Posted by Jaeyoung Lim on November 21, 2015 at 5:00pm
Multirotors are underactuated, thus controlling interaction with the environment such as aerial manipulation has some problems. However, although these problem can be addressed using multi-DOF actuators or some novel control techniques, multirotors suffer from short flight time and limited payloads.
The video below uses a spherical joint to connect multiple quadrotors to the structure and use each quadrotor as rotating thrust generator.
This way the quadrotors may benefit both in flight time and payload capacity while maintaining the agility of the quadrotor. Some groups have also used tethers to use multiple quadrotors on a single aerial platform.
I am interested in implementing this system using the APM flight stack to fly outdoors. However, it seems that APM does not support attitude control on ROS. Curious why px4 supports attitude set point topics but not APM.
Posted by Jaeyoung Lim on October 21, 2015 at 5:00am
This project started out as an experiment. Most multirotors have their rotors in a planar configuration. I noticed this is mostly true even when the props are titled in racing quads. (which is actually unnecessary). The idea is that if the moment arms do not change, standard flight controllers should be able to control non-planar shaped quadrotors as long as the control board is mounted near the center of gravity. I decided to try the idea out and it turns out it is able to fly pretty well.
Basic Theory
Quadrotors control their attitude using thrust generated from each rotor on the arms. The torque which control the attitude can be calculated as the picture below. Moving the rotors along the z axis of the quad does not change the moment arm which results in the same amount of torque. The moment of inertia may increase due to the displacement of the motors(further out from the center of gravity) but this can be controlled with a little more of P gain in the controller.
Build
The configuration and part list is shown below. – Motors : Turnigy Brushless motor Aerodrive 1200kv – Props : 10X4.5 SF props – ESC : Multistar 20A UBEC – Flight Controller : KK2.1 – Battery : Zippy Flight Max 11.1V 3000mAh – Frame : Tarrot carbon fiber quadrotor frame v2 Used two tarot quadrotor frames and mounted each frame using pennuts. Below is the picture of initial fitting the parts before wiring.
The battery was mounted just below the flight controller so that the center of graivity should be near the flight controller.
ESCs are mounted on different plates. I tied mounting everything symmetrically to prevent it from messing up the inertial moments.
