"Autofocus" motor to Tal 100RS , quick and cheap and simple ...

[Steve Ward]

Thought this might be a bit of a pain to complete , but as it turned out it was all done and dusted in under an hour and cost the princely sum of £ 1.40 ... 

Had looked at getting something machined up to fit the 82mm focuser body but it meant machining out of a solid billet as there's no pipe between 3" and 4" readily available.

Solution was a rubber lined 2-1/2" ---  75 - 80 mm pipe clamp , am M10 x 20 bolt and an M6 x 80 bolt + 2 M6 nuts.

The pipe clamp fits perfectly between the ring that holds the focuser to the tube and the tension/lock screws without fouling either.

First step was to remove the Tal focus wheel , undo one small screw and off it comes , much easier than breaking the threadlock on the Skywatcher wheels.

Then pack the spindle out with insulating tape until the sprung motor connector fits snugly , tighten up the two grubscrews til they bite. 

Next fit the pipe clamp to the tube lining the M10 boss up with the two screws to centre.

I replaced one of the clamp bolts with the M6 x 80 bolt which takes the end up beyond the top of the M10 threaded boss on the clamp , this allowed me to fit one nut level with the top of the boss giving a flat mounting surface for the bracket.

The bracket is cut from a 2" length of 1" x 4" aluminium box section , by far the simplest way of getting 90 degree cornered brackets , it's impossible to bend a piece of flat without cracking .

First mark out the hole positions by lining the end up with the motor plate , drill the holes ( 1 x 10mm , 1 x 7mm ) and slip the bracket over the M6 bolt ( after putting one of the nuts on the bolt and roughly levelling with the top of the boss.)

Cut the M10 bolt to about 15mm long and bolt the plate in position temporarily.

Now mark the position of the motor fixing holes and the amount to remove from the top surface to allow for accessing the lock screw. , remove the bracket , drill and tap the holes to M4 , cut out the required corner and you're done.

Fit the bracket over the M6 bolt , fit the M10 bolt and gently tighten , doesn't need more than a nip , spin the first M6 nut up to the underside of the bracket and fit the top M6 nut and nip up.

Fit the two M4 screws through the motor plate into the bracket and nip tight , very fine thread in aluminium so don't overdo it.

Sorted .... 

[Peter Drew]

Nice solution. 

[nightfisher]

Nice, very nice indeed.

Your of to a flying start, here is what i tried with my 100rs

 http://stargazerslounge.com/topic/124176-tal100rs-motor-focus/?hl=tal+motor#entry1231450

[nightfisher]

Just coming back to this thread, think i might be stealing the pipe clamp idea 

also a thread worth bumping due to amount of people that have now bought this scope

[Steve Ward]

Hi Jules ,

I have a "spare" clamp here if you trouble finding one , got mine from BSS if there's one nearby.

[nightfisher]

Thanks steve but its not going on the TAL, and i dont as yet have the focuser so i dont know the OD

[woldsman]

 

found this thread useful when attempting an autofocus mod to a Tal 100 RS for Lunar imaging. Couldn't source the right sized pipe clamp & so opted for a tube ring solution, which I think is probably the way to go for a stable long term solution.

Here are the details.

1. CNC tube ring, 103mm diameter flocked to reduce the diameter slightly.  Fits perfectly on the OTA.

2. I was nervous about removing the original focus knob as on my 100 RS it didn't look designed for safe removal. In any case, the Tal 100RS has a tapered tube and lacks mounting threads needed for a more standard

autofocus attachment direct to the Crayford focuser. I opted instead for a 3-D fine focus knob that fits over the existing focus knob to enable a belt and pulley solution.

The supplier was Spencer-3D who has a store on eBay.  The design incorporates a three bolt & nut system set in the middle of the ribbed pulley wheel - the bolt fits down in a cut-out slot fitted in the inner diameter.

With a slight bit of sanding it fitted exactly.  Standard of the 3D printing and speed with which the order was executed both excellent. 

3. ZWO EAF stepper motor. I sourced a preowned 12v model which kept the costs down a bit.  There are alternative cheaper stepper motors that would work but the ZWO functions seamlessly with Sharpcap, which is the image capture software I'm using. The motor sits on some wedge shaped pieces of polystyrene (hidden in the photo). 

4. Timing belt and pulley: I went for a 6mm wide belt and a 20 toothed pulley. There are some online calculators that work out required belt length. Hardest thing to source was the pulley as I needed one that would fit the ZWO EAF and which had a grub screw to fix it in place.  It's also important to match a GT pulley and belt or a XML pulley and belt. The driven wheel is 55.52mm and the driver (pulley) is 12.05mm and so the velocity ratio is 4.6, which means that for every five turns of the EAF driver the driven fine focus knob rotates approximately once.

5. Washers and mounting plates: I went down to the local DIY store and came back with some light metal plates as pictured. 

 I think this is a relatively non-invasive autofocus mod that preserves the scope's original features. It is also easy to switch between auto and manual focus, as needed.

Clear skies!

 

 

 

Edited May 29, 2023 by woldsman