This letter presents a method to sense motor torque of multirotors in steady state, without additional torque sensors by using the measured input voltage, throttle setting and rotational speed. Torque, rotational speed and current of a brushless direct current (BLDC) motor with electronic speed controller (ESC) are measured on a setup using seven different propeller sizes as torque loads, seven input voltages and 20 throttle settings. The resulting rotational speed, torque and current are measured to create a data set spanning the feasible operating range of this motor with speed controller. A novel model for a BLDC motor with ESC based on only four parameters is proposed and trained on the data of only one propeller as torque load and the data without torque load. This model results in torque errors less than $\text{0.01 Nm}$ or 4.6% of the data set range for 90% of the data set. For the highest accuracy, the whole data set is re-mapped into a practical 3D lookup table using local fits and results in torque errors less than $\text{0.005 Nm}$ or 2.3% of the data set range for 90% of the data set. This method can be used for system identification, control design, system monitoring and benchmarking.

This paper presents experimental results on the relation between forward airspeed, pitch angle, and power consumption of a quadcopter unmanned aerial vehicle. The quadcopter consists of an interchangeable spherical body, four cylindrical arms, and small propellers mounted at 1 m diagonal distance to minimize interference between body and propellers. This simple geometry facilitates results reproduction and comparison with simulation. Two different takeoff masses and four diameters of spherical bodies are tested for their steady-state speed and power for pitch angles up to [Formula: see text]. The steady-state horizontal flight is recorded with on-board sensors at the end of flying long straight lines at a constant pitch angle in wind-still conditions. The best effective lift-to-drag ratio increases for smaller bodies and occurs at higher speeds for increasing mass. Results show that the equivalent frontal surface stays constant for pitch angles further than [Formula: see text] up to the maximum recorded [Formula: see text] and increases linearly with the frontal surface of the body.

This paper presents experimental results on the relation between forward airspeed, pitch angle and power consumption of a quadcopter UAV. The quadcopter consists out of an interchangeable spherical body, four cylindrical arms and small propellers mounted at 1m diagonal distance to minimize interference between body and propellers. This simple geometry facilitates results reproduction and comparison with simulation. Two different takeoff masses and four diameters of spherical bodies are tested for their steady-state speed and power for pitch angles up to −45◦. The steady-state horizontal flight is recorded with on-board sensors at the end of flying long straight lines at a constant pitch angle in wind-still conditions. The best effective lift-todrag ratio increases for smaller bodies and occurs at higher speeds for increasing mass. Results show that the equivalent frontal surface stays constant for pitch angles further than −5◦ up to the maximum recorded −45◦ and increases linearly with the frontal surface of the body.

This paper presents the modeling of the performance of small propellers used for vertical takeoff and landing micro aerial vehicles operating at low Reynolds numbers and in oblique flow. The blade element momentum theory, vortex lattice method, and momentum theory for oblique flow are used to predict propeller performance. For validation, the predictions for a commonly used propeller for vertical takeoff and landing micro aerial vehicles are compared to a set of wind-tunnel experiments. Both the blade element momentum theory and vortex lattice method succeed in predicting correct trends of the forces and moments acting upon the propeller shaft, although accuracy decreases significantly in oblique flow. For the dataset analyzed here, combining the available data of the propeller in purely axial flow with the momentum theory for oblique flow and applying a correction factor for the wake skew angle results in more accurate performance estimates at all elevation angles.

Multi-rotor Unmanned Aerial Vehicles make use of multiple propellers, mounted on arms, to produce the required lift. This article investigates the influence on propulsion system efficiency in hover due to the configuration of these propellers. Influence of pusher or puller configuration of the propeller, number of blades, shape and dimensions of the arm, coaxial and overlapping propellers, is presented. A dedicated test bench that allows testing of various experimental setups is designed and built in order to realistically represent multi-rotor arms. Test results show that a two-bladed pusher configuration is most efficient and slenderness of the arm has more influence on efficiency than shape. A coaxial propulsion system approaches the efficiency of a single-prop system at high disk loadings. Finally, interference effects due to overlapping propellers are discussed.

This paper describes a control approach for transitioning VTOL UAVs controlled by differential thrust, allowing to fly in all flight phases spanning a continuous transition between hover and cruise flight. A quaternion based attitude controller makes use of an additional reference frame that is rotated by the transition angle with respect to the body-fixed frame. This approach allows intuitive control and applies to various vehicle configurations. After building a simulation model, a small series of tests is used to build and validate maps of the flight characteristics of the vehicle. These maps are inverted and used to control the vehicle's velocity. Test flights with a custom built VTOL UAV for transition angles up to 70°, validate the control approach.

This paper presents the design and control of VertiKUL, a Vertical Take-Off and Landing (VTOL) transitioning tailsitter Unmanned Aerial Vehicle (UAV), capable of hover flight and forward flight for the application of parcel delivery. In contrast to existing transitioning UAVs, VertiKUL is not controlled by control surfaces, but exclusively by four propellers using differential thrust during hover flight, transition and forward flight. A numerical design method optimising range and payload is developed for initial sizing. A simulation model is implemented in Simulink to evaluate different control strategies before conducting test flights. A unique mid-level control strategy enabling intuitive control of VertiKUL which requires no pilot skills is developed. Fluent transition from hover to forward flight is achieved through an autonomous control strategy. Attitude control based on quaternions instead of Euler-angles is implemented to avoid singularities. The resulting design, VertiKUL, is built and test flown.

This paper presents the design and control of VertiKUL, a Vertical Take-Off and Landing (VTOL) transitioning tailsitter Unmanned Aerial Vehicle (UAV), capable of hover flight and forward flight for the application of parcel delivery. In contrast to existing transitioning UAVs, VertiKUL is not controlled by control surfaces, but exclusively by four propellers using differential thrust during hover flight, transition and forward flight. A numerical design method optimising range and payload is developed for initial sizing. A simulation model is implemented in Simulink to evaluate different control strategies before conducting test flights. A unique mid-level control strategy enabling intuitive control of VertiKUL which requires no pilot skills is developed. Fluent transition from hover to forward flight is achieved through an autonomous control strategy. Attitude control based on quaternions instead of Euler-angles is implemented to avoid singularities. The resulting design, VertiKUL, is built and test flown.

This paper presents experimental results of the full 3-axis force vector and 3-axis moment vector acting on a propeller, commonly used for a Vertical Take Off and Landing Micro Aerial Vehicle (VTOL MAV). Measurements were carried out in a wind tunnel using a high resolution 6-axis force/moment sensor embedded in a customized test rig at several wind speeds, propeller rotational speeds and angles of the propeller shaft with respect to the air stream. Results show strong moments acting on the propeller in forward flight and unstable conditions in descending flight. Power calculations reveal a decrease in power consumption during slow forward flight and how motor efficiency can be maximized.

This paper describes a parameter selection method and performance assessment for the preliminary design of Vertical Take-Off and Landing Unmanned Aerial Vehicles (VTOL UAVs) that use a combination of wings and a set of electrically powered propellers for providing lift and thrust during cruise flight. This method allows us to quickly evaluate the possibilities of current technology for a given set of user and missionspecific requirements, and to create a preliminary design to meet these requirements. To this end, the acceptable range for the variable design parameters is predetermined and the parameters to optimize are identified. Mass and power models are presented for the components of the UAV and a novel model for a propeller in oblique flow conditions is applied. The models are used in a design algorithm that calculates all combinations of components. All feasible solutions are selected and displayed to the user after which the optimal solution can be chosen. A design case is presented and a sensitivity analysis shows the influence of different design parameters on this case.