Hand Paddle Control
41 - inch Telescope

The hand paddle buttons have the following function when used for telescope control:



Left - Guide

Center - Set

Right - Slew
X-Y Stage Control
X-Y Stage Control

Principles of Operation The operation of the hand paddle is similar, in principle, to the tracking function. The Superior cards provide an option called pulse at external rate (PE). The appropriate index card will accept an external frequency, and the command
YM-x! (for RA) or
XM-x! (for DEC)
causes that motor to run at half that frequency for x pulses. Notice that the frequency can be applied to the PE pin without the motor running. It is necessary to give the move command above in order to initiate a move. That also means that the PE option can never be made into a "free running" mode, vis., the number of motor pulses must always be specified. The tracking command has been discussed before. The only change required to run the hand paddle is a change of rate. In order for the motion to be quasi-continuous while still permitting changes of state to be recognized, three_c sends short command sequences like those above, where x has been adjusted so that motion appears continuous. This is most easily accomplished by computing x based on a percentage of the rate. If you think of this percentage (P) as the "time" the motor is running, then simple kinematics shows that the number of pulses (x) issued in that time (P) is just RP, where R is the rate. The value of P (called FACTOR in three_c) can be adjusted under the menu option "Tracking Control."
The three rates available are:
1. Guide - the slowest rate (nominally 75 Hertz). This rate is most useful when the target is visible in the main field of view. It is implemented so that no backlash compensation is necessary on an east move. Moves to the east simply apply a slower rate in the westerly direction. The rates actually issued are:
West rate = track rate + guide rate
East rate = track rate - guide rate
2. Set - the middle rate (nominally 1000 Hertz). This rate is useful when the target is within the finder field of view.
3. Slew - the high speed rate (nominally 20000 Hertz). The principle of operation for the slew moves is different than explained above. This rate takes advantage of the ability of the Superior Indexer card to automatically perform ramping operations. Three_c sends the slew rate, the acceleration (4000 microsteps/sec2), and the direction. The Superior cards will ramp the motor(s) to the high speed, maintain the speed at the high rate, and ramp back to track rate upon release of the button.
All of the rates permit combination moves (i.e., NW, SE) and ignore illegal or illogical combinations (i.e., EW). Rate switching "on the fly" is permitted.
Offset Stage Operation Buttons 6 and 7 control the motions of the offset stages on the three channel photometer. Pressing button 6 (accompanied by a beep) begins the process. A second press of button 6 signals that the left hand stage is to be moved. A press of button 7 at this point signals that the right hand stage will be moved. The second button press to select the stage is accompanied by two beeps in quick succession. Now the compass point buttons (buttons 1 - 4) have been redefined to move the offset stage instead of the telescope. The rate switch (5) still allows three different rates to be selected. When the offset stage has been repositioned, pressing button 7 (accompanied by a single beep) returns the hand paddle buttons to their original definitions. During the movement of an offset stage, the pulses are tracked so that the program always knows the absolute position of each stage.
The coordinate system of the photometer is Cartesian centered on the center stage. Positive x is toward the right hand stage, positive y is in the direction of the post-aperture eyepieces. The unit I use is motor pulses. The right hand stage is centered at (8280,0) and the left hand stage is centered at (-8280,0).
Telescope Focus The hand paddle is the preferred method of accessing focus control. Pressing button 7 redefines buttons 1 and 3 (previously North and South). Buttons 1 and 3 now drive a stepping motor connected to the shaft of the secondary mirror. The rate switch (5) can still be used to select the rate at which the focus motor runs. Pressing button 7 a second time disables focus mode.