Aerospace · Multirotor aircraft
Counter-rotating coaxial rotors on individually speed-controlled electric motors, charted against a 2005 quadrotor testbed and a 1991 coaxial model craft.
The technical question
The research approach
The research charted the European patent and its American sibling separately, each from its own claim language. It followed the drive unit from radio-controlled coaxial models through ducted-fan designs to a university quadrotor testbed, and kept the German claim’s wording apart from the English chart that reads it.
Chart each claim on its own words and keep the weakest limitation of each in view.
Submitted claim chart · European patent
Nordic Unmanned · EP 2 035 276 B1
Claim 1 · Inventive step · B, hold 62
Select a limitation to inspect the original reference page and its highlighted evidence.
Limitation 1f · B 80 · Weakest
STARMAC computes a net thrust value for each rotor and drives each motor by its own output; within the pair, Kinoshita rotates each propeller at a speed independent of the other. The claim asks for the capability, which these documents state.
Passages on the original page
The control inputs for each rotor corresponding to pitch, roll and yaw are computed separately, and then added to the altitude input and the nominal thrust to yield the net thrust value for each rotor.
R10-DASC · The Stanford Testbed of Autonomous Rotorcraft for Multi Agent Control (STARMAC) · Printed p. 12.E.4-8
What the score reflects
The weakest limitation. The owner will cite craft that run a unit’s two rotors together, at equal speeds or on one motor. Each is another design or an option beside the independent drive; none says a unit’s motors should not have individually variable speeds.
R10-DASC · Printed p. 12.E.4-8 · R2 · Claim 1, column 5, lines 44–45
Original reference · R10-DASC
Hoffmann et al. · 23rd Digital Avionics Systems Conference, Salt Lake City, 24–28 October 2004 · Authors’ copy
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Authors’ copy of the conference paper, hosted on the authors’ university pages. Printed pages 12.E.4-1 to 12.E.4-10.
Original document page. Highlights identify the quoted passages.
Recorded assessment: 18 October 2026. Scores assess the evidence for this ground; they are not probabilities of invalidity. P1 is the reason to combine, a claim-wide point. The claim’s authentic text is German; the chart’s English reading is shown.
The STARMAC paper describes a four-rotor aircraft with fixed-pitch blades, a quadrotor, flown autonomously outdoors. The claim’s German word, “Fluggerät”, is read as “aircraft”.
The words are plain. The date rests on the conference proceedings of August 2005, ten months before the priority date.
R10 · STARMAC, IEEE/RSJ IROS 2005 · Printed p. 468
The companion STARMAC paper mounts four fixed-pitch rotors at the ends of a cross frame, each rotor on its own motor: four drive units where the claim asks for at least three.
The owner may read “drive unit” as the assembly that carries both rotors. That reading goes to limitation 1d, where each unit gains its second rotor; for the count, STARMAC’s four rotor-and-motor units are the units.
R10-DASC · STARMAC, DASC 2004 · Printed p. 12.E.4-1
The on-board controller drives each motor through its own pulse-width-modulated output, and each rotor’s thrust follows the voltage applied to its motor. Each unit therefore has a first rotor on an electric motor whose speed is set.
The owner can argue that a voltage-commanded motor is not “speed-controlled”. The claim’s own words settle it: “gesteuert” (set) stands beside the closed-loop “Regelung” of limitation 1c.
R10-DASC · Printed p. 12.E.4-4
STARMAC flew autonomous hover with closed-loop control of attitude, altitude and position: inner loops through the motor voltages, an outer position loop fed by GPS. Its companion paper puts the controller on board the craft.
The two papers describe one testbed by one group and are scored as two references. Neither says in so many words where the outer, horizontal position loop runs; the answer is the companion paper’s “all control functions onboard”.
R10 · Printed pp. 468, 470 · R10-DASC · Printed p. 12.E.4-8
R10 · Original p. 468 R10 · Original p. 470 R10-DASC · Printed p. 12.E.4-8
Kinoshita gives each rotor of a coaxial pair its own variable-speed motor, the two propellers turning in opposite directions. Given that unit, each of STARMAC’s drive units has a second rotor on a second speed-controlled electric motor.
