V0.1 Movable Pulley Z Drive Mod

There already are belt-driven mods like theFPVGeek's V0 Z Belt mod and MathematicalPotato's adapted version for V0.1. This is my attempt to combine the timing belt with a movable pulley system.

• M4-like driving gear(1:4) with movable pulley on Z bed(1:2), resulting in a 1:8 speed ratio, provides higher torque and step resolution. The bed doesn't drop when the Z motor is disabled.
• Using a NEMA14 stepper motor (no tight restriction in length) provides another path for V0 to V0.1 upgrade by reusing the Z motor.

BOM (Some can be obtained from the original setup)

Fasteners

• 11 x M3x8 BHCS
• 2 x M3x10 BHCS
• 4 x M3x12 BHCS (2 extra is needed for kirigami bed)
• 5 x M3x16 BHCS
• 2 x M3x20 BHCS
• 3 x M3 Washer
• 2 x M3 Threaded Insert (4 extra is needed for kirigami bed)
• 4 x M3 Hex Nut
• 3 x M5x20 BHCS/SHCS
• 3 x M5 Hex Nut
• 1 x M5 Washer (about 1mm thick, doesn't have to be accurate)

Motion

• 3 x GT2 20T Pulley (6mm wide / 5mm bore)
• 1 x GT2 Belt Loop (6mm wide) - 188mm
• GT2 Open Belt (6mm wide) - about 790mm
• 8 x F695 2RS Bearing
• 1 x 5x60mm Shaft
• 1 x NEMA14 Stepper Motor (LDO-35STH42-0504AH, others might also work)

Mechanism

As shown in the following figure, the belt drive on the motor is a 20T:80T system.

The driven belt path with constant belt length is a movable pulley system with the two belt ends fixed at the upper and lower parts of the frame.

Instructions

Assembly of Each Component

Note the places that need threaded inserts. You can pre-apply them.

1. M4-like driving gear

   

   

   This is very similar to Voron M4 extruder. Just mind the placement of the F695 bearings. You can refer to Nero's video guide for details about assembling Voron M4.

   The 80T_gear_7mm.stl provided is a thinner version of the M4 toothed gear with 7mm of tooth width instead of 9mm to save a little weight and space. Both should work here.

2. Bed Holder (for Stock V0.1)

   

3. Kirigami Bed Holder

   

4. Top Idler

   

5. Top Endstop Mount

   Use the stock Z endstop and the two M2 self tapping screws.

   

Assembly

1. Preload 2 M3 nuts at the marked slot on page 32 of the manual.

   (Note: If you don't want to take the frame apart, it can be mounted without these two nuts but it may be less rigid. Don't tighten the belt too much then. NOT TESTED!)

   

2. Make a loop on one end of the belt and press it into the printed part. Then mount the printed part to the frame with 2 M3x8 screws.

   

3. Mount each component to the frame (don't fully tighten up yet). There should be preloaded nuts if you followed the V0.1 manual. The two upper components and their nuts can be slid in from the top.

   

4. Route the belt path as shown in the mechanism figure.

   The upper belt end should go through the upper_belt_end.stl as shown below.

   (Tip: Temporarily lower the upper idler to have enough belt length to get the belt end though the holder.)

   

5. Slightly adjust the position of each component so the bed holder is at the middle of the extrusion and the four marked segments of the belt are as parallel to the Z rails as possible.

   

6. Belt tensioning.

   First mount the top endstop holder about 2-4mm lower from the top horizontal aluminum extrusion. Loosen the mounting screws and pull the excessive belt through the holder.

   Slightly tighten the mounting screws so the belts doesn't slip out while the endstop mount is still moveable. Pull the endstop holder upward to adjust the belt tension then fully tighten the mounting screws.

   

   (Note: As marked in the figure, the top idler mount and endstop mount should be about flush with the bottom of the horizontal aluminum extrusion. Make sure the mini-AB doesn't crash into the screw heads or printed parts.)

   

Klipper Settings

• Old format (1.8 degree motor and 16 microsteps):

[stepper_z]
step_distance: 0.0015625

• New format:

[stepper_z]
rotation_distance: 40
gear_ratio: 80:20, 2:1

Photos (some may be outdated)

Here's a video of testing the bed motion:

Changelog

2022-07-18

• Updated the upper parts again for new appearance and more clearance for the toolhead.

2022-05-03

• Added the adapted bed holder for kirigami bed designed by @zalupa#9238. Go to ./kirigami_adaptor for the files.

2022-04-20

• Redesigned the upper parts (again) for the following purpose:

  • Fixed an issue that the screw rubs slightly against the belt. Thanks to @zalupa#9238 on Discord for pointing out the issue!

  

  • Changed print orientation for better part strength.
  • Symmetrical design for aesthetics.

2021-11-09

• Redesigned the Z endstop mount to hold the belt better (The previous version might get loose overtime).
• Change some dimensions slightly for stronger parts.

2021-08-26

• Initial release