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Scaling Down - The Optimal Choice?. Fritz B. Prinz Departments of Mechanical Engineering and Materials Science and Engineering Stanford University Stanford, CA 94 305. Outline. Scaling laws Physics Engineering performance (power, power density) Mechanical tolerances
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Scaling Down - The Optimal Choice? Fritz B. Prinz Departments of Mechanical Engineering and Materials Science and Engineering Stanford University Stanford, CA 94 305
Outline • Scaling laws • Physics • Engineering performance (power, power density) • Mechanical tolerances • Manufacturing Processes • Examples • Turbine engine • Mites (millimeter sized flaps) • Mesicopter
A World Apart 10-4mm-1 10-1mm-1 104 - 102
Scaling of Strength and Stiffness Failure Load Failure Load per Weight Bending Stiffness per Weight Beam
Scaling of Moving Objects • Find relation between: • Mass m • Length l • Time t
Scaling of Length and Time k = 2 elastic K= -1 electro - static motor, gravity (Kepler’s third law)
Scaling of Mass For v << c Relativisitic:
Electro Static Motors In theory: Assuming all dimensions e.g. gaps can be scaled down
Constant Field In practice: E = constant
Scaling of Critical Dimensions? Electro static /magnetic motors l Tolerance
A Manufacturing Issue Determined by manufacturing process Determines quality of machine Traditional mechanical machines Integrated circuits May not be achievable Even
Turbine Combustion Engines Power Density (1/l) - Thrust to Weight T/W = 5.6 T/W= 7.6
Operating Temp. (OC) Current (metal) design Design incorporating ceramics M-Dot Micro Engine for Drone Aircraft Weight (g) Thrust-to-weight ratio Thrust (N)
Shape Deposition Manufacturing ( SDM) From RP and CNC to . . . RP CNC 1960 1990 2000
Sangkyun Kang: Mold Shape Deposition Manufacturing • Builds wax molds via SDM using Soldermask temporary part material • Gel cast ceramic slurry into • sacrificial mold
Ceramic Inlet Nozzle Fully dense Silicon Nitride Strength ~ 400 - 600 Mpa as sintered RMS ~ 0,5 micro meter
Micro Flaps for Aero Elastic Control • Maximize flight time of Unmanned Air Vehicle (UAV) Front view
Suggested Solution • Aeroelastic control using trailing edge effects • Concept • Span-wise lift control via micro-flaps Micro-flaps
Flap Surface 6 mm Airfoil Approach • Design & Manufacture Micro-flaps Requirements • Small size (6 mm) • Large deflection (± 75°) • Frequency (10s HZ) • Material strength
1 2 3 5 4 6 Build Sequence in SDM
Micro Flap for Aero - Elastic Control Clearance ~ 50 micron
Aerodynamics • New results for very low Re airfoils • Very thin sections required • Maximum lift increases as Re decreases below 10,000
Rotor Optimization • Chord, twist, RPM, blade number designed using nonlinear optimization • 3D analysis based on Navier-Stokes section data • Rotor matched with measured motor performance (50 000rpm)
Aerodynamics • Navier-Stokes analysis of rotor sections at unprecedented low Reynolds number • Novel results of interest to Mars airplane program • Nonlinear rotor analysis and optimization code
SDM Rotor Manufacturing 1. Micro-machine bottom surface of rotor on wax 2. Cast epoxy 3. Remove excess epoxy 4. Machine top surface of rotor 5. Melt wax
Scaled Down Mesicopter • Insect-Scale Aerodynamics • 3D Micro-Manufacturing • Power / Control / Sensors
Mesomotor Rotor Stator Anker- spule REM-Aufnahme des 2mm-Motors Explosions- ansicht des Motors
Shaping of Electrodes Sputtering of seed layer SEM Micro- graph of etched silicon Plating SEMMicro- graph of plated electrode
EDM of Amorphous Metals Electro Discharge Machining
Massively Parallel Mechanical Systems One Electro Static Motor Many Electro Static Motors