Focus drive mods

[morls]

Hi,


I'm adapting a little skywatcher motor to use with my Baader steeltrack focuser. The Baader motor looks like a great piece of kit, but I can't justify the $1000 price tag. The second photo is of the skywatcher unit, which I have, the others are the Baader which I'm trying to emulate.

My first step is to source a timing belt to run between the focuser and motor, and a small cog wheel to put on the motor. Does anyone have any ideas on the best place to get these items?


Cheers
Stephen

[Pepper]

Minature Bearings Australia are great for small belts.
Huge selection.
Also do pulley wheels to suit.

[morls]

Thanks Steve, I'll check them out.

[Merlin66]

I’ve fitted the SW motor to all my solar scopes....six so far.
Miniature Bearings can supply a 6mm bore pulley to suit theSW motor.
I use a thirty tooth pulley and a 100 tooth XML timing belt.
Works very well for me.

[morls]

Excellent info, thanks Ken.

[Merlin66]

Some images of the various SW focus drives.

[The_bluester]

Assuming they are not one of the things on perpetual backorder at the moment, have you considered the ZWO EAF? I have been running one of those for nearly a year with zero issues. If I keep imaging with my SCT I will probably make an adapter and fit one to that in place of the Celestron focus motor it has on it now as that lacks a temperature sensor.

[morls]

Hi Paul, no I haven't thought of the ZWO. I saw the skywatcher and thought it looked good enough for my needs, at a good price and able to be software controlled if need be. Temperature sensing isn't something I need to worry about at this stage. The ZWO stuff seems to be pretty solid though, so maybe down the track I'll go that way.
It's also good to have a lockdown project...

[Mickoid]

My lockdown project has been building a motorised drive for my crayford focuser. Cost me about $50 in parts and quite a few hours labour, it's finished now but it would have been easier and not much more expensive buying a SW one. It was fun to build though, it works on pulleys. Most of the stuff I got at Jaycar.

[morls]

I'm at a bit of a loss when it comes to these types of parts. Can anyone help me identify the pitch of this belt? It's the one used in the Baader drive, and fits my focuser. I think I can count 68 teeth.

[Merlin66]

Stephen,
Measure the distance from peak to peak of the teeth - this will give you the pitch. This, and the width of the belt should allow you to find a suitable XML type timing belt equivalent.

[morls]

Thanks Ken. I've got the following measurements from the focus cog:


diameter = 33.5mm
36 teeth
width of teeth (belt width) = 6mm
gap from centre of tooth to centre of adjacent tooth = 2.8mm (approx, as close as I can tell)

[Merlin66]

https://www.smallparts.com.au/store/subcategories/timingbeltsandpulleys/?v=709
Don't see a match for the pitch you measured.
Maybe a 3mm pitch??
The circular tooth shape - don't think is a standard "timing" belt profile.....

[Merlin66]

Stephen,
I'd send the image of the pulley to the guys at Miniature Bearings, they've been very helpful to me in the past.
They could probably identify to type of belt....

[Pepper]

These? https://www.minibearings.com.au/store/partslist/beltstiming3000mmpitchhtd6mmwide/

The 36 teeth is halfway down page. Looks like May be in stock too.
Link is for the 6mm wide htd 3mm pitch.
There is a seperate pages for wider 3mm pitch belts.

[Merlin66]

Steve,
well done!
:thumbsup:

[Saturnine]

Steve
A word of caution, going by the photo of the pulley, that is not a standard timing belt profile, which is a truncated "V" shape, as in XML belts.

The rounded teeth of the pulley ( and belt ) shown in the photo is an SP profile. Still a standard engineering drive belt profile though and commonly available. Does the belt that you have in the photo, have any other numbers printed on it other than shown . From your measurements of diameter and teeth number I get a pitch of 2.92mm, most likely 3.00mm, a standard pitch.

https://www.pfeiferindustries.com/timing-belt-identification-and-replacement.

Not advocating this company, just examples of belt profiles and pitch, don't forget about the width as well.

Hope this helps.

Cheers

[morls]

Lot's of help, thanks everyone.

I think the belt I want might be an HTD profile? Just going by comments I've seen in other forums which mention the Baader system can use HTD belts.

[Saturnine]

:thumbsup:Sounds like you've got it sorted out -

[morls]

I've placed an order, the only potential issue is the narrower bore of the pulley. The only option with 16 teeth, which is my estimate of the Baader version, has a bore of 4.8mm. The skywatcher motor shaft is 6mm, but has a couple of adapters that I might be able to work with. There is a round socket in the end with a diameter of 4mm, plus a grub screw, so hopefully I can cut someting down to fit.
At any rate, this is a big step forward, thanks for the help.

[Saturnine]

If you have to enlarge the bore to 6mm, lock the pulley in a vice, if you have one and drill it out , carefully, with an 6mm drill bit. doesn't matter if the hole ends up being a little larger at one end, the lock screws will take care of that. At the speeds involved with focusing any run out will be hardly noticeable unless the belt is over tensioned, which again, at the speeds and weight that needs to be moved, the tension does not have to be much.
Alternately, if you know someone with a lathe, would not take long to drill it out and be a bit more accurate also.

[morls]

Sounds like a good plan. Hopefully there'll be enough material to drill out the bore.

[Saturnine]

When and if you have to drill out the bore, be sure to remove the grub screws first and it goes without saying that aluminium is a soft metal and the drill bit may bite into the metal and grab. If using a hand power drill use a lower torque setting in case it does bite. Good luck.

[morls]

Thanks for the tips, I wouldn't have thought of that.

[Saturnine]

:thumbsup:

[morls]

Turning now to the mount for this motor, the Baader motor fits 25mm - 27mm dovetails, but it's very hard to find anything I could use as a substitute. Ideally, I'd like to get a pre-existing clamp, but I'm not sure if there are any available in these sizes. I thought of a finder scope clamp, but these are too large. Any ideas? I'll attach a Baader pic, and photo of my focuser drive unit with the dovetail. The tension thumbscrew on the drive unit is removed when mounting the motor.

[morls]

There are plenty of 11mm mounts/clamps (for gun sights) and some 20mm, but I haven't been able to find anything around 25mm - 27mm. I think I'll have to make a mounting block out of wood, and use threaded inserts to run grub screws under the dovetail.

Once I get the belt and pulley I'll be able to size up the mounting block.

[morls]

I ended up making the mounting base out of wood, and it's come up pretty well. Hopefully some clear skies tonight so I can try it out. Thanks for the help.

[Merlin66]

Stephen,
Looking good.
Belt looks a little slack, how does it function?

[morls]

It seems ok. I'm taking my cue from the Baader manual:


Now slightly push the drive pinion until the pulley is slightly under pressure
(Img. 4) and tighten the four screws again. A good rule for the right pressure is that you should be able to twist the pulley at its longest part for 90° without applying force. If in doubt: better keep it too loose than too tight. If the pulley is too tight, it can happen that the SD II can't move the focuser and will stall.

[Merlin66]

OK, if it works, then that’s what’s it’s all about.

[morls]

So far so good. There is zero shaking now when focusing, and the amount of control is way above what I've ever had with this scope. The belt and pulley are well matched for the focuser, and the response is very direct and immediate. No play at all.

I can use the stock Mak focuser (mirror shift) to get close, and the motor to fine tune. This is great.