FISCHER Fischertechnik Bionic Robots, Manual

Page: 21 / 64

We use the 0-1 edge of the pushbuttons for synchronizing in this program.
In the moment when the pushbuttons are pressed, the cranks of all four
legs have the correct position with respect to each other. We'll call the
project JOE.MDL.
You can see that Joe moves a lot more slowly and ponderously than Mike
and Jack. Due to the necessary shifting of weight, the body wavers rather
strongly and the walking style is far from being as elegant as that of the
six-legged robots.
If you feel like it, try to get this model to walk around curves. Simply try
to see if you can do it. Good luck!
5. Walking on Two Legs
5.1 Two-Legged Walkers
Walking on two legs did not originate in the species of mammals, but
instead was first practiced by a few reptiles. Monitor lizards, iguanas,
agamidae and run-lizards only use their hind legs when running away.
This lets them achieve big steps and consequently become very fast.
They need strong hind legs for this, a long balancing tail and flat terrain.
Birds are also two-legged creatures. The ostrich is the fastest among
the birds that run. It can achieve continuous speeds of up to 60 km/h.
The most perfect two-legged creature is man. The completely upright gait
requires the stretching of the hip joint. This is achieved by the large
buttocks muscle. The legs can also be “locked in place” in the knee joints
and consequently fixed in an energy-saving position.
Movement on two legs is the most difficult of all gaits, because it requires
a pronounced sense of balance in addition to the described anatomic
prerequisites. People think of walking on two legs as a matter of course and
simple. But if we consider that when one leg is lifted, the whole body is
resting on only one leg and must be balanced, we realize that keeping your
balance during this movement type is structured in a very complicated
fashion. Even a newborn person is not able to walk immediately on two
legs. He first crawls “on all fours” before he stands up and learns to walk.
At Waseda University in Tokyo, two-legged robots have already been
developed, which move using numerous joints, various sensors, cameras
and high-performance microprocessors and maintain their balance by
shifting their weight.
But that would be too much work and complicated for our Bionic Robots
construction kit. We have seen that we are already reaching the limits of
what we can do with walking on four legs with a fischertechnik model.
5.2 Model Jim
But to make sure that we do not only consider this topic in theory, we have
designed a two-legged skier here at the end. We call him Jim. Although he
does not have a lot to do with two-legged walkers, he is very nice and tries
his best to move forward in some way. You should not
miss the chance to have this fun. You can find the model
in the assembly instructions on page 27.
You can simply use the JOE.MDL project as a
program. You need not even change is at all.
Jim also functions using it and prods slowly
forward.
But we want to give you one more task to
perform.
Task 1:
Program Jim, so that he walks
approx. 50 cm forward, the turns to
the right 180°, walks the same path back
(forwards), then turns 180° to the left, walks the
same path again, etc. Use the terminal parameter EA for the
number of steps straight ahead, EB for the number of steps
left and EC for the steps right. Use E8 as reset pushbutton again.
Tips:
Save the JOE.MDL project under JIM.MDL. Make a Straight ahead
subprogram out of the main program (select and cut out function
blocks, create a new subprogram via EDIT - SUBPROGRAM, insert
the function blocks, and supplement SUBIN and SUBOUT; also refer
to the LLWin manual).
Create the required subprograms LEFT and RIGHT from this
subprogram using the command SUBPROGRAM - COPY. Change the
motor rotation direction in it and the query of the motor directions
correspondingly. Use a different control variable for motor 2 in each
ubprogram.
Then program the main program similar to MIKE_DANCE.MDL,
except that you use the settable terminal parameters EA-EC for
the number of steps. You have to try out how many steps Jim
needs to turn 180° or to move forward a half meter.
Solution:
The main program is shown below. If required, you can see the
subprograms directly on the screen. We also call the project
JIM.MDL.
19
GB+USA
Bionic. engl.QXD 16.11.2001 10:35 Uhr Seite 19