SecKit Tank v2 prototype alpha with DAB direct nozzle probing

"DAB" is the new extruder carriage consisting strong roller guides to enable direct nozzle probing. When DAB is unlocked, the whole extruder & hotend can be slid up for a 2~3mm. A microswitch is used as the sensor.

"Wobble Wafer SFU12" (for 1204 ball screws) is the variation of Wobble Wafer (for T8 lead screws). It has 4 DoF that can cancel the possible wobbles in XY direction and tilt in Z from imperfect ball screws.

Tank v2 alpha features:
- Build volume: 350x350x400
- Gates LL-2GT-RF 9mm belt
- Stacked industrial F604zz bearings as long-life idlers
- Minimal gap between 2 XY belts to minimize the torque to XY linear blocks for high acc/speed movements
- Lightweight MGN9H linear guide and carbon fiber back tube as X gantry.
- MGN12C linear guides for longer life.
- Mounting holes in the frame for 4 CoreXY steppers
- 3 ball screws as Z drive, with 3 Wobble Wafer SFU12 installed
- CAN bus toolhead with NEMA14 round stepper
- BTT Octopus Pro + 5 TMC2209 for XYZZZ + EBB36 for E
- Red emergency stop button
- [optional] DAB extruder carriage for direct nozzle probing
- [optional] PTC chamber heater
- [optional] 5" HDMI Klipper screen


To be improved in the beta version:
- To gain more space, place 2 Z drives at the front and 1 Z drive at the rear side, as the locations in Tank v1.
- Use belts and pulleys to scale up the torque and stopping force of Z steppers, but not direct drives.
- Extend the legs of the bed toward the ball screws to lower the torque to the bed brackets.
- Mounting points for toolhead and bed drag chains.

P.S. this prototype is vinyl-wrapped for personal customization.