Sim to real · Volume 1
Adaptive Robot Arm
Write an arm simulator that models a servo whose firmware you can’t read, compare classical control with learned adaptation, then run the trained model on a desk arm you designed and printed. Nine modules end in measurable gates, and eight tasks, from waving hello to throwing a ball into a cup, put each build to work. Every result belongs in the report, including the runs that fail.
Start on your laptop. Buy the hardware when you reach Module 6.
Make the theory move
The same question runs through every build: what must a network learn so a hidden vector captures a robot’s real dynamics?
The answer becomes a simulator, a fair benchmark, a learned controller, and a desk arm you designed, printed and built.
An arm simulator you wrote and can explain line by line, including a model of a servo whose firmware you cannot read.
One benchmark that scores the stock servo loop, PID, gravity feedforward, EKF-adaptive and learned adaptation on the same perturbation set, in sim and on hardware.
A robot arm you designed in CAD, printed and built, running your trained model with an unknown payload.
A public repo and episode series that document every gate and every task on the ladder, including the ones that failed.
The curriculum
Nine modules. Each one has a lesson, a lab, a deliverable, and a measurable gate. Keep the evidence, including the results that surprise you. On the map, each episode companion sits next to its module.
Arrow keys move between modules and episodes.
The task ladder
The modules add tasks to the arm’s repertoire, roughly from easy to hard. Each task except the melody runs in sim first and then on the printed arm, and Module 9 replays the whole ladder. Sim checks are automated; hardware checks need a video for trainer review.
Before you begin
Read the lesson, implement the lab, and keep the evidence for the module’s gate: the result, the commit, the configuration, and the seed.
“Studied” is a reading bookmark. A passed gate is a reproducible result. Hardware gates also need a trainer’s review of your logs and video.
There is no fixed time estimate: progress depends on the builds and debugging. Part 1 needs no hardware purchase or paid cloud compute.
The physical part
The kit costs about €505 in parts, including a Bambu Lab A1 mini printer at its October 2026 price of €189 and a sixth servo for the test rigs. If you own a printer with a 180 mm bed, it is about €315. Part 1 needs only a laptop, so the purchase can wait until Module 6.
| Part | Quantity | Budget | Build note |
|---|---|---|---|
| Feetech STS3215 12 V 30 kg·cm servo (ST-3215-C018) | 6 | €159 | Five for the arm and one for the bench and torque stand, which is also the spare; the 7.4 V version fails the Module 6 torque gate on the example arm, and several shops list the 12 V one as backordered. |
| Waveshare Bus Servo Adapter (A), SKU 25514 | 1 | €6 | It takes 9–12.6 V, so the 12 V supply plugs straight into its barrel jack, and a jumper chooses USB to the laptop or its UART header to the Pico 2. |
| 12 V 5 A desktop supply with 5.5/2.1 mm plug (Mean Well GST60A12-P1J) | 1 | €18 | Its 5 A covers one stalled servo while the others move; two stalls, or a throw that drives several joints at full effort, can trip its overload protection and cut the whole arm. |
| Mains cable, IEC C13 to Schuko | 1 | About €5 | The supply has a C14 inlet and comes without a cable. |
| Inline switch for the 12 V line (the kill switch) | 1 | About €5 | It cuts every servo at once and the arm falls limp, which also releases an arm that holds its last goal after the laptop stops; closing it must move nothing until you re-arm. |
| Bambu Lab A1 mini | 1 | €189 | Skip it if you own a printer with a 180 mm bed; 189 € is its October 2026 price at 3DJake, against a regular 319 €. |
| PETG filament | 1 kg | About €20 | PETG rather than PLA, because the servos run warm under load and PLA softens around 60 °C. |
| M3 heat-set inserts | 100 | €9 | For joints that are opened again and again, where a thread the screw cut itself would wear out. |
| M2 and M3 screws | 1 set | About €10 | Parts that stay closed take M3 screws straight into a 2.6 mm hole, where the screw cuts its own thread. |
| Raspberry Pi Pico 2 with headers | 2 | €13 | One reads the torque stand’s load cell through the HX711 and streams it to the laptop; the other runs the model and the safety supervisor on the servo bus in Module 9’s Round 2. |
| 1 kg load cell with HX711 | 1 | €18 | On a 15 cm lever it reads at most about 15 kg·cm, so the torque stand measures up to half of stall; it later becomes Volume 2’s thrust stand. |
| USB webcam (Logitech C270) | 1 | €18 | Its AprilTag ground truth is independent of the servo encoders; calibrate it with a checkerboard, because its absolute accuracy depends on that calibration. |
| Ping-pong balls | 6 | €4 | For the throw; throw only these, and keep faces out of the throw line. |
| 8-note children’s glockenspiel | 1 | €10 | For the melody, which tests the real command path and so has no sim version. |
| Calibration weights, 10–500 g | 1 set | €17 | Known masses for the payload cups, the payload step and the pendulum bench, where known masses at known lengths identify the servo. |
| String (fishing or kite line) | 1 roll | About €3 | For the swinging weight, the ball in a cup and the payload latch’s pull cord, which drops the payload step’s weight from outside the arm’s reach. |
| Open SimpleFOC joint (optional): DFRobot 2804 gimbal motor with AS5600 encoder, plus a SimpleFOCMini driver | 1 | About €26 with import VAT, plus shipping | For the Module 8 stretch: the same fits on a motor whose firmware you can read; whether it stays a stretch, becomes core or is dropped is still open. |
The arm is desk-sized and weak, but it still pinches. Keep hands out of its reach while torque is on, keep the kill switch in the 12 V line within reach, and stall at most one servo at a time. Several shops list the 12 V servo as backordered, so check the stock before you order. Parts list with shop links (CSV) ↓
Follow the experiment
Read the written companion to every planned episode. Recording and customer access are forthcoming; the Free and Customer labels show the intended recording release track.
The course’s opening question: what must a network learn so that a hidden vector captures a robot arm’s real dynamics?
Read companionRigid-body dynamics, a servo whose firmware stays closed and a shared 12 V supply, with four checks to run before trusting any of it.
Read companionA frozen benchmark turns the gap between a nominal arm and a changed one into failures you can reproduce and explain.
Read companionAn EKF estimates the payload and a disturbance torque per joint, with a lesson in what a static hold can’t reveal.
Read companionOne encoder, four objectives and one linear probe: the ablation that can confirm or overturn the course’s answer.
Read companionCausal timestamps, held-out arms and the right observation channels matter as much as the network.
Read companionA privileged teacher, a history-only student and a new reward that throws a ping-pong ball, all in the sim you wrote.
Read companionA parametric arm in build123d, drawn around a torque budget and a print bed, that writes its own physics into the sim.
Read companionPrint, build and calibrate the arm, then make its first moves on stock settings, every one of them through the safety supervisor.
Read companionWeigh, swing and load the printed arm and the kit’s sixth servo until CAD, sim and hardware sit in one table with error bars.
Read companionEvery controller off-board through the same USB route first, then the learned model on the Pico 2, with the safety supervisor on in both rounds.
Read companionThe task ladder replayed on the printed arm, each task with a check fixed in advance and every result reported, whatever it shows.
Read companionChoose your depth
All written lessons, companions, and downloads on this site are accessible now. These tracks describe the planned series and its teaching resources.
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