Charge

"Everyone plans what their robot will do," she said, "and forgets to plan whether it has the power to do it. That's the whole craft: a power budget." She tapped the meter. "Every part draws current, measured in milliamps. The motors are the thirsty ones — they can pull a hundred times what a sensor sips. The brain, the radio, the gripper, the lights, all drinking from the same battery at once. And a battery isn't bottomless — its capacity is a fixed number of milliamp-hours. Draw more per hour, and it empties sooner. It's simple arithmetic, and skipping the arithmetic is how a robot dies two feet from the finish."

She pointed at a robot stranded mid-floor. "That one had a great plan — cross the room, grab the ball, come back. But nobody added up the draw. So here's how I do it: I list every part, measure its current draw, and multiply by how long each part is actually on — that's the duty cycle. The motors run the whole trip; the gripper only fires once; the lights only need the dark stretch. Sum those, and I get the total energy the mission spends. Then I compare it to the battery's capacity — and I never let the plan use the whole battery."

"Why not all of it?" a young builder asked.

"Reserve margin," Charge said. "I keep maybe twenty percent in the tank, because the real world always costs more than the plan — a longer path, a stuck wheel, a cold battery that gives less than its rating. And there's a nastier failure than simply running flat: brownout. When too many thirsty parts fire at once, the voltage sags below what the brain needs, and the robot doesn't stop cleanly — it resets, or behaves erratically, mid-task. So the motors and the brain can't just share one rail thoughtlessly."

She held up two options. "When the budget doesn't fit, most people reach for a bigger battery. But you can also trim the spending. Dim the lights when it's not dark. Slow the motor on the easy stretch — power rises steeply with speed, so a slightly slower robot lasts far longer. Turn off the radio between messages. Spend where it matters; save where it doesn't."

"So I plan the power, not just the plan," the builder said slowly, "or it quits at the worst moment."