Loki Crosses the Pond — Part 1
Loki and Shelob on display at Yuri's Night,
Moffett Field, CA, April 12, 2008.
failure? I neglected to have the feet overlap so
that the CG of the bot was always over a foot.
I had made the body wider, but not the feet longer. After a
few tests, I determined a good length for the feet and
made another pair. I may still use the first pair of feet by
making a narrower body with a smaller controller board.
The Don Tronics DT106 board holds some promise, or I may
just design a new dedicated board from scratch.
Loki Gets Legs
Depending on your resources, you can build the body
parts of Loki in several ways. As mentioned, I drew the
parts in CAD, and milled them out with my CNC’d Sherline
mill. Not everyone has CNC of course, so the usual
procedure is to lay out the parts with a blue dye and a
scriber, and then cut them out. Drill all the holes first. PCB
stock is easy to cut; a bandsaw makes simple work of the
exterior contours. Dremel has a new scroll saw I’d love to
have. Of course, a hand tool would also work. Mind the
notches! Although exact location is not critical, they
should be similarly located on matching parts. None of the
dimensions are critical, and the decorative holes can be left
out at the builder’s discretion. I like all the curves and
holes, especially in the body and upper “decks.” The
curves could be left out, which would also simplify
making the parts. For the large holes in the body,
you’ll want to drill holes near the corners, and then
saw between them to remove the material. Finish up
with a small jeweler’s file, and they should be good.
“Nibblers” are also useful for this job. Make two sets
of “LokiFootPartsV2” and “LokiSonarPlate,” and one
“LokiBody2.” You’ll also need one “LokiIRbracket” of
one sort or another.
An alternate way to lay the parts out is to print
out full scale templates on a laser-jet printer, then cut
them out and Scotch-tape them onto the PCB stock
(follow the templates to cut out the stock). One could
even lay out a PCB, etch it, and then cut out the
parts. I don’t know if it would be any more useful for
the home PCB maker, or if a PCB house would accept
the job and route them out for you. Just a thought.
To put the legs together, trial-fit the pieces, then clean
them up with fine sandpaper and de-grease. Assemble a
foot, heat the copper foil up using the tip of the iron in
contact with both pieces of the joint, and quickly tin. Tack
solder the joint in a place or two. Keep testing the foot for
a good flat stance on a flat surface as you tin and tack
solder the remainder of the joints. Then go back and
form good small fillets between the pieces. No harm in
practicing on some scrap first!
Notice that the two brackets the knee servos bolt into
are made of aluminum. I would have used aluminum for all
the pieces, but I can’t solder aluminum! A simple bend of
these pieces in a bench brake makes quick work of these
parts. The aluminum may be a little harder to work with. In
light of this, I also have drawings of this bracket for making
them from PCB stock.
You’ll also note that the bracket holding the two IR
sensors is made of aluminum angle. You can buy angle, or
Upside-down view of Loki showing battery and plastic hold-down.
SERVO 06.2008 51