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Active and passive stabilization of body pitch in insect flight.

Ristroph L, Ristroph G, Morozova S, Bergou AJ, Chang S, Guckenheimer J, Wang ZJ, Cohen I - J R Soc Interface (2013)

Bottom Line: Flying insects have evolved sophisticated sensory-motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities.By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability.Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Cornell University, Ithaca, NY 14853, USA. ristroph@cims.nyu.edu

ABSTRACT
Flying insects have evolved sophisticated sensory-motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.

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Stability and control properties of insect flight. Dimensionless reaction TRXN/TI versus pitch damping TP/TI time scales for fixed TF/TI = 5.1, as appropriate for a fruit fly. The light blue regions indicate intrinsic stability due to strong damping, and the white region indicates intrinsic instability that may be controlled with fast reactions. (a) Coloured contours correspond to a control performance metric of the ratio of instability to reaction time scales. Good control (blue) is achieved by strong damping or fast reactions, while poor control (red) corresponds to weak damping and slow reactions. (b) Coloured contours correspond to a control performance metric of the phase margin. Generally, good performance is achieved with a phase margin of at least 45°. (Online version in colour.)
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RSIF20130237F5: Stability and control properties of insect flight. Dimensionless reaction TRXN/TI versus pitch damping TP/TI time scales for fixed TF/TI = 5.1, as appropriate for a fruit fly. The light blue regions indicate intrinsic stability due to strong damping, and the white region indicates intrinsic instability that may be controlled with fast reactions. (a) Coloured contours correspond to a control performance metric of the ratio of instability to reaction time scales. Good control (blue) is achieved by strong damping or fast reactions, while poor control (red) corresponds to weak damping and slow reactions. (b) Coloured contours correspond to a control performance metric of the phase margin. Generally, good performance is achieved with a phase margin of at least 45°. (Online version in colour.)

Mentions: The passive and active aspects of flight stabilization are then unified in figure 5a, which plots contours of this performance metric as a function of the dimensionless pitch damping and reaction times. Qualitatively, one can think of the horizontal axis as indicating decreasing passive stabilization, the vertical axis as indicating decreasing active stabilization, and the contours as the overall control performance. Here, a given insect should be viewed as a set of four independent time scales, namely the three physical time scales (TI,TF,TP) as well as its reaction time TRXN. Intrinsic or passive stability is achieved if (blue region) and, in this case, the value of TRXN is irrelevant since no active control is needed. If this condition is not met, then flight is intrinsically unstable and TINST is determined by the three physical time scales. Control performance can then be quantified by the ratio TINST/TRXN. For example, a performance of TINST/TRXN = 6 (light blue curve) can be achieved by a family of solutions ranging from slow reactions but high drag (upper left) to fast reactions and low drag (lower right). In general, the value of TINST/TRXN increases as one moves down or to the left, quantifying the better flight control that one expects with faster reactions or increased damping.Figure 5.


Active and passive stabilization of body pitch in insect flight.

Ristroph L, Ristroph G, Morozova S, Bergou AJ, Chang S, Guckenheimer J, Wang ZJ, Cohen I - J R Soc Interface (2013)

Stability and control properties of insect flight. Dimensionless reaction TRXN/TI versus pitch damping TP/TI time scales for fixed TF/TI = 5.1, as appropriate for a fruit fly. The light blue regions indicate intrinsic stability due to strong damping, and the white region indicates intrinsic instability that may be controlled with fast reactions. (a) Coloured contours correspond to a control performance metric of the ratio of instability to reaction time scales. Good control (blue) is achieved by strong damping or fast reactions, while poor control (red) corresponds to weak damping and slow reactions. (b) Coloured contours correspond to a control performance metric of the phase margin. Generally, good performance is achieved with a phase margin of at least 45°. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043156&req=5

RSIF20130237F5: Stability and control properties of insect flight. Dimensionless reaction TRXN/TI versus pitch damping TP/TI time scales for fixed TF/TI = 5.1, as appropriate for a fruit fly. The light blue regions indicate intrinsic stability due to strong damping, and the white region indicates intrinsic instability that may be controlled with fast reactions. (a) Coloured contours correspond to a control performance metric of the ratio of instability to reaction time scales. Good control (blue) is achieved by strong damping or fast reactions, while poor control (red) corresponds to weak damping and slow reactions. (b) Coloured contours correspond to a control performance metric of the phase margin. Generally, good performance is achieved with a phase margin of at least 45°. (Online version in colour.)
Mentions: The passive and active aspects of flight stabilization are then unified in figure 5a, which plots contours of this performance metric as a function of the dimensionless pitch damping and reaction times. Qualitatively, one can think of the horizontal axis as indicating decreasing passive stabilization, the vertical axis as indicating decreasing active stabilization, and the contours as the overall control performance. Here, a given insect should be viewed as a set of four independent time scales, namely the three physical time scales (TI,TF,TP) as well as its reaction time TRXN. Intrinsic or passive stability is achieved if (blue region) and, in this case, the value of TRXN is irrelevant since no active control is needed. If this condition is not met, then flight is intrinsically unstable and TINST is determined by the three physical time scales. Control performance can then be quantified by the ratio TINST/TRXN. For example, a performance of TINST/TRXN = 6 (light blue curve) can be achieved by a family of solutions ranging from slow reactions but high drag (upper left) to fast reactions and low drag (lower right). In general, the value of TINST/TRXN increases as one moves down or to the left, quantifying the better flight control that one expects with faster reactions or increased damping.Figure 5.

Bottom Line: Flying insects have evolved sophisticated sensory-motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities.By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability.Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Cornell University, Ithaca, NY 14853, USA. ristroph@cims.nyu.edu

ABSTRACT
Flying insects have evolved sophisticated sensory-motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.

Show MeSH
Related in: MedlinePlus