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  • Ville Puoskari

DIY gear reduction for 100mm Esprit focuser

I've had some problems with belt slipping with my focuser, so I decided to redo the parts that attach the focuser shaft to the motor. To start with the project I ordered a 100 tooth and 24 tooth MXL timing pulleys and a belt for them from Motionco. They arrived quite fast via air mail and their calculator for central distance of the pulleys was a priceless tool that made designing so much easier. The reason I'm using a reduction at all is that my focus motor (USB_Focus V3) lacks the power to move a 2kg imaging train if its attached directly to the focuser shaft even when using their largest motor rated for 4.5kg payload.. Also the motor is glued to the back of its own reduction - and keeps falling off so I secured it with a zip tie and super glue. Some day I will upgrade this just because it's so horribly designed product that doesnt match the specs of the manufacturer but for now I'll keep it on the scope. But lets get back to the reduction, I started off by making threads to a random focuser knob I happened to have from previous projects. A wise man would have ordered a coupling but since Im under pressure to get everything done in time I had to improvise.

After the hole was drilled and I started making the threads using a threaded pin. Because this piece is aluminium it was quite easy to work with. Then I gently tapped a M6 bolt through the 100 tooth gear and threaded it to the adapter I just made. After that I attached the focus motor to the Losmandy plate of my telescope and slipped the toothed belt on the gears. Im quite happy with the results, it seems very sturdy and free of backlash thanks to the great quality of the gears. One major benefit of this system is also that the focus motor can stay on the mount if I need to remove the optical tube assembly from it because the motor is attached to the Losmandy rail beneath the scope. Easier cleaning and maintenance is always a plus!


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