Remote Radio Control of Insect Flight
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30-10-2010, 11:03 AM
Remote Radio Control of Insect Flight
Applied Electronics and Instrumentation
College Of Engineering, Trivandrum
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Micro and nano air vehicles (MAVs/NAVs) – defined as aircraft with total mass <100 g and wingspans <15 cm are the subject of intense research and development. Despite major advances, MAVs/NAVs still present significant trade-offs between payload mass, flight range, and speed. Currently, the principal limiting factors are the energy and power density of existing fuel sources and the complexity of flight dynamics in very small flyers.
Insects have flight performance (as measured by distance and speed vs. payload and maneuverability) unmatched by man-made craft of similar size. Moreover, both the flight dynamics and the neurophysiology of insects are increasingly well. In biology, the ability to control insect flight would be use¬ful for studies of insect communication, mating behavior and flight energetics, and for studying the foraging behavior of insect predators such as birds, as has been done with terrestrial.
In engineering, electronically controllable insects could be useful models for insect-mimicking MAVs/NAVs.
A cyborg, also known as a cybernetic organism, is a being with both biological and artificial values (e.g. electronic, mechanical or robotic) parts. Fictional cyborgs are portrayed as a synthesis of organic and synthetic parts. Cyborgs may be represented as visibly mechanical or as almost indistinguishable from humans (e.g. the Terminators from the Terminator films). Cyborgs are also often portrayed with physical or mental abilities far exceeding a human counterpart. Real cyborgs are more frequently people who use cybernetic technology to repair or overcome the physical and mental constraints of their bodies. While cyborgs are commonly thought of as mammals, they might conceivably be any kind of organism.
According to some definitions, the metaphysical and physical attachments humanity has with even the most basic technologies have already made them cyborgs. In a typical example, a human fitted with a heart pacemaker or an insulin pump (if the person has diabetes) might be considered a cyborg, since these mechanical parts enhance the body's "natural" mechanisms through synthetic feedback mechanisms. Some theorists cite such modifications as contact lenses, hearing aids, or intraocular lenses as examples of fitting humans with technology to enhance their biological capabilities; however, these modifications are no more cybernetic than would be a pen or a wooden leg.
The term is also used to address human-technology mixtures in the abstract. This includes artifacts that may not popularly be considered technology; for example, pen and paper, and speech and language. Augmented with these technologies, and connected in communication with people in other times and places, a person becomes capable of much more than they were before. This is like computers, which gain power by using Internet protocols to connect with other computers. Unlike human cyborgs that appear human externally while being synthetic internally, a Lobster looks inhuman externally but contains a human internally. Bruce in his universe of Shaper/Mechanist suggested an idea of alternative cyborg called Lobster, which is made not by using internal implants, but by using an external shell.
It is a wonder that somebody turning an insect into a deadly assassin for the military. Though it seems outlandish, it’s about halfway there, the “CYBORG BEETLE”. The Pentagon has funded a project and implimentation at UC Berkley in which scientists have successfully grafted electrodes and tiny radio antennae to flying beetles--allowing researchers to steer the beetles by remote control. These cyborg beetles are both fascinating and terrifying--the project and implimentation is helping scientists discover new insights into how beetles fly.
Figure showing a Cyborg Beetle
But experts are also already discussing the possibilities a remote-controlled flying beetle can offer the military. In this project and implimentation a beetle is converted to a Cyborg. A beetle is mounted with a microcontroller system which helps in linking the beetle movements to a computer control.
We know that there are a lot of insects similar to beetle. Then why they selected beetle for this experiment. God has a fondness for beetle, because they are the organism with the maximum number of species. So it is very easy to get them for this research purpose. This also avoids problems regarding extinction of the species. The second thing is that they have a wide size range, so a cyborg beetle can be developed in any size range as required. The size of beetles varies from 1 mm to 10 cm.
