Tasco 1603EF motor focuser and LT70AZ mods

[DaveL59]

Not sure if its been covered before as I didn't find any topics on this one via search.

So while browsing around on the bay I came across these, available as new old stock from the US. A google around found a couple threads on CN and elsewhere and seems to say they aren't at all bad and might be usable on other scopes. So I figured what the heck, buy 2 and maybe improve the usability of the wobbly LT70AZ and perhaps add ease of use to my other scopes at not too much cash.

This morning the postie called and dropped off a package which contained

 

Had a quick look at the LT70 and hmmm, almost but not quite. Methinks some minor mods may be needed here:

As you can see the drive part is off-centre to the scope control but I think I can see why:

Initial thoughts are to cut the Tasco bracket to match the length of the metal focuser plate and it may then snug in just right. I'll also need to figure a good way to interface to the focus knob or just remove it and fit something that suits better. Ideally non-destructive tho in case I want to return it to OEM for sale down the road but the simplest route may well be to cut matching slots for the motor unit to engage with and I do like "easy" 😉 

For the TAL100RS I'll need to make a bracket up as that is a much wider plate under the focuser as well as the focus shaft being thicker, so the Tasco bracket won't be a direct fit as-is. Will again need a means to interface as I defo do not want to hack the TAL knobs about

So what about the SW130 newt? Well, dead easy in fact. First pop the silver trim disc out of the focuser knob. The Tasco bracket is an easy fit under the focuser tube too.

Now the U-bracket in the tasco slides neatly into the exposed wheel and secures to the bracket

The button you can see to the top of the unit is the clutch release so you can manually focus if needed for rapid/large adjustments.

So there you have it, a low cost motor focuser 🙂 

So I do plan on making a few mods to these to slow the rotation rate such that you can achieve finer focus adjustments and also to make the lead detachable from the motor unit. Along the lines described in the CN thread here:
https://www.cloudynights.com/topic/32182-do-you-want-a-good-cheap-focuser-unit/

According to the thread these run at around 1 rev/7 secs which seems a bit coarse to make small tweaks to focus, tho of course I've yet to try this out in action. I may find they are just fine but reducing the turn rate seems a useful mod so will likely do that on one at least.

 

Edited November 7, 2020 by DaveL59

[DaveL59]

so having a play and considering what the CN thread says about a resistor in series or parallel with the motor I tested the motor at 0.7 ohm. Any high value resistance across this will bleed off some current but will not make much difference unless it is very low value I think, as in <10 ohms. I connected some I had across the motor and while you can slow it to a degree I wasn't convinced this was going to work well. Using a 250 ohm wirewound pot I had to get below 7 ohms to make much difference and the real reduction was below 3 ohm, so effectively if you all but short the battery the motor will run slower. Upside is 3v across the motor, but you need to shunt almost half the current to slow it down.

So I put a resistance in series with the motor instead, ok it drops the voltage to the motor and but it does still turn, more slowly:

The above with a 25 ohm resistor doubles the no-load rotate time, going from 8 sec to around 15 sec. But on the SW130 it turns much more slowly and can stall if there's much resistance. Upside was very fine control of focus I expect, but perhaps just a bit too weak. So...

Since I had a few 15 ohm ones left over from the dew heater for the skycam dome I figured give it a go. After all, lower R means a shade more volts across the motor and a touch more current flowing. Off-load rotation slower than without but faster than with 25R, perhaps 12-14sec vs the original 8-9 sec. On the SW130 much slower but more able to drive past any resistance. So I've modified both with this value for now and will see how that goes, I can always revert to a lower value if needs be.

So far a nice easy mod hidden inside the motor casing. I'm fine with this regulating to a very slow speed since fast focus changes can be done by hand using the button on the side to disengage the gears. Am considering if a bypass switch across the resistor might be worth fitting for when battery starts to fade or when using heavy eyepieces, after all I'm seriously dropping the voltage across the motor this way. One for later tho when I receive the parts for the detachable connector and revisit the internals.

Edited November 7, 2020 by DaveL59

[DaveL59]

so keeping busy while I wait for news on kitty's eye op I thought I'd hack the bracket to suit the LT70AZ. Also trimmed a plastic block to give me an interface I can epoxy/screw to one focuser knob. Seems the simplest solution rather than trying to rip one off then fitting something. This wat while it will show it means the scope can be used with the motor removed too with no dangerous/sharp bits for little fingers to catch on.

