Peter continues his viscous aerodynamics analysis comparing Clmax/Re data for the 4402 and the 4404. He added
a test point at Re 12000and provided curve fits for use in the 3D rotor code. The current Cl/Cd fit does well with
Cd/alpha, but overestimates Cl at Re=12000 by as much as a tenth or two.
Several contacts were pursued to obtain data on feasible battery technology for the early prototypes and later mesicopters. We found data from JPL and from a company that manufactures Lithium-Polymer batteries. (http://www.yardney.com/lithion/cocompli.htm)
These batteries have an energy density of 130 mWh/g. Assuming a battery voltage of 3 V, we get 45 mAh per gram. The 2 C discharge capability means that we can draw 90 mA from that type of battery. Currently we drive each motor with 50 mA per coil, i.e assume 80 mA per motor. The motor controller would switch two motors in series, therefore we can drive all four motors with 160 mA (and that at a current range that is well above the rated limit for the motors). Bottom line: If we can get one of these batteries, we're set. Possible problem: They don't build small batteries, but focus on big stuff. Rudi talked to one of their folks and they said they can make the small batteries we want.
Lithium-ion Technology
outstanding energy density - 325 Wh/t
excellent specific energy -130 Wh/kg
long operating life -2100 deep cycles
continuous 2C rate
rapid recharge capability - C rate
broad temperature capability: -40° C to +65° C
This lithium-ion technology is the result of more than six years of continuing, applied research and development by the staff of Yardney Engineers and Scientists.
Ilan produced some optimized rotors that Shelly manufactured. These were tested on the pendulum scale and produced substantially more thrust than the original rotors. At one point we measured approximately 760 mg of thrust before the motor died.
The rotors and motors were combined in a 4-rotor mesicopter prototype. The rotors are co-rotating so tests of this device must be constrained.
Masses include 4x325 mg for the motors and rotors, 80 mg for the structure, and about 100 mg for the speed controller
and other items. This leaves about 1.5 g for batteries, implying a respectable flight duration when our batteries
are finally sorted out.
Gary Fay and Ilan have started some analytical work of mesicopter stability and will begin testing some larger
scale mesicopters to achieve passive stabilization. The work is currently one dimensional, and looks at restoring
forces and damping of half a mesicopter (2 rotors) on a pendulum.
Ilan presented a status report on the mesicopter work at the NIAC meeting in D.C.. Several contacts with NASA personnel at Johnson, Goddard, Glenn, and JPL were made which may be of great help in a second phase of the work.