Measuring Energy in Physical AI: Where You Put the Meter
A robot energy figure is only meaningful once you say where the meter was and which definition of energy you used. This module builds both, on one two-axis instrument, and ends with a reporting record a reviewer can actually check.
▶ Start the course ← All coursesWhere this sits, and what moves it.
Binding constraint · Where the meter sits. A robot energy figure is a coordinate on two axes -- the measurement plane and the definition of energy -- and a number without both is not wrong so much as unreadable.
Robot energy numbers were compared across papers as though they were the same quantity. They were not, and no convention existed to say so, so the literature accumulated figures that could not be put beside each other.
This module builds the two-axis instrument and ends with a record a reviewer can check. What does not exist -- this review did not locate one -- is an agreed joules-per-task standard for robots, the way efficiency standards exist for motors and appliances.
Someone writes that standard, and the field it serves is already large enough to need it. The precondition is not more instrumentation; it is agreement on the plane and the definition, which is exactly what a student leaves this module able to state.
Every hard thing was impossible until the constraint that made it impossible was named. How we read a frontier →
One motion, every way of measuring it
Establish that a robot energy number is a coordinate, not a fact: it depends on the measurement plane and the energy model. As of June 2026 one voluntary method covers six-axis industrial arms; for every other morphology, and for the task denominator, both choices are still yours to state.
- L3Where you put the meterSame motion, same robot, four honest meter positions. How far apart will the highest and lowest readings be?Measure one motion at four planes and show the answer changes.→
- L3Three ways to lose the same jouleAn axis brakes and returns energy to the shared DC link. A mains meter watches the whole cell. Which of the three fates of that joule can it tell apart?Split braking energy into recycled, exported and burnt, and show a mains meter cannot separate them.→
- L3The one-volt raceTwo drives share a bus, each with its own braking chopper. You mistune one threshold by a single volt out of 380. How does the braking energy split?Show that a comparator tolerance, not the control law, can decide where a machine's energy goes.→
- L41/T³ and 1/TYou slow a point-to-point move down by a factor of two and fit the energy against duration. What exponent do you get?Fit the scaling exponent for two published energy models and show they disagree.→
- L4The reporting recordNine fields separate a reproducible robot energy figure from a bare number. How many of them do the existing standards already supply?Build an energy report a reviewer can check, using what the existing standards already supply.→