Just need to clean up the rough edges and touch up the paint. With this mod the bracket fits nicely and the axles align so hopefully I'll have this all sorted during the afternoon 🙂 

I notice there is a slight lag when changing direction on the SW130 (as also reported on CN) which is down to the gap between spines inside the knob being slightly wider than the tag on the focus motor. I'll maybe epoxy some of the offcut metal from the bracket into the gap to close that for a better fit later on too.

[DaveL59]

So, after a spot of lunch, sanded the surface of the block and the control knob, prepped some epoxy and fitted it all up

Will allow a decent cure period then likely drill for a couple screws just to keep things secure, then paint etc and that should make the LT70AZ much more usable, at least eliminating the wobbles when trying to tweak focus 🙂 

Decided to order a couple 100R wirewound multi-turn pots. Might be a bit on the large side, well defo for the hand controller but should be able to fit above the motor and may allow a bit finer control with one turn being 10R. Can then test series/parallel to see which gives the best result for speed control.

[DaveL59]

While kitty sleeps his vet visit off I thought I'd get this finished up. So drilled a couple holes and used thin self-tappers thru the block and into the OEM focus knob to keep them bound together.

As you can see, ended up off-centre with the plastic block but important part is the short edges which are pretty much bang on 😉

Added the drive unit back on

and tested the focus movement. Perfect, nice and slow and smooth 🙂

So out with a black paint pen to retouch the metal edges I'd cut and also the white plastic so it blends a bit better

Now I just need to figure a solution for the TAL100RS should I want to use it on there too. Likely that'll be to make up a bracket and a block to replace one focuser knob for the unit to engage with.

Edited November 4, 2020 by DaveL59

[DaveL59]

So while poorly kitty is asleep upstairs, I thought I'd have more of a play with this on the LT70AZ pictured in the above post. I found that having slackened the focuser screws to ease the focuser action there was a degree of tilt in the focuser shaft as you change direction using the motor drive. Tightening up a touch resolved this reasonably well and still allowed the motor to drive. Perhaps the 15R resistor is sapping a bit too much from the motor but it does work and fine focus adjust was nice and easy, eliminating a lot of the wobbles which was the reason for doing this mod. I did notice tho that changing focus direction caused the image to move up/down a touch - well using a barlow'd SPC900 in a flip mirror diagonal quite a bit in fact but via a 25mm plossl not that much if you get what I mean here. May have a look at some teflon tape inside the focuser to help keep the drawtube riding straight and level another time.

Overall tho this arrangement is working nicely and will likely be improved once the 10-turn 100R pot arrives and can be tested/installed. I will then be able to tension the focuser a touch further and adjust the pot so the motor can still provide enough drive to overcome the extra drag that will create.

One thing I did notice was putting the other motor on initially, the gap in the drive bracket is slightly wider so there was a lag in direction change owing to a small amount of play against the plastic block. Might have to label these if I dismount the motor so I put them on the right scope 😉 

 

[DaveL59]

Thought I'd have a closer look at the LT70 focuser. It is a cheap affair, all plastic as you may expect on such a low cost scope. As I noticed above the inner drawtube rocks because there is too much space between the internal ribs and the drawtube. Shame they didn't design it to have the 2 ribs opposite the pinion really as that may have improved the movement quite a bit.

So I applied a layer of teflon tape to the 3 bearing ribs, still a lot of play so another layer and then a third

The focuser now has only a small amount of rock as you change direction but has also increased the tension in the focuser movement which runs smoothly along its travel. Important to layer the tape so that it goes beyond the previous layer at the other end to make refitting the drawtube easier and it not catch on the edge of the tube as it is inserted.

I wonder if perhaps less layers at the back and more at the front may improve the rock and result in less tension, but I can try that if I ever revisit this again, probably when the tape needs renewing which could be a while.

Once reassembled and the focus motor refitted there isn't enough oomph for it to drive the modified focuser. So disconnected the resistor and wired direct to the motor as it originally came, reversing the earlier mod I'd performed and now it works fine, slowly cranking the focuser giving a nice steady movement. Faster focus via the manual override can be used to get things close so the slow speed isn't really an issue. So for this one I'll only add a connector so the hand control can be removed for storage as there seems little need to dull the motor to achieve finer control.

Edited November 8, 2020 by DaveL59

[DaveL59]

Today arrived the 100R 10-turn 2W wire-wound pots and in-line power connectors. So to while away some time (vet after lunch) I figured I'd have a go at the final mods to one of the focuser units.

