Half Scale Prototype

Why buid a 50% Prototype?

The idea is to build a 1:2 scale prototype before starting with the real thing to gain some experience with the flight controller, the Ardupilot software and all the required technology. Since the real FlyRider will become 2 meters wide and 2 meters long, the prototype will become 1 by 1 meter. The frame is built from 15 mm aluminum square tubes.

Motors

Motors for the prototype are EMAX MT-2216, according to the supplier they shall provide 0,95 kg of thrust with a 10 x 4.5 prop at 14,8 V (4S) and 14.6 A. The real FlyRider aircraft is planned to have a 1,5 / 1 thrust to weight ratio. With a total peak thrust of 5,7 kg the weight limit for the prototype is 3,8 kg to achieve the same thrust to weight ratio.
As motor speed controller (or ESC = Electronic Speed Controller) I use a Hobbywing X-Rotor 20A ESC. Since the EMAX MT 2216 consumes 14.6A at full power, a 20 Amp ESC should be sufficient, especially since no long duration flights are planned with the prototype.

    
    Parts Required for Prototype 

    6 x EMAX MT 2216 motor (or similar)
    6 x Hobbywing X-Rotor 20A ESC (or similar)
    2 x 5000 mAh LIPO with min. 20 C  (or similar)
    1 x Pixhawk Flight Controller
    1 x LIDAR

Batteries

As batteries I need a set of 4S Lipos (14.8 V) which can at least provide 45 A to be able to use one Lipo for 3 motors. A 5000 mA battery is able to provide 45 A for more than 6 minutes, enough time for the planned test flights. Make sure that the batteries have the C rating to be able to provide the current needed to get full thrust out of the engines. The C rating, quite simply, refers to the capacity of energy the battery can safely discharge, represented as a multiple of its overall capacity. Thus a 5000 mAh 20 C battery should be able to provide 100 Amp peak current (5A * 20C = 100A) - at least in theory. It is best to have a discharge rate overhead of 30%. For a 5000 mAh 20C battery a discharge with 45 Amps should be no problem.

Pixhawk Flight Controller

Initially “Pixhawk” was a student project at ETH Zurich. Little did the team know that it would end up having such a large influence on the drone industry. Today pixhawk is one of the leading flight controllers for UAVs and drones.

First Flights And Tuning

Unfortunately, the first flights were extremely unstable. There was always a lot of movement around pitch and roll, yaw hardly worked at all. So I started to tune the Ardupilot. You can find all the relevant information on the Ardupilot website.You can use the graph below to estimate the correct MOT_THST_EXPO value for your aircraft.

PID Controller Initial Setup

The next settings are meant to get your PID controller acceleration and filter settings into the right approximate range for your vehicle. These parameters are critical to the tuning process. The PID controller default values for axis P/D/I values are usually safe for first test hovers of most vehicles.

INS_ACCEL_FILTER: 10Hz
INS_GYRO_FILTER: 40Hz for 10 inch props
ATC_ACCEL_P_MAX: 110000 for 10 inch props
ATC_ACCEL_R_MAX: 110000 for 10 inch props
ATC_ACCEL_Y_MAX: 27000 for 10 inch props


I have changed INS_ACCEL_FILTER to 10 and INS_GYRO_FILter to 40 Hz.

Motor Setup and Vibration Check

it is very important to ensure that the thrust curve of your VTOL motors is as linear as possible. A linear thrust curve means that changes in the actual thrust produced by a motor is directly proportional to the thrust being demanded by ArduPilot.

MOT_BAT_VOLT_MAX: 4.2v x 4 Cells = 16.8 V MOT_BAT_VOLT_MIN: 3.3v x 4 Cells = 13.2 V ATC_THR_MIX_MAN to 0.1 MOT_THST_HOVER to 0.25 (I had to set it to 0.35 to have enough thrust)

The vibrations are within the normal range (at least until the hard landing).