The rating rests on P1, the reason to fit Kinoshita’s unit to each of STARMAC’s units. The structural reading of “drive unit” is met, since Kinoshita’s pair is one coaxial assembly.
R2 · US 5,071,383 · Column 4, lines 53–54 · Claim 1
Kinoshita’s two propellers rotate in opposite directions, each at its own speed; Pauli’s upper and lower propellers are driven to opposite rotation independently of each other.
STARMAC turns rotors of different units opposite to each other, not the two rotors of one unit. The limitation comes with the unit of 1d and rests on P1, with no open point of its own.
R2 · Claim 1, column 5, lines 43–45 · R3 · DE 102 56 916 A1 · [0007]
STARMAC computes a net thrust value for each rotor and drives each motor by its own output; within the pair, Kinoshita rotates each propeller at a speed independent of the other. The claim asks for the capability, which these documents state.
The weakest limitation. The owner will cite craft that run a unit’s two rotors together, at equal speeds or on one motor. Each is another design or an option beside the independent drive; none says a unit’s motors should not have individually variable speeds.
R10-DASC · Printed p. 12.E.4-8 · R2 · Claim 1, column 5, lines 44–45
The reason to give each of STARMAC’s four units a second, counter-rotating rotor on its own speed-controlled electric motor, Kinoshita’s unit, for the patent’s own problem: a more compact craft for the same payload that keeps flying when a rotor fails. The art states the reasons, and Spirov and Pedersen had already put a counter-rotating pair in each of four units.
Two references in the same field with a reason stated in the art would rate higher; the point is held at 82 for the owner’s two answers, a remark that multi-rotor craft are harder to balance and a hindsight argument. This point affects the 1d–1f ratings.
Claim chart · Combination rationale
Submitted claim chart · United States patent
Nordic Unmanned · US 8,328,128 B2
Claim 1 · Obviousness · C, hold 7
Select a limitation to inspect the original reference page and its highlighted evidence.
Limitation 1j · C 58 · Weakest
Louvel’s loop corrects a tilt by raising one propeller’s speed and lowering the opposite one’s; within a pair, Kinoshita holds the heading with equal speeds, climbs with both and turns by a difference.
Passages on the original page
If the information supplied by the sensor (61) indicates that the aircraft is tilting towards the right side, then the correction consists in increasing the speed of the propeller 11, decreasing the speed of the propeller 13, meanwhile the speeds of the propellers 10 and 12 remain unchanged.
R1 · Louvel, US 2002/0104921 A1 · Printed p. 4
What the score reflects
The weakest limitation. No reference controls attitude and position through the individual speeds of both motors in each of three or more coaxial units, so the loop over eight motors is the combination’s (W2), and the narrow reading of “attitude and position control” (W1) carries over from 1a.
R1 · [0100] · R2 · Column 5, lines 4–7
Original reference · R1
United States patent application publication · Electrical remote-control and remote-power flying saucer · 8 August 2002
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Public copy of the patent document as published by its patent office; served by Google Patents.
Original document page. Highlights identify the quoted passages.
Recorded assessment: 18 October 2026. Scores assess the evidence for this ground; they are not probabilities of invalidity. W1 is the reading of “autonomous attitude and position control” and W2 the reason to combine; both are claim-wide points.
Louvel describes a remotely controlled, remotely supplied aircraft powered by propellers driven by electric motors, able to hover and move in the three directions of space.
Literal and in plain words.
R1 · US 2002/0104921 A1 · [0007]
Louvel’s on-board tilt sensors and yaw gyro feed a closed loop that holds the attitude, cancels yaw and moves the craft through its four motor units. The examiner read the term as automatic control by programmable electronics, as the patent itself does.
Under the owner’s narrow reading, closed-loop attitude and position control on board, Louvel’s loop runs off board and the craft is piloted through a handle; the chart then rests on STARMAC and Wobben. Scored at W1.
R1 · [0042], [0091]
Louvel’s four lift propellers, one per drive unit; after the combination, the upper rotor of each coaxial pair.