The third thing is that they are very strong flyers. The average velocities of them are between 2 – 6 km/h and the maximum velocities is 7–14 km/hr. The flight duration is 10 min – 3 hours, which provide them with all the advantages needed. They have very hard exoskeleton and hard forewings, so we don’t have to worry about any protection during experiments. The next thing is that they are easy to rear and breed. So it’s not difficult to get required number of beetles for the experiments.
They are generally harmless to humans. So there is no danger in experimenting with them. Another important feature of them is their very hard shells. This acts as a very protective covering for their body. So we don’t have to bother much about the protection from various hazards. They have a natural preventive measure to avoid it.
The beetle that was used for the experiment was Mecynorhina torquata. It is a having the size parameters like 7cm long, 10 g weight, and a payload capacity of 30 % of its total weight.
A picture showing Mecynorhina torquata
Mecynorhina. Torquata (ca. 6 cm, 8 g) were collected from fruit gardens in Texas, USA. Beetles were kept in groups of 30–40 in terrariums (40 cm × 27 cm × 32 cm) on organic peat misted with water daily to keep relative humidity near 40–50%. They were also imported from insect suppliers (United States Department of Agriculture, USDA permit). Small M. torquata beetles were kept in separate terrariums (20 cm × 15 cm × 15 cm) containing woodchips.
The beetles were fed sliced apples every 2–3 days. The temperature in all terrariums was maintained near 28°C. Lamps were used to create artificially day/night cycles (15 h light/9 h dark) and sheet heaters controlled by thermostats were used to control temperature. The beetles used in experiments were distinguished from yet-unem¬ployed ones but treated with the exact same feeding and care.
A humidity of 60 % was always kept in terrarium. All surgical experiments were carried out after anesthesia in a freezer. All these conditions reduced the rate of wasting of the beetles due to death of the beetles during breeding.
To ensure identical test conditions, the beetles were individually enclosed in small plastic cases (10 cm diameter and 5 cm height) for 24 h without feeding prior to flight initiation experiments. The small cases physically prevented the beetles from unfolding and oscillating wings. Each beetle was then placed in a −10°C freezer for 5 min to anesthetize it.
This process is the implanting of the microcontroller system onto the beetle’s body. This is not done on a fully grown beetle because it cannot adjust with this new part attached to it. So this implanting is done during the pupa stage of the beetle itself. The whole process is shown in the diagram below.
The microcontroller is glued on to the head region and various electrodes are implanted onto the optic lobes, brain, and wings.
Two small holes using a needle were carefully pierced through the beetle cuticle; (1) at the interior edge of the left compound eye for left optic lobe and (2) at the interior edge of the right. Two electrodes were implanted into the left and right optic lobes.
1. RF Transmitter
Flight commands were generated by custom control soft¬ware (BeetleCommander v0.98) running on a personal computer interfaced via a serial port with the transmitter (CC2431 micro-controller mounted on a Chipcon Texas Instruments SmartRF 04EB).
BeetleCommander v0.98 allowed for in-flight control of stimulus parameters including frequency, number and duty cycle of adjusted amplitude pulses to stimulated sites. Command sig¬nals were transmitted using the CC2431’s built-in 2.4 GHz IEEE 802.15.4 compliant RF transceiver broadcasting on a single chan¬nel (1A, 2.480 GHz) using direct sequence spread spectrum RF modulation.
The transmitter sent a command to the receiver every 1 ms for 300 ms when instructed to do so. The flight commands were mapped to appropriate amplitude pulse trains at the beetle’s neural stimulators by BeetleBrain v0.99b running on the receiver. To adjust the applied amplitude to a value other than the 3.9 V originally supplied from the lithium ion battery, the surface mount resistors were soldered to create voltage divider.
2. RF Receiver assembly
The RF system used two Chipcon Texas Instruments CC2431 microcontrollers (6 mm × 6 mm, 130 mg, 32 MHz clock, 2.4 GHz IEEE802.15.4 compliant RF transceiver); one acting as the beetle-mounted RF receiver and one as a computer-driven RF transmitter base station. Based on the circuit diagram, we designed and manufactured a custom PCB [16 mm × 13 mm, FR4 (rigid), 500 mg] for the receiver. The microcontroller and the other components including surface mount resistors, an oscillator and a folded dipole antenna were assembled on the PCB as shown in Figure 2 in Supplementary Material. The microcontroller was then loaded with a custom signal-generating software (BeetleBrain v0.99b).
