercard
containing all the custom wiring can be unplugged. This
helps whenever you want to make changes or add more
features later on.
Both processor boards have built-in voltage regulators
to drop down the 7.2V battery power for the processor and