Literal and in plain words.
R1 · [0029]
Each propeller is driven independently by an electric motor, and the control unit sets the speed of each motor through its own pulse-width-modulated drive.
The owner can argue that a PWM current drive is not “rotary speed-controlled”; Louvel’s own words, “control the speed of each electric motor”, settle it.
R1 · [0030], [0061]
Kinoshita’s second propeller sits below the first on the same axis, the two turning in opposite directions; Pauli and Xing show the same unit, and Spirov and Pedersen give each of four ducted fans two counter-rotating units.
The reasons to combine are stated in the art (W2), but the owner has a colourable different-problem answer in Xing’s remark about multirotor balance.
R2 · Column 4, lines 53–54 · R3 · [0007]
Kinoshita drives each propeller of the pair by its own variable-speed motor, the two rotating in opposite directions; Paul puts such counter-rotating electric motors in every one of three units.
No multi-unit reference calls the second motor speed-controlled; that comes from the single-pair references by the combination. A narrow open point.
R2 · Claim 1, column 5, lines 43–45
Within the pair, Kinoshita rotates each propeller at a speed independent of the other: both up or down to climb, a difference to turn. Across the craft, Louvel sets every motor’s speed separately.
A live open point: no reference varies the speeds of both motors of each of three or more coaxial units individually; one reference disclaims per-rotor speed control, another feeds both motors of a fan from one module.
R2 · Claim 1, column 5, lines 44–45 · R1 · [0061]
Louvel’s two crossing boards form four arms radiating from the central part, each arm end carrying one motor-propeller unit, with no member joining the motors.
Louvel’s solid casing side area is attached to the board ends, a ring tied to the arm ends. The patent’s own dependent claims add such protection rings to the same frame, so the clause excludes drive units secured to each other, not a guard on the arms. Narrow.
R1 · [0031], [0032]
One board bears two motors and the other board the other two: one motor-propeller unit at each arm end.
Literal.
R1 · [0032]
Kinoshita mounts the second propeller on a rod shaft that runs through the first propeller’s sleeve shaft; Xing uses a core shaft inside a hollow sleeve.
If the owner reads the limitation to require coaxial motors, the chart rests on Paul’s concentric motors and on documents the owner may try to antedate. Narrow.
R2 · Claim 1, column 5, lines 54–56
Louvel’s loop corrects a tilt by raising one propeller’s speed and lowering the opposite one’s; within a pair, Kinoshita holds the heading with equal speeds, climbs with both and turns by a difference.
The weakest limitation. No reference controls attitude and position through the individual speeds of both motors in each of three or more coaxial units, so the loop over eight motors is the combination’s (W2), and the narrow reading of “attitude and position control” (W1) carries over from 1a.
R1 · [0100] · R2 · Column 5, lines 4–7
Read as the examiner and the patent read it, automatic control by programmable electronics, which Louvel’s sensor loop meets. Under the owner’s narrow reading, closed-loop attitude and position control on board, the chart rests on STARMAC’s on-board loops and on Wobben.
A claim-wide point that limitations 1a and 1j depend on. These pages show the STARMAC loops the narrow reading falls back on.
Claim chart · Claim construction
The reason to fit Louvel’s quadrotor with the coaxial pair in which each rotor has its own speed-controlled electric motor: the art states it (torque cancelled within the pair, flight on one motor, more lift, more efficiency), and a 2004 four-unit craft took the step.
Counted once for the chart. The owner has a colourable answer: Xing’s remark that a multirotor’s balance is hard to control, and hindsight.
Claim chart · Combination rationale
Also recorded in the research
2 backup grounds beside the submitted chart
Each alternative ground below was researched and recorded with the submission. Its verdict is the one recorded in the research; alternatives are not scored on the band scale unless the record scores them.
