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AWR - Universal Drive Box

DESCRIPTION

This is an Intelligent drive box for all types of stepper motors. It is a variant of the Microstep Drive Box having the same protocol requirements and functions. However, it does not generate Microsteps but operates the normal stepper motors in half step mode. It is a dual programmable UNIVERSAL FREQUENCY GENERATOR (FRGEN) with Intelligent Handset interface. The generated frequencies are then converted in a power stage to drive the stepper motors. It can drive any low voltage stepper motors including AWR, Vixen MT1 steppers, Intes Micro, GEM, Celestron + others.

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
SYSTEM2	200	n/a	n/a	n/a
SYSTEM4	200	n/a	n/a	n/a
SYSTEM5	n/a	400	500	500
FRGEN	????	3850	3250	????

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

NOTE: The specification available with this drive box is generally better than the bi-level drive box previously offered.
In some circumstances the bi-level drive box is appropriate and will be supplied. PRICES

ustep system drawing

ADVANCED END TO FREQUENCY GENERATOR DRIVE BOX

For the advanced telescope facility, AWR offer expanded input output facilities in addition to the Universal drive box. These include:

Three User programmed RELAY OUTPUTS for control of apparatus such as Dome movements, DC focus motor controls or use in OVERRIDE stop. These relays will operate by using the three USER keys on the IH keyboard.
An input for the INDEX position sensor placed on the RA worm shaft to provide for periodic error correction.
An OVERRIDE stop input to operate by limit switches so that the telescope cannot drive into certain areas.
Autoguider input, either CCD TTL standard input (Meade PICTOR or SBIG ST7-8) or by a relay box (as provided by SBIG ST4 or Starlight Express). Both connector types are provided.

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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