How to implement rc command on virtual joystick? - dji-sdk

Question

I need to implement a Tello command, which is rc a b c d on a virtual joystick. From different forums, I came to know that for virtual joystick, we need to use rc commands to move the Tello drone. But I don't know how to implement it. In their SDK documentation, they have mentioned it as
a:left/right (-100~100) b: forward/backward (-100~100) c: up/down (-100~100) d: yaw (-100~100)
What do these negative values mean? How can I use the rc command to move the drone?
This is the virtual joystick code which I am using:
JoystickView joystick = (JoystickView) findViewById(R.id.joystickView);
joystick.setOnMoveListener(new JoystickView.OnMoveListener() {
#Override
public void onMove(int angle, int strength) {
// code goes here
}
});

Answer 1

The values -100~100 normally are the velocity for their respective axis. Depending on the coordinate system set and the control modes for the axes, the aircraft move along the axis corresponding to the value. Based on the code you provided I assume the strength value represents the percentage how much the stick is pushed/shifted and the angle value shows the direction into which the stick is pushed.
For the virtual Sticks you need to set the Control modes and coordinate system by accessing the flight Controller:
setRollPitchControlMode(RollPitchControlMode.VELOCITY);
setYawControlMode(YawControlMode.ANGULAR_VELOCITY);
setVerticalControlMode(VerticalControlMode.VELOCITY);
setRollPitchCoordinateSystem(FlightCoordinateSystem.BODY);
The modes chosen above ensure that the virtual controller behaves the same as the default physical remote controller.
Additionally you need to activate the virtual Sticks with the setVirtualStickModeEnabled method before you can use them.
Now for the continuous control over the aircraft you need to send the virtualStickData with at least 5 Hz:
SendVirtualStickDataTask task = new SendVirtualStickDataTask();
this.timer = new Timer();
this.timer.schedule(task, 0, 200);
In this example SendVirtualStickDataTask extends TimerTask and only sends the current pitch, roll, yaw, and vertical throttle values to the drone via the sendVirtualStickFlightControlData method from DJI SDK inside the run() method of TimerTask.
Finally the current pitch, roll, yaw, and vertical throttle values are set inside your onMove() method you posted in your question. E.g. you can use the trigonometric functions sin and cos to determine the x- and y- parts of the strength value, something like this:
pitch = Math.cos(angle)*strength;
roll = Math.sin(angle)*strength;
Please note that the angle needs to be radian and you probably need to cast the angle/strength to float. Furthermore depending on how the angle value is determined you need to adjust the value accordingly.
The second joystick can be used to control the vertical throttle and the yaw. you will need a bit of fine-tuning and testing.
For the control modes/coordinate system, the following DJI SDK Documentation is helpful (scroll down to "Virtual Sticks"):
https://developer.dji.com/mobile-sdk/documentation/introduction/component-guide-flightController.html
DJI also has a basic code example for the virtual Sticks usage:
https://developer.dji.com/mobile-sdk/documentation/android-tutorials/SimulatorDemo.html
I highly recommend using the DJI Flight Assistant 2 Software to test your code before you attempt to fly in the real world.