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Camera Gimbal

Purpose / Design Goals

The camera gimbal stabilizes the camera and reports information about where the camera is pointing to the OBC. This information is then used to calculate the position of objects on the ground during localization. This system must be very precise - a 1 degree error can translate to multiple feet on the ground, reducing our accuracy for payload drops.

Components

  • Motors
  • Encoders
  • IMU
  • Control/Driver Board
  • Camera/Lens

Mechanical Considerations

  • Stiffness - the axes of rotation should remain as square as possible so that when the controller is commanding movements to correct the orientation, they are moving in the correct direction.
  • CoG - the axes of rotation should be go through the center of gravity, so that the motors do not need to expend energy when the gimbal is at rest. This also makes getting a good tune much easier.
  • Vibration isolation - the camera gimbal won't be able to smooth out high frequency vibrations, so this needs to be solved mechanically by isolating the camera gimbal from the aircraft. Possible materials that could be used are steel wire, silicone, and TPU.
  • Wiring - wires should be lightweight and flexible so as not to influence the camera gimbal as it moves. Prerable to have neat cable management for installation/servicing.
  • Location of PCBs - separate IMU module and driver board or all integrated on one PCB?

Electrical Considerations

  • Calcualting orientaiton - there is an IMU placed on the camera that provides 3 axis angular rate and linear acceleration. These are integrated over small time steps to keep track of where the camera is pointing. These sensors have significant drift when using this method, so need to be corrected. A method of doing this could be to poll the Pixhawk for its orientaiton, and then use relative offset information from the motor encoders to inform the gimbal controller of where it should be pointing based on the "ground truth" provided by the Pixhawk. There will be slight misalignments as the camera flexes relative to the aircraft due to being on vibration isolators, which is why we can't just just use the motor encoders to calculate pointing direction from the Pixhawk orientation.
  • Interfacing with the OBC - pointing information synced with when the camera is exposing needs to be sent to the OBC so it can tag pictures with metadata about where the camera was pointing when it has taken a picture.