Gimbal

Gimbal axes (Ronin Mx) can be controlled from an OSDK (On Board Software Development Kit) installed in a micro controller (Raspberry Pi) that connects to the N3 flight controller unit.

Some limitation of this control system are:

• When setting the gimbal angles in absolute or incremental mode, yaw will follow the UAV attitude.

• The angles range are limited in the gimbal API. Till now, the maximum range allowed is
  Roll -20 to +20 degrees
  Pitch -90 to  30
  Yaw -320 to 320

• The movement process takes a couple of seconds which prevents the gimbal to follow the drone movements closely. This would limit the final test to a step by step movement of the drone.

• RF source polarization angle
  The change of the polarization angle is obtained by rotating the pointing vector that aims towards the desired coordinates on ground, relative to itself. This appears as a roll rotation, while keeping the yaw and pitch, as seen from the telescope. From the angles of this vector, a solution is found for the three gimbal actuators.

• Flight test at UC observatory , Santa Martina.
  The pointing stability was tested by  mounting a laser on the gimbal and follow the laser spot on ground, while flying the drone at a given point in order to obtain an angle of 45 degrees. The gimbal was controlled so it continuosly changes the polarization angle from -20 to 20 degrees, while it keeps aiming towards a target on floor.  The tests were made during day time and the laser could only be seen when the drone was not too faraway (25 m) but we could confirm that the gimbal keeps pointing in the good direction. It is pending a test at night from a larger distance.

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Coordinate definition:

• There are two coordinate systems, one for the actuators and another for the payload:

  • The actuator coordinates are given by their encoders, and refer to the position of the previous actuator.

  • The pitch and roll payload coordinates refer to gravity and are defined by the forward and sideward vectors on the payload horizontal plane. The yaw coordinate refers to the forward direction of the drone.