Losmandy Gemini System

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Instruction Manual - Level 4 (pdf) NEW May 2006
Pricing Information
Gemini Accessories
Gemini Quick Start
Gemini Software page
Gemini Servo Motor Installation Instructions
Tips for use with SBIG Cameras and Autoguiders

The Losmandy Gemini system is a DC servo motor based GOTO computerized positioning system designed for the Losmandy HGM200, G-11 and G-8 mounts.

The system can be ordered with all new Losmandy mounts, or easily retrofitted by users who already own a G-8, G-11 or HGM200 mount. The new Gemini system simply replaces the existing stepper drive motors and electronics, with hex keys plus a small pair of pliers being the only tools required to upgrade the drive.

The Gemini system has many features designed to quickly and accurately point the telescope to an object, then track it with even higher precision than the previous digital stepper drive used by Losmandy.

The choice of servo motors gives two main advantages over stepper motor based systems.

  • Servo motors run with a continuous smooth rotation, rather than discreet steps as with stepper motors.
  • They also have very high torque, even at high slewing speeds.

As a result the Gemini system can deliver up to *10 degrees per second slewing rates, yet still retain motor positional information of around 1/10th of an arc second. (*maximum speed with the G-8. Expect approximately 6 degrees per second with G-11 and HGM200 models )

The Gemini system will also accept inputs from optional shaft encoders (the same as used in Losmandy digital setting circles), which allow the telescope to be positioned by hand, yet still retain pointing information. Hand movement of the telescope will drop positional accuracy to that of the shaft encoders, but this can be easily refined using a quick synchronization or alignment position from a nearby object, which will return the system to full motor encoder accuracy.

Gemini can be used as a stand alone system in the field. It can be powered by any 1500+mA, 12-18 Volt DC source. No personal computer is required. A user brightness adjustable LED display allows navigation through all internal databases for field use without a PC. The following databases comprising about 41,000 objects are built into the Gemini system, more than enough to keep even the most avid observer busy for some time!

  • Messier catalogue                        (110 objects)
  • NGC revised NGC                         (7840 objects
  • IC revised IC                                (5386 objects)
  • Sh2 Sharpless 2                           (313 objects)
  • Bright Stars                                  (167 Objects)
  • SAO Stars                                    (17635 Objects)
(The above database links will take you to ASCII text listings of each catalogue)

The Gemini system has an impressive list of features

  • Very High Precision pointing to less than 1 arc minute
  • Object search mode with user definable search radius
  • Sidereal, Solar Lunar and King tracking rates
  • User brightness adjustable LED display
  • Up to 256 alignment stars permitted either side of the meridian
  • Menus are accessed by the standard Losmandy 4 button hand paddle 
  • A deluxe hand paddle that repeats the Main panel display information
  • RS232 serial port control by a PC using software such as The Sky, Guide 7.0 or Palm Planetarium
  • T-Point (Software Bisque) Compatible
  • Internal real time clock that displays, UTC, Local Mean Time an Sidereal Time
  • Up to 10 degrees per second slewing (G-8)
  • User definable Guiding, Centering Slewing and GOTO speeds 
  • Permanent Periodic error Correction
  • Allows manual telescope movement with optional shaft encoders
  • Southern and Northern Hemisphere operation
  • Retains position information after power off (for permanent observatory use)
  • EPROM upgradeable software

A Deluxe Hand Controller (pictured above, right) is standard for all Gemini systems.. The hand paddle features membrane switches which provide excellent tactile feedback, while providing a moisture proof seal for the internal electronics. The display works in parallel to the main electronics, allowing users to access all of the main panel functions via the palm of their hand.

Gemini uses a Meade LX200 command sub-set, with most LX200 commands being implemented.  The user can update the internal real time clock via the PC link as well as user location information. Coupled with The Sky by software Bisque and CCD camera, users can confidently determine the positions of minor planets and comets, and place them on a CCD detector time and time again.

The Gemini design incorporates surface mounted PC board technology for reliable performance in the field. The main control board also has autoguider and accessory ports to allow full remote control of the system, either via a local PC, via a LAN or via the internet. (Gemini has been successfully tested with Software Bisques IAS server software)

The Gemini system has built in "T-Point" like pointing software that can use from one to many stars to refine its pointing accuracy. With multi-star modelling pointing accuracy has been measured to within three arc minutes around the entire sky, and to less than one arc minute with short slews from an updated position located within a few degrees of a reference  object. Gemini is also fully T-Point (Software Bisque) compatible. Extended personal computer based T-Point modelling runs can give better than 1 arc minute positioning accuracy across the entire sky! Further, with Gemini's warm re-start option, previously stored PC T-point data can be reused without the need to conduct a short mapping run

How accurate is Gemini? 

