5. HIL Simulation Platform

The HIL simulation platform includes a Real-time Motion Simulation Software— CopterSim and a 3D Visual Display Software—3DDisplay.

5.1. CopterSim

Double-click the CopterSim shortcut on the Windows desktop to open the CopterSim software, whose UI is presented in Fig. 3.50. The default simulation model and parameters are the same as for the Simulink multicopter model used in the SIL simulation system (see Fig. 3.1). This is because the CopterSim is developed based on the code generation technique with the Simulink multicopter model. CopterSim needs to run on a 64-bit Windows computer platform with a serial port and a MicroUSB cable to communicate with the Pixhawk autopilot (see Fig. 3.42).

Fig. 3.50 CopterSim main UI

CopterSim sends sensor data to the Pixhawk autopilot, and then the autopilot solves the motor PWM control signal and returns it to CopterSim. As a result, the Pixhawk autopilot can perform real-time control on the simulated multicopter in CopterSim, as well as control a real multicopter. Meanwhile, CopterSim will send the attitude and position information of the multicopter to the local network through the UDP protocol, and the 3DDisplay receives the multicopter flight information to complete the corresponding real-time 3D scene display.

As shown in Fig. 3.50, the UI of CopterSim is divided into two parts. The upper part, presented in Fig. 3.50a, is the input interface to design a multicopter by selecting popular components on the market. The lower part presented in Figs. 3.50b–e is the interface to connect with the autopilot for HIL simulation. Note that CopterSim enables by default only the basic functions required by this book. Registration is required to use many other practical functions, such as swarm simulation, high- fidelity UE4 scenes, and HIL simulations for other aerial vehicles (e.g., fixed-wing aircraft). Please, see Appendix A for more information.

Click the “Model Parameter” button in the middle of the CopterSim UI in Fig. 3.50b. The model parameter configuration dialog in Fig. 3.51 will pop up; the model parameters stored in the previous simulation will be displayed here. The parameter dialog in Fig. 3.51 mainly includes two parts: the hover information (hover endurance, throttle, output power, motor speed, etc.) and the basic multicopter parameters (total mass, the moment of inertia, size, thrust coefficient, and drag coefficient). Clicking the “Restore to Default Params” button on the dialog in Fig. 3.51 will restore the model parameters to the default values; clicking the “Save and Apply Params” button will store the current parameters to the database for subsequent HIL simulations.

Fig. 3.51 Model parameter configuration dialog

CopterSim also allows readers to directly modify the model parameters on the right page of Fig. 3.51. For example, enter the same parameters as the multicopter model used in Simulink SIL simulations (the parameters are stored in file “e01.SoftwareSimExpsiconInit.m”). Then, click the “Store and Apply parameters” button in Fig. 3.51 to store and apply the model parameters. The “noise level (0–1)” in Fig. 3.51 allows selecting the noise level of the simulated sensors, where “0” denotes that the sensor noise is not enabled, and “1” denotes that the noise level is consistent with the real Pixhawk autopilot. A noise level between 0–1 or larger than one can also be selected to represent the noise level of actual sensors. This enables the possibility of testing the anti-interference ability of the designed control algorithms.

After the multicopter parameters and the noise level are configured, as shown in Fig. 3.51, connect the Pixhawk autopilot with the computer. A few seconds later, the serial port of the Pixhawk autopilot will be listed in the “Select Pixhawk Com” dropdown menu. Select the Pixhawk serial port (usually described by the text “FMU”), and click the “Start Simulation” button to start the HIL simulation. As shown in Fig. 3.52, the messages from the Pixhawk are printed on the CopterSim UI, which indicates that the HIL simulation is running correctly. During the HIL simulation process, clicking the “Stop Simulation” button will stop the HIL simulation, and clicking the “Restart Simulation” will re-initialize the multicopter position and states to their initial values.

Fig. 3.52 HIL simulation with CopterSim

5.2. 3DDisplay

Double-click the 3DDisplay shortcut on the Windows desktop to open the 3DDisplay software. As shown in Fig. 3.53, the “3D Scene Viewer” on the left side of the 3DDisplay UI presents the current flight status of the multicopter in the 3D scene. The basic flight parameters are displayed in the upper right window of the 3DDisplay UI, including motor speed, position, and attitude information. The flight trajectory of the multicopter is displayed on the lower right window of the 3DDisplay UI.

Fig. 3.53 User interface of 3DDisplay

5.3. Flight Tests with HIL Simulation Platform

In the HIL simulation platform, when controlling a real multicopter, it is convenient to control the simulated multicopter with a real RC transmitter to perform basic actions, such as arming, taking off, manual flight, landing, etc. The detailed steps are described next.

(1). Push up the POWER switch to turn on the RC transmitter.

(2). Correctly connect the computer with the Pixhawk hardware system (including the Pixhawk autopilot and the RC receiver) and start the HIL simulation in CopterSim according to the procedure mentioned above.

(3). As shown in Fig. 3.54a, arm the Pixhawk autopilot by moving the left-hand stick on the RC transmitter (CH3) to the lower-right corner for 2–3 s.

Fig. 3.54 Arm and disarm of Pixhawk autopilot through RC transmitter

(4). Pixhawk is successfully armed when its LED turns from slow flashing to always on, [1] and the CopterSim print message “Detect Px4 Armed” is received from Pixhawk. If arming Pixhawk fails, please disconnect all hardware and software and repeat the above steps.

(5). Pull up the left-hand stick on the RC transmitter (CH3) for the multicopter to take off and fly up to a certain altitude. Next, vertically move the left-hand stick to verify the vertical motion control of the multicopter.

(6). Horizontally move the left-hand stick on the RC transmitter (CH4) to verify the yaw angle motion control of the multicopter.

(7). Vertically move the right-hand stick on the RC transmitter (CH2) to verify the pitch angle control as well as the forward and backward motion control of the multicopter.

(8). Horizontally move the right-hand stick on the RC transmitter (CH1) to verify the roll angle control as well as the left and right motion control of the multicopter.

(9). Change the position of the top-right switch on the RC transmitter (CH6) to verify the mode switching control of the multicopter.

(10). Pull down the left-hand stick on the RC transmitter (CH3) to land the multicopter to ground.

(11). As shown in Fig. 3.54b, move the left-hand stick on the RC transmitter (CH3) to the lower-left corner for 2–3 s to disarm the Pixhawk.

(12). Click the “Stop Simulation” button on the CopterSim UI to stop the HIL simulation. Then, disconnect all software and hardware connections between the computer and Pixhawk.

Notes

[1]	Higher Pixhawk hardware (e.g., Pixhawk 2/3/4/5) starts to discard LED module, so an external I2C LED module is required to observe the lighting effect.