PYTHON · NUMPY

Where you put the meter

Measure one motion at four planes and show the answer changes.

01Challenge

Two axes on one shared DC link run a single point-to-point move. You will meter it at the mains, at the cabinet, at the DC link, and at the four motor terminals. The physics is identical in all four cases. Show what the numbers do.

Predict firstSame motion, same robot, four honest meter positions. How far apart will the highest and lowest readings be?

02Model

A robot cell has one motion and four honest places to put an instrument. At the mains you see what the building pays. At the cabinet you additionally see the braking resistor. At the DC link you see energy passing between axes that never touches the supply. At the motor terminals you see each axis in isolation and regeneration disappears entirely. All four are correct measurements of different questions.

03Guided practice

Run the plant cell, then the four-plane cell. Read the spread. Then open the live instrument and reproduce it by clicking the four plane buttons — the numbers should track.

04Feedback

PASS WHEN You measured one motion four ways and got four answers.

If your run fails, check:

The spread is not noise and not error — every plane is measuring correctly.
The per-axis sum is highest because regeneration is invisible to it: each motor is metered alone, so energy one axis returns is never credited to the other.
This is why datasheet power figures are not comparable between manufacturers.

05Retrieve & space

Name the four measurement planes, from the wall inward.
Which plane makes axis-to-axis regeneration invisible, and why?
A paper reports 'energy per cycle' with no further detail. What can you conclude?

06Mastery & project

State a robot energy figure with its plane attached, and explain to a reviewer why the plane is not a detail.

Take any energy claim from a recent robot-learning paper. Determine which plane it could have used. Note whether the paper says.

GO FURTHER · THE LIVE PLAYGROUND

Open the instrument ↗ — Two axes on a shared DC link. Move the meter, slide the phase, watch the number change.

← Measuring Energy in Physical AI: Where You Put the Meter Three ways to lose the same joule →

PYTHON · NUMPY

Where you put the meter

The plant is given. Your job is to read the four numbers and say which one a wall meter reports.

You read

the arrays and values already in scope

You change

the code you write in each cell

Fixed

the dataset and the checks that grade you