An IMU is not delivering data

What ArduPilot says:

• PreArm: Accels not healthy
• PreArm: Gyros not healthy

The IMU is the chip that holds the gyros (which measure rotation) and the accelerometers; most boards have two or three. Every one that was found at start-up must keep delivering fresh samples, and there must be at least one. A sensor is also marked unhealthy when it has had read errors since start-up while another has had none. The message says which kind of sensor failed, not which chip.

What to do, most likely first

1. A start-up glitch: the sensor did not come up cleanly this time (cold, damp, a hard power cycle).

   CheckPower off, wait a few seconds, power on. If the message is gone and does not return, that was it.

   FixReboot once. A sensor that fails again and again is not a glitch: go on to the next causes.

2. The board's 5 V supply dips or is noisy, and the sensor resets.

   CheckWatch the board voltage in the ground station while servos move or the video transmitter starts; on USB alone some boards run low.

   FixPower the board from a regulator that holds 5 V under load; feed servos and video from their own supply.

3. The sensor is damaged: after a crash, water, or a board that was overheated.

   CheckThe message returns at every boot, or comes and goes when you tap or flex the board gently.

   FixReplace the flight controller. Do not fly on a board whose IMU drops out, even if a second IMU still works.

Parameters to look at

Where to do it:Firmware Inspector