Shelly has been fabricating a number of rotor designs, trying to get good surface finish and accurate section shape without flashing or warping. Since CNC milling plays an important role in shaping the rotors, availability of appropriate end mills and machine accuracy are considered crucial for success. The smallest available ball end mills are 0.254 mm with a flute length of 0.762 mm. Feasible machining strategies are subject to these constraints. In addition, resolution of CNC cutting steps was chosen as one micron. Surface quality mainly depends on the magnitude of chosen cutting steps.
Scott spent some time planning tests using our pendulum apparatus to determine lift generated by the smaller and larger wings that Shelly made.
We tested two different rotor designs using a pendulum-type apparatus. We measured the horizontal deflection of the motor and rotor, and used this determine the lift generated at various speeds. The first rotor tested had a diameter of 15mm, and the second, larger one was 30mm. The smaller rotor is the design that Shelley created, and the larger one is the same design scaled by a factor of 2.
Both rotors produce the same amount of maximum lift, about 170mg. However, the speeds are quite different: 685 Hz (41,000 rpm) for the small rotor, and 168 Hz (10,000 rpm) for the larger rotor. So the lift/drag ratio is much better for the larger rotor.
It seems that a good next step would be to do the same test using one or more "optimized" rotor designs that Ilan and/or Peter generate. This will provide some validation for the design model, as well as give us some idea about the effect of rotor design variations on performance as measured by lift. While we wait for the optimized rotor design, Shelley is currently fabricating (and we will test) 3- and 4-bladed version of the 15 mm design.
The 3 millimeter diameter micro motor, made by RMB miniature bearings, Inc., was used to power propellers. During testing, horizontal deflections of pendulum were measured at different motor frequencies Deflections were used to calculate motor thrust and compare with the computational estimates.
The effect of the following propeller parameters was investigated: Rotor diameter, number of blades, pitch angle of the blades, and the shape of the leading edges of the blades.
Ilan has undertaken some larger-scale experiments on mesicopter stability. It appears that it may be possible to fly an unaugmented (naturally stable) version of the design which would make flight tests possible earlier in the program.