Loki Crosses the Pond — Part 1
Another upside-down view of Loki.
Katie, Loki's admirer (Nemesis?) looks on.
bend it up from aluminum plate. Cut a thin notch to allow
the angle to be bent back to match the drawing. Here
again, I felt aluminum was the best material for the job,
however, it too can be made up from PCB stock. Take your
pick; there are PCB-style drawings for it, as well.
Now is a good time to electrically center each of the
servos, and then attach the servo horns square to the
servos. This can be done by the controller board, or a servo
driver accessory available for this purpose. Position the
servos to 1,500 μs. The screws used can be the self-tapping
screws supplied with the usual servo horns, or 2-56 screws
in case you have machined servo horns.
To give Loki his legs, we’ll start by bolting the pair of
shoulder servos into the body as per the graphics. Next,
bolt the L-brackets onto the installed shoulder servo horns.
This order is required as the knee servos block access to the
screws of the shoulder
Bolting on the knee
servos is next. It’s a little
cramped up near the
shoulder servo horn,
but you’ll find that a
wrench will help here.
Some users might want
to use the nylon snap
rivet fasteners available
for R/C servos. They
work well in blind areas
such as these.
The feet can now
be bolted up to the servo horns of the knee servos. With
the spine shafts of the servo only allowing rough squaring
of the servo horns, alignment won’t be perfect. Later
we’ll determine and enter servo offsets into the controller
to correct for this. Actually, we don’t quite “square” the
shoulder servo, anyway. Loki has a little problem with his
feet, as you’ve probably noticed. They are too long! In
order for them to both lay flat on the floor, we’ll actually
stagger them a little, to keep Loki from tripping over his
The controller board will be mounted by means of four
1/2” spacers. An additional set of four spacers mounts the
two “sensor decks” on top of the controller board. The IR
bracket shares the two screws used to mount the controller
board, and is mounted below the body. You’ll need four
long 4-40 screws (upper) and four short 4-40 screws (lower)
for this task.
Two identical sensor decks are to be made. Solder the
rectangular plates to these boards as before. Small gussets
(corner braces) can be added if desired,
but they haven't proven necessary. You’ll
bolt the Bluetooth transceiver to one
(add a lock washer from a toggle switch)
and the ultrasonic rangefinder to the
other. The rangefinder is mounted on a
pair of 5/8” long 4-40 screws, and two
3/8” spacers. Also mounted below the
controller board is the battery. I secured
my battery with a thin (0.025”) sheet of
flexible PCB stock I had on hand. You
could also just use rubber bands!
Noki Body 1.1
I should say a little about the
controller board I used. Most any
controller board and processor can
probably be used on a bot this size. I had
on hand several bare QwikFlash boards
purchased from the PICbook website
Drawing to make Loki's body. Make from
1/16” PCB stock.
52 SERVO 06.2008