Watson Industries, Inc.
SPS-P230 Rev A 10/17/2017
7
Position Mode
Position or “P” mode is a relative positioning mode. It uses the rate gyros to detect motion on the
pan axis and hold the platform in the last commanded position relative to the vehicle. The tilt axis
operates differently. In Position mode, as well as Inertial Mode, the tilt axis stays stabilized and
will maintain an inertial position irrespective of vehicle motions. Position Mode is activated by
pressing the Position Mode button on the Joystick Controller. When the platform is operating in
position mode, the LED on the position mode button will be illuminated.
Error Correction
Short-term disturbances will not affect the stable mount system, but as these errors become longer
term, joystick commands will become necessary to correct them. Two common sources of long-
term errors for the “P” mode are discussed below.
Centrifugal Force:
The centrifugal force from turns at a significant speed could pull the pointing angle into error over
time, depending on the pointing angle. If this is a problem, setting the system time constant to a
higher time interval may help.
Delta Velocity (Acceleration):
The compensation for forward acceleration is the same as the centrifugal force compensation.
Safety Features
Over-current detection:
There is current sensing for each axis of this system that is connected to the micro controller. If
sustained excessive motor current is detected (i.e. greater than one amp on either axis), the system
will reduce the drive circuit gain by a factor of 4 to reduce the drive current. The gain will be held
low for 2 seconds after the current is below the limit. Since the components of the system are
balanced, the only regular cause of sustained over current is driving against resistance such as an
obstruction. Such a load on the system could cause the motor to burn out and this must be
Vehicle Motion
Vehicle Motion
Position Mode
Inertial Mode
