Synscan PRO Goto Backlash problem

Posted by XTSee on 20th January , 2009


In my previous post about my new Celestron C6-S telescope, which I upgraded to Goto using the SynScan PRO Version 3 Goto Upgrade Kit for EQ5 I mentioned that the direction keys didn’t appear to be responding correctly.

In one direction they will nudge tiny amounts, but in the opposite direction, it slews several minutes/degrees of sky very quickly, then slows down to tiny adjustment again while I hold the key down, then when I release the key it stops, and then hit the opposite direction again it slews the same amount  back again.

The motor Backlash thing is just bugging me (being impatient), and I’m sure that it is either my not understanding how its supposed to work, or else I’ve got some setting wrong, e.g. the Backlash, or I did my
alignment wrong. My friend explained to me however that backlash is normally only a very tiny compensation - nothing massive.

I’ve found only one post on Cloudy Nights forum which hinted about the reverse-before-forward thing, and that was someone else asking a similar question, but not getting an answer on it!  The movement when viewed thru the 25mm EP is probably 1/4 of the FOV diameter.

It makes 3-star aligning very frustrating, which is why I’m sure there’s just something wrongly set.

Perhaps I should factory reset, or try turning the Backlash settings OFF altogether? They were set at B° 12′ 13″ (yes that is a “B” I guess for Backlash?), but 12 mins 13 secs not only sounded a lot to me, but seemed an odd sort of figure, so I tried setting to just B° 00′ 05″ but it didn’t improve it, so I wonder if its a  re-boot/re-align kind of thing to make it effective. But even after turning off/on the distance it moves seems to be exactly the same.

I’ll check the Firmware versions tonight, and try updating if necessary, and do some more experimenting indoors.

Failing that it’ll have to be a post on CN, because I searched for bloody ages in several of the sub-forums to no avail, and some Googling.

I found the following Knowledge Base article on the Celestron site Support section, which helped me understand Backlash a bit better:-

My CG-5 (Advanced GT) mount keeps moving after I release the arrow button. Is this backlash?

After some more experimenting tonight the backlash swivel is perhaps about 0.5 to 1 degree (like the width of the main blob of the double-cluster), so quite a lot, and was making it very difficult to judge just how much to wind BACKWARDS by (not affected going forwards), before releasing the key, at which point it automatically returns (forwards by the backlash amount) to its original position less the amount you adjusted backwards by.

Part of the frustration was slowness, because the software would start slewing slowly for about the first 20% of the travel, accelerate to a high speed for the main distance of the backlash adjustment, then decelerate for the last 20%, before switching control over to the Backwards RA key which I’m still holding down waiting for it, so I can make my adjustment (at one of the 9 low to high Slew Rates that I have chosen).

So quite annoying and it turns out I was right to think so…..

Next I downloaded the SynScan EQ firmware updater software from this Skywatcher support page, and downloaded ALL versions of the firmware from 3.10 up to 3.23, so I could read the release notes.

Following the instructions provided on the above page, I hooked up the USB/RS232 converter and booted the hand controller into Update mode, then ran the update which detected the controller and uploaded the latest firmware and sky database.

Its got several bug fixes and some new features (ie. GPS control if the scope has it, other info like Temperature, Voltage, improvements to Alignment Procedure, Periodic Error Correction, etc), and most importantly the backlash now seems to work properly!

At least as far as I can tell - by the time I had done this, clouds, hurrumph.

Also the “B” in the degrees column has gone, so now it reads like 0° 00′ 00″, and even if I set a considerable 10 arc-minute setting (0° 10′ 00″), the amount the scope slews before actually starting to adjust is miniscule, and almost instantaneous. The letter “B” in the numeric degrees column just doesn’t sound right at all, and I wonder whether had I factory reset the hand controller, maybe that would have fixed the problem without doing the hand controller firmware update?

So I’m pretty sure thats fixed it :)

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2 Responses to “Synscan PRO Goto Backlash problem”

  1. More fun with the C6-SGT XLT SCT Telescope | Jims Orion XT10 Astronomy Blog

    [...] 3-star alignment was very easy and accurate now the backlash is fixed. Backlash needs tuning though. I thought with each star I aligned on, 1, 2, 3, it would [...]

  2. How to improve worm gear backlash on Celestron CG-5 Equatorial Mount | Jims Orion XT10 Astronomy Blog

    [...] problem with the Backlash setting in the SynScan Pro V3 Goto Upgrade hand controller (which was fairly easily fixed by a firmware update to correct the excess Backlash adjustment), my interest was piqued and I wanted to check at an early stage that my scope and mount were [...]


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