Available sensors and controls

For the sake of convenience, control values are also included in the sensor list. This list includes most of the signals available in the communication protocol. This protocol being common to several DJI drones, some signals does not makes sense for the Tello (e.g. longitude & latitude that are only available for drones equipped with a GPS).

NB: With a small abuse of language, all the data sent by the drone are denoted as “sensor measurement” or “sensor values” even if some of them are computed signals or drone status.

Sending controls

Takeoff and landing are achived using takeoff() and land(). They both accept an optional bool parameter blocking. The default value blocks the program execution until the end of the takeoff or landing phase. Note that the takeoff phase can be quite long as it includes internal initialization (Inertial Measurement Unit (IMU), etc). An optional timeout parameter can also be passed.

The drone is control by the four stick positions: left_right, forward_backward, up_down and yaw. There also exist a fast_mode switch.

The stick positions can be set four at a time using send_rc_control(). The fast_mode can be set using set_fast_mode().

Individual axis movements can be set using the following methods (they all start with move_). They all requires parameter in the 0-100 value range.

• Longitudinal axis: move_backward(), move_forward()

• Vertical axis: move_up(), move_down()

• Lateral axis: move_right(), move_left()

• Rotation around vertical axis : move_clockwise() move_counter_clockwise()

Alternatively, the individual stick position can be set in the -100/100 range using: set_forward_backward(), set_left_right(), set_up_down(), set_yaw()

You may also perform accrobatic flips (they all start with flip_) using: flip_back(), flip_backleft(), flip_backright(), flip_forward(), flip_forwardleft(), flip_forwardright(), flip_left(), flip_right(),

Reading sensor values

There exists a few different ways to get the sensors values. All the related methods of the tello_ctrl object start with get_.

First, it is possible to get the list of all the available sensors using get_sensor_list().

You may them get some (or all) the values using their names with get_sensor_values_by_name(). Alternatively, you may retrieve the values using their index with get_sensor_values_by_index(). You may use get_sensors_idx() to retrieve a sensor index using its name.

get_sensor_values_by_name() should be prefered method as it is robust to future code change. There is no garanty that in the future release of the `tello_ctrl` package, the sensor list remains in the same order.

Here are the methods available to retrieve data:

• Sensor by name or index

  get_sensor_list(), get_sensor_values_by_index(), get_sensor_values_by_name(), get_sensors_idx()

• Drone state

  get_accelerometer(), get_drone_velocity(), get_euler_angle(), get_ground_velocity(), get_gyros(), get_position(), get_position(), get_position(), get_position(),

• Drone status

  get_fly_mode(), get_mvo_pos_valid(), get_mvo_vel_valid(),

• Miscellaneous

  get_battery(),

• Controls

  get_fast_mode(), get_control(),

Sensors

The name of the available sensor measurements are given on the following tables. Each table corresponds to one message send by the drone. Note that the given explanation on each individual signal can be quite approximative.

Flight data

Flight data

sensor name	type	explanation
battery_low	bool	True when the battery percentage is lower that the low battery threshold.
battery_lower	bool
battery_percentage	byte	battery state of charge (0-100)
camera_state	bool
down_visual_state	bool
drone_battery_left	byte
drone_fly_time_left	float
drone_hover	bool	True when the drone is flying standstill
em_open	bool
em_sky	bool	True when the drone is flying
em_ground	bool	True when the drone is on the ground
east_speed	byte	a
electrical_machinery_state	bool	a
factory_mode	bool	a
fly_mode	byte	‘’1’’ stands for flying. ‘’6’’ stands for hoovering or grouned ‘’11’’ stands for taking off ‘’12’’ stands for landing.
fly_speed	float
fly_time	float
front_in	float
front_lsc	float
front_out	float
gravity_state	float
ground_speed	float
height	int	Low resolution altitude
imu_calibration_state	int byte
imu_state	int byte
light_strength	int byte
north_speed	int byte
outage_recording	int byte
power_state	int byte
pressure_state	int byte
smart_video_exit_mode	int byte
temperature_height	int byte
throw_fly_timer	int byte
wifi_disturb	int byte
wifi_strength	int byte
wind_state	int byte

MVO (Monocular Vision Odometry)

The Tello Drone uses a low resolution near infra-red downward facing camera to film the ground. This camera allows to estimate the drone position using some how the same principle as computer mouse do. Basically, by measuring two frames, one can estimate the displacement. However, this estimation is not error free. The actual position being obtained by accumulation of this displacement, it is therefore subject to a possible drift (accumulation of small error over time).

MVO data

sensor name	type	explanation
velX, velY, velZ	float	Velocity in th drone frame
posX, posY, posZ	float	Velocity in th drone frame
velX	float	Velocity in th drone frame
posCov1, posCov2, …, posCov6	float	Some element of the Kalman filter covariance matrix
velCov1, velCov2, …, velCov6	float	Some element of the Kalman filter covariance matrix
tof	float	Time of fligh sensor (ultrasonic?)
tofUncertainty	float	Uncertainty on the tof measurement
mov_valid_velX, mov_valid_velY mov_valid_velZ	bool	Indicate if the velocity are valid
mov_valid_posX, mov_valid_posY mov_valid_posZ	bool	Indicate if the velocity are valid

IMU (Inertial Measurement Unit)

The Inertial Measurement Unit consists in 3 gyroscopes and three accelerometers. Using a Kalman filter, it is possible to estimate the drone X,Y, Z acceleration and velocity as well as angles and angular speed. When a GPS is available, if is also possible to estimate the drone position with a high frequency and accuracy. Unfortunately, the Tello drone is not equipped with a GPS. The position information is likely to be 0.

MVO data

sensor name	type	explanation
longitude, latitude	double	Drone position. N/A
baro, baro_smooth	float	barometer pressure. Helps estimating the altitude
accX, accY, accZ	float	Acceleration in the drone frame
gyroX, gyroY, gyroZ	float	Angular rotation speed in the drone frame
qW,qX,qY,qZ	float	Quaternion
velX, velY, velZ	float	Velocity in the drone frame
yaw, pitch, roll	float	Euler’s angles

exIMU (Extended Inertial Measurement Unit)

By combining the Inertial Measurement Unit and the Monocular Vision Odometry, it is possible to get a better estimation of the position and angles. All the corresponding sensor name ends with _VO.

exIMU data

sensor name	type	explanation
velX_VO, velY_VO, velZ_VO	float	Velocity in the drone frame
posX_VO, posY_VO, posZ_VO	float	Position in the drone frame
dist_VO	float	tof sensor
vel_VO	float	Velocity from the tof sensor
rtkLat_VO, rtkAlt_VO	float	RTK position (N/A)
error_flag_VO	int	Error flag

Controls

The tello_ctrl object allows sending control to the drone. The actual control values can be retrieved along the sensor measurements using tello_ctrl:get_sensor_values_by_index() or tello_ctrl:get_sensor_values_by_name().

The controls corresponds to the stick four position and a fast_mode command.

controls

sensor name	type	explanation
left_right	float	value in the -100/100 range
forward_backward	float	value in the -100/100 range
up_down	float	value in the -100/100 range
yaw	float	value in the -100/100 range
fast_mode	bool	True to activate the fast_mode