K3's AstroPhotography
"When I consider your heavens, the work of your fingers, the moon and the stars which You have set in place, what is Man that You are mindful of him?" -- Psalm 8:3,4

Detailed review of Astromeccanica's DA-1 DELUXE dual axis drive system
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:

  Vixen
SD-1
Vixen
DD-1
Astromeccanica
DA-1 DELUXE
Vixen
SkySensor 2000-PC
Drive axis RA only RA + DEC RA + DEC RA + DEC
Drive speeds 2x, 16x fast, pause and reverse (16x) 1.5x, 2x, 32x fast, pause and reverse (32x) 2x, 8x and MAX,
Max can be choosen from the following:
32x RA, 32x DEC
64x RA, 64x DEC
128x RA, 128x DEC
260x RA, 520x DEC
multiple speeds
up to 1200x (5/s)
Accuracy 0.005% against
sidereal rate
0.005% against
sidereal rate
not listed not listed
Operational
temperature
-10C ... +50C -10C ... +50C -10C ... +35C not listed
Power supply 6.5V - 12V DC 7.5V- 12V DC 10V - 15V DC 12V DC
Torque 0.4 Nm 0.3 Nm 1.06 Nm not listed
Motor type MT-1
Nippon PF42-48I3
MT-1
Nippon PF42-48I3
Saanyo Denki
103H548-0440
MT-2
Motor holding torque 0.054 Nm 0.054 Nm 0.265 Nm not listed
Computer control No No Yes Yes
Autoguiding function No No Yes
(ST4 autoguide connector + PC guiding with webcam)
Yes
GOTO capability No No GOTO lite
(will be supported by K3CCDTools soon)
Yes
(compatible with many PC programs)
PEC function
(Periodic error correction)
No No No Yes
Display No No LCD
2 lines x 8 characters
variable backlight
LCD
2 lines x 20 characters
variable backlight
Note     * Belt drive system (vibration elimination, backlash elimination)
* No need for additional clutches - axis knobs can be freely rotated
* Slack correction
* Satellites tracking
* GOTO without need of polar aligning
* Connector for optional encoder unit (feedback axes position read out)
Dimensions 106mm x 52mm x 25mm 140mm x 52mm x 36mm 126mm x 68mm x 24mm 188mm x 100mm x 45mm
Weight 190g 220g 180g 370g
Price w/o VAT,
including motors
(December 2002,
Europe)
~ 250,-Euro
(not including additional clutch for axis knob)
~ 460,- Euro
(not including additional clutch for axis knob)
720,- Euro ~ 1300,- Euro

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:

  DA-1 + GPDX GEM1
Normal operation (RA 1X, DEC stopped) 0.45 A 0.20 A
RA stopped, DEC stopped 0.48 A 0.21 A
RA 8X, DEC stopped 0.48 A 0.14 A
RA 1X, DEC 8X 0.68 A 0.32 A
RA 8X, DEC 8X 0.68 A 0.26 A
RA 1X, DEC 520X 0.40 A n/a
RA 260X, DEC stopped 0.55 A
(acceleration 0.88 A)
n/a
Module switched off 0.11 A 0.00 A

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 -6.6C. 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 -10C according to manual (and even -15C 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 -10C 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 +6C!!!

Imagine a situation - Star party in open field. You are picking off your equipment from car. The ambient temperature is 0C. 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 -10C 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:

Adjustment value Worm shaft period Error RA drift
-15 597.1468 s -0.20 % -1.83 "/min
-16 599.6013 s 0.21 % 1.87 "/min
-17 602.0654 s 0.62 % 5.59 "/min

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:

Feature Explanation
Main Menu
MAX speed configuration Enables to define speed which is assigned to MAX button:
32x RA, 32x DEC
64x RA, 64x DEC
128x RA, 128x DEC
260x RA, 520x DEC
Autoguiding correction speed Enables to fine adjust guiding speeds separatelly for RA and DEC axis. This is very powerful feature and it enables ultra fine tracking accuracy. The options are following:
Fast RA speed - from 1.1X to 2X
Slow RA speed - from 0.9X to 0.5X
DEC speed - from 0.2X to 1.7X
RA tracking speed adjustment Enables fine adjustment of RA speed. It is useful for observing Moon and Sun, which are moving accross the sky not exactly in sidereal speed.
Display backlight and contrast adjustment User can adjust display exactly according his/her demands.
Advanced Menu
Torque RA/DEC It is possible to set one of three values of RA/DEC torque - low, middle and high
Slack RA (fast and slow) Enables to eliminate mechanical backlash of the mount gears in RA axis
Slack DEC Enables to eliminate mechanical backlash of the mount gears in DEC axis
Low battery warning threshold Enables to set up voltage value, when "Low battery" warning appears
Emiglobe Possibility to select North or South hemisphere
Gear RA/DEC Enables to set up number of teeth of the gears separately for RA and DEC axes. It supports the following values:
144 (Vixen GP/SP and similar)
180 (Losmandy GM8, G9, etc.)
240, 300 (Bellincioni and custom mount)
360 (Losmandy G11, Bellincioni, etc.)
Sidereal speed fine adjustment Enables to adjust exact sidereal speed in 0.39% steps.



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
Remark (11.02.2003)

After some consultations with Astromeccanica company I was told, that they are just finishing circuits for more fine adjustment of RA. The new models of DA-1 will be equipped with ultra fine adjustment with 256x finer adjustment step. That means +/-0.0008% precision!
They are also working on low temperature problem.
In the next future, DA-2 unit keyboard (descendent of DA-1) will be noticeable improved with higher and backlighted keys.

It is a good news, that Astromeccanica is listening to customers' demands. I will add new test results to this page as soon as I receive the new DA-1 module.


See
Equatorial Mount Tracking Errors page

Back to Vixen GP-DX equipped with Astromeccanica's DA-1 drive system

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Last Update: 11.02.2003