References
R4 · JP 2002-347698 A (Ishigaki Foods) · R6 · US 2005/0061910 A1 (Wobben) · R1 · US 2002/0104921 A1 (Louvel)
Recorded verdict
Recorded as a fallback only, not scored. Under a broad reading of “Antriebseinheit”, a functional pair of counter-rotating rotors each on its own motor, Ishigaki has three such pairs with individual prime movers, Wobben supplies the individually variable speeds and the autonomous attitude, altitude and position device, and Louvel the speed-based attitude regulation. The owner will argue the structural reading of claims 6 and 7, under which Ishigaki’s pairs are units opposite each other across the hub, not one unit, and its computer runs the engines so as to rotate at uniform speed; 1f then rests on Wobben and Louvel, not on Ishigaki.
At least three drive units, each with a second rotor turning opposite its first.
“中心対称をなし、かつ反転する揚力発生用プロペラ(23)(23)を有する揚力発生用プロペラユニット(20)(20)が、３対設けられている”
three pairs of lift-propeller units with centrally symmetrical, counter-rotating lift propellers are provided
R4 · JP 2002-347698 A · [0024] · PDF p. 3
Six units in three counter-rotating pairs, each propeller with its own prime mover; the Japanese original is quoted with the researcher’s translation.
Means for autonomous attitude and position control.
“the aircraft according to the invention has a device for automatic control of the flight attitude and/or the flight altitude.”
R6 · US 2005/0061910 A1 · [0013]
The device can also be coupled to a GPS system so as to head automatically for a predeterminable position.
The rotation speeds of the electric motors of each drive unit are varied individually.
“Associated with each motor 10 is an inverter 14 which permits individual actuation of each motor 10.”
The speed-based attitude regulation.
“The function of the control unit (3) is to control the speed of each electric motor by adjusting the current in each of them by a pulse width modulation (PWM) current drive.”
References
R5 · WO 2004/101357 A2 (Spirov and Pedersen) · R4 · JP 2002-347698 A (Ishigaki Foods) · R1 · US 2002/0104921 A1 (Louvel) · R2 · US 5,071,383 A (Kinoshita)
Recorded verdict
Recorded as alternative starting points, not scored. With Spirov and Pedersen as the primary: four electric lift units, each motor individually speed-controlled, an on-board automatic attitude loop and, in an alternate embodiment, a counter-rotating pair in every duct, with Kinoshita, Pauli or Xing adding a motor per rotor and the pair’s individual speed control; weaker than Louvel on 1g, the ducts sitting in a saucer body rather than on arms. With Ishigaki as the primary: six arms from a hub, counter-rotating pairs, one prime mover per propeller and computer control, with Louvel for the speed-based attitude control; weaker on 1g, the side rods joining the units, and on 1f, the computer running the engines at uniform speed. The chart also names US 2006/0016929 A1, a counter-rotating ducted fan whose two propeller stages have their own windings and controller, in place of Kinoshita, without a held copy or a quote.
Autonomous attitude and position control provided by at least three drive units.
“The hover control system uses an XYZ sensor arrangement and associated control circuitry that dynamically determines an inertial gravitational reference for use in automatically and continuously determine the speed needed for each fan in order to keep the craft at a desired orientation.”
A scanned page: the quote is shown beside it without highlights.
A first and a second rotor in each unit, each on its own speed-controlled motor, turning opposite.
“In an alternate embodiment that provides for more efficiency, each of the ducted fans 40 has two counter-rotating multi-bladed units.”
R5 · WO 2004/101357 A2 · p. 19
Kinoshita, Pauli or Xing add a motor per rotor and the pair’s individual speed control.
With Ishigaki as the primary: the drive units on arms from a central hub.
“中心対称をなし、かつ反転する揚力発生用プロペラ(23)(23)を有する揚力発生用プロペラユニット(20)(20)が、３対設けられている”
three pairs of lift-propeller units with centrally symmetrical, counter-rotating lift propellers are provided
R4 · JP 2002-347698 A · [0024] · PDF p. 3
Six arms from a hub; the side rods joining the units are the weakness on 1g.
Individually variable speeds and the speed-based attitude control.
“The function of the control unit (3) is to control the speed of each electric motor by adjusting the current in each of them by a pulse width modulation (PWM) current drive.”
The two rotors of each unit disposed coaxially.
“said second propeller securely attached to a rod shaft which extends longitudinally through said sleeve shaft”
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