spacer, and wheel.
Strider won’t be fully capable of this omni-directional
motion, as the two back wheels can’t be moved under
command like the legs can. But Strider can do a pirouette,
much the same as a show horse, i.e., he can make a circle
with his two front legs around the two stationary wheels.
okay, the wheels actually rotate but the center of the axle
between the two wheels stays in place. So, what we have is
the two legs being capable of moving in any direction, with
the wheels basically just following.
Both models of steering can be simplified to a “bicycle”
model (front steerable and rear non-steerable wheels);
this method of steering only allows us to turn in circles of
about twice our length. The round hexapod (or octapod,
for that matter) could be considered a “unicycle” model,
and capable of rotating around its own center.
Keep fingers clear of the legs when first powering
up. The servos can move very fast and can pinch! Legged
robots have also been known to “jump” off of tables when
first powered on.
Assuming you’ve adjusted your legs using the
PowerPod utility as described earlier, you’re ready to try
some initial moves. The control program powers up the legs
in steps to avoid damage. With only two legs, this is not
much of a chore, but should be observed carefully. If the
legs are assembled incorrectly or other than a left and right
pair (and on the proper sides), subsequent incorrect
motions may cause the legs to strike each other and
possibly cause damage. Be ready to remove servo power
should this happen. Careful setup with PowerPod should
reduce the likelihood of this.
Once powered up, you might try the “Circle” and
“Triangle” commands. After that, a gingerly tug on the
right joystick to take a step or two should cause the legs to
make a few gait cycles and reward your efforts. After that
48 SERVO 10.2009
— if all is well — a full-fledged walk on a kitchen or
hardwood floor is recommended. Deep pile rugs will
probably give Strider problems — he gets his feet caught!
Driving the Creepy Hybrid
To drive Strider like a car, pull back a little on the right
joystick and then use the left joystick Y-axis (left-right) to
steer. Or, you can translate (go in various directions without
steering) using just the right joystick. A push forward on
the joystick and Strider will back up.
Rotation controlled by the left joystick X-axis
(horizontal) is called steering. It’s not really steering
because if you try to turn while both right joysticks are
centered, the robot will rotate in place (pirouette).
The left joystick’s Y-axis (vertical) changes the robot’s
The Triangle button lowers the front end (legs) to the
ground, then turns off all the servos; press the Triangle
button again to turn the servos back on and reset the
program to default settings.
The Circle button returns the robot to setup position
(all servos at 1,500 mS) which is useful for checking
You can control the speed of walking via left and right
keys on the D-Pad. Up and down on the D-Pad increases or
decreases the amount of leg lift.
The original AH3-R code running on a hexapod will, of
course, have many more moves. The chassis can be tilted
and rotated considerably, and some additional changes to
the gait can be made. There are even “FLY” and “ATTACK”
modes! Most of these moves are not possible with only two
Links to Resources
Legs, Servos, PS2, Battery, BB2, SSC- 32, PowerPod
Atom Basic, Atom Pro Basic, MBasic Pro Compiler
SchmartBoard jumpers, Eight-bit PIC Module A
Hi-Tech PICC- 18 Compiler
DM164120-3 PICkit 2 28-pin PIC Demo Board
Microchip Datasheets, ICD 2, MPLAB
DT106 Development Board