Model Jack; The Design; The Programming - fischertechnik BIONIC ROBOTS Begleitheft

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Now Mike should function perfectly. This program is also on the CD under
MIKE_OBSTACLE.MDL. You can also integrate the improved subprogram in
the MIKE_TEMPLATE.MDL project. If E5 and E6 are not queried in another
program, that does not matter at all. We have stored the improved template
under MIKE_TEMPLATE_OBSTACLE.MDL.
Now that we have dealt with the first six-legged robot in detail, let's turn
to the second model, which also has six legs. We call it Jack.

3.3 Model Jack

Jack is also one of the six-legged fischertechnik models. However, the
design of his legs differs considerably from those of Mike's.
Now build the model as described in the assembly instructions starting on
page 12. By the way, the assembly steps 1-13 are the same for Mike and
Jack. Consequently, you need not disassemble Mike completely before you
start to build Jack.

3.3.1 The Design

The leg design of Jack also involves a four-bar mechanism. The construction
type used here is called an inverted slider crank. The connecting shaft
is ositioned in a movable longitudinal guide, which swings back and forth
when the crank rotates. The curve, which the base of the leg moves along,
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does not have such an ellipse shape as the model
Mike does, but is more of a circle.
As a result, Jack's body goes up and down more
during walking than that of Mike. The steps are
shorter. But Jack can overcome small obstacles,
which Mick cannot. This gear design also reminds
us more of a leg than is the case with that
of Mike's. When Jack walks, it looks like he is
walking on stilts.
He also moves in the three-foot gait of insects.
It is also important for this model to align the
cranks precisely as in the assembly instructions, and
to tighten the binding pieces and nuts well.

3.3.2 The Programming

It is logical that you can use programs for Jack with which Mike functioned
too. Try it!
Task 1:
Operate Jack using the MIKE_OBSTACLE.MDL program. What can
you observe?
Observation:
The model walks forward and backward without any problems.
But it falls over forward when it turns to the left or right.
Task 2:
How can you explain this?
Solution:
The two models have different leg designs. The pushbuttons E1-E4
are also activated at a different position on the leg. Consequently,
the way in which Mike turns need in no way function for Jack –
bad luck.
Of course, we don't like this at all and want to find a solution as quickly
as possible.
Task 3:
Try to program Jack, so that he detects obstacles as Mike does,
but does not fall over forward when he turns.
Tips:
Save the MIKE_OBSTACLE.MDL project under the name
JACK_OBSTACLE.MDL and make the necessary changes there.
When Jack turns, both motors can also run simultaneously. The
alternating switching on and off is eliminated. The legs must be
in the correct starting position at the beginning of turning, i.e.,
after walking backward.
Left turn (counter-clockwise):
If the model should turn to the left, the crank of the front left leg
must point backward at the beginning of the turn, and that of the
front right leg must point forward. This is the case when the
pushbutton E2 on the left side and the pushbutton E1 on the right
side are pressed during walking backward and then released again.
Right turn (clockwise):
If the model should turn to the right, the crank of the front left leg
must point forward at the beginning of the turn, and that of the
front right leg must point backward. This is the case when the
pushbutton E4 on the left side and the pushbutton E3 on the right
side are pressed during walking backward and then released again.