First of all I would like to introduce Astromeccanica company. Astromeccanica is an Italian company which produces wide range of astronomical equipment from various camera adapters through stable tripods, pillars, counterweights up to astronomy cameras and electronic drive systems for mount.

Even a very good mount without proper drive system cannot provide good performance. Recently I bought Vixen GP-DX with DA-1 DELUXE dual axis drive system. I decided to look at it in detail.

First of all I want to declare, that my intention was to truly test the equipment. I didn't want to emphasize neither positive nor negative aspects of the equipment. Simply said, I was curious about real performance of my setup.
However, I cannot exclude completely, that some of my conclusions are only my subjective points of view. But all my measurements were done by using precise measuring equipment.

For Vixen GP-DX mount there are several possibilities, how to equipe it with drive system. Vixen company offers very simple single axis drive SD-1 with one motor and hand controller which offers 2x and 16x speed for slewing (reffered to sidereal speed). Dual axis drive DD-1 from Vixen provides provides 1.5x, 2x and 32x speed for both RA and DEC axes. Vixen also offers its perfect top product - SkySensor 2000-PC with GOTO capabilities, database of almost 14000 celestial objects and lot of other functions. But its price is even higher, than price of GP-DX mount!

Astromeccanica offers DA-1 kit, which fills the empty space between simple Vixen's DD-1 drive and luxury SkySensor 2000-PC drive.
Here is a table which enables to compare the above mentioned products:

More information about the DA-1 product you can find on Astromeccanica's web page:
http://www.astromeccanica.it/dual_axis_drive.htm

In depth view

DA-1 DELUXE dual axis drive kit for Vixen mounts consists of the following items: Dual axis control unit DA-1 2 complete stepper motors with cases and mounting connections 2 toothed belts and 2 pulleys to put on each worm gear Set of 3 wrenches to fix screws (screws are included too) PC remote control software with autoguiding function CD-ROM with driving software Instruction manual with color graphics and pictures Connection cables (incl. serial port cable for PC) 5 meters power cable with two different connections (connecting terminal for car batteries and for power supplies) Two year guarantee ASTROCARD for any production defect

The first thing which a user must do is to mount motors, pulleys and belts. I didn't need to do it, because I ordered DA-1 kit together with GP-DX mount and it arrived with mounted motors. I estimate that mounting procedure cannot take longer than 15-20 minutes. Manual with color pictures is a very good guider for this task.

After setting motors up the control unit can be connected to motors and to power supply. Power supply can be any DC supply with voltage from 10V to 15V and must be able to supply about 2A current (it depends on set motor torque - see bellow in the text).
After switching power supply on, the display shows the startup procedure (shows "ASTROMECCANICA   DA-1" text with progress bar). Then RA motor starts to work.

The first impressions

a, Hand controller

I must admit, at first I was afraid, that DA-1 control unit is rather big (according to photos), but I found it comfortable to hold it in my hand. It's heavier than my old controller for GEM1, but I consider it as advantage, because it sits nice on place, when I put it. My GEM1 control unit was too light, so I have often a problem, that cables (especially in winter, when cables are inflexible because of cold) drew the unit down. The display is well readable. I appreciated very much the possibility to set up its contrast and back illumination. I adjusted back illumination to such value, that it is nicely visible, but not disturbing my night vision during observation. The hand controller is equipped with membrane keyboard, which is in my opinion not a very lucky solution. It is easy to clear and maintain such type of keyboard, but not such easy to use it in the night. The situation is even more complicated during winter with gloves. Nevertheless I got accustomed to it rather soon. But I would recommend to use classical buttons in future products (my old GEM1 hand controller was very easy manageable, even with winter gloves). The operation of DA-1 impressed me very well. I like the menu items. DA-1 dispose of many powerful functions and adjustments.

DA-1 and GEM1 control units side by side

b, Power consumption

As I used to use my small 12V/4Ah accumulator for supplying my old GEM1 equatorial mount, I was very curious about current consumption of DA-1.
The results of measurements are in the table:

During measurement the supply voltage was 12V. DA-1 motor torque was set to LOW value (default value).

As you can see, power consumption of DA-1 module driving GP-DX mount is about 2x higher than consumption of GEM1 drive. When we consider higher load capacity of GP-DX and higher torque of DA-1 motors, DA-1 has very acceptable power consumption. Also it is comparable to power consumption of Vixen's DD-1.

I was a little bit dissapointed, when I powered off the unit (through menu command). I found out, that it had rather high idle consumption - about 110mA. So if DA-1 runs on batteries, it should be switched off by unplugging it from power supply.

I also tested tolerance of DA-1 unit to low voltage. DA-1 unit enables to set up low voltage warning. The lowest available value is 10V. It is quite high value for using 12V accumulator, which is able to work until 9V. I tested DA-1 unit with 9V power supply and it worked reliably in spite of "Low battery" warning displayed. (Note: If supply voltage is under set value, the display is always illuminated.)

Users with higher torque values have to reckon with higher power consumption (up to 2.5 A). But don't forget, that holding torque of DA-1 motors is almost 5x higher than MT-1 holding torque.

All in all, I can say that I am satisfied with DA-1 demands on power supply.

c, Work under low temperatures

As soon as clear sky appeared I went to my balcony to test the new equipment. The ambient temperature was -6.6°C. I set up equipment and checked it. Everything was OK. Then I unplugged 12V power supply and left equipment for some time to cool down. Later, after attaching 12V again, DA-1 modul didn't started. I repeated switching on/off more time, but DA-1 didn't work. I started to be afraid that DA-1 was damaged, but after some minutes of warming up the module (in my hands), it was working OK. The working temperature of DA-1 module is -10°C according to manual (and even -15°C according to Astromeccanica's website).

