barebaric/belt-sander

An edge belt sander that can be mostly 3D printed

Mostly Printed Edge Belt Sander

Aug 31st, 2024: The sander is now finished and works successfully for me. I will add more documentation in the future.

Project Goals And Design Constraints

In this project I am designing and building an edge belt sander. Design constraints:

• Using only 3D printed components + widely available off-the-shelf hardware (as far as possible) to make it fast and easy to reproduce.

• For belt size 915 x 100 mm (but may offer other configurations in the final release).

• Speed controllable brushless motor.

• Belt change and alignment adjustment with no tools. I had to compromise, because after adding the electronics there was not enough space for a large belt alignment screw - belt alignment now does require a hex key driver

• Low profile form factor of less than 14cm - the sander should fit into a drawer when not in use.

• Modular design to allow for customization and faster/cheapter iteration during development.

• Ideally: Option to power from two 18V batteries.

Checklist And Roadmap For First Release

• Prototype a rough full model to ensure the dimensions fit

  • Version 1

• Design, test, and refine the lever mechanism for the belt tightener

  • Done after testing more than 20 different prototypes: type 1, type 2, type 3

  • Latest iteration, successfully printed and tested

    

• Choose a motor

  • Dismissed: 997 motor, mostly due to ventilation requirements.

  • Dismissed: Skateboard motor type 1. Doesn't fit into desired envelope (see design constraints above). It is too long with the shaft included.

  • Dismissed: 6384 motor. Just about fits, but with no space left for routing the cable securely and more expensive because it requires large bearings.

  • Chosen: 90 mm skateboard motor type 2

    

• Choose a BLDC controller

  • Dismissed: SNR8503M BLDC controller module for insufficient documentation. Is is also too close to the motor power limit, so may be risky to use anyway.

    

  • Dismissed: ZS-X11D1 module. Power limit too low & documentation insufficient.

    

  • Chosen: MKS XDrive (ODrive) Mini

    

• Choose a microcontroller

  • Dismissed: NodeMCU ESP8266 with 0.96 display. Large form factor made panel dimensions too large.
  • Chosen ESP32 S2 Mini with separate display.

• Create CAD models for all electronic components

  • 90 mm skateboard motor

  • MKS XDrive (Odrive) Mini

  • Brake resistor (3rd party model found)

  • 10k Potentiometer (3rd party model found)

  • Power switch (3rd party model found)

  • 1.3" display

  • Microcontroller (3rd party model found)

• Build and test the electronics

  • Order parts

  • Double check polarity of xdrive connectors, they use red for GND in some cases! (GPIO-connector seems wrong in photos)

    The connector is indeed wrong - red is GND. Be careful.

  • Figure out maximum power draw of VCC pins of ODrive. (Sufficient for microcontroller+display? Otherwise need a separate step down module)

    Should suffice: The XDrive uses an STM32F405RG, which according to its data sheet can provide a maximum of 240mA at 3.3v on Vdd. The OLED display draws 0.08W = 24.2mA, the ESP8266 has a maximum draw of 170mA and much lower with WiFi disabled. To be safe I'll keep WiFi disabled on the controller.

  • Install Logic Level Converter between ODrive and microcontroller

  • Install Hall sensor filter capacitors

  • Assemble the whole setup

  • Install and test the thermistor

• Software

  • Potentiometer to set velocity

  • Configure and test ODrive with motor

  • Resolve "ENCODER_ERROR_ILLEGAL_HALL_STATE" issue by adding filter capacitors: Encoder error ERROR_ILLEGAL_HALL_STATE

  • Figure out microcontroller / ODrive communication. Details of the investigation documented here

  • Temperature sensor

  • Display

  • Retrieve and display actual speed from ODrive

  • Actually send the set speed to the controller.

• Design and refine an electronics enclosure module to fit into the sander

  

  • Potentiometer knob

  • Panel for display and speed knob.

  • Enclosure with mount plate for ODrive Mini and brake resistor.

  • Final assembly

• Design and refine hub driven roller with the skateboard motor.

  • Design done.

• Create the new overall assembly tying everything together.

  • Fully model the design: Draft done

  • Create new belt aligner.

  • Go through every feature (screws, bearings, etc.) to try and reduce the amount of different hardware needed.

  • Check and refine all models.

  • Print, test, refine, iterate

• Make a backing plate from steel or aluminium.

• Design and build the final base plate.

Incorporate lessons learned from V1 prototype

• Provide more clearance (1.5mm on each side?) between rollers and housing, to fit washers on both sides.

• Make left carriage bearing cutouts larger - 23mm probably. It doesn't need tight clearance, as it is pulled to the right anyway.

• Separate the carriage arm from the bracket, make them connectable using screws. For better printability/modularity.

• Make the arm shorter, to make more space for electronics in the unit.

• Recess the tightener knob into the unit. Knob became obsolete with new lever design

• Bottom could be 2mm slimmer because it will be seated in a base plate anyway. Not slimmed down because space was needed for routing the cable in it.

Potential extensions after V2

• Dust extraction

• Oscillating unit

• Reduce velocity based on proximity sensor