Walking On Six Legs; The Way Insects Walk; Model Mike; Assembly Of The Model - fischertechnik BIONIC ROBOTS Begleitheft

3. Walking on Six Legs

3.1 The Way Insects Walk

The way insects walk is excellently suited as a model for the drive of
mechanical six-legged robots. In what is called a three-foot gait, three of
the six legs are always raised at the same time from the ground: the front
and back leg of one side together with the middle leg of the other side.
The legs, which remain on the ground (displayed in black), form a stable
three-legged construct, so that the model always remains stable upright
and does not fall over during walking.

3.2 Model Mike

3.2.1 Assembly of the Model

Build the six-legged robot Mike now (see the assembly instructions on page
4). Load the power unit while you assemble it, so that you have sufficient
energy to drive the model later.
The legs of the module are designed in such a way that a four-bar mecha-
nism is produced. The construction type of the four-bar mechanism is called
a crank and rocker mechanism. Driven by a crank, the movable elements of
the gears sway back and forth. The distances between the individual joints
and the position of the base (the
lower end of the leg) are selected
so that the base moves elliptically
when the drive crank rotates.
This creates movement, which is
similar to a step when walking.
The six cranks, which drive the
legs, must be aligned precisely
as shown in the assembly
instructions. The three legs, which
touch the ground at the same
time, have the same crank set-
ting. The cranks of the three legs,
which are in the air at this time, are rotated by 180° for this. The correct
setting of the cranks in relation to each other ensures that the model can
walk in the correct step sequence, the three-foot gait.
The binding pieces and nuts, with which you attach the screws and toothed
gears to the axles must be tight, so that they do not shift during the
walking.
The right and left sides of the model are each driven by a motor (this is
required for walking around curves). You must make certain for this that
the middle leg on the one side is always in the same position as the front
and back legs on the other side. This is synchronized by the software via
the pushbuttons E1 and E2.
Use the interface diagnosis to test whether all pushbuttons and motors are
connected correctly. Rotation direction of the motors: counter-clockwise
rotation = forward.

3.2.2 The First Program

Now we are going to start to teach Mike something. The model should
first walk straight. We will deal with walking around curves and reacting
to obstacles later.
Task 1:
Program the model, so that it walks straight with a three-foot gait.
Use the pushbuttons E1 and E2 for synchronizing the left and right
legs. Make certain that the front and back legs on one side and
the middle leg on the other side always have the same position.
Also use pushbutton E8 as reset button.
Tips:
Program a separate control process for each motor. Control the
process for motor M2 using a variable VAR2.
If you do not
need the
interface during
programming,
interrupt the
power supply
between the
power unit and
the interface to
save energy.
Solution:
The program for
walking straight
looks like this:
GB+USA
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