Minimalist Motorised Focusser for MAK127

[Macavity]

Never a serious project (reflecting my dodgy DIY!) but here's my minimalist motorised focusser for a MAK127.

It has the merit that it works surprisingly well - All for rather little effort and about £40~50 total outlay!

Rather than copy my dubious methodology, slavishly, here are links to:

Electric Motor: Miniature Epicyclic Motorgearboxes : Motors & Gearboxes : Maplin (231:1 Version)

5:1 Belt Drive: motionco_Pulleys & Belts_Aluminium MXL Timing Pulleys_Buy Online (60:12 Teeth)

I did have to get my "tame CNC machinist" to enlarge the larger

pulley's hole from 5mm to 15mm (For a Tenner!) - The diameter of

the metal sleeve under the (carefully removed) rubber focus grip.

The motor (plus reduction) provides pretty much the "right" speed at a (max) 12V DC,

with possibilities to reduce the voltage (9V, 6V, 3V even?) for fine focussing.

Now I can at least SEE solar images on Notebook screen in darkened shed...

[Merlin66]

Nothing wrong with that!

Looks like a pretty good solution.

Well done!

Ken

[A McEwan]

Excellent job!

[Macavity]

Thanks guys - Perhaps I overdid the faux-modesty. LOL. But, I am impressed with the functionality - I had believed such things were in the realm of the "rather pointless". Now quite a convert to the potential of motorised focussing.

[ponytale]

thanks for the useful links , great job on focuser!!!

[Arushin]

Hi,

Fantastic job on this!

Sorry, but I am a technical retard and really would appreciate your help. Followed the links to the pages you kindly provided and am desperate to put one of these together, but am confused as to exactly what the part numbers I need are and how many etc. How are you powering the motor?

You should market this little gizmo.. you could make a fortune!

[Macavity]

The exact part numbers are:

Electric Motor: Miniature Epicyclic Motorgearboxes : Motors & Gearboxes : Maplin (231:1 Version)

The motor: Order Code: N07BQ - One off

5:1 Belt Drive: motionco_Pulleys & Belts_Aluminium MXL Timing Pulleys_Buy Online (60:12 Teeth)

The pulleys were:

Aluminium MXL Pulley, 12T, 3mm Bore [PL012AL]

Aluminium MXL Pulley, 60T, 5mm Bore [PL060AL]

I believe the drive band was the 80 Tooth version?

I think it ONLY FAIR to suggest this might not be the easiest project for a "technical retard". <wince>

The larger gear requires the attention of a CNC machinist to get it to fit the focusser shaft. The tolerances (non-elasticity!) of the drive belt, require a bit of ingenuity in the fitting. Also, I don't really FINISH things. <G> I lashed together a small box with a DPDT switch to feed the power - You will need leads, small power connectors, the ability to solder etc. Even then the finished product will lack the simplicity / utility of commercial (push-button) units.

OVERALL too, I have to admit that the torque available from the (albeit nice little!) motor is a bit marginal. If the infamous Skywatcher lubricant is a bit "thicker" and the focusser stiffer, it may not work. If you remove the focussing knob, be careful the scope innards (mirror etc.) don't disappear into the OTA too! Moreover, if I were going to repeat the job, I might base it on a commercial electrical focusser (SERVO) motor with more torque. Plus you get a pre-built handset / battery with BUTTONS to work it e.g.

SkyWatcher Auto Focuser | Telescope Accessories | Rother Valley Optics

I believe a design based on one of these is described on SGL.

Sorry if that's not much help. I am none too great at DIY, but I do e.g. know how to "bodge" things. And such is born of many years of solving hardware frustrations... to which there are few short cuts?

[DrRobin]

Hi,

Your motorised focus mod looks really good. As a complete beginner (just bought a 127 Mak) I can already see the benefit of this mod as I find the focus really difficult, esp. with a CCD.

One quick question, how did you attach the motor to the OTA? A couple of pictures would be really handy.

Finally I looked for the Skywatcher auto-focuser mod on this site but couldn't find it, do you have a link?

