EQ3-2 DEC axis direct drive mod.....

[stan26]

Thought I would share this very simple yet affective mod I have done to my EQ3-2 to achieve better guiding results. All EQ3-2's have a fair bit of play (backlash) in the DEC axis, and although stripping the mount re-greasing and tweaking the adjustment screws does make a difference it still leaves to much backlash for successful guiding using the DEC axis.

I noticed that there where 3 points where backlash was happening. 1, the DEC motor gearbox, 2, the external shaft drive cogs, 3, the worm gear in the mount.

The first thing I done was remove the gearbox from the motor drive unit. There isn't much play here but there was definitely some slop in the output shaft gear (this is the gear that drives the steel shaft that comes out of the motor unit) A simple solution here was a dab of superglue to stick the gear to the shaft. That cured that. Next I tuned the worm gear meshing by adjusting the 4 screws and 1 center grub screw on the DEC worm shaft housing. After about half an hour of balancing the adjustments I had reduced the overall backlash by quite a bit During this process I notice that my DEC axis securing bolt (the one that go's right through the middle of the DEC where the nut is behind the polar scope cap) was to tight, causing stiction of the bearings resulting in jumpy movements by the motor. I slacken of the bolt untill I had a good balance between little slop in the head but loose enough to freely spin by just pushing it lightly with my finger.

After all this I still had some backlash albeit nowhere near as much before I started. I noticed that when slewing the DEC motor at 8x speed the nylon gear would turn for a short while before the backlash was taken up to turn the brass gear on the wormshaft. The only way to get rid of this was a direct drive mod.

For this mod I simply done away with the external gears and used the black busing that the nylon gear originally fixed to as my direct drive coupling. I had to make to mods to the black bushing bit. The diameter of the brass shaft is to wide to fit the original hole on the bush. This is because the output shaft on the motor is smaller. So I had to match up a suitable drill bit (6mm from memory) and bore out to half the depth of the bush to accommodate the brass shaft. I then found a small fine thread screw to use as my fixing grub screw to clamp the bush to the brass shaft and drilled a matching diameter hole right through the end of the brass shaft and the coupler bush. The brass shaft was quite tricky to drill through with just a hand drill. The important bit here was to make sure I drilled the holes so they lined up through the centre. Then the grub screw was tight was wound in tapping its own thread as it went. The shafts are now fixed!

Now to secure the motor out away from the DEC head at the end of the shaft assembly. I found the perfect bit of scrap metal at work. It looked like an old table frame. I cut off a section and done the rest at home. By pure coincidence the box section already had a captive nut welded in to that was the perfect match size for the bolt I need to secure it to the DEC head. I simply cut it to length measured and drilled out a hole for the DEC motor fixing bolt, then bolted it all together. Job done!

I now have very minimal backlash and IMO a perfectly guidable EQ3-2 setup.

Here are some pics of the mod. Sorry i don't have any pics of the other bits I mention earlier. Also some screen shots of the graph whilst guiding in PHD using an un-modded webcam and home made 60mm guide scope of around 250mm FL. I'm not to clued up at this stage on the guide graph but I think for an EQ3-2 its pretty good.

Also my first guided image using 5min subs

Stan:cool:

[RikM]

That's outstanding. Well done on all counts, great mod and great pic.

Of course you realise you are using the wrong scope on the wrong mount, with the wrong guide cam and an unmodded camera to boot

This really goes to show that it's the imager more than the kit that creates these great pictures.

[stan26]

Thanks Rik.

To be perfectly honest I think I'm using the WRONG hobby altogether! Skint with 2 kids + astrophotography just don't mix!

that said I have a nice little Canon L 200mm 2.8 prime on its way which should solve the wrong scope issue giving some lovely widefield captures, and I'm sure the EQ3-2 can handle a camera lens. Then its a case of getting that cam modded!

Stan

[Chris]

Hey Stan, you don't hang about you don't, I second the vote for outstanding its quite a brave thing to attempt in my opinion, and I'm guessing it wont matter if the gearing ratio is now different to standard, because its all about the computer being able to accurately make adjustments which it couldn't do as well before because it was blind to the backlash? And thanks for writing this thread its quality, you might have really started something with all these on the cheap mods, I recken you paid very close attention to the trademark A-team scene where they drive their normal car into an old barn somewhere, do a load of welding, then drive out in something from Mad Max!

