Walking On Four Legs; The Way Mammals Walk; Model Joe; The Design - fischertechnik BIONIC ROBOTS Begleitheft

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4. Walking on Four Legs

4.1 The Way Mammals Walk

To design a walking robot with four legs, let's use nature as a model again
and take a look at how mammals move.
The slowest and most reliable gait is a step. One leg looks for a new place
to position itself, while the body of the animal is support on three legs. The
animals move by taking steps on opposite sides in the following sequence:
rechtes Vorderbein, linkes Hinterbein, linkes Vorderbein, rechtes Hinterbein
vorwärts. The black boxes represent the legs, which are on the ground, and
the white boxes represent the lifted leg.
If we want to use this gait for a walking robot, we need to consider the
following:
Imagine that you saw off one leg from a table with four legs. What
happens? Right, the table falls over. Consequently, the three legs no
longer form a stable tripod, as was the case with the six-legged models.
This complicates the design of a four-legged robot.
The faster mammals move, the more instable their gait becomes. Let's
take a brief look at the gait trotting. The legs are lifted synchronously
in a diagonal direction during trotting. But before they touch the ground,
the two other legs are already lifted. This means that there is no contact
at all to the ground at times.
You can certainly imagine that a gait in which there is no contract to the
ground at times is not necessarily suited to a fischertechnik model, in which
the interface and power unit should be contained.
Consequently, let's try it using the gait "step."
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4.2 Model Joe

4.2.1 The Design

Now build the model as described in the assembly instructions starting on
page 20.
The design of the legs is the same as for Mike. But the position of the
cranks, which drive the legs, must be completely different for Joe. The
cranks are offset from one another by 90°. You must align it exactly as
described in the assembly instructions. The left and right sides are again
synchronized via the two pushbuttons E1 and E2. Then we get the required
step sequence.
To make sure that the model does not fall over as soon as a leg is lifted,
the center of gravity of the model must be set so that the model tips at
the correct moment and is supported by the leg taking the load just then.

4.2.2 The Programming

We will only program walking straight ahead for this model.
Task 1:
Program Joe, so that he moves forward in the gait step.
Tips:
Use a separate process for each motor, and synchronize the two
sides using the pushbuttons E1 and E2.
Use E8 as reset pushbutton.
Solution: