No Drill OnStep Parts Apertura AD10

3/30/2025: Changed the design of the Az gear. Now it uses a clamp instead of sandwiching it between two knobs. The wedge idea was a bust too.

This project does contain 2 parts that I remixed for my situation. Link at the end of the description. The rest are inspired by this project but the parts were created from scratch in Fusion. All the parts should fit on Ender 3 or larger printers.

I needed a way to mount steppers to my Apertura AD10 Dobsonian telescope. It had to be a reversible design that required no drilling/cutting of the factory parts.

BOM of non-printed parts:

1x 5/16x4" NC hex head bolt
1x 5/16" NC nut
1x M5x25 socket head bolt
6x M6 nut
4x M6x45 hex head bolt
2x M6x16 hex head bolt
1x M5x50 hex head bolt
2x M5 nut
6x M4x12 hex head bolt
6x M4 nut
8x M3 socket head bolt (stepper mounting)
2x GT2 20T pulley, 8mm shaft
1x 900mm x 10mm (I had a 6mm handy) GT2 belt, closed (Az belt)
1x 2M x 6mm GT2 belt, cut-to-length (Alt belt)
2x 100:1 geared steppers, 8mm shaft
1x stepper brackets (https://www.amazon.com/dp/B00Q6F51C0)
1x OnStep controller (beyond the scope of this post)

Printed parts:

4x Clamp Knob
1x everything else

For Onstep calcs: the Alt gear is 320 teeth, Az gear is 300 teeth. 

Assembly:

Attach the Alt gear to the right side bearing on the scope tube. You'll need to use caution when removing the bearing from the tube to mount the gear. There's not really a good way to get the M6 nuts & gear installed w/o removing the bearing from the tube (4 screws on inside of tube). There should still be some adjustment for balancing the tube w/ the gear mounted. Install the 20T GT2 on the stepper shaft. Attach the stepper to the mount clamp using M3 screws. Use the coupler sleeve and tray to splice the 10mm belt after cutting to the needed length. The stepper mount needs to be almost at the bottom of the side panel to clear the OTA. The stepper mount uses 2 M6 bolts, 2 M6 nuts and 2 Clamp Knobs. A closed belt can be used, but the length of travel for rotating the tube is less than the distance between the gears. The coupler won't hit either end if you set it close to the Alt gear with the tube horizontal or near the stepper with the tube vertical.

While the OTA is off the rocker base, take the factory bolt out and thread the 5/16" bolt up from the bottom. Use blue (or orange but NOT red) loctite to help hold it tight in the factory threaded insert. Reassemble the rocker box & small thrust bearing as normal. Insert a 5/16" nut in the Base Tension Wheel and screw it down to put some pressure on the thrust bearing. Just enough to take up the slack. Too tight and the gear will slip on the bolt. 

Install the M5 socket head bolt in the “Knob” part; another press fit. Slot an M5 nut into the pocket on top of the Az gear and thread the Knob into it. This is the best way so far that I've found to clamp the gear to the bolt. It may require using an Allen wrench to get it tight enough depending on the friction of your base bearing. Loosen the knob for manual aiming of the rocker.

Attach the Tension Dove to the Az motor clamp using 2 M4x12 bolts and nuts. The Az mount clamp uses the other 2 M6 bolts, 2 M6 nuts and 2 Clamp Knobs.

Attach the stepper motor bracket to the Dove Slide using M4 bolts and nuts. Insert the M5 nut into the slot in the Dove Slide and then slot into the Tension Dove part. Put the M5 bolt into the Az Belt Tension Knob (it's a press-fit) then run it through the Tension Dove and Dove slide to thread into the M5 nut. Fix the stepper to the bracket using M3x6 bolts. Install the 20T GT2 pulley on the stepper shaft.

Swap one pair of the stepper wires if the AZ runs the wrong way. I tried reversing it in the config, but it didn't make a difference.

Operation:

So far, the Alt drive is rather solid and tracks well as long as the OTA is balanced and the belt is reasonably tight. The Az drive works, but I'm looking for ways to reduce flexing of the dovetail slide (PETG is a contributor, use PLA or a CF filament instead). 

When setting the home position in the OnStepX app, it is expecting the base to be on level ground, the tube to be horizontal and pointed North. After that, connect to the controller w/ Sky Safari (or whatever is compatible) and pick an object to view.

Stepper mounts modified from: https://www.thingiverse.com/thing:5531109