The pot is wired in parallel to the motor since it can go from 0.5R up to 100R and gives a good reduction in the first half a turn from the end limit. Now the downside of this is it has to go in the motor housing since it is way too big for the hand controller. I don't feel that's much of a problem as this will be used more for fine focus anyway. The in-line power is a regular 5.5/2.1mm plug/socket affair which means no long trailing lead when assembling the motor onto the scope as well as allowing an easy disconnect if the cable gets snagged.

Assembly does mean you have to leave the pot loose and slip the cover on and then with a finger ease it back across and thru the mounting hole. Not hard to do tho and there's more than enough space to clear the drive tang.

You'd want to mount it on the side that'll face the user when it's on the scope, ideally. In my case I've fitted to the LH focuser wheel, YMMV.

Not sure if I'll bother to fit a control knob as the pot turns very easily, if I find I need to then I guess I'll have to order something to suit 🙂 

I may well do both mods to the other one that is now on the LT70 even tho that doesn't now seem to need rotational speed control having teflon taped the focuser drawtube path as per the previous post. As that slackens up it may prove beneficial and I do have the extra pot specifically for the purpose after all.

[DaveL59]

So while I seem to be on a bit of a mr fixit spree today I thought I'd revisit the LT70AZ focuser and Alt SloMo control. Decided to remove the teflon tape and only apply to the side opposite the focuser pinion but increased the layering to 5 strips. That seems to have relaxed the tension in the focuser movement but still give good drag for the motor focuser, will see how it tests on celestial targets when I next get a change to play outdoors.

Looking at the SloMo adjuster, I never liked the slop and suspected this was down to play in the internal threading. I'd had a look previously at this but it was resisting attempts to open it

The red line indicated a slot in the ring next to the silver shaft and there's a corresponding one opposite. Awkward getting a pin wrench placed well because of the eyelet but after a lot of force I got it to turn and unscrew. It's glued to keep it secure. Ran a 14x1mm tap in to clean the thread before reassembly.

Now we can see what's inside. Pics post mods as I forgot to do any before I altered things, so dismantled to take some😉 

 

The eyelet is held with a nut and washers but had some play, so I added a nylon washer to reduce that.
You can't fully tighten this as it needs to allow the adjuster to rotate reasonably freely around the shaft or you'll have no adjustment or it'll be excessively stiff. Now as ever I can't find the plumbers tape when I need it so I cheated and put a little of the teflon tape I had removed from the focuser, laid beyond the end of the thread as shows so that it'll be retained in place as you screw the rod back into the adjuster.

Note the thread is greased but it really doesn't have any drag to it and the thread is loose in the nut, hence there's fair amount of play if you rock the bar in/out of the adjuster. With this tape there's almost no play at all yet the action when adjusting is nice and smooth. The teflon tape will probably last a lot better than PTFE plumbers tape too. I've not glued the eyelet carrier threads as yet, will do that later if I feel it needs it.

So reassemble by screwing the bar back into the adjuster knob, refit the eyelet and tighten it up, refit to the scope/mount and result, smooth movement and no slack. OK there's still the U fork itself that flexes, but hopefully these mods will improve the perceived feel when using this low-end LT70AZ scope a little bit.

Edited November 12, 2020 by DaveL59

[markse68]

Hi Dave, nice improvements you’re making  Where did you get that ptfe sticky tape? I used to have some like that but it’s long been used up

On my 114az i think the lions share of the alt adjuster slop (there’s a lot!) is actually the bolt through the eye bolt- was planning to shim that at some point but haven’t got round to it yet

Mark

[DaveL59]

6 minutes ago, markse68 said:

Hi Dave, nice improvements you’re making  Where did you get that ptfe sticky tape? I used to have some like that but it’s long been used up

On my 114az i think the lions share of the alt adjuster slop (there’s a lot!) is actually the bolt through the eye bolt- was planning to shim that at some point but haven’t got round to it yet

Mark

thanks Mark.

The teflon tape I used was this stuff
https://www.amazon.co.uk/Machine-Suitable-FoodSaver-Cabellas-Gdrtwwh/dp/B089F77XNJ/ref=sr_1_2_sspa?dchild=1&keywords=teflon+tape&qid=1605199621&sr=8-2-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEzSllEQVY3MFZYSDNRJmVuY3J5cHRlZElkPUExMDAxNTU1Tjk4RE9YMFFYV1EmZW5jcnlwdGVkQWRJZD1BMDQyNDM3NTM5WE9FSEI0ODZGMDAmd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

Been useful to improve the focuser movements too as its sticky-backed so can be located and pressed to secure into place. Used it on the little NG dob and the SW130 newt to good effect.

