3D Printing Tracked Robot

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

  • Track (2)
  • Motor Plate (2)
  • Drive Motor Bracket (2)
  • Drive Spindle (2)
  • Drive Plain Cog (4)
  • Drive Sprocket Cog (2)
  • Drive Sprocket Shaft (2)
  • Bearing Plate (2)
  • Tube Clamp (4)
  • Idler Hub (4)
  • Idler Wheel (4)
  • Idler Drive Axle (4)
  • Tension Rod Adaptor (4)
  • Tension Thumbwheel (4)
  • Locking Thumbwheel (6)
  • Electronics Chassis (1)
  • Cutter Motor Bracket (2)*
  • Cutter Wire Stack (2)*
  • Target (1)*
  • Roof Socket (3)*
  • Roof Plug (2)

* these parts are identical to their wheeled robot counterparts

The Assembly.scad file in the assembly folder shows how all the parts for one track side is assembled, including purchased parts like motors and bearings and non-printed parts like the aluminium tubes, threaded rod and baseboard.

track assembly

Track

This part needs to be printed in TPU95 for flexibility. Slicer generated Support is essential for the underside of the teeth; Tree Support is recommended for it's ease of removal. 15% Honeycomb Infill is also recommended, but the Honeycomb Infill Pattern is not available in the standard version of Cura Slicer. The closest looks like Tri-Hexagon, or Cubic/Grid/Triangles. Care needs to be exercised when printing this component, because the circular track extends to the edges of the build plate leaving no room for a skirt. The first layers should be monitored closely.

track belt

Motor Plate

The motor plate has holes and a shroud to mount the motor. The selected motor is a Planetary Gear Motor with Speed Reduction Carbon Brush Technology and D Shaft DC 12V (45RPM), which has performed well in trials. Cheaper alternatives will probably work just as well. Worm-drive motors have also been used successfully. A different motor would require different mounting hole arrangements. Note that the motor rpm needs to be higher than that for the wheeled robot (30rpm) - as the tracked drive sprocket is smaller than the wheel! 45rpm is probably the lowest I would recommend, and I would choose 60rpm for my next build.

Bearing Plate

The bearing plate serves to keep the structure rigid vertically, against the tension of the track. The housing is designed to accept a bearing 8mm id x 16mm od x 5mm thick.

Drive Sprocket

The drive sprocket is assembled from 5 parts. The spindle is a tight push fit onto the motor shaft, so this hole size might need to be changed for different motors. The spindle provides a hexagonal shaft over which the plain cog and sprocket sandwich is slid. The axle screws into the spindle, is secured with a locking thumbwheel, and projects into the bearing in the bearing plate. The printed axle can be replaced with a section cut from an M8 Shanked Stainless Steel Bolt for enhanced strength.

Drive Motor Bracket

This part provides additional support for the terminal end of the motor.

Idler Hub

When slicing rotate this part to lay flat on the build plate. The hub is designed to accept a pair of bearings 6mm id x 16mm od x 5mm thick, which are pushed in.

Cutter Motor Bracket

Black PETG is the recommended filament for printing most parts (not track), 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.

Electronics Chassis

The chassis parts can be printed in PLA if required. The chassis is designed to slot into a black ABS project box 220mm x 120mm x 75mm.

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.

Roof Socket

The Roof Sockets need to be printed in TPU to fit nicely with the roof plugs and pillar, 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.

Roof Plug

The roof plugs (PETG) can be glued into holes in the top of the electronics box, and provide seating for the rear roof sockets (TPU).

Baseboard

The baseboard is not printed but cut from 9mm plywood.