It is desired to be a able to control a micro aerial vehicle (MAV) in unknown and cluttered environments. To do this we need full control over the six degrees-of-freedom of the MAV body. The MAV should be able to hover in place with any body orientation. Additionally, we want to be able to arbitrarily orient a sensor or gripper attached to the MAV body during flight. Traditional MAVs do not yield a perfect solution to this problem since they are generally underactuated, i.e. the are equipped with fewer actuators than degrees-of-freedom. Therefore, we have developed the Omincopter MAV to handle these sorts of tasks. The applications for such MAVs range from search-and-rescue, security, surveillance, mapping, and remote sensing applications.
Drawing inspiration from omnidirectional wheels, the Omnicopter design, shown below, allows for agile movements in any planar direction with fixed (zero) yaw, pitch and roll angles. It has five propellers: two fixed major coaxial counter-rotating propellers in the center used to provide most of the thrust and adjust the yaw angle, and three adjustable angle small ducted fans located in three places surrounding the airframe to control its roll and pitch.
Increasing or decreasing the five propeller’s speeds together generates vertical motion. The yaw movement results from different speeds of the two counter-rotating coaxial propellers. The roll and pitch motions can be generated using two methods (M1 and M2). For M1, fixed ducted fan angles with varying fan speeds are used; and for M2, varying both the angles and speeds of the ducted fans are employed for attitude control. With method M1, the difference between the speeds of Fan 4 and 5 produces roll motion coupled with lateral motion. The pitch rotation and the corresponding lateral motion result from the difference between Fan 3’s speed and the collective effect of rotation
of Fan 4 and 5. The second control method (M2) is to adjust the angles of the surrounding ducted fans, with the fan’s speeds variable or fixed, to generate the roll and pitch motions. This control method, or operating mode, allows for lateral force vectors to be applied to the airframe while keeping a planar, zero attitude configuration. This design feature is unique to the Omnicopter, when compared to traditional quadrotor and tri-copter designs. It allows for steady point-to-point lateral translation in the presence of external disturbances, such as wind, as well as a better abilities to interact with and manipulate the environment.
An Omnicopter prototype in the fixed vertical ducted fan angle configuration has been constructed, as shown below. The skeleton of the airframe is made from 0.125” diameter carbon fiber rods along with custom connecting joints laser cut from ABS plastic. The body of the Omnicopter is made from Deprom 6 mm thick hobby foam that was similarly laser cut to size. The two center propellers are 10 x 7 3-blade Maser Airscrew propellers from Windsor Propeller Company, Inc. (masterairscrew.com). They are attached to two BPU2212/10 brushless outrunner motors from BP Hobbies LLC (www.bphobbies.com) which are controlled with two Thunderbird brushless 18 Amp electronic speed controllers (ESCs) from Castle Creations, Inc. (www.castlecreations.com). The three ducted fans are 50 mm EDF (electric ducted fans) from Toysonics.com operating on three Great Planes Speed 120 brushed motors (www.greatplanes.com) with Blue Arrow 10A brushed ESCs (www.bluearrow-rc.com). Custom mounts for each of the ducted fans were 3D printed out of ABS plastic. The Omnicopter uses the ArduPilotMega from 3D Robotics (3Drobotics.com) for an IMU and on-board control. A XBee transceiver module allows for wireless data logging of the IMU data on a local PC. The entire system is powered with two Thunderpower 3-cell 1350 mAhr
Lithium Polymer batteries (www.thunderpowerrc.com). The prototype weighs 2 lbs 3.5 oz. with an available payload at 80% power of approximately 2 lbs 6 oz (.1 kg). This initial prototype is currently configured for remote control with a Spektrum AR8000 8-Channel DSMX Receiver and DX8 8-channel transmitter (www.spektrumrc.com). A second generation prototype is currently under construction with a larger payload and small servos enabling the control of the angles of the ducted fans.
Y. Long, S. Bai, P. Patel, D. Cappelleri, "A Low Cost Attitude and Heading Reference System Based on a MEMS IMU for a T-Quadrotor", Proceedings of the ASME IDETC/CIE 2011, August 28-31, 2011, Washington, DC, USA.
Y. Long, S. Lyttle, N. Pagano, D. Cappelleri, "Design and Quaternion-based Attitude Control of the Omnicopter MAV using Feedback Linearization", ASME International Design Engineering Technical Conferences (IDETC), Chicago, IL, USA, August 12-15, 2012.
Y. Long, S. Lyttle, D. Cappelleri, "Linear Control Techniques Applied to the Omnicopter MAV in Fixed Vertical Ducted Fan Angle Configuration", ASME International Design Engineering Technical Conferences (IDETC), Chicago, IL, USA, August 12-15, 2012.