Mark's Featherweight: "Petrichor"

Hi! I’m starting to build a Featherweight. It is a pretty conventional setup, with 4wd and a brushed-motor driven lifter.

I’m hoping to use this to prove some electronics will do what I expect, and see if the parts I’ve selected will immediately destroy themselves.

The design is not complicated - but I’ve chosen, perhaps unwisely, to use 3d printed gears again to drive the weapon. Obviously this involves a great deal of torque, but according to my back-of-vape-box* calculations it might not fail immediately, plus they worked really well on my Beetle.

So here’s a few teaser pics:

CAD using FreeCAD because I am a masochist.

“Tuned machine” franken motor/ planetary 36mm gearbox with 8mm output shaft. Feels pretty chonk, spins at roughly the right speed. I expect this to work, the gearbox has only 1 stage and is 5:1. These are RC car brushed motors which have ridiculous amounts of power for their size, but they sound pretty rough when running.

  • NB: “back of vape box” calculations are like back-of-fag-packet but not so precise because vape boxes are smaller.

Literally the current state of construction is a few pieces of 18mm thick MDF (standing in for HDPE, to test construction techniques), a pile of paper with printed templates, and a box of motors and bolts.

Some parts of this robot will need to be custom machined by me with my limited metalworking skills, but I think it should be do-able. Most of the structural parts will be made from HDPE.

Some bits will be 3d printed but mostly internal fixings and such like.

I might do a few things like anti-stacking bumps with 3d printed TPU as that works super well.

Ah, you love to see it!

Loving the concept and 3d printed part abuse is something I’ll be watching with interest.

I will always go to bat for ‘proper’ rc 540 motors as they’re often remarkably well built and the low turn flavours for crawlers and F1 are ripe for abuse at robot voltages.

Update: I have successfully made a few bits of wood with holes in roughly the right places. At least

  • I now know a bit better how to drill 36mm diameter holes
  • I have shown that my barrel nuts work
  • My 3d printed barrel-nut-drill-guide works a treat:


It’s a very simple 3d print which grabs the edge of a piece of material (18mm MDF or 20mm HDPE, I made several variants) and has holes of the right size and location, to guide a drill in the right spot.

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