crankshaft so it spins true and the main
journals are concentric with the servo
centerline. (See my video at www.youtube
My cranks had very slight warping/runout,
so I simply eyeballed it to get it as true as
possible. There is some flex in the A-frames to
accomodate this. Add the leg linkages and
A-frames to build two separate halves of the
robot per the instructions. Check out
_xZu8 where my servo is simply held by a tape strap
In the stock configuration, the two halves press
directly together, allowing the cranks to engage and
rotate as one. Two 2 mm steel rods run through the
A-frame edges to keep everything together. However,
our hacked TheoBot is wider by two servos. Adding a
7 mm central bay makes our chassis wider to
accomodate both servos.
I turned three 1/4" styrene rods on a lathe per
the diagram, which pressed beautifully into place
after drilling the ends with a #17 drill (0.173").
Alternatively, K&S 7/32" brass tubing (stock #130)
from a hobby shop can be used to make spacers.
Roll-cut three 2. 9" lengths and glue them around
the A-frame posts using thick gap-filling CA. Or, for
you minimalists, the original steel rods could be used
as spacers, again using gap-filling CA to glue the rods
inside the A-frame post holes.
After installing your spacers of choice, fabricate
a servo support from sturdy tape or better yet, sheet
plastic. Use a servo tester to drive the servos and
align them properly (no binding) as you glue or tape
them to the panel.
The new center bay is an ideal fit for the same
5 cm x 7 cm circuit board which fit perfectly into
SpiderBot. I also used the same electronics as in
SpiderBot: a USB 5 VDC booster, PICAXE 20M2
controller, Sharp IR distance sensor, TSOP4038 IR
54 SERVO 04.2014
Comparisons of stock fan-driven Strandbeest kit to Theobot with added center servo/electronics bay.