In the field of aerial robotics, one of the key challenges is to enable aerial manipulators to exert substantial forces on the environment. Enabling this will allow the technology to perform meaningful tasks airborne, such as cleaning or grinding surfaces. While in contact and applying a large, continuous force, control of the UAV's attitude is a challenge. In this work, we show that a regular (PID-based) attitude controller is incapable of stabilizing aerial manipulators that apply physical contact forces on the environment that are comparable to the UAV's weight. We present a novel control algorithm that uses an LQR-optimized state feedback on the roll and yaw angle while in contact. Experiments on a UAV of 1.5 kg show that the proposed controller is capable of applying a contact force of over 15 N-equal to the UAV's weightsustained for several minutes.

Legged locomotion involves periodic negative and positive work, which usually results in high power consumption. Improvement of the energy efficency is possible by using energy storage elements to reversibly store the negative work performed during a walking or running cycle. While series elastics with high impedance (high gear ratio) actuators are widely used, we investigate the application of parallel stiffness with highly backdriveable actuators. We specifically show that the use of parallel springs in a bounding quadruped with a flexible spine can lower power consumption by over 50%. I. INTRODUCTIONIn legged locomotion, every gait cycle involves both positive and negative work. Because most actuators cannot store negative work, the application of series compliance in walking robots is a widely used approach to increase energyefficiency (see for instance [1]-[4]). When high running speed is desired, the series compliance is often forgone to obtain a higher force bandwidth or control authority ([5]-[7]), sacrificing the energetic advantage of reversible, passive storage.Although with the series compliance approach low mechanical cost-of-tranport can be achieved, it should be noted that even when an electric actuator does not deliver any mechanical power, most will still use electrical power due to (thermal) losses, e.g. through coil resistance. Nonbackdriveable (high gear ratio) motors with series compliance can reduce loss during negative work, but the effective inertia becomes very large and the force bandwidth goes down.Very little attention has gone to the application of parallel stiffness, even though it enables the use of springs for reversible energy storage-even on existing systems-without complicating control or changing the actuator bandwidth. Duindam and Stramigioli [8] have conceptually shown that parallel springs with backdriveable actuators can lead to energy-efficient locomotion; and Yang et al. [9] have proven its merit in a bipedal robot.In this paper we investigate the application of parallel stiffness to a high-speed running quadruped, the MITCheetah, employing the passive energy storage to reduce power consumption. In Section II we introduce the system: both the robot and the dynamic model used for simulations. Section III describes the simulation experiment; the application of parallel springs is discussed in Section IV. Then we show the effect of applying optimal parallel springs in Section V and finally we discuss these results and possible future research on this subject in Section VI.

ver since the start of aviation, birds and airplanes have posed a mutual risk: Birds are killed when struck by aircraft, but, in return, bird strikes cause billions in damage to the aviation industry. Airports employ bird-control methods such as audiovisual deterrents (like scarecrows, lasers, and noise), weapons, and chemicals to relocate, suffocate, or otherwise terminate the birds [2]. While the latter methods work, they are ethically questionable. The problem of audiovisual deterrents is that they quickly lose effectiveness due to habituation. The approach that works consistently is the use of predator birds to scare off the prey birds and permanently relocate them away from runways. However, the predators themselves cannot be precisely controlled and, in turn, also pose a threat to airplanes.The Robird is a robotic bird mimicking a peregrine falcon in appearance, weight (730 g), size (112-cm wingspan), and flying speed / . 16 m s ^h Most importantly, the Robird is a flapping-wing aerial vehicle, mimicking the method of flight of a real falcon. The similarity in appearance and dynamics means that other birds cannot distinguish real falcons from the Robird. This allows the Robird to be used for effective and nature-friendly bird control. From a research perspective, the Robird is most interesting. Much is still unknown about how the Robird flies. The challenges lie in understanding its aerodynamics and improving its autonomy.

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This paper proposes a unified energy-based modeling and energy-aware control paradigm for robotic systems. The paradigm is inspired by the layered and distributed control system of organisms, and uses the fundamental notion of energy in a system and the energy exchange between systems during interaction. A universal framework that models actuated and interacting robotic systems is proposed, which is used as the basis for energy-based and energy-limited control. The proposed controllers act on certain energy budgets to accomplish a desired task, and decrease performance if a budget has been depleted. These budgets ensure that a maximum amount of energy can be used, to ensure passivity and stability of the system. Experiments show the validity of the approach.