There are two essential parts in bat robot design: 1) structural components and 2) electronic components. The structural components make up the skeleton of the robot including body, shoulder, wings, membrane, joints etc. and the electronic components provide forces and torque to power movements. Figure 1 shows a bat robot compared to its model bat.
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| Figure 1. Bat robot |
1) Structural components
The structural components of the bat robot in figure 1 were designed by SolidWorks CAD and fabricated
via ABS
3D printing. All parts are hollow plastic structures to minimize overall weight and the designs try to mimic the morphology of
the biological
counterparts as close as possible. The biomimetic framework is provided through the study of morphology of the bat and in particular proportions are crucial for a good design. For instance, in this case wing-to-body
mass ratio was 0.410 for robot, while it is 0.404 for bat. However the actual parameters of the robot are about half of the bat. Figure 2 shows the structural components. Also for a good design of the structural components the following factors should be take into account: i) wingspan (it defines the area of the wings,
larger wingspans induce larger lift forces but also produce larger drag forces), ii) wing-to-body mass ratio (this ratio is crucial for the proper
impact of wing inertia into the production of body accelerations), iii) kinematics of flight (it is mainly represented by flapping
frequency) and iv) aerodynamics of flight (flapping motion amplitude, wing’s angle
of attack and wing camber).
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| Figure 2. Structural components of bat robot |
2) Electronic components
The electronic components consists of motors and SMA (Shape Memory Alloys) actuators. For the bat bot from figure 1 the following actuators were used:
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| Table 1. Actuators for bat robot |
Here flapping motion is the upward/ downward motion of the wings and morphing motion is the folding/ unfolding motion of the wings.
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| Figure 3. Motor for flapping motion |
Figure 3 shows the motor in the body of the bat robot. For the flapping motion the motors are connected through transmission bars and gears to the respective shoulder joints. The two gears rotate at maximum 625RPM to achieve maximum wing beat frequency of 10Hz. The axe of gears rotation are placed to allow each wing to cover an angle of q1=120° during flapping (L1 = 2.5cm).
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| Figure 4. SMA actuator for morphing motion |
Figure 4 shows the SMA actuators which power the morphing of the wings. They are composed of NiTi and were selected because they can contract upon electrical heating and recover without any thermal process. Also SMAs have sensing capabilities, so no additional external sensors are needed, which would make the system much heavier.
Using these features the bat robot can be sufficiently powered and supported to mimic flying motion and in case of failure the features of the biological bat should be examined to find solutions and improvements.
References:
- J.D.Colorado, 2012, BaTboT: a biologically inspired flapping and morphing bat robot actuated by SMA-based artificial muscles, Universidad Politecnica de Madrid
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