Pictured is a T-Point summary of a 60 star mapping run with a Losmandy mount fitted with Gemini.

Note the Sky RMS pointing of 26.27 arc seconds.

While some manufacturers claim incredible accuracies with their GoTo systems, few will actually state actual results as shown above.

While single star alignment assumes that your Losmandy mount is accurately polar aligned, the Gemini system only requires rough polar alignment to deliver excellent pointing accuracy across the entire sky using multi-star alignment models.

antares m16
m17 bug
ring lagoon
m22 m27

The above CCD image mosaic demonstrates the early pointing accuracy of the Gemin/G-11 system, using a three star alignment model, the telescope was slewed from (in rows, left to right)  Antares, M16, M17, Bug Nebula, M57, M8, M22, M27, Optus 1b geosyncronous satellite (small streak lower frame). At the completion of each slew, no fine adjustment was performed, and a single 20 second CCD exposure was taken.

As can be clearly seen, the tracking accuracy the Losmandy Gemini system is excellent, even without PEC, which was not used in the above exposures, stars are perfectly round. The PEC menu allows for permanent error corrections to be stored in the non-volatile memory of the Gemini system.

Gemini +
The Ultimate Hand Controller

Pictured is a palm PC being used with The Sky pocket PC software to control a Losmandy/Gemini mount. What makes the system unique is Gemini's ability to align on a PC object.

Just tap on an object on the Palm PC display and slew to it. Any residual position errors can quickly be modeled by Gemini's additional align to PC object function.

Up to 256 stars on each side of the meridian can be used to create a pointing model. You do not have to know the name of the alignment star....just tap on it!

Only Losmandy Gemini gives you T-Point like accuracy in the field with no other software or accessories!

The model updates around the last alignment object, hence for short slews the system can easily position objects on "every commercially available CCD every time" , a feat yet another telescope under $40,000 can now accomplish!  ;-)

Gemini's non-volatile memory and Real Time Clock data also allows the system to be powered off, and restarted at a later time with no loss of modeling data or positional information. The re-start position accuracy is only limited by the accuracy of the internal clock, which can be updated to within a fraction of a second via a PC.  These features make the Gemini system ideal for Astrometric and Photometric surveys (e.g. Comet and Asteroid hunting, Supernova patrols, Variable star studies) and are well suited to permanent telescope installations.

Gemini Troubleshooting Guide

Below are common problems that first time Gemini users can encounter. The list is far from exhaustive, but will help those looking for a quick solution.

Mount tracks for wrong hemisphere.
Make sure correct mount type, Latitude/Longitiude and time zone data has been entered.

Can not enter single character object identifier, e.g. get getting M40 instead of M4
Use the HC buttons to scroll to the -> symbol to terminate data entry.

Motor(s) Slew Uncontrollably on Start-Up
Probably a poor connection between main panel and motor. Re-seat motor cable connections. If this fails, try replacing/swapping cable which may be defective.

Strange Characters in Deluxe Hand Paddle display
Try Re-setting CMOS. Also check to see you have the latest EPROM software

Mount takes a long time to centre object
The object may be close to a east or west limit, where it will slew the last few degrees in centering mode.

Mount Continuously Beeps!
You have hit a east or west limit. Slew away from limit. If this happens straight after start-up, limits or lat/long may be incorrectly set. Cold start mount, check limits.

Poor object centering accuracy
Check that you have not mis-identified a star. Make sure your mount is within a degree or two of the pole. Also when sighting stars  make sure they are well spaced in RA and Dec, and are accurately centered prior to making an additional align. Many star diagonals will de-centre stars when the diagonal is rotated.

Mount will not autoguide/calibrate
Check you are Photo-mode. The autoguider port will only work with this mode active. Make sure you have not left Gemini in Menu mode, and have switched back to Sidereal (or Solar/King ).

"Autoguider Error" on Display
You have plugged a SBIG ST7/8/9/10 or similar .TTL guider cable directly into the autoguider port. Gemini requires an optocoupler or SBIG relay box with these cameras.  Only the SBIG ST4 and STV will plug directly into the autoguider port.