The TARS Power System

TARS has a computer that needs steady, gentle power and a set of motors that yank huge, spiky currents, and those two things do not get along. Getting the power system right is the difference between a robot that runs reliably and one that mysteriously reboots every time it moves. The good news is that this is not new territory for you: it is the voltage regulation, careful wiring, and multimeter work you already did when you built your own board in Month 2.

Why the servos and the Pi need separate rails

The single most important idea here is separation. Servos are motors, and a motor pulls a large, sudden gulp of current the instant it starts to move, especially several servos moving at once. The Raspberry Pi, by contrast, is a computer that wants a clean, steady five volts and nothing dramatic. If you powered the Pi from the same rail as the servos, a servo's current spike would sag the shared voltage for a moment, and that dip is enough to crash the Pi or corrupt its memory, which shows up as random reboots and freezes right when the robot moves. So you split the battery into two regulated rails: one at roughly six volts feeding the servos, and a completely separate steady five volts feeding the Pi. Keeping noisy motor power away from sensitive computer power is a fundamental design principle you will meet again and again.

Buck converters are the Month 2 regulator, grown up

A buck converter is a step-down regulator, the exact same job the 7805 did on your DIY board, taking a higher voltage and delivering a steady lower one, but more efficient and, importantly, adjustable. One buck converter takes the battery's twelve volts down to about six for the servo rail, and another regulator supplies the five volts the Pi needs. The adjustable kind has a tiny screw you turn to set the exact output, and you turn it while measuring, never trusting the number printed on the board.

Set the voltage by measuring, then wire it

Here is where your Month 2 multimeter habit protects your hardware. Before you connect anything sensitive, put the meter on each buck converter's output and turn its screw until it reads the target: about six volts for the servos, five volts for the Pi. Do this before the Pi is ever connected, because a converter accidentally set to twelve volts will destroy a Raspberry Pi in an instant, and there is no undo. Setting each rail under measurement, confirming it with your own eyes, is cheap insurance against an expensive mistake. A power switch on the battery input lets you turn the whole robot on and off cleanly, and an optional current sensor can watch how much power TARS is drawing and even shut it down safely if the battery runs too low, protecting both the cells and the Pi.

Respect the battery

TARS runs on a lithium battery, and lithium demands respect. Use the correct charger for it, never short the terminals, keep an eye out for any heat or swelling, and always disconnect the battery before you change wiring. This is the same safety-first attitude you brought to mains wiring in the smart-home month, applied to a different hazard. A robot is not worth an injury or a fire; treat the battery like the serious component it is.

When you finish, re-check both rails one more time with the meter, confirm your polarity, and only then connect the servos and the Pi. If the Pi boots and holds steady while the servos twitch, your power system is doing its job: giving each part exactly the clean power it needs.