I thought the same re the eyelet so a while back added a tiny bit in there too but turned out the worst play was in the threads and also the eyelet being too loose in the carrier, hence the nylon washer. Feels a lot better now, kinda like the feel of loose scratchy knobs on a cheap amp vs the smooth quality feel on the better gear if you know what I mean.

[markse68]

9 minutes ago, DaveL59 said:

Feels a lot better now, kinda like the feel of loose scratchy knobs on a cheap amp vs the smooth quality feel on the better gear if you know what I mean.

nice! I have some binocular grease which might help give it a nice feel too 😉

Mark

[DaveL59]

That was my plan initially but feeling how slack the threads were and finding they were greased already I decided something more was needed. As you'd expect on the bottom end gear, close precision in cutting the threads was clearly not a consideration. I guess the weight of the scope leaning on it would mean many won't notice it or recognise the level of movement vs the shaky viewing and so "it'll do" was good enough 😉 

Edited November 12, 2020 by DaveL59

[DaveL59]

Probably shoulda started a thread on the LT70AZ really but since the focuser was to improve it I'll add here anyway. Today I took the U-yolk off the tripod to see if I could improve it's AZ motion since it wasn't that free when trying to make small positional adjustments. It is secured with an allen bolt from underneath and once removed it just pulls away. Celestron grease the bearing surfaces and use a large plastic washer to bear the load between the yolk and the boss. Now I found this would need a bit of a push so smooth fine motion wasn't great especially with the design of the parts giving a narrow bearing surface primarily on the inner 1.5mm or so of the washer. So I wiped off the grease from the parts and applied a layer of teflon tape around the central part of the yolk that engages into the boss. Also laid teflon tape on the bearing side of the plastic washer before refitting it. Reassembled and now the motion is smooth and needs little input to move.

Sorry I forgot to take pics, greasy hands and touchscreens aren't an ideal mix so it didn't seem smart to do that at the time. 

Perhaps part of the problem may have been overtightening of the retaining bolt but of course I didn't check that before the mod. With the bolt snug enough to allow easy movement, the teflon tape takes up any rock so the yolk now seems a lot more stable as well as easier to move when needed. There is still a little rocking in the Alt retainer on the yolk but I wasn't able to remove that this time around, will need to find my smaller spanners as access to the nut is a bit restricted, but I found rotating that 180 degrees reduced the rocking significantly.

Checking out against a distant tree, the combo of the electric focuser and the previous mods made to the Alt adjuster and now the yolk for AZ motion, I think it has greatly improved the cheap LT70AZ. Sure it's still wobbly when handling but I can now move the scope around the target smoothly and the focuser is a nice vibration free experience when making fine adjustments. I did do the speed mod on this focuser too, not that it was essential but I figured some finer control was worth a few mins of fettling time 🙂 

Time will tell how well this mod lasts tho as the AZ lock screw will bite into the teflon tape and will need to be undone enough so it isn't dragging across the surface. Thinking about it, might have been better to apply it in cup on the boss side so it stays put with a gap for the lock bolt. Will see how it goes and if needs be it's an easy few mins to redo later on.

Edited November 26, 2020 by DaveL59

[StevieDvd]

Not sure you should be using a yolk on your mount you might get egg on your face 😂

Or is the yoke on me?

[DaveL59]

doh! and of course spell-check won't have picked that up lol

[DaveL59]

So, long time since I posted on this thread but last mods I've now done to the LT70AZ have been to add some vintage wooden tripod legs, which much improved the wobbles/damping time but still found that the OEM yoke wasn't all that stable as well as not being all that smooth in the AZ movement. So the other day postie dropped off a new yoke that I'd found on the bay, advertised for 76/700 reflectors but thought I'd try it and see as the measurements were only just a little wider.

Fitted up and I may need to add a collar to the pivot pegs on the scope but the screws do seem to hold it nice and stable so maybe not.

I did find the AZ was a snug fit for the OEM adjuster rod but it fits and slides fine, I had to loosen the retaining nut a touch to allow the fixed part to turn more easily else the rod binds when trying to lower the scope. Also can't swap the plastic scratch protector over as there's no free play between the rod and anchor point.

So here it is, mounted up and on the wooden legs

After a quick daytime test it was nice and stable and moves smoothly and with the motor focuser, getting good focus is nice and easy with no wobbling about. Last thing I'll need to sort I guess will refurb the old legs and make a spreader arrangement, probably will just fettle some chain, maybe use the hanging chain arrangement off a hanging basket. Don't have to look too pretty after all, just stop the legs doing a drunken spread-eagle 😉 

 

Edited July 9, 2022 by DaveL59