Page updated: 17 June 2010
Optimizing the Results of Meade's Autostar Telescopes' Drive Training
 
Careful drive training is one of the important settings for Meade's Autostar equipped telescopes when it comes to achieving successful GOTO's. Although the manuals do stress it, many questions continue to rise about the optimum procedure. While the drive training procedure itself may seem relatively straightforward, optimum results require careful attention to the sequence of events during the training cycle. First, a short explanation of how training works inside the telescope's gearboxes. The illustrations below are of an ETX-125EC and an LX200ACF gearbox. Although the gearbox differs in other scopes, the concept remains identical. The same goes for the drive training procedure.
 
As one gear in a telescope's gearbox turns it will not immediately engage the next gear. It first has to take up slack (space in between the teeth of gears) before the teeth engage and the motion is passed. This happens between each of the gears before your telescope will move as intended. This is often refered to as "backlash". What drive training does is making the Autostar controller calculate how long the motor in an axis must be powered before the slack is removed in the entire gear train and actual motion is of the telescope is attained. If your telescope's drives are undertrained the Autostar controller will assume the scope is moving when in reality the gears are still taking up the slack. If the drives are over trained the scope will be slewing while the Autostar controller assumes it is still taking up gear slack. Both of these errors make your GOTO's inaccurate.

How does the Autostar controller calculate how much the gears have moved? Incorporated in the drive assembly are sensors called 'encoders'. Small toothed wheels which turn in front of a LED. Every time the encoder senses the light is blocked by one of these teeth it counts a 'tick'. The number of ticks tell the Autostar controller how far the gears have turned.

So will training take care of bad GOTO's? Yes, if you do it correctly. Sure, if you carefully centered the object you trained on every time, your GOTO's will improve. However, a lot of Autostar telescope users don't realize it is very easy to take up slack twice in the drive training procedure, although it really should be taken up only once. Your GOTO's may be acceptable, but I'm convinced much better result can be achieved by following the correct procedure.
 
What happens when the Drive Training procedure is initiated?
 
(this example focuses on the declination axis of an Autostar telescope, the same applies for training the right ascension axis of such a scope)
 
Autostar asks you to center the reference object. You do so and press [ENTER]. The scope will now slew downwards a certain amount, and slightly back upwards. Next the controller asks you to slew upwards using the key on the keypad, until the reference object is again centered in the eyepiece. What the Autostar controller did is slewing your telescope to a position below the object, reverse the direction of movement (thereby taking up the slack in the geartrain) and having you tell it through the controller how long to spin the gears to recenter the object. What you really told the controller is how many encoder ticks it needs to count before it is back at the reference point. It already knows how many ticks it slewed the scope downwards and back upwards, all it needs to know is how many ticks are needed to bring it back to the original position. The controller will do the math for you and determine the amount of slack to take up the next time you GOTO an object. That's what drive training does.
 
What can go wrong?
 
If you centered the reference object by slewing your scope upwards, you introduced a rather large margin of error into your training. Since in the declination training process the scope will first slew downwards, the following is happening:
- Gear slack is taken up (because you moved it upwards to center the reference point).
- The telescope slews downwards.
- Gear slack is taken up again (because it has to reverse the direction of slewing).
- The telescope slews slightly upwards.
Now you recenter the reference point. Should you be satisfied? Not really: The gears took up slack twice, while the Autostar controller calculated how much slack it took up only once.
 
How to counter double slack
 
Before starting the training process, always center the reference object by slewing the telescope downwards. When doing so the gears will only have to take up slack once and this will make the results of your drive training more accurate than ever.
When training the right ascension axis always center the reference object by slewing the telescope towards the left. Be careful, the scope will move counter-clockwise but the image in your eyepiece will be moving in the opposite direction. Knowing this, the worst thing you could possibly do when you start your training is centering the object by slewing upwards and towards the right. The gears would then take up slack twice in both the right ascension and the declination axis.
In a nutshell, here's the procedure:
- Center the reference object by first pointing the scope higher than where the object is.
- Using the controller slew the telescope downwards until the object is centered. Do not overshoot, you don't want to reverse the direction you were slewing in. If you do overshoot, start over.
- Scroll to the "Train Drives" menu in the Autostar controller and select "Dec/Alt Train".
- Since the reference object is already centered you can press [ENTER] again.
- The telescope will now slew downwards, slightly upwards (thereby taking up the slack) after which you again recenter the reference point using the keypad.
- When the reference object is again centered press [ENTER] and the telescope will move upwards, slightly downwards after which you again center the reference object. Press [ENTER] and you have finished training the declination axis.
- Repeat this process for the right ascension axis training procedure, using the technique described above.
 
More thoughts on Drive Training
 
Use a distant, elevated object such as a lamp post, antenna or a chimney to train on.
Use the highest magnification you can obtain, preferably while utilizing a crosshair or reticle eyepiece. If you don't have one, center the reference object near the edge of the FOV and attempt to return to that position as accurately as you can.
Use the slowest speed possible for maximum accuracy. Be sure to stop slewing when the object is exactly centered again, do not overshoot. Should an overshoot occur, start over...
Remember to not use your right ascension and declination percentages. I reset them to zero before I train to take out any interference it may cause. Reenter your values after the drive training is complete.

After completion of your training, take a moment to test it on landmarks. If you trained carefully you will immediately see improvement.

As long as you make no physical changes to your telescope's drives (tuning, maintenance), drive training does not need to be repeated.
Increased precision and significantly higher reliability can be obtained by replacing the nylon gears in older LX200 drives with metal ones. Peterson Engineering Corporation's Sky Division sells "Buck's Precision Gears" as a replacement for the LX200's original gears.
Newer versions of Meade's GOTO telescopes (ETX-90 & -125AT/PE, LXD-75 and LX200R/ACF) are fitted with metal gears as a standard.
 
To be able to read and record the drive training results it is useful to update the controller's firmware using Richard Seymour's software patch, available for both the #497 Autostar controller (ETX-90/105/125, LXD-75 and LX-90) and Autostar II (LX200GPS, GPS-SMT, R and ACF).