Later I was told, that DA-1 unit works reliably even in lower temperatures, but it must be non-stop switched on. I tested it later and I can confirm, that it worked reliably also in -10°C ambient temperature.

Anyway, personally I am not satisfied with such behaviour of DA-1 unit. It is quite limiting for me to have DA-1 unit continously switched on. When I need to switch the DA-1 unit off for some time (e.g. when I want to change some photo equipment or to reverse my Newtonian during observations near meridian), first of all I need to disconnect the DA-1 hand controller and put it into warm place. Astronomers with cold observatories may not be happy with such hand controller behaviour.

I was very curious about limiting temperature necessary for correct module start up. After extensive measurements I found out, that DA-1 hand contoller cannot start up when ambient temperature is under +6°C!!!

Imagine a situation - Star party in open field. You are picking off your equipment from car. The ambient temperature is 0°C. While you are setting up the mount and scope, the DA-1 hand controller is getting cold. Finally, you and your friends are ready. You are switching the power on, but DA-1 hand controller cannot start up. Your friends are already observing, while you are thinking over, how to warm up your hand controller... Brrrr!

Although DA-1 unit is usable up to -10°C frost, if it is continously switched on, I think, that DA-1 developers should reflect about the above things.

d, Computer control and autoguiding

In my opinion the most powerful feature of DA-1 is computer control and autoguiding ability. Astromeccanica provides together with DA-1 kit also DA-1 command set documentation. DA-1 is controlled through serial port. CD-ROM delivered with DA-1 kit contains a special program, which enables to control DA-1 unit.

Autoguiding feature of DA-1 forms from GP-DX mount a proffesional equipment for very long exposures. This is necessary for taking deep-sky photographs.
DA-1 enables autoguiding also without computer - using ST4 autoguider. It also supports computer autoguiding with webcam.
DA-1 sofisticated menu system enables to adjust guiding speeds separately for RA and DEC axes.

e, Testing under sky - practical experience

DA-1 offers 3 slewing speeds 2X, 8X and MAX. I like very much a possibility to set up MAX speed (it is very easy by means of menu). User has 4 options:   32x RA,   32x DEC   64x RA,   64x DEC 128x RA, 128x DEC 260x RA, 520x DEC With such speed range I need to use my clamps for releasing RA/DEC axes only very rarely. 260x RA speed means a little bit more than 1 degree per second. In DEC axis it is even 2°/s. The work with DA-1 is really very nice and comfortable. I like very much gradual speed increase and decrease when MAX slewing speeds are used. It is very considerate towards the mount's gears. DA-1 also enables to eliminate backlash of the mount. It is a "must" feature for observing the Moon - then you can "walk" through the Moon's features without annoying waiting while backlash is overcome.

DA-1 motor with belt system

I also like microstepping feature of the drive controller. The belt gear system has ratio 1:4 (the motor wheel has 16 teeth, the worm shaft wheel has 64 teeth). As DA-1 drives the motor with 1600 microsteps per one motor's revolution, it means 6400 (!!!) microsteps per one revolution of worm axis. This is really very fine gearing!

During my measurements of Periodic error (look at GP-DX Mount - Periodic error) I noticed, that drift in RA axis is rather high. At first I thought, that polar alignment was not good. But after testing DEC drifts I found, that problem is in RA motor speed. Fortunately, I found in advanced menu possibility to adjust RA speed in fine steps. After some measurements I settled at adjustment value -16.

But after a longer measurements I found that the speed was a little bit faster, than accurate RA speed should be. So I set adjustment value to -17. I measured RA drift again and I found out, that this value is slower than exact RA speed. I spent a lot of time with various measurements. My conclusion: The adjustment step for RA speed is rather rough - 0.39%. This means, during one period of worm shaft (exact period should be 598.3611sec), the step is 2.33s!!! This step is really rough. The worst case, which could appear is, if the exact speed lies just in the center between the two step values. I have tested two DA-1 modules and they both have the exact value just in the middle :-(.

Simple said, I couldn't adjust accurate value of RA speed. Here is table, which shows my measurements:

I was rather disappointed with results of my measurements. DA-1 RA speed is only a little bit more accurate than RA speed of my simple GEM1 mount.

My measurements revealed, that RA speed of DA-1 drive system is very stable (in wide temperature range), but not very accurate. I think, that this is a real pity for such sofisticated product like DA-1 is.

I also tested the possibility to freely rotate RA/DEC worm axis knobs. I found that they can be used only if DA-1 unit is switched off. But it is OK - I need them only if I don't use DA-1 hand controller. I appreciate this feature, because sometimes I am too lazy to setup all the cables for only a short visual observation. Then manual control is very welcome for me.

Features

DA-1 motor drive is equipped with a lot of useful features, which make from it a sofisticated device. They are organized in two menu. Here is a table listing them:

Conclusion

Pros: DA-1 is equipped with many functions and possibilities (MAX speed setting, elimination of backlash of mount's gears, ...) Belt drive system (reduced vibrations, backlash elimination, no need of additional clutches for manual rotation of axis knob) 6400 microsteps per one revolution of worm shaft High torque motors, possibility to set up motor torque from menu system of DA-1 Computer control Autoguiding + possibility of fine adjustment of guiding speed Very good price for such equipment Cons: +/-0.2% RA speed error (1.8"/min), while Vixen's SD-1, DD-2 offers +/-0.005% low temperature operation problems membrane keyboard is not very comfortable in the night

GP-DX + DA-1 assembly

See Equatorial Mount Tracking Errors page

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Last Update: 11.02.2003