Simcoe Skies Astronomy

PICfocus Electronic Focuser - Mounting to the OTA

click image to enlarge Mounting the stepper motor to the OTA was a daunting task. The biggest problem was doing it without using any invasive "surgery" (like taking the focuser base off and reinstalling it, which I was squeamish about). Also, I wanted to be able to remove it without much trouble if ever the need arose. First I popped the metallic cover off the focuser knob and centered and hot-glued my large gear in place.
I settled on clamping the stepper motor mounting onto the base of the existing focuser, by using two 1" square aluminum stock pieces 6.5" long running parallel to the length of the OTA, and securing it with 8/32 threaded rod through on each side of the focuser base. To "lock it down", one hole was drilled in the square stock at the middle of each side, then the unit was "clamped" in place with the threaded rod, and these holes were used to guide a 1/8" deep hole INTO the focuser's plastic base. The holes in the aluminum were then tapped and the holes in the plastic base were enlarged slightly. This provided a means to use 6/32 bolts THROUGH the aluminum stock, into the plastic base - locking it in place. Aluminum L-stock was then bolted to the square stock to provide a mount for the stepper motor. Aluminum stock was purchased at Home Depot.

click image to enlarge This image shows a head-on view of the PicFocus motor mount. Note the threaded rod, tight against the focuser base on the upper and lower sides. The stock finderscope has been removed (I use a telrad finder, which I find to be MUCH easier). The gears were purchased at an electronic surplus store, and have a 5:1 ratio (50:10 teeth). The L-stock that the stepper motor is mounted to has a V-groove in it to provide clearance for a central protrusion around the stepper's shaft. In this shot, you can also see the adjustment slots in the L-stock (for sliding the motor & its gear closer to the focuser knob gear).
click image to enlarge This is the rack & pinion side of the focuser. The motor shaft and gear is behind the larger gear. You can still move the focuser easily by hand (hey, detented focus control!), as long as the stepper is not powered up (either off or in power save mode).
click image to enlarge Here's another view, showing the motor. The light/dark contrast doesn't show the dark focuser knob gear well (I should stick to astrophotography). To remove the stepper assembly, back the locking bolts out, loosen the nuts on the end of the threaded rod, and the whole thing will slip over the eyepiece holder. Slick!

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click image to enlarge	Mounting the stepper motor to the OTA was a daunting task. The biggest problem was doing it without using any invasive "surgery" (like taking the focuser base off and reinstalling it, which I was squeamish about). Also, I wanted to be able to remove it without much trouble if ever the need arose. First I popped the metallic cover off the focuser knob and centered and hot-glued my large gear in place. I settled on clamping the stepper motor mounting onto the base of the existing focuser, by using two 1" square aluminum stock pieces 6.5" long running parallel to the length of the OTA, and securing it with 8/32 threaded rod through on each side of the focuser base. To "lock it down", one hole was drilled in the square stock at the middle of each side, then the unit was "clamped" in place with the threaded rod, and these holes were used to guide a 1/8" deep hole INTO the focuser's plastic base. The holes in the aluminum were then tapped and the holes in the plastic base were enlarged slightly. This provided a means to use 6/32 bolts THROUGH the aluminum stock, into the plastic base - locking it in place. Aluminum L-stock was then bolted to the square stock to provide a mount for the stepper motor. Aluminum stock was purchased at Home Depot.
click image to enlarge	This image shows a head-on view of the PicFocus motor mount. Note the threaded rod, tight against the focuser base on the upper and lower sides. The stock finderscope has been removed (I use a telrad finder, which I find to be MUCH easier). The gears were purchased at an electronic surplus store, and have a 5:1 ratio (50:10 teeth). The L-stock that the stepper motor is mounted to has a V-groove in it to provide clearance for a central protrusion around the stepper's shaft. In this shot, you can also see the adjustment slots in the L-stock (for sliding the motor & its gear closer to the focuser knob gear).
click image to enlarge	This is the rack & pinion side of the focuser. The motor shaft and gear is behind the larger gear. You can still move the focuser easily by hand (hey, detented focus control!), as long as the stepper is not powered up (either off or in power save mode).
click image to enlarge	Here's another view, showing the motor. The light/dark contrast doesn't show the dark focuser knob gear well (I should stick to astrophotography). To remove the stepper assembly, back the locking bolts out, loosen the nuts on the end of the threaded rod, and the whole thing will slip over the eyepiece holder. Slick!