Help with EQ6 Rebuild - RA axis

[LucasB]

Hi Everyone,

I am after some advice regarding the rebuild of my EQ6. I have stripped down my EQ6, regreased all of the bearings, replaced the worm bearings and I am now reassembling. I have tuned the DEC axis with no problems and it is as smooth as silk with no backlash but it is the RA axis which is giving me a lot of trouble. It seems once adjusted I move the axis with a piece of tubing over the worm and one way it is smooth but when I turn it in the opposite direction it is very jerky. The axis goes tick tick tick when I turn the tubing. When I loosen the clutch and move the axis to the other side of the mount it is smooth in the opposite direction (where it was previously jerky) and jerky where it was smooth. I have the counterweight bar extended but I still think the DEC head maybe a little heavy.
I spent two hours perfecting the DEC and it is great. I must have spent another 3 hours on te RA with no luck. I have thought of removing the DEC axis and doing the RA Axis first but I don't think there would be enough load to give me the feel I require for adjustments.

What can I do to adjust this axis?
Wondering what other have done to adjust the RA axis?

Would appreciate some input if you can help,
Thanks
Lucas

[Steffen]

Speaking from experience with tuning HEQ5 Pro, so YMMV...

Does it move smoothly in RA if you move the RA worm carrier out of the way? That should reveal whether there's anything wrong with the ball and conus bearings on the axis. On the HEQ5 Pro mount there's also a washer next to the brass worm gear (clear on one axis and red on the other), if you forget that the axis moves jerky in places.

Next, I'd put the drive bits back, one at a time. Does it move smoothly with the worm gear engaged but the motor and transfer gear disengaged? With the transfer gear back? With the motor back?

Cheers
Steffen.

[LucasB]

Thanks Steffen. Yeah it is a process of elimination at the moment. The weight of the dec axis definitely doesn't help with the RA axis adjustment. I have found that if I do the RA axis first and just aattch the worm carrier for the Dec axis the mount is balanced and I can tune the RA well. I also believe the lock nut on the RA was a little loose so I have tightened it but it has changed the worm engagement so further tweaking needed before next test.

Lucas

[Tandum]

Lucas,
I have some web links that might help :-

http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20Strip%20Down%20Home.htm

http://www.youtube.com/watch?v=a8G-gpCpQ20&feature=fvw

http://www.astro-baby.com/EQ6-Supertune/EQ6%20Super%20Tune%20Guide.php

One tip, it's not an engine block, finger tight plus is all you need.

Hope they help.

[Nico13]

Lucas I would think you should have it fully balanced on both axis when doing your fine adjustments so you may want to add some weight to help it out. Hope this helps.

[peter_4059]

I agree with Ken - it needs to be balanced or you get this effect. I found partially extending the CW shaft with the dovetail saddle removed enabled me to balance the RA.

[bojan]

Yep, balance it.. or, try to introduce a slight un-balance so the motor must work against it.
We are talking here about situation where the backlash, friction and elasticity of the mount-telescope-counterweight structure play together and produce this effect.

[LucasB]

My apologies for the very late reply and thank you for your input Robin, Ken, Peter and Bojan. You are all correct - I have taken more care to balance the RA axis accurately and have had great results. I have also put in pulleys and a timing belt and completed a small 2 cycle test and the pk to pk is about 8.2 arcsecs. If I apply a PE curve it will be down to approximately 3 arcsecs pk to pk so happy days.

Thanks again.
Lucas

[RobF]

Be good to see some pics or hear what parts you used for the belt mod Lucas? Sounds like a great outcome.

[LucasB]

No worries Rob. I don't have any pictures of the disassembled mount but I do have a spare set of pulleys and a timing belt I can post later when I take some pics. I bought them from HPC gears already bored out. It was a little more expensive but I am not that handy with a lathe.
Also I made a little mistake in my previous post. The PE was + 8.2 arcsecs so about 16.5 arc pk to pk in total but with the PEC applied it would be + 3 arcsecs or 6 arcsecs pk to pk with RMS of 1.4 arcsec

Much better than the 50-60 arcsecs pk to pk from the factory.:thumbsup:

Lucas

[Steffen]

Hi Lucas, that's what I've been thinking of doing for a long time. You eliminated the transfer gear that way, right? If you can point me to the correct size belts and pulleys I'd much appreciate that, and I'd might have a go myself.

Cheers
Steffen.

[bojan]

Hi Steffen,
you may want to see what I have done re this..
http://www.iceinspace.com.au/forum/showthread.php?t=69560
The thread above is not up-to-date, though. now I have 400 s/rev steppers direct with no gears (only timing belt), powered by microstep driver (Pololu) and controlled by SoundStepper.. discussed here:
http://www.iceinspace.com.au/forum/showthread.php?t=90164&highlight=pololu+driver

Belts and pulleys came from https://sdp-si.com/eStore/Catalog, however the cheaper option is Smallparts (http://www.smallparts.com.au/.. the parts are the same but postage and handling is much cheaper, especially if you are buying more than one part)

There is also a lot of info on Yahoo groups (EQ6)

[Steffen]

Thanks Bojan, I remember those threads. Now, I'm not planning anything as invasive, I simply don't have the tools. I'm hoping to simply throw out the transfer gear and run a belt from the motor pulley to the gear on the worm axle.

Cheers
Steffen.

[bojan]

From outside or inside?

[Steffen]

I wasn't planning on replacing the motors, or re-machining the motor mounting plates. Just removing the transfer gear on its poor bearing and running a belt from the pulley to the larger gear. I realise that I would probably have to replace the pulley and/or gear to mesh properly with the belt and to keep the belt from slipping off. I don't mind taking the whole assembly apart for that, I've done that before to change the lubricant and adjust the gear mesh.

Cheers
Steffen.

[bojan]

Then, this is the thread for you:
http://www.iceinspace.com.au/forum/showthread.php?t=60667

My mod is the same, the difference was I used smaller gears, so they fit nicely inside, without machining of the worm gear covers, like in Luke Bellani's thread
However, you need to be careful of reduction - if you are not planning to change the controller, then the gear ratio must remain the same as original (not sure about your mount.. you can count the teeth on motor and worm and calculate this (you can forget about tthe transfer gear in the middle, it doesn't go into equation.. I went for 12/60 = 5, since the control software I am using is/was fully configurable).

[RobF]

Gee, I had pretty well assumed you had to run EQMOD with a modified gearing ratio (and throw away the handset) if you did a belt mod. If its possible without lathing or changing the housing, could be tempting.

[Steffen]

Exactly.

Thanks Bojan for the links, plenty to ponder there…

Cheers
Steffen.