Tips · Power
Servo jitter: separate power vs shared Arduino 5V
A servo that twitches, resets the board, or refuses to hold angle is often starving for current — not a bad sketch. Split the motor supply from the logic rail.
Hooking an SG90 (or several) straight to the Arduino’s 5V pin feels tidy: one USB cable, one board, done. It works for a light bench demo. Add load, a second servo, or a tendon that binds for a moment, and the rail dips. The MCU browns out, the servo chatters, and “jitter” looks like a software bug.
What the servo actually draws
A hobby servo’s control wire is a low-current PWM signal. The red and brown (or black) wires are the motor and gearbox load. Stall and start currents are far above what a USB-powered regulator likes to share with the microcontroller:
- Idle / light hold — tens to a few hundred milliamps.
- Moving under load — often 500 mA–1 A peaks per small servo.
- Stall or bind — spikes that yank the shared 5V down and reset the MCU.
Separate supply, common ground
Give the servo(s) a dedicated 5–6 V pack or a proper regulated supply sized for peak current. Keep the Arduino on USB or its own regulator. Tie the grounds together so the PWM signal has a return path — without a common ground the servo hears noise and can jitter even with “enough” volts.
A bulk capacitor across the servo supply (near the connectors) helps swallow short current spikes. Do not power a multi-servo hand from the Arduino 5V pin and expect stable code.
A practical rule for builders
- Signal only from the board — yellow/orange wire to a PWM pin; never route motor current through the MCU.
- Motors on their own rail — battery pack or bench supply rated for peaks, not average.
- One shared ground — logic ground and motor ground connected at a single point near the board.
That is why animatronic and mechanism packs treat power as part of the build, not an afterthought. Clean code cannot fix a sagging rail — and a solid supply makes calibration, tendons, and classroom demos look like engineering instead of a reboot loop.