[Rob L]

Thanks Stan,

That's a great easy to follow writeup - and the thing I like most, it might be just about doable for a diy numpty like me

I'm having my own guiding woes at the moment (simple gpusb, 9x50 finderscope, spc900nc combination). But a mount strip and regrease together with this mod, should hopefully provide a solid starting point.

Rob

[stan26]

No worries Rob, What problems are you having I may be able to help..? (guiding related that is, not other personal problems:D)

Stan

[jnp]

That's a top class mod, its simple but with a high yield.

Should also work on Dual axis EQ5 setups too.

cheers

John

[JamesF]

Excellent work, Stan. Very impressed.

I may well give my (older model) EQ3-2 a rest whilst I do some Messier hunting with the ST120/AZ3 and pull it all apart to do something similar as the backlash on mine is absolutely dreadful.

James

[Quatermass]

I think you have just become the astrophotography forums DIY modding master Stan very impressive work. Necessity is the mother of invention as they say. My modded EQ5 mount project is going quite well I'm happy to say but all credit to you for giving me the courage to dive in at the deep end.

[malc-c]

Stan, have to echo QM's comments in the post above - nice mod you've done

There's a lot of mount mods going on at the moment, your EQ-3 mod, QM's EQ5 mod, my HEQ5 belt drive mod and Georges EQ6 belt drive conversion - hopefully encouraging others to take the plunge

[JamesF]

I've been looking at the DEC motor coupling on my EQ3-2 this afternoon and it strikes me that some of the reason for the backlash might be the rubber bush against which the brass gear is fixed. Getting that out of the equation seems like a fine idea. On my mount at least, I can't really feel any significant play in the worm drive though I've not taken it apart to have a look (not sure there's anything much I could do there anyhow).

I take it the reason that you have the DEC motor mounted on a fairly long arm is so that it clears the rest of the mount body?

James

[stan26]

and I'm guessing it wont matter if the gearing ratio is now different to standard, because its all about the computer being able to accurately make adjustments which it couldn't do as well before because it was blind to the backlash?

Hi Chris, that's correct. Gear ratio is even less important in DEC because DEC is not constantly tracking the guide star as it travels east to west. It just makes periodic adjustments for incorrect polar alignment (not to be confused with periodic error which is mechanical error within the mount in the RA axis)

BTW, Its your turn to guide on the cheap now...

stan:)

[Quatermass]

Im stuck with my conversion at present. My lvi autoguider wont calibrate correctly because the guiding speed on the dual axis kit at 2x lowest is too fast!

Very frustrating so I may have to consider phd laptop and webcam.

sigh

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[steppenwolf]

Very impressive and the Orion shot speaks volumes for your ingenuity - well done!

[stan26]

I've been looking at the DEC motor coupling on my EQ3-2 this afternoon and it strikes me that some of the reason for the backlash might be the rubber bush against which the brass gear is fixed. Getting that out of the equation seems like a fine idea. On my mount at least, I can't really feel any significant play in the worm drive though I've not taken it apart to have a look (not sure there's anything much I could do there anyhow).

I take it the reason that you have the DEC motor mounted on a fairly long arm is so that it clears the rest of the mount body?

James

Hi James, I would suspect that if you are experiencing slip within the clutch unit it would mean you need to tighten the silver turn knob some more. I have on more than one occasion have this happen to me where friction between the brass gear and the silver knob caused it to work loose in one direction. Not a great overall design if you ask me. If fully tight then IMO there shouldn't be any sort of measurable backlash.

When you say you can't feel any backlash in DEC, Have you tried this with the manual flexi turn knob attached (motor gears not engaged) and with the mount fully loaded with scope/camera or whatever else you hang off it...? (sorry if this is all obvious to you) You need the mount loaded to get a realistic idea of what the backlash is like in use.

