Video of the Alan Bond Servo Controller in action
Servo Slower by Alan Bond
SERVO POSITION CONTROLLER
This module was developed for the control of servo operated guns and cranes mounted on the decks of model boats, but aircraft, military and robotics modellers etc will doubtless find other applications for it. It combines the functionality of an R/C switch, a servo-slower and a servo stretcher in a single unit not much larger than a standard servo. See the video above to see the servo controller in action.
The R/C switch function detects joystick positions either side of a centre deadband and sets the servo moving slowly in the appropriate direction. Releasing the stick (to centre) at any time stops the movement and holds the servo position achieved. The end of travel limits for port and starboard can be individually set by the user. Also, if the servo can cope with being (mechanically) over-driven, the usual +/- 45 degrees of available swing can be extended up to a full +/- 90 degrees, thereby avoiding having to gear up the servo shaft to achieve such an angle of rotation - this solution is also free of the backlash and jerkiness associated with gearing or chain drive. Note that many servos have asymetric limit stops about 1.5mSec neutral, and the 180 degrees may need to be achieved by +100 degrees one way and -80 degrees the other. This is of no consequence, simply reposition the servo arm on its splines until a symetric swing is achieved. The traverse rate of the servo can be set to take from approximately 2 to 30 seconds from end-to-end (180 degree swing)
The link that can be seen at the left hand side of the board is inspected at power up and if not in the 'run' position the module enters a 'set-up' mode. Now the servo is controlled by the potentiometer only, and the clockwise limit of travel can be adjusted. When this is finalised, a press of the tactile switch allows the potentiometer to set the anti-clockwise limit of travel. A final press of the switch reverts the module to 'run' mode where the potentiometer now controls the speed of traverse.
This module, built on stripboard, is available as a kit (Technobots part number 3403-015) and includes all parts, colour assembly booklet and a programmed PICAXE chip but excludes the optional case. Follow the above link where on the 'downloads' tab you can get the assembly booklet for further details. A pre-programmed chip 3803-114 is also available on its own.