- Get ECEF of antenna tracker (only once at beginning) (Michelangelo)
- Get ECEF of drone (Jun Ho)
- Find delta ECEF of drone & tracker (makes tracker origin, but directions are still in ECEF) (Jun Ho)
- Use rotation matrix to rotate origin of our tracker coordinates to point north (ECEF -> ENU Which axis is north will depend on code) (Stephen)
- Convert our delta drone coordinates to spherical (ENU_XYZ -> ENU_Spherical) (Stephen)
- Get gyroscope direction of tracker (ENU_Spherical) (Ian)
- Find delta angles between current tracker direction & desired direction (Ian)
- Output direction to motors to desired direction (Stephen)
Ian Webster
UTAT UAS | RnD Division
The antenna tracker is a multifaceted electrical, software, and mechanical project. The goal of the antenna tracker is to have an autonomous drone-tracking device that uses telemetry data from a drone to compute the desired tracking angles to "follow" the drone's flight path in real-time.
The tracker will need to use it's own location data with the recieved telemetry data from the drone to compute the target angles to move the tracker.
A GPS or gyro module could be used to track z-position (altitude), pitch, and yaw of the tracker, and move the motors accordingly until the (z, p, y) vector is within a suitable range of error of the true computed vector. (i.e. 0.1 degrees)
- 2x 12V DC Motors rated at 0.82A stall current, so P = 12 * 0.82 * 2 = 19.68W
- L298N DC Motor Driver (25W max power)
- A microcomputer or microcontroller
- Raspberry Pi
- Arduino
- GPS Module (mounted to the antenna on the tracker to identify tracker's position)
- Use velocity and acceleration data to more precisely move the tracker according to the drone movement (but for now, just use a feedback system with a specified tolerance to move the tracker's motors until the location of the tracker is aligned with the drone's position)
- Intelligent movement to minimize power drawn from motors (i.e. move 30 deg instead of 120 deg)
Drone / Pixhawk -> GCS (Ground Control Station) -> Antenna Tracker
Get GPS Data of Drone -> Get GPS Data of Tracker -> Move the Tracker to follow Drone's Current or Future Predicted Position
- Use MavSDK to pull GPS data from drone (pixhawk) to ground control.
- Ground control sends this GPS data to Rpi/Arduino (tracker computer).
- Use tracker computer to compute angle to control the antenna motors.
- Learn about MavSDK
- Simulate a drone OR use pull live GPS coordinates from a drone's pixhawk
- Receive drone position data using mav-sdk with python.
- Communicate the drone position data to the antenna tracker computer
- Use the antenna tracker computer to compute the new position of the tracker to follow the drone's position
- Goal: Should take in tracker GPS and Compass Data, and Antenna GPS Data, and return absolute angles (in xy-plane, and with z-axis) to move the tracker to.
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lon and lat angles defined with respect to center of earth as ORIGIN
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alt is defined with respect to surface of earth (sea-level) as reference (0 m)
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lon = lambda = angle made within xy-plane (0 deg lon) where -90 deg = west, +90 deg = east
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lat = phi = angle made with the z-axis (0 deg is equator/xy-plane) where -90 deg = south, +90 deg = north
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Supplied by the Drone's GPS: (assume 2 is the drone for now. May write code to abstract this to deal with corner cases (i.e. -180, etc.))
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<lat2, lon2, alt2> -
Supplied by the Antenna Tracker's GPS:
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<lat1, lon1, alt1> -
Supplied by the Antenna Tracker's gyro:
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<tracker_theta_xy_gyro, tracker_phi_z_gyro> -
tracker_theta_xy_gyro = the angle the tracker actually makes in the xy plane (this is NOT lon), treating the tracker as the ORIGIN
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tracker_phi_z_gyro = the angle the tracker actually makes with the z-axis (this is NOT lat), treating the tracker as the ORIGIN
Option 1: Tracker can move to absolute angle (lat/lon), i.e. using servos and compass/gyro, treating itself as the origin, North as reference for xy-plane angle.
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phi and delta_lon are the absolute angles to move the servos TO!
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TODO: Make considerations if lon2 > fff or lon2 < ... -> i.e. use abs val? or +180, etc...
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"target_phi" = absolute angle to z-axis-> target angle to move the tracker to, if xy-plane is 0 deg, and +z is 90 deg [-phi = -z, +phi = +z . The drone's current value of phi is tracker_phi_z_gyro] -
"target_lon" = lon2 - tracker_theta_xy_gyro-> this is not really a delta. It's an absolute target angle to go to. lon2 is the drone, and tracker_theta_xy_gyro is the angle the tracker is currently pointing in the xy-plane (North as 0 deg). -
[Note: lon2 = target angle to move tracker (angle in xy plane), assuming the tracker was pointing directly outwards on lon1. This would be a bad approximation of delta_lon on its own, because we need to take into account the actual direction that tracker is currently pointing, using tracker_theta_xy_gyro]
Option 2: Tracker moves towards the target angle by moving by an incremental angle relative to its current direction
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until we're within a certain range of error of the true directions.)
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delta_phi = target_phi - tracker_phi_z_gyro-> This is a delta. It's a relative angle to move the tracker's angle with the z-axis in order to point to the drone. -
delta_lon = lon2 - lon1 - tracker_theta_xy_gyro-> this is a delta. It's a relative angle to move the tracker to get to the final target angle.
Option 3: Tracker moves in the direction of the target absolute angle, and tries to achieve this position within some tolerance
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(closer to a control systems approach - calculate the estimate, then move the tracker's DC motors)
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Ideally have the same tolerance as the antenna itself
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We would use the same formulas as Option 2, but then make inferences on which direction to move the tracker based on the drone's current values of
<tracker_theta_xy_gyro, tracker_phi_z_gyro>. -
For example, if the drone's delta_phi is increasing (target_phi is increasing), we should reduce tracker_phi_z_gyro until we notice that tracker
phi_z_gyro/target_phi <= antenna_phi_error_tolerance, where the best case would result in delta_phi == 0. TODO: think of how to avoid divide by 0 problem. -
We should do something similar for the longitude.
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delta_phi = target_phi - tracker_phi_z_gyro-> This is a delta. It's a relative angle to move the tracker's angle with the z-axis in order to point to the drone. -
delta_lon = lon2 - lon1 - tracker_theta_xy_gyro-> this is a delta. It's a relative angle to move the tracker to get to the final target angle.