1923

Item 1923

DESIGN: Electrotor-SloMo - Rotorhead - Synchronization - Overview

Primary Considerations:

Very seriously consider and work toward electrical or magnetic rotor-to-rotor synchronization. This is particularly applicable to UAV and R&D toward eventual manned flight. In addition to redundancy etc., see Regenerative Braking below.

Reasons for Synchronization: Review the list below , restructure and prioritize. And list the solutions to alleviate these problems

Concern:

The blades of the Intermeshing and the Interleaving rotors may accommodate a light 'stropping' of the blades. However, the serious threat is the when the blades of each rotor close on each other. The blades must intersect with the respective blades being above or below the other. With outside forward rotation the intersection angles are; [from DESIGN: Electrotor-SloMo ~ Rotor - Disk - Blade to Blade Clearance - Intermeshing - 3-blade]

For the Intermeshing the vertical gap between the tip of one rotor's blade (@ 143º azimuth) and 62" radius on the other rotors blade (@ 203º azimuth) is 8". A single degree of opposing longitudinal tilt on the two rotors results in a decrease of this gap by 2.5"

For the Interleaving the blades never overlap; UNLESS they were to get considerably out of sync.

Potential Causes:

Perturbations.

Total loss of power;

Both battery-packs loose charge. Potential solution:- Short-term power provided by capacitor for flare and touchdown.
Power wiring disconnect in both circuits
Both sub-controllers fails
Supervisory controller fails.

Unequal power in the 2 motors.

Loss of power in 1 motor.

Loss of power in both rotors.

Locked Rotor(s) ~ no solution.
Magnet comes loose and does not break up into small pieces.

Friction within a motor due to off-center air gap.

Synchronize the aero-rotors or the motor-rotors?

Probably the aero-rotors.

Methods:

Electrically:

One RRPM sensor at 0º azimuth on one rotor and at 60º azimuth on other rotor, if the rotors are 3-bladed. If the indicators are not synchronized have the slower one accelerate and/or the faster one decelerate.

There could be three independent sets of sensors and comparators for redundancy.

The above retardation might be braking by the motor, or by a mechanical retarder, or an aerodynamic retarder.

Hall Effect Sensor:

Encoder - Absolute:

Sensorless ?

Regenerative braking: Would it be advantageous to include the regenerative braking for use when the 'out of sync' exceeds a certain angle? This regeneration would act as a brake on the leading rotor and the addition power could be used as a short-term increase in power to the lagging rotor. Work out at some time what the maximum out-of-sync angle is for the rotors to experience blade to blade contact. The possible maximum flapping (bowing of the blades) must also be included when evaluating this condition.

______________________

Build a counter for the RRPM and then upgrade it to a comparator for twin rotor synchronization.

Rough work up of information.

LM555 and LM556 Timer Circuits & The 555 IC
Hall Effect Interface IC MAX9921

Consider using the hexadecimal computer components

Hall Effect Sensor:

Comparison circuit:

Output to digital display and output to speed controllers.

Put on MAKE page if this item is to be built.

Mechanically:

Mechanically interlocking the rotors; at the hub, blade, motor, etc.
Might a pair of fans (complete with outer rims) also serve as a pair of gears that interconnect the two rotors?

Aerodynamically:

Perhaps giving the cooling fans on the two motors the ability to independently increase their drag (and their induced airflow over the stator).

The leading rotor would have its fan driven to retard the rotor. How ever this might have adetrimental effect due to the cooling of this motor and its resultant increase in efficiency.

This is not going to solve the problem quickly enough and if the fan improves efficiency it should probably be there in the first place.

Some combination of the above:

Synchronization of Aero-Rotorheads:

Good:~ This directly synchronizes the item (rotorhead) that must be in sync.

Good:~ The rotorhead has a large diameter than the motor's rotor.

What is the number of 'teeth' that are required to provide effective mechanical synchronization [Must/should be dividable by 3]. Nine are required.

Concern: Only one operational motor will increase the pitch in its rotor head only.

Solution:~ Full duplicity within both motors should overcome this concern.

Concern: This halves the electronic gearing. ~ not good because torque is required.

Synchronization of Motor's Rotors:

Good: It gives the maximum electrical gearing, while maintaining synchronization if one motor fails.

? Good:~ Unequal power to the rotors will increase the pitch in one, and this will proved yaw..

? Concern:~ There will be a torque-roll coupling applied to the craft. However, it will be less than 6º and weight-shifting should accommodate it.

Dampers may be required.

Perturbation Consideration re Torque-Pitch:

From the following it appears that perturbations should have little to no effect in changing the pitch of the rotors:

The pitch angle is based on the torque between the rotorhead and the motor-rotor. The rotational inertia of the rotorhead is far greater than the rotational inertia of the motor-rotor. Therefore a change in power by the pilot(on the motor-rotor) will result in a fast change in the pitch whereas a change in the drag (on the rotorhead) will have a slower change in the pitch angle.
Hopefully, this will also mean that a perturbation on one rotor will not be detrimental to electrical synchronization.
This also supports the hope that only the motor-rotors need to be synchronized and the rotorheads do not.

Inertia:

Rotorhead:

The mass of the 3 blades is 2.5 lb each and the rotorhub is 10 lbs

Moment of Inertia: J_M = ¹/₂Mr² ; Blades = ¹/₂x (3 x 2.5) x (900) = 3,375 in-lb, Hub = ¹/₂x 10 x (42.25) = 211 in-lb; Total = 3,586 in-lb.

Motor's Rotor:

The mass of the motor's rotor is 6 lbs.

The radius of gyration is

Moment of Inertia: J_M = ¹/₂M(R² +r²) = ¹/₂x 6 x (5.5² + 4.8125²) = 160.23 in-lb

The Ratio between the two is 3,586 / 160 = ⁺/_- 22 : 1

Notes:

A Note

Both rotors do not have to know whether their azimuthual position is ahead of AND whether their azimuthual position is behind that of the other rotor. Both rotors only have to know whether they are ahead OR or they are behind. In other words, the sensing device(s) only need to read one situation and it is the same type of situation that is read by both the sensor or the synchronization devices on both electro-rotors.

Musings re Rotor-Rotor Synchronization:

Torque [ft-lb] = 5252 * HP / RPM

If the rotational velocity of the two rotors and the power at the two motors is equal than the torque of the two rotors must be equal.

Theoretically, if the torque at the two rotors is equal and the pitches of the blades at the two rotors are equal then the thrust of the two rotors must be equal.

The potential concern is the accuracy of the torque-pitch coupling device.

Proposed method:

Hold synchronization ~ This is paramount.
Dissymmetry of thrust might cause a roll.
Because fuselage is tightly coupled to the two rotors in respect to roll, movement about the X-axis will result in the inertia of the fuselage resisting initial roll.
Then the off-center of the gravitational pull on the fuselage will tend to resist the roll.
Perhaps the above will suffice.

Remember the rotors MUST retain synchronization if there is a loss of power in one or both rotors.

This is a critical argument for total electrical redundancy; in each motor.

Redundancy due to two motors will not work because the powered rotor will be experiencing increased pitch whereas the 'slaved' rotor will not.

Initially displayed: May 28, 2010~ Last Revised: October 27, 2011

The above utility invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use it. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.