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I.9.3) Retracts

Retractable gear is useful when a camera is being used, ensuring that the (fixed) gear doesn't appear in every frame.

Powered retracts are available from Hobbyking, etc., and are wired as a servo but are either 'up' or 'down'. A screw mechanism is used to ensure they lock in position.

(c) HobbyKing

A camera gimbal requires two servo inputs and only two servo inputs are available on the bottom of the CX-20 / Quanum Nova. It does, however have two 12V outputs.

A quick and dirty solution was to use an HC-SR04 ultrasonic sensor to measure the distance and send the servo a 'full on' or 'full off' signal. The weapon of choice (and massive overkill) was a Parallax Propeller 'Mini' board.

The prop sends a trigger pulse to the Trigger pin of the sensor and waits for a signal on the Echo pin, after which it measures the length of the pulse on that pin. The duration of the pulse on the Echo pin represents the distance between the sensor and the reflecting surface.

If the measured distance is more than 3m away a value of 1 is added to a scrolling buffer of eight bytes; if less than 3m, a zero is added.

The gear is retracted when all eight bits are '1'; the gear is extended when all eight bits are '0'. This is very simple filtering that gives sufficient hysteresis to ensure the gear doesn't flap up and down.

In the video below the Propeller Protoboard is supplying 12V to the Propeller Mini board. The servo represents the landing gear and tilting the sensor brings the range under 3m (i.e., to the ceiling of the room) or more than 3m (the length of the room). 

SonarGear - Archive [Date 2016.04.11 Time 18.15].zip
Hugh Neve,
Apr 11, 2016, 10:23 AM