Three dudes from Caltech just designed the first robotic bat. Alireza Ramezani, Soon-Jo Chung, and Seth Hutchinson scored the cover article with their research published in the latest issue of Journal of Science Robotics, detailing the successful construction and flight of the multi-articulating, adaptive flapping of our favorite flying mammal.
Modeled after the species, Rousettus aegyptiacus (the Egyptian fruit bat), the robot does indeed look and move like a bat–Well, a creepy, mechanical, translucent bat. The crew claims it is among the agilest of flying robots ever built. They also claim that because it’s so light and squishy, it poses far less risk to humans than quadrotors and other rotorcraft.
If you’ve ever been interested in how bats fly or advanced robotic motion, the research is nothing short of amazing. The group was inspire by the insight and applications of flapping aerial robotics and the inherent challenge.
From an engineering perspective, understanding bat flight is a rich and interesting problem. Unlike birds or insects, bats exclusively use structural flexibility to generate the controlled force distribution on each membrane wing. Wing flexibility and complex wing kinematics are crucial to the unrivaled agility of bat flight.
A carbon-fiber framework is the bones of the bot. The skin stretched over those bones is a custom fabricated, 56-μm silicone membrane. Loaded with sensors, an 8-channel receiver, four coreless DC motors, five magnetic encoders at each joint and controlled by an ST microcontroller, the whole package weighs a mere 93 grams (0.20 pounds). It’s also autonomous–no wires, no remote control. To determine the sophisticated movement, they looked at the changing flight pattern of bats, extrapolating and grouping them into three dominant degrees of freedom (DOF).
B2’s flight mechanism consists of the left and right wings, each including a forelimb and a hindlimb mechanism. The left and right wings are coupled with a mechanical oscillator. A motor spins a crankshaft mechanism, which moves both wings synchronously dorsoventrally while each wing can move asynchronously mediolaterally. The hindlimbs that synthesize the trailing edge of the wings can move asynchronously and dorsoventrally. If it were not for mechanical couplings and constraints, the morphing mechanism of B2 would have nine DOFs. Because the physical constraints are present, four DOFs are coupled, yielding a five-DOF mechanism.
Obviously, simple fabrics or nylon films would not work for the skin. They realized the limb movement defined the shape of the wings during flight and that any membrane used would impart a moment of intertia across the flapping axis and affect the torque output due to additional tensile forces. To solve this, the team constructed a custom, highly-durable, silicon-based membrane to match the elastic characteristics of a biological bat wing.
To produce an ultrathin and stretchable skin, we used two ultraflat metal sheets with a 10-μm flatness precision to sandwich our silicone materials. This ensures an even and consistent pressure distribution profile on the material. We synthesized a polymer in which two components—one containing a catalyst and the other containing polyorganosiloxanes with hydride functional groups—began vulcanization in the laboratory environment… [adding] hexamethyldisiloxane, which reduces the thickness and viscosity of the silicone, in an experimentally determined ratio
While this little guy mimics the biology and kinematics of a real bat, it can’t actually take off by itself yet. For now, testing involves two different flight manuveuers: a banking turn, a swoop and a dive. They launched the bat by hand, and even though this affected the flight somewhat, the batbot compensated and stabalized within the first 20 wingbeats, matching commands to adjust the pitch and yaw for the various manuevers.
The paper is a fascinating read, with the result revealing some very interesting findings on dynamics and control, design scheme and material science. There is supplemental material on the project, including videos and other data captured in the tests. You can view this material here.