Biomechanics lab project:
Mimicking biological locomotion
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Introduction
Terrestrial locomotion modes vary form walking, running, jumping and crawling to rolling.
Animals employ one or more of these modes for locomotion, and the most important deciding
factor is the absence or presence of limbs. Walking and running behavior are the common
mode of locomotion in humans and quadrupeds. Jumping (or saltatory) locomotion, i.e.
movement by hopping or jumping, is found in many insects e.g. fleas and grasshoppers, as
well as vertebrates such as frogs, kangaroos and rabbits. Limbless locomotion (crawling) exists
in terrestrial animals which either do not have limbs or their limbs are too short for legged
locomotion. Snakes, for instance, are highly evolved crawlers that can employ completely
distinct modes of crawling each one of which is suited for different environments.
The main objective of this project is to get a deeper understating of terrestrial locomotion
in nature. This will be achieved not only by exploring locomotion behaviors in nature, but
also by designing and building a structure that mimics a biological locomotion behavior, using
a soft robotic kit provided to you. You will work with the kits in groups for a limited amount
of time and mimic any biological terrestrial locomotion behavior of your choice. The details
on the soft robotic kit and your assignment are presented below.
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Soft robotic kit
The components provided to you for the assignment are outlined below. In addition to these
components, you are allowed to use other soft materials such as cardboard, plastic rods,
adhesive tape etc. for your implementation.
1. Arduino-micro based actuator board (fig. 1).
2. Two servo motors (fig. 2(a)).
3. Silicone sticks (fig. 2(b)).
4. A battery pack (fig. 2(c)).
5. Jumpers for adjustment of motor amplitude, speed, and phase (fig. 2(d)).
2.1
Usage
1. Connect servo motors to the actuator board using three-pin motor connectors (see fig.
1).
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Figure 1: Actuator board
Figure 2: (a) servo motor, (b) silicone sticks, (c) battery pack, (d) jumpers for actuation
adjustment.
2. Connect the battery pack to the white two-pin power connector (see fig. 1) on the
actuator board. Be sure not to connect the battery pack to any other pins on the
actuator board, as it may damage the board permanently.
3. Completing the above two steps will get the kit running (i.e. the servo motors moving!).
4. In order to adjust the phase difference, speed (frequency of oscillations) and amplitude
of the servo motors, use jumpers (shown in fig. 2(d)) to close (as many as desired of)
the ten “actuation adjustment pin pairs” shown in fig. 1.
5. The actuation adjustment pin pairs are numbered 1 through 10 as shown in fig. 1.
• Pairs 1-5 and for the adjustment of phase difference between the two motors. The
default phase difference is 0◦ . Pairs 1-5 correspond to 6◦ , 12◦ , 24◦ , 48◦ and 96◦
phase differences respectively, and can be combined. For instance closing only
pair-1 will introduce a 6◦ phase difference between the two motors, closing only
pair-2 will introduce a 12◦ difference, whereas closing both 1 and 2 will introduce
an 6◦ + 12◦ = 18◦ difference.
• Pairs 6 and 7 are for adjusting oscillation amplitude of the servo motors. The default amplitude is 30◦ (i.e. 60◦ peak-to-peak oscillation). Pairs 6 and 7 correspond
to addition of 20◦ and 40◦ in the amplitude. It means that closing only pair-6 will
result in a 30◦ + 20◦ = 50◦ amplitude whereas closing both 6 and 7 will result in
a 30◦ + 20◦ + 40◦ = 90◦ amplitude.
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• Pairs 8-10 are for oscillation frequency adjustment. The default frequency is 0.2
Hz. Pairs 8-10 correspond to addition of 0.1, 0.2 and 0.3 Hz respectively to the
oscillation frequency. For example, closing pair-8 will result in an oscillation frequency of 0.2+0.1=0.3 Hz, whereas closing all three will result in an oscillation
frequency of 0.2+0.1+0.2+0.3=0.8 Hz.
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Assignment
• You will work in groups of three.
• Your first task is to design a structure that mimics a biological terrestrial locomotion
behavior.
• You will then develop the structure using the above mentioned kit. In this Biomechanics
course, you have studied how the stiffness of a structure effects locomotion. Your task
is to construct the structure twice with materials of different stiffness. You will then
observe and analyze the difference between the locomotion of the two structures.
• You can use the glue sticks (or other soft materials as mentioned the previous section)
to create a structure and the two servo motors to actuate the structure. Hint: For
construction of the structure with a different stiffness, one idea is to split the glue sticks
lengthwise, but you are free to employ other ways/materials for achieving this.
• Each group will have two days to work on the project (at Center for Biorobotics). Each
group will choose a two-day slot that suits it the most (using a Doodle page).
Note: Please note that you are not allowed to alter (or add any new) electronic
components in the kit. It is also not allowed to reprogram the Arduino module
included in the kit.
3.1
Grading criteria and deliverables
You will make videos that clearly show the principle as well as the locomotion of your structures. Later, in the class, you will have to give a 5-10 minute presentation explaining what
biological locomotion behavior (and species) you mimicked, your design, how well your structure mimicked the biological behavior (and how you measured it), the effect of material
stiffness on your design etc.
Acknowledgment
We are thankful to Xiaoxiang Yu and Fumiya Iida from ETH Zurich for their work on softbodied locomotion, which inspired this project.
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