Gear ratios wrong?

[Dave_D]

This is a but 'unscientific' but i just fixed a laser pointer to the saddle on my Vixen GP, marked the wall at the centre of the laser spot with a cross (about 15 feet away) and did a full 360 degree RA rotation using eqmod without reversing direction. after supposedly 360 degrees, the positions don't match up.... this can't be right can it? could this explain my atrocious guiding failure and my RA guiding going haywire. This is using a synscan EQ5 upgrade btw.

eqmod toolkit shows my gearing set to auto and the values in one of the eqmod config files agrees with the values on the eqmod prerequisites webpage.

 

[Peter Drew]

Does this repeat exactly or is it random ? If the former it could be a drive electronics error, if the latter a mechanical issue.

[Dave_D]

i've repeated it twice with same result

[Peter Drew]

Thanks. It's a small amount by visual standards but not one you would wish for if imaging. I would have thought that if the gear ratios were wrong then the error would be much larger. Interesting problem.

[jambouk]

It is asthough the dec has moved slightly too...

[1parsec]

If you rotate 2 full revolutions, does the error double too ?  

Check what 3 revolutions gives too.  ( assuming you have enough slack in your cables !)

[nigelg]

Have you got the tracking checked in Eqmod ? This will the mountto rotate 360 degrees + the time it took to rotate.

 

Nigel

[Dave_D]

On 18/01/2017 at 22:48, jambouk said:

It is asthough the dec has moved slightly too...

no, the RA axis is at about 45 degrees at the moment so i can fiddle...

[Dave_D]

oh here's something interesting... marking the laser spot and doing a full rotation to bring the laser spot back to the same place, ascom shows a difference of 4' 30" (i full rotation was 24h 4' 30" give or take the accuracy of my eyes) which to me, is uncannily close to the difference between a clock day and a sidereal day... coincidence?

[Peter Drew]

Could be a "no problem" problem.   

[jambouk]

Even if the RA axis was at 45 degrees the dec axes could still be rotated.

Does the laser fail to line up if you just manually do a 360 degree rotation of the RA when the mount is otherwise turned off. I thought the original problem was that, and not related to slewing. Therefore a physical / mechanical issue rather than an issue potentially caused by electronics.

James

[michael8554]

Could be miscounting encoder "ticks", so takes more ticks to turn a full 360, or the setting is wrong.

Not sure how this would affect your guiding though.

IMHO when guiding the RA tracking rate is not altered by the encoders, the RA motor is only affected by PHD corrections, the encoders just keep track of where you are.

What were your "atrocious guiding failures" ?

Michael