3D Printing

Openscad and stl files can be found in the github repository. The following parts can be printed:

  • Wheel
  • Flange D Adaptor
  • Wheel Bearing Mount
  • Drive Motor Bracket
  • Omniwheel
  • Omniwheel Bracket
  • Cutter Motor Bracket
  • Cutter Wire Stack
  • Component Tray NodeMCU & Pico
  • Target
  • Handle
  • Roof Socket
  • Battery Foot

The robot-assembly.scad file in the robot folder shows how all the parts are assembled, including purchased parts like motors and batteries and non-printed parts like the baseboard.

robot assembly

Wheel

The printed wheel is designed to be bolted to a metal flange for increased strength.

Flange D Adaptor

The D adaptor is a snug fit inside the 10mm hole of the wheel flange. This gives secure transmission from the 6mm D shaft to the wheel, and provides anti-vibration security for the grub screw.

Wheel Bearing Mount

It is possible to omit this part and fix the wheels directly to the motor shaft (direct drive), however, the robot weighs in excess of 5Kg and all this weight can have a detrimental effect on the motor gearbox, despite the motor's ability to function.

Drive Motor Bracket

This part is designed to allow the motor to be fixed in any of 6 positions, providing some adjustment for mow height in the direct drive configuration, but the offset motor shaft must align with the bearing otherwise.

Omniwheel

The omniwheel is printed in two sessions: the sub-wheels and the frame. Sections of 5mm perspex rod are used to secure the sub-wheels into the frame, and held in place with a spot of glue.

Omniwheel Bracket

The omniwheel bracket uses a hirth joint to enable the height of the omniwheel to be adjusted. This may be necessary depending on the robot wheel configuration. A 6mm carriage bolt, washer and captive nut are required to lock the joint. Alternative inner joints with different angular offsets can be printed, if the height of the omniwheel needs tweaking.

Cutter Motor Bracket

Black PETG is the recommended filament for printing the above parts, but the Cutter Motor Bracket can be printed from TPU to benefit from anti-vibration.

Cutter Wire Stack

The files for this component generate 4 stackable washers which allow lengths of 2mm strimmer line to be inserted for the cutters. The washer stack is bolted to a smaller metal flange which is secured to the motor. This is the primary mechanism for setting the mow height. Additional washers can be added as spacers.

Component Tray NodeMCU & Pico

The component tray can be printed in PLA if required. A version for the NodeMCU and one for the RPI Pico is included. Tray holes accept standoff pillars to mount the Motor Controller, Relay Board, Patch Board and Device.

Target

This component should be printed in white filament, for best optical performance. In addition, slicing with no Top Layer and gyroid infill exposes the texture and provides a nice anti-reflective surface.

Handle

Carrying the robot to the lawn can be tricky, especially if you employ the hinged bogey configuration. The handle can be accessed by removing the roof, and then the battery weight is evenly distributed when lifting.

Roof Socket

The Roof Sockets need to be printed in TPU to fit nicely with the roof pillars, even after many insertions. The roof is made from a piece of A3 sized plywood, which enables 2 sheets of Self Adhesive Black Velvet Felt (as used for lining drawers) to provide a non-reflective background for the target.

Battery Foot

The battery feet serve to position the batteries, and provide a tunnel for velcro straps so the batteries can be secured. This allows the robot to be turned upside down for maintenance on the drive train and cutters, without the batteries falling out!

Drive Train Cover

The purpose of this cover is to protect the motor and drive train from grass clippings. It is printed flat and then folded around the pair of brackets, before being screwed to the baseboard.

Baseboard

The baseboard is not printed but cut from 9mm plywood. The hole sizes and positions are detailed in the baseboard drawing file. This file is scaled to A2, to accommodate the full baseboard, so zooming to 50% enables it to be printed on A4 paper. However, if you print it at full scale it can be used as a template to mark the hole positions on the baseboard. Technically, you only need to print the top-left quadrant (page-1) because each quadrant is a mirror image.