The wire electrodes were soldered on the output pads. The circuit diagram in Figure 2 in Supplementary Material shows, for example, the case when two wire electrodes for stimulating left and right optic lobes were soldered on two of the output pads, P1_5 and P1_6, respectively. To power the microcontroller, tow wires were soldered to two pads on the PCB: one was connected to GND and the other one to the DVDD (AVDD was also lined together to this pad).
A rechargeable micro lithium ion battery (Micro Avionics, 3.9 V, 350 mg, 8.5 mAh) was then attached to the PCB with a piece of double adhesive tape. The negative and positive terminals of the battery were connected to the two wires coming from the GND and DVDD pads, respectively, when the RF receiver was in use.
Six small holes were carefully pierced on M. torquata: (a) at the center of the head between the compound eyes for the brain, (b) toward the posterior end of the pronotum for the counter electrode site, © midway between the sternum and notum of mesothorax for the basalar flight muscles, and (d) at the interior edge of compound eye for the optic lobe (see Figure 1). The RF receiver was then mounted on the beetle’s posterior pronotum and attached with beeswax. The terminals of wire electrodes coming from the output pads on the PCB were implanted into the brain, posterior pronotum, left and right basalar flight muscles, and the left and right optic lobes.
FEATURES OF MICRO CONTROLLER
The CC2430 is a true System-On-Chip (SOC) for wireless sensor networking ZigBee /802.15.4 solutions with location detection engine hardware onboard allowing location accuracy of around 3 meters or less. It enables ZigBee nodes to be built with very low total bill-of-material costs. The CC2430 combines the excellent performance of the leading CC2420 RF transceiver with an industry-standard enhanced 8051 MCU, 128 KB flash memory, 8 KB RAM and many other powerful features. The CC2430 provides the market’s most competitive ZigBee solution. The CC2430 is highly suited for systems where ultra-low power consumption is required. This is achieved by various operating modes. Short transition times between these modes further ensure low power consumption.
• Location Engine accurately calculates the location of a node in a network
• High performance and low power 8051 microcontroller core.
• 2.4 GHz IEEE 802.15.4 compliant RF transceiver (industry leading CC2420 radio core).
• Excellent receiver sensitivity and robustness to interferers
• 128 KB in-system programmable flash
• 8 KB RAM, 4 KB with data retention in all power modes
• Powerful DMA functionality
• Very few external components
• Only a single crystal needed for mesh network systems
• Low current consumption (RX: 27mA, TX: 25mA, microcontroller running at 32 MHz)
• Only 0.9μA current consumption in power-down mode
1. Flight initiation and cessation
In Mecynorhina torquata, alternating positive and negative potential pulses between an electrode implanted into the brain and a counter elec¬trode implanted into the posterior pronotum of the adult insect reproducibly generated flight initiation and cessation with success rate of 56% (N = 9) in fully tethered and weakly tethered beetles. Flight initiation occurred either during or immediately after the negative potential pulse (following a positive pulse) was applied to the beetle. For each insect there was a voltage threshold for flight initiation (median 3.2 V).
Below this voltage, legs stretched or contracted but flight did not start. Legs folded inwards during negative pulses and extended into the correct flight posture during positive pulses, which suggests that positive pulses activate at least some of the complex motor patterns of flight initiation, while negative pulses activate an opposite set of muscles. In the weakly tethered and fully untethered condi¬tions, some beetles collapsed briefly when stimulated, which indicates that the stimulus caused not only muscle movement coordinated with wing oscillation but also uncoordinated muscle movement associated with generalized neural depolarization.
Above figure shows Initiation and cessation control of Cotinis texana beetle during tethered flight; (top) audio recordings of tethered beetle, (bottom) applied potential to the brain (with counter electrode inserted into posterior pronotum). The applied potential waveform is identical but frequency varied.
