Specifications

5
2.2 BASIC OPERATION
When first activated, the Pyxis or Pyxis 3-inch rotates HOME to find the 180 degree position
angle point which is detected with a magnet mounted in the rotating main drive gear and a Hall
effect sensor mounted in the circuit board. Once the magnet is found, the unit reverses direction
and rotates to the 0 degree position angle. The Pyxis will not accept any commands until the 0
degree position angle is obtained. If the unit fails to home properly, an error code is sent on the
serial cable to the operating PC and the unit will stop to wait for additional commands.
A small red LED indicates that the circuit is powered on when illuminated. In the SLEEP model,
the LED will flash at a steady rate. See the Pyxis.exe control program HELP file for more
information about the SLEEP mode.
The main gear of the Pyxis rotates with a rated torque of 13 inch-pounds. This degree of torque
should be adequate to handle most of the common CCD cameras from SBIG and others.
However, if the camera is severely off-balanced or cables to the camera are snagged, the main
drive gear will slip. No damage to the unit is possible but the position angle will be lost and the
Pyxis would have to be homed again.
Because the stepper motor operates in a pulse fashion, there is a considerable amount of gear
chatter when the Pyxis is rotating to a new position angle. While disconcerting to listen too, this
chatter is normal to the operation of the unit. The degree of chatter is a function of the motor
speed. At the default pulse delay of 8 milliseconds (nn = 08), the chatter is minimized. This
variable can be changed with CTxxnn command (see Table 4-9) to allow for other rotational
rates. The new delay variable entered in this way is stored in EEPROM. Some caution should be
exercised to avoid using very long delays since the Pyxis will have to finish homing or moving to a
new position angle before any new delay variable can be entered.
Since the Pyxis 3-inch uses a worm gear, the chatter mentioned above is barely perceptible and
the default settings for pulse delay of 6 should be kept. However, if the instrument package is
well balanced, it may be possible to decrease the pulse delay in order to increase the rotational
rate. Lower pulse delay numbers will decrease running torque which may result in lost steps.
Because of the increase in torque for the Pyxis 3-inch care should be taken to prevent cables
going to the instruments from becoming snagged. Since this model uses a worm gear instead of
the spur gear, the stepper motor is powered off when the unit is not rotating. This reduces
considerably the power requirements and the resulting heating of the unit. In the idle state, the
Pyxis 3-inch uses less than 0.1 amps.