Design the arm in CAD

Code the arm, print one joint, prove the torque budget.

Design a parametric arm in build123d around real components and the way FDM parts print, have the wiring plan reviewed before the first power-on, and turn slicer estimates and weighed servos into the sim’s Params. Two torque gates check the design: 2:1 against derated stall at full reach, and rated torque for every pose that holds the drone.

Written lesson + build labEvidence-based gate

The goal for this build

What you’ll be able to do.

Model the components as mass blocks and draw the harness in WireViz for review before the first power-on.
Build a parametric arm and its test props in build123d, drawn in the zero pose.
Design every part for its print orientation, and print and test one joint first.
Write Params from slicer estimates and weighed servos, and prove both torque gates.

What to have ready

Module 1 done; this module can run alongside Modules 2–5
The Module 2 controller, for the figure-eight and dock checks in sim
A printer with a bed of at least 180 × 180 mm, or a print service, and a scale that reads to 0.1 g
The hardware kit, bought now if not before; no CAD or electronics background is assumed

Download the course starter ↓

Free account

Read the lesson, run the lab, pass the gate.

The whole course is free. Create an account to unlock the lesson, the build lab, the task and the gate command for this module, and to download the starter kit.

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03 / Prove it

Keep the evidence.
Then run the gate.

What you ship

cad/ with the parametric build123d model and STL exports of every part
cad/wiring.yml with its rendered diagram, reviewed by the trainer before the first power-on
cad_to_params.py and the Params it writes from slicer estimates and weighed servos
The test joint, assembled to become Module 8’s pendulum bench
A torque table and the sim figure-eight and dock runs, with commit, config and seed

Module 06 gateEvidence required

Every printed part fits a 180 × 180 × 180 mm build volume.
The gripper reaches 0.30 m from the base axis at table height, which covers the benchmark, the drawing area and the dock.
Every pitch joint has a torque margin of at least 2:1 with the 230 g dummy drone at full horizontal reach, from stall torque derated by 11/12 for the voltage the cables lose.
The pad and the cradle sit where holding the dummy drone needs at most the servo’s rated torque (10 kg·cm) at every joint, and so does every pose the dock path holds, so an arm that stops anywhere on it can keep holding the drone.
The Module 2 controller draws the figure-eight with the CAD arm in sim within the nominal gate, an RMS error under 2 mm on the slow figure-eight.
The trainer reviewed the wiring plan before the first power-on.

With a free account: the gate command and how to record your evidence.

The story behind the build

Episode companions.

EP 07I designed a robot arm in Python

Written companions are available now. Recordings and customer access are forthcoming.

Made it through the lesson?

Save your reading progress here. Record your gate result in your project.