AWR - Universal Drive Box
The frequency generation part has a maximum speed of about 8500 steps per second and is extremely smooth when changing between frequencies. The acceleration parameter is programmable along with rates for tracking, guide, centre, move and slew. The maximum speed achievable depends on the stepper motor used.
The power stage is based upon a HIGH VOLTAGE constant current CHOPPER circuit driving motors in half step mode. This overcomes mechanical resonances that can make small stepper motors stall at certain speeds. It has an internal High Voltage generator as standard. All high speed slewing requires this. A bonus is that the circuit now has a low speed torque control which defines the maximum motor current. In many cases the torque at low speeds is many times that required and so it is possible to turn it down and so economise on supply current. An additional advantage is operating the stepper in half step mode and so reducing the step size in the sky. For example the normal sidereal drive rate of a Vixen MT1 motor on the SP GP-DX mount is about 10 steps per second, now increased to 20 steps per second with this drive box.
As an example of what this drive box is capable have a look at the Sheffield University Observatory web site. They have our electronics driving their large 24 inch Cassegrain telescope. The power stage comprised off the shelf high voltage chopper stepper motor drive with a 500 Watt power supply. Step resolution is 0.1 arc seconds yet it is capable of driving up to 0.8 degrees per second.
|MOTORS - MAXIMUM STEPS PER SECOND|
|DRIVE SYSTEM||AWR STEP2||AWR STEP3||VIXEN MT1||AWR STEP5|
The table shows the extra performance available with the high voltage chopper drive board. It is now possible to get sensible slewing speeds (with torque) on previous systems without changing motors. GOTO control needs a reasonably short transit time and going at 0.5 degree per second or thereabouts is required. The normal sidereal rate will be about 20 to 30 steps per second so these figures correspond to large speeds with the FRGEN.
|PERFORMANCE WITH FRGEN|
|TELESCOPE MOUNT||MAX SPEED||STEP SIZE|
|INTES MICRO D6||0.5 deg/sec||0.32 arc second|
|VIXEN SP GP-DX||0.7 deg/sec||0.78 arc second|
|ORION Optics GEM||0.3 deg/sec||0.37 arc second|
For the advanced telescope facility, AWR offer expanded input output facilities in addition to the Universal drive box. These include:
The diagram above shows the functionallity of the drive box in diagrammatical form, and here is a picture of the MICROSTEP ADVANCED version.
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