The power system — two parts
A single rechargeable lithium cell (a couple of dollars) and a DC-DC boost converter (about a dollar). The cell is not a fixed voltage — 4.2V fresh off the charger, ~3.7V most of its life, sagging past 3.2V when empty. The boost board takes whatever the cell is doing and holds the output at the voltage you choose: a steady 5.0V, set with the tiny brass screw. Your robot behaves the same on a full battery as on a nearly empty one.
The 5V rail
Cell + ──▶ boost IN+ Cell − ──▶ boost IN−
Boost OUT (set to 5.0V) = the robot's 5V rail:
rail ──▶ servo red wires
rail ──▶ DRV8833 VM
rail ──▶ ESP32 5V pin
One common ground: cell, boost, driver, ESP32. (always!)Setup order matters: meter the boost board before anything touches its output — they ship set to random voltages, often 9V+, which kills 5V servos instantly. Screw it down to 5.0V, wire the rail, add a slide switch between cell and boost, and charge only with a lithium USB charger board.
What I wish I knew
- Never trust a boost board out of the bag. Meter it, set 5.0V, every board, every time.
- Charging discipline. Lithium charger boards only; don't run below ~3.2V; a puffy or warm-at-rest cell gets retired, no exceptions.
- Brownouts love thin wires. Long, hair-thin jumpers sag right when motors gulp. Keep power wiring short and thick.
- The mAh on the label is fiction. Expect about half; when a cell performs, buy more of exactly that one.
- Put a switch on it. A ten-cent slide switch beats pulling battery leads with your fingers.
⏱ Your 60-second challenge
Meter your boost board straight out of the bag.
Post the out-of-the-box voltage in the YouTube comments before you adjust it — let's see the wildest number anyone gets. Mine was 9.1V.