[bojan]

Well, time has come to test the new gearboxes..
And now I have mixed feelings about the whole project and all the noise on the internet about Synta products.. at least the noise concerning the recent Synta products (my mount is one year old now).

When planning the upgrade, my main goal was to reduce high frequency components from PE spectrum, allegedly generated by horrible gears and even worse grease used in original Synta gearboxes.. I was quite aware that there is not much that can be done about PE intruduced by worm gears pair.

But, what I ended up with was the situation not much better..

Yes, the PE amplitude is almost halved, from 24 arcsec what was before now I have ~16 arcsec. I am attributing this improvement to much smaller backlash, because I spend considerable time adjusting the meshing on the mount before assembly of the RA shaft. Also, some of it may be due to different phases between worm gear and gearbox.. I should do the proper PE analysis by FFT (I do not have autoguider yet so this must be done by careful measurement on the images, pixel-by-pixel.. the awful job I do not want to do really)
But the high-pitch PE components are still there, in almost the same amount, something I did not expect to see on the test shots.
My gearboxes also introduced its own PE components, this is quite visible on the attached images (the second one is with original, the first image is with new gearboxes) as "wave" with 1/4 period compared to the main one (corresponding to one rotation of the worm shaft). This is due to the second stage of my gearbox (I am using two stages, identical gear pairs - 20/80).
The original Synta gearbox has the last gear pair reduction ratio 1/3, and this is also visible on the second image as wave with 1/3 period.. and surprisingly, the amplitude appears to be somewhat smaller)
Also, my gearboxes are very loud, and I can even "feel" the stepping vibrations by placing my hand over DEC shaft housing (this is only when slewing with 16x speed of course.. Darren's mod uses microstepping for tracking, so this is not the issue at all).

I opened one of original Synta gearboxes and found out that:
- the first pair of gears (on the motor shaft) is helicoidal and plastic, that is why they are so silent.
- the grease used appeared to me to be of very reasonable quality (judging by the smell and touch)
All this is in direct contradiction with dreadful reports found on some webpages which promote installation of Conrad gearboxes (mentioning "un-defined material used for gears" and goo-like stuff used for lubrication)

So, what happens now?

What was left of original mount (in terms of tracking) is as follows:
- Bearings on the RA shaft (replaceable.. maybe I will try this later)
- worm gear pair (not that i can do much about it..)
- transfer gears (47 teeth, they can eventually be replaced with timing belts.. to be tried later when I find something suitable).

Back to the drawing board....