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Old 23-01-2021, 06:38 PM
Rocket (Ed)
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Focus Drive for Skywatcher Mak 127

I wanted to put a focus drive motor on my Mak 127, but the commercial options are expensive. I have a JMI motor focuser for my Meade SCT, but it doesnt easily fit the Mak focus knob. However, the hand control works with any DC motor. Here is a simple bracket, made from a bent and twisted aluminium strip, and a geared DC motor from eBay. The bracket mounts to the OTA via a lengthened bolt from the Vixen dovetail to the tube, and a bolt to one of the tapped holes on the dovetail, so no modifications are needed to the OTA or dovetail.
The motor couples to the focus knob with a GT2 belt and a toothed pulley on the motor. The toothed pulleys and belts are available cheaply from eBay, for use in 3D printers. I bought a 1 metre section of belt, cut it to length and joined it with a piece of bicycle inner tube and Selleys Power Grip adhesive. (There are a lot of discussions on the web about joining these belts). Alternatively, a belt of the right circumference is probably available on eBay.
The tension on the belt can be altered by washers under the Vixen dovetail, or if a wider aluminium strip is used, by pivoting the motor from the top hole, with a slot at the bottom. However, other than some slop in changing direction, tension doesnt seem critical and there is enough grip between the toothed belt and the rubber focuser knob.
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Old 24-01-2021, 03:32 AM
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Merlin66 (Ken)
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Ed,
Looks very functional. Well done!
On my C9.25/ C11 I used the same solution. Using XML belts/ pulleys and the SW electronic motor.
Worked well for me.
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Old 24-01-2021, 12:32 PM
Rocket (Ed)
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Motor Focus Applied to Vixen Refractor

Ken, thanks for your comment. You have achieved a much neater packaging, using the axial motor, nicely done. The right-angle geared motor mounts more neatly on a refractor than my Mak example, here it one on an FL80.
Note that I made up a toothed belt to fit snugly over the focus knob, with the teeth outwards, mating with the drive belt, because there wasnt enough grip on the hard plastic focus knob. The alternative is to take the knob off, and mount a toothed pulley on the 8.5mm focuser shaft. A 60-tooth wheel is about $12 on eBay, and I have one on order. The 6mm mounting hole on the gear wheel will need drilling out, but there is plenty of material in the hub of the larger gear wheels (unlike the smaller one on the motor shaft). Ed
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Old 24-01-2021, 12:45 PM
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Merlin66 (Ken)
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Ed,
Yes a belt drive is a good solution....
I have the SW motor belt drive mounted on all my telescopes focusers.
Works very well for me.
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Old 31-08-2021, 04:23 PM
Rocket (Ed)
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Alternative Motor Focuser on Mak-127

Here is an alternative way to add a motor focus to the Mak 127, re-using a Meade focus motor from an SCT. The aluminium bar fits under the dovetail plate, with a layer of rubber (from a bike tube) underneath.
The motor fits over the Mak focus knob, which has two 1 cm wide rings made from road bike tube to build up its diameter to match the ID of the motor. It is fixed in place with the bolt used to fix it to the collar on the Meade mirror cell.
Running the aluminium under the dovetail plate allows the telescope to move forward in the mount for balance.
The motor can be quickly swapped between the Mak and the SCT.
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