During flight, wing oscillation frequency could be manipulated by modulating the wing oscillations with the neural stimulator. For M. torquata, it was observed that progressively shortening the time between positive and negative pulses led to a “throttling” of flight where the beetle’s normal 76 Hz wing oscillation was strongly modulated by the 0.1–10 Hz applied stimulus. A repeating program of 3 s, 10 Hz, 3.0 V pulse trains followed by a 3.3-s pause (no stimulus) resulted in alternating periods of higher and lower pitch.. High speed (6000 fps) video showed that during stimulation, wing oscillations had a 5.6% greater frequency than during un-stimulated flight. For, brain stimulus at 100 Hz in the same manner led to depression of flight. Set on a custom pitching gimbal,beetle could be repeat¬edly made to lower its attack angle to the horizon when; note how stroke amplitude is visibly reduced. Ten of eleven tested beetles showed this tendency. Occasionally, stimulation resulted in flight cessation. In free flight, this
corresponded to a controllable drop in altitude when stimulated. One second of stimulus resulted in a 60-cm median drop in altitude (range 33–129 cm).
Elevation control of a free-flying Mecynorrhina torquata beetle: temporal height-change of a flying beetle (ten flight paths).
3. Turn control
Turns were elicited by stimulus of the left and right basalar muscles with positive potential pulse trains. In M. torquata, the basalar muscles normally contract and extend at 76 Hz when they are stimulated by ∼8 Hz neural impulses from the beetle nervous system. It has been reported that the flight muscles produce maximum power when they are stimulated directly by electrical pulses at 100 Hz. During flight, a turn was triggered by applying 1.3 V, 100 Hz positive potential pulse trains to the basalar muscle opposite to the intended turn direction. A right turn, for example, was triggered by stimulating the left basalar mus¬cle. The success rates for left and right turns were 74% (N = 38) and 75% (N = 52), respectively. Half second of stimulation to the left and right basalar muscles of free-flying beetles resulted in a 1.7° and −9.0° median inclination angle, respectively, and 20.0° and 32.4° median yaw angle, respectively. During flight, beetles tended to adjust their attitude so as to fly parallel to the ground plane. This intrinsic characteristic of beetle flight made it possible to elicit turns in a desired direction with just one degree of control.
1. Military spy
Small remote-controlled insects which can spy on anyone without the notice of anyone can be developed from this cyborg beetles. It also reduces the high costs associated with the spy.
2. Micro and nano air vehicles
In engineering, electronically controllable insects could be useful models for insect-mimicking MAVs/NAVs. Furthermore, tether less, electronically controllable insects themselves could be used as MAVs/NAVs and serve as couriers to locations not easily accessible to humans or terrestrial robots.
3. Study of biological behavior
In biology, the ability to control insect flight would be use¬ful for studies of insect communication, mating behavior and flight energetics, and for studying the foraging behavior of insect predators such as birds, as has been done with terrestrial robots
This is the first-ever wireless flight control microsystem using a small RF receiver mounted on a live beetle and an RF transmitter operated from a base station. Flight initiation and cessation were accomplished by neural stimulation of both optic lobes while turns in free flight were elicited by muscular stimulation of basalar flight muscle on either side.
This project and implimentation will be of great use in the future in a lot of fields. Even though a lot more research and developments has to be made it still opens a new door to scientific researches. It also give a new and easier way for the study of various organisms.
1. Radio-controlled cyborg beetles: a radio-frequency system for insect neural flight control, h. satoi, y peerii, e. baghoomiani, c. w. berry, m.m maharbiz
2. D. J. Pines, F. Bohorquez, "Challenges Facing Future Micro-Air-Vehicle Development", J. Aircraft, vol. 43, pp. 290-305, 2006.
3. A. Bozkurt, A. Paul, S. Pulla, A. Ramkumar, B.Blossey, J. Ewer, R. Gilmour, A. Lal, "Microprobe Microsystem Platform Inserted During Early Metamorphosis to Actuate Insect Flight Muscle", Proc. IEEE MEMS 2007, pp. 405-408.
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