It is clear
that an error , repeating over a time of 15s is playing ! Easy to
find, the connection motor / worm is made with 40 tooth gear , so
one turn of 600s makes one new tooth very 15 s .
VIXEN SP-DX
Equatorial mount advanced testing
(can be usefull for clones like SP, EQ4, EQ5, GP, GP-DX , synhta HEQ5 ... )
Please forget my extra poor english !
PART ONE : USING THE MT1 MOTOR, which is the regular motor that comes with the DD1 handpad.
I wanted to improve the autoguiding beahviour of the mount, because it was a little bit jerky. As a sidehand effect, i started to hope having a periodical shape error, instead of having a jerky error. But at this point i must say this mount has a very good peak to peak error , lets say +/- 8"
This unipolar motor is 48 steps / turn, with a 120:1 gearing , is easily driven with the mel bartels system, without any modification, goto are a little bit slow ( 0.5 °/second of time ) but extremely precise. I never miss any object since a long time !
First i have switch to a quartz driven driver, build using the david rowe stepper projekt, it give me following graph :
It is clear
that an error , repeating over a time of 15s is playing ! Easy to
find, the connection motor / worm is made with 40 tooth gear , so
one turn of 600s makes one new tooth very 15 s .
I have searched a way of putting the gear away , replacing it by pulley and belt, see the picture for details, and please note i'm still using the MT1 motor, you just need to find the right pulley / belt combination.
Result is seen in the following graph, the error is much smoother, and autoguiding acts much better !
Following graph is plotted in the fourrier domain, it shows that the 15s error has gone, and has been pushed to 20s b and reduced of 50% the value ! Unfortunately a 60s error is now there, but it is very smmoth and esay to handle with autoguiding.
As i have read on carsten's internet site, the proof of the pudding is in the eating, so no other solution as a little quick and dirty autoguiding test under the star : the mount stays in RA in +/- 3 arcsecondes peak to peak interval ( DEC of the star approx 0° ). Very good ! In DEC situation is not so good because of backslash problem in the the gearing, and very long exposure are hard, it is OK up to 5 minutes but not more.
I have used another setup , the imaging pc is linked to the bartels PC via RS232, it works as the van duin emulator.
Setup :
80mm fd=10 schmidt-cassegrainian telescope, vesta , albert van duin LX200 emulator wired in // with mel handpad buttons.
LINKS
www.astro-electronic.de very good motor see SECM3 motor with 10:1 gearing
www.boxdoerfer.de very good motor , and sinusoidal driver for stepper motor
http://www.astromeccanica.it/dual_axis_drive.htm nice pulley and belt commercial motor system
http://xmcvs.free.fr/spdx/index.htm my site about the bartels system.
http://www.newastro.com/wodaski/review_GP_DX.htm very good test of the GP-DX mount
www.nc-step.de card for driving one or three motors in step / halfstep mode, card for one motor in micro-step mode, power, optocoupling ... germany, english version available.
http://www.terra.es/personal9/angel.caparros/eq6_mod.htm page in spanish on a EQ6 modification, pulley belts and FFT analysis.