Spektrum AS3X vs. SAFE Technology

The Technical

Differences

When operating Horizon Hobby BNF (Bind-N-Fly) aircraft and flybarless helicopters, two stabilization acronyms frequently appear: AS3X and SAFE. While both systems utilize the onboard flybarless receiver to assist pilot input, they operate on distinct control loops and fulfill different flight dynamics functions.

AS3X (Artificial Stabilization – 3-aXis)

Primary Function: Wind and Turbulence Rejection (3-Axis Gyro Rate Control).

AS3X continuously calculates angular rotation rates across Pitch, Roll, and Yaw. When an outside force (such as a wind gust) shifts the aircraft, AS3X applies counter-corrections to maintain the trajectory commanded by the pilot.

SAFE (Sensor Assisted Flight Envelope)

Primary Function: Attitude Limiting & Self-Leveling (Accelerometer Integration).

SAFE builds on top of AS3X by bringing accelerometers into the control loop. It measures absolute tilt relative to Earth's horizon, imposing strict limits on pitch/roll bank angles and returning the aircraft to level flight when sticks are centered.

Technical

Breakdown

1. Sensing Hardware & Control Loops

  • AS3X: Uses 3-axis MEMS angular rate gyroscopes. It tracks how fast the aircraft is rotating around an axis (degrees per second). If stick input is neutral and rotational velocity is detected, it opposes the movement. It has no concept of "up" or "down"—only rotational motion relative to its current position.
  • SAFE: Incorporates 6-axis sensing (combining 3-axis gyros with 3-axis accelerometers). The accelerometers detect gravitational acceleration, allowing the flight controller to calculate absolute spatial attitude relative to ground level.

2. Flight Characteristics & Pilot Input

  • Under AS3X Alone: The pilot retains 100% control over pitch and roll attitudes. You can roll inverted, perform continuous loops, or tilt to extreme bank angles. The aircraft stays at whatever orientation you set until you manually command a change. The feel behind the sticks is uninhibited, simulating a much larger model flying through smooth air.
  • Under SAFE Mode: Control stick positions directly map to target bank and pitch angles rather than rotational rates. Releasing the control sticks commands a 0-degree angle target, causing the flybarless controller to return the model to level flight. Additionally, soft electronic limiters prevent the model from rolling or pitching past defined safety thresholds (e.g., maximum 35-degree roll).
Comparitive

Overview

Feature AS3X Mode SAFE Mode
Primary Purpose Smoothing out wind/turbulence Self-leveling and crash prevention
Sensor Hardware 3-Axis Rate Gyroscopes 3-Axis Gyros + 3-Axis Accelerometers
Self-Leveling No Yes (returns to level when sticks are released)
Bank/Pitch Angle Limits Unrestricted (360° rotation) Restricted (enforces maximum tilt limits)
Aerobatic Capability Full 3D / Inverted flight capable Restricted to upright, limited-angle flight
Pilot Control Feel Direct angular rate response (natural) Attitude-position mapping (self-correcting)
Visual

Reference & Demonstration

Watch this visual comparison detailing how AS3X and SAFE operate across different receiver modes on a 3-way switch:

Summary of

Differences

  1. 1. AS3X (3-Axis Gyro Stabilization):
    • Core Function: Rate Gyro Dampening.
    • Behavior: It measures angular rate of change (rotational velocity) around the Pitch, Roll, and Yaw axes using a 3-axis MEMS gyro.
    • Goal: Counteracts outside disturbances (wind, turbulence, torque turns) to make the aircraft feel like a larger, heavier, perfectly trimmed model.
    • Control feel: Does not limit bank/pitch angles and does not auto-level the aircraft when sticks are centered. If you roll the model upside down and release the stick, AS3X holds that upside-down attitude.
  2. 2. SAFE Mode (Self-Leveling + Envelope Limits):
    • Core Function: Absolute Angle Stabilization & Attitude Control.
    • Behavior: It relies on accelerometers alongside gyros to calculate the aircraft's absolute spatial attitude relative to gravity.
    • Goal: Prevent orientation loss and facilitate easy recovery.
    • Control feel:
      • Angle Limits: Prevents the pilot from pitching or rolling past set thresholds (e.g., max 30°–45° tilt).
      • Self-Leveling: Releasing the control sticks forces the aircraft to immediately return to level flight.