The arm is that long purely because of how far the motor sits out on the end off the worm shaft. You notice I have used the brass shaft adaptor and not drilled the actual wormshaft itself. This makes it longer, but you could do away with it. The reason I didn't drill the wormshaft is because I used the logic that it would be better to mess up the adaptor rather than the wormshaft. The adaptor I could get re made if need be. The wormshaft complete with its wormgear I would have to source from skywatcher etc etc...... As for clearance I did check this when doing the mod and its tight! when spinning the DEC 360* it clears the black RA clutch knob by millimeters!

BTW one tip I can give you is, I have found with my DEC BL adjustment that tight (stiff) is not good. The worm shaft does not need to be wound tight up to the internal gear to get rid of BL.

Stan

[Ags]

Brilliant pic and an excellent mod.

[stan26]

Im stuck with my conversion at present. My lvi autoguider wont calibrate correctly because the guiding speed on the dual axis kit at 2x lowest is too fast!

Very frustrating so I may have to consider phd laptop and webcam.

sigh

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Don't give up QM!, I'm sure you can tweak things. Unfortunately I know diddly squat about the LVI, but surely you can adjust the command input settings? i.e guide pulse aggressiveness/duration etc...? I'm still getting to grips with PHD but I have the HC set to 4x speed, but I think any speed would work.... I'm not sure if all the various guiders/softwares account for set slew speed during the calibration process...?

If you do decide to go PHD/webcam its a mega cheap solution. The interface port will be your only real cost (and obviously you'll need a laptop or nearby PC)

Stan.

*EDIT* scub that^ just read your current updated progress EQ5 mod thread. Sorry to here about this problem QM...now on my way over to your thread to write......stan:confused:

[stan26]

Thankyou to others who have commented!

stan

[Chris]

Hey Stan, I sold my mount today for 200 pounds, I'm also going to sell my OTA, take a few bits and bobs down cash converters, empty the loose change jar, and add all this to the overtime pay I've just got for working xmas day, new years day, and well some of every weekend in Jan including today, then I'm going to further add a couple of hundred quid I've saved previously and in total I'm hoping to have about 800 pounds to spend on an imaging setup which is getting on for double the cost of my first imaging rig, any ideas? I'm going to give this a lot of thought basically I've been torn between modifying my eq5 or saving for a better setup, and I was looking on astrobuy as I often do just to being nosey and some one very close by was after a driven eq5, so I offered him mine, and then I had second thoughts but thought I would leave it in the lap of the gods, i.e. if he wanted it I would sell it and put the money in the fund, or if he didn't I would keep the mount and mod it, the gods have spoken I guess:)

[Chris]

Hey Quatermass, I've been thinking about your issue with the 2 times speed on the hand controller being too fast for your LVI, I know that you're not keen on having a laptop involved My first thought was to alter the speed of the switching, could you swap out the 3 position switches with variable resistors thus giving many more increments to choose from? there might be a reason way this wouldn't work but its just my initial thoughts. I take it the 60mm fracs at Scopes n Skies wheren't upto the job, come to think of it they were a bit on the long side I hope you find a solution soon, I'll keep my thinking cap on. Oh yes, any thoughts on my possible 800 pound imaging rig budget? I will put this question up on a seperate thread, I might have to factor in weight as I struggled lugging my first imaging rig only short distances, probably because I'm 9 stone 6 with a twitchy back from years of lifting patients in care of the elderly

[malc-c]

Chris, I don't think swapping the switches for a pot will work. The microchip used in the handset is probably set to have each switch connected to individual I/O pins so it knows what rate to run at. Using a pot would require an Analogue to digital conversion and then it's only programmed to run from 2x to 8x sidereal rate on those inputs.

[Quatermass]

hi chris im no good with electrics was scared to modd the dual axis kit. Im thinking the phd laptop route might be my saviour now oh if only these things were simple

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[Chris]

Thanks Malc I hadn't considered the chip control, and that an analogue resistor wouldn't work with the chip.

[Chris]

Hi Quatermass, yeah, laptop and Phd might be the way forward, you've done bonza so far though just the last hardle

[Quatermass]

Its the only way forward that I can see with the auto guider being a pain. PHD is really great

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