Image of the day

Captured by
Terry Wood

Jupiter (clearer) Nov 5th 2023 w/Mewlon 180c

My Account

New to Astromart?

Register an account...

Need Help?

Preliminary test results of the MClennan Gearbox M

Started by fblue, 01/17/2009 07:44PM
Posted 01/17/2009 07:44PM | Edited 01/17/2009 08:31PM Opening Post
Good news, I got a chance to test last night. The results were nothing less than startling! I only did testing while auto-guiding, but that was where I got the first data, so it allowed me to compare the data from guide logs from PHD taken before and after the gearbox was installed. The logs were imported into PECPrep and PE was calculated for the Frequency Spectrum Graph. The other PE data was uncorrected so that all PE was shown as it was logged by PHD with no smoothing.

The peak to peak overall PE was reduced to about 16" after installation from 3.5" before installing the gearbox. There was no sign of any gearbox noise more than .1-.2". The biggest error was now the 79 sec error of .5" which is the worm. The PE graph was so changed, it looked like it was from another mount! To say that I was amazed would be an understatement. :^) Every aspect of the PE was reduced by a factor of maybe 3.5x!

It seems that the gearbox was responsible for a lot more of the PE than I originally thought. So many spikes that were at intervals that I could not isolate their source, appear to have been caused by the teeth and gears or the shafts running without bearings in the original gearbox. Not sure exactly which were the culprits, but I believe the nylon gear was probably responsible as well as the smaller pinion for a lot of it. I think that the teeth of the Nylon gear are very uneven and that each one creates another spike of PE that is added to the overall PE and that much of this then appeared to be worm related.

That was what Roland said when he reviewed a PE graph I posted. He said the gearbox was a big area for improvement and he was more than correct! His pointing out that the plastic gear and the non-precision stamped gears of the gearbox were causing a great deal of noise was not only true, I had underestimated its impact.

So, I am pretty convinced that this is a very significant improvement for the G-11. I guess it will require others to make this mod and test to see if my results are a fluke or not, but I did do more than one test last night in different areas of the sky to be sure that I was getting good data. The results were identical on these tests, so totally repeatable.

I did a 5 minute unguided shot, just to see what it would look like. There was a little drift due to my polar alignment, but there was no signs of PE in the stars, just a slight elongation of all stars from the drift.

I am waiting now for the other gearboxes to arrive so that I can replace the DEC box. It won't have as great an impact, but it will certainly help and the noise level should be significantly reduced.

I will try to get some screen shots of the before and after tests in PECPrep and post them later so that you can see the difference.


[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 01/19/2009 07:55PM #1
You still have the Ovision worm installed?

Rolando