I am an electronics enginner (design and development), perhaps I could add to the project on the [electronic] drive control, you know variable speed drive?

Regards

DrRobin

[lee allen]

i have mk 127 telescope and i am goin to try to make a auto focus that can be produced and sold on ebay. i program and set cnc's. so will be easy to make and produce the parts. the question is can you get the servo and control box already made up at maplin and at what sort of cost??? can anyone help

lee

[Macavity]

I think, in retrospect (always a good thing!), and with ready availibility...

: Rother Valley Optics Telescopes, Binoculars & Accessories

...is the way I will go - If this project continues (sometime)! I bought one of the above, for my ST102 refractor. I may well buy another. Simply, the servo motor has plenty of (more) torque, and you get a push button box, speed control etc., thrown in. By the time you've done the "R&D", and electronic design yourself, bought the parts, it's £40-odd, well spent? Of course, there is the "mechanics", but with e.g. a (my) repositioned dovetail bar, solutions will be rather individual?

I think it is worthwhile using a "pukka" belt drive, rather than the sometime, "hoover belt" idea [teasing]? The (CNC-machined) MXL toothed pulley makes an attractive (useful) manual focussing knob, if nothing else!

I believe there is a NICE version, based on this servo motor, somewhere else on the forum.

[NickK]

That's awesome

Do you get any vibration at high magnification?

[DrRobin]

Hi,

I bought one of the SW electric focusers (about £45) and a 60 tooth/15 tooth gear wheel from motionco as mentioned above to give a 4:1 reduction.

The 60 tooth pulley was widened to 15mm using a 14 mm HSS drill (toolstation.com £3.50 ish) and then filed with a round and half round file to 15mm diameter. Unfortunately no one seems to sell a 15mm drill. I chose the 15 tooth pulley since it has a larger diameter centre and with drilling it out to 6mm the smaller pulley would not have left enough material. I also only drilled about 5mm down, just far enough for the lock nut to get a hold.

The belt was calculated by taking the distance between shaft centres (multiply by 2) and then add half the circumference of each pulley. I then chose the nearest belt which was 100 T.

The 15 tooth pulley was widened to 6mm to fit on to the sw electric focuser. I used a vertical drill (piller drill) and an engineer's vice to drill the two pulleys and as I have access to a drill there was no charge.

To mount the sw electric focuser, I used the thin bracket which came with the motor and drilled a hole in the end. The dovetail was then removed and the screw replaced through the bracket and clamps the bracket in place.

A word of warning, only use the thin bracket, since if the dovetail doesn't fit flat against the side of the OTA then it will introduce an angular error when the OTA is elevated. This might only be small, but at high magnifications or with a CCD Webcam might be enough for the object to move out of frame.

To secure the bracket to the OTA and stop it moving, I fitted a small piece of rubber sheet between the bracket and OTA (see photo). Finally the bracket wasn't long enough so used two 10mm M4 stand offs between bracket and motor. This also moves the back of the sw electric focuser away from the mount and allows for better balance. Stand offs and rubber sheet were both 'borrowed' from work but I guess Maplin sells them. If not send me a message and I will send you couple FOC.

I haven't had chance to try it out on any sky objects yet as we haven't had a clear night, but daytime focusing is much improved.

I did try the sw electric focuser with an o-ring prior to taking delivery of the pulleys and can confirm that the pulleys are a great improvement. The o-ring put too much load on the motor when tensioned and the stretch and backlash was a bit of a problem.

The belt drive is smoother and the 4:1 reduction gives a much higher level of control. There is of course still backlash but you soon get use to this, especially if you have tried manual control on your mount.

I intend to set up my focuser with the eyepiece I use the most and then mark the pulley at the 12 o'clock position. I will then record the positions for all other eyepieces/camera and barlow combinations, so when a change is made I can quickly refocus.

If a large number of turns is required the belt can be slipped off the large pulley which is then free to turn, before putting the belt back on, usefull if swapping between eyepiece and CCD.

I have attached a couple of pictures of my finished efforts.

Robin

[lee allen]

all the parts have come today! the skywatcher auto focus and timed gear wheels!! DrRobin i had the same idea now all the parts have come and fixing plates! thinkin if the belt comes off after long use! fittin big nylon washer with fixin screws on both sides!! was thinkin for a quick fix try if you can wedge some think to push the back of the motor out. to make the belt run square to the other!! no work till monday!! so gutted!!!

[Macavity]

Wahey - Great (practical) developments!

I guess, for the ultimate, one might add another, popular interweb idea: A few soldered wires, interface "chip" inside the box - To simulate button pushes. D-type socket, maybe? Onwards to FULL computer control!

[DrRobin]

Hi,

Lee, the belt hasn't come off so far, even though it's not perfectly aligned. The small pulley has flanges which keeps the belt running true and it doesn't appear to move on the large pulley.

Mac, I was thinking along your lines of a microprocessor interface, perhaps with presets, but without feedback you could only do it on time and it probably wouldn't be that accurate.

The alternative would be a stepper motor which do have feedback. Either solution would just need a serial port running ASCOM focuser standard which I think is RS232 (serial port)

I have done this sort of thing at work before with single chip processors (e.g. PIC or AVR), not sure how long it would take to build a prototype or when I could find the time to do it.

You started a great idea.

Regards

Robin

Robin

[DrRobin]

Hi,

I have found a low cost USB microntroller module based on a PIC, which could be programed with an ASCOM interface and output to drive the sw motor. This would allow the focuser to be used from a PC for Auto Focus applications E.g. Sharpcap.

The sw motor doesn't appear to have an encoder output so movement would need to be based on time, but this should still work.

Anyone got any suggestions for features?

[lee allen]

thanks to DrRobin and Macavity! started work on this project today at work, now that's what i call getting payed for lol. bored out 60t pulley to dia 12mm and 10mm deep and made a collar 12.5 mm long with same id(inside dia) and 17.5mm od(outside dia). as i went for the 12t pulley it cant be bored out to 6mm! so had to send off for the 15t pulley and new 8" belt! to fix the motor to the dovetail, i have made a aluminum block to side over the dovetail bar with fixing screws. so it can be adjusted on the bar and on the motor for tension on the belt. so waiting for the rest of the parts! thanks again. will post pics soon(prob next week).

[lee allen]

[lee allen]

not sure how to post pic on here but added a album on my profile!!! project finished and looks but works mint wobble no more lol

[Loki Calavera]

I've was looking for a fix to the Nexstar 127 wobble when focusing and came across this thread.

Brilliant job Macavity and Robin. The finished products look incredible! I guess now is the time for me to become a DIY expert!

*goes back to catching up with the thread*

[DrRobin]

Hi,

Thanks for your message, I replied. Good luck, let me know if you need any more help.

[JamesF]

Once you've fitted one, you never look back

On my ST102 when I had one fitted I decided I could take it or leave it, really, but on the Mak it is absolutely fantastic. They ought to ship from the manufacturer with one.

James

[rodrigol]

I started modding my 127 SLT today. Have ordered all the parts but noted too late that I use the standard SCT visual back, instead of the 127 one. The 60 teeth wheel will not fit. I decided to do a dry run using Lego wheels and came up with what you see in the picture below. I did not replace any of the bit on the motor shaft. Just the 100 teeth belt and it runs smooth. Not tight and I do not have any back lash.

[DrRobin]

Hey that's great, what ever works best. If you find that your existing set up works I would stick with it. I left the stock knob on at first and just used a thick rubber belt. It worked okay, but slipped a little bit, so I went to the toothed cog and drive belt.

These motor focus mods make the scope so much easier to use, I am amazed that Skywatcher/Celestron don't fit them as standard or at the very least offer them as an upgrade.

[Gina]

That looks fine to me - nice job I may get an SCT or Mak sometime in the future and if I do I'll definitely motorise it. I think that without a slow motion drive a motor drive is essential.