Rangefinder Ground Clearance (GNDCLEAR)

Description

GNDCLEAR tells the autopilot how high the Lidar sensor is sitting when the drone is on the ground.

When the drone is stationary on its landing gear, the Lidar reading isn't zero (because the sensor is usually a few centimeters off the dirt). This parameter allows the flight controller to subtract that height so that the reported "Altitude" is exactly zero on the ground.

Tuning & Behavior

• Default Value: 10 cm.
• Recommendation: Measure the distance from the sensor face to the floor and enter it here.

Rangefinder Address (RNGFND1_ADDR)

Description

RNGFND1_ADDR sets the unique identifier used to communicate with the sensor over a digital bus.

• For I2C sensors: This is the 7-bit I2C address (e.g., 0x62 for LIDAR-Lite).
• For DroneCAN sensors: This is the Node ID assigned to the sensor.
• For Serial/Analog sensors: This parameter is generally ignored.

Tuning & Behavior

• Default: 0 (Use the driver's default address).
• Setup: Only change this if you have multiple identical sensors on the same bus and have reconfigured one to a non-default address.

Rangefinder Voltage Function (RNGFND1_FUNCTION)

Description

RNGFND1_FUNCTION defines the relationship between the sensor's output voltage and the actual physical distance. This is only used for Analog sensors.

• 0: Linear (Standard). $\text{Dist} = (\text{Volt} - \text{Offset}) \times \text{Scaling}$. Used for most ultrasonic and infrared sensors.
• 1: Inverted. $\text{Dist} = (\text{Offset} - \text{Volt}) \times \text{Scaling}$. Used for sensors where voltage decreases as distance increases.
• 2: Hyperbolic. $\text{Dist} = \frac{\text{Scaling}}{\text{Volt} - \text{Offset}}$.

Tuning & Behavior

• Default: 0 (Linear).
• Recommendation: Check your sensor's data sheet. If the graph of "Distance vs Voltage" is a straight line, use Linear. If it's a curve, you may need Hyperbolic.

Rangefinder Offset (RNGFND1_OFFSET)

Description

RNGFND1_OFFSET provides a linear correction to the distance measurement.

For Analog sensors, this is an electrical offset in Volts (e.g. the sensor outputs 0.2V even at 0cm). For PWM sensors, this is an additive offset in centimeters (e.g. to account for the sensor being mounted 10cm inside the fuselage).

$$ \text{Distance} = (\text{Voltage} \times \text{Scaling}) + \text{Offset} $$

Tuning & Behavior

• Default: 0.
• Calibration: Place the vehicle at a known distance from a wall. If the reported distance is consistently too short, increase the offset.

Rangefinder orientation (RNGFND1_ORIENT)

Description

RNGFND1_ORIENT defines the pointing vector of the distance sensor.

Correct orientation is vital for the EKF and flight controllers to know whether they are measuring altitude (Down), distance to an obstacle (Forward/Side), or height above the vehicle (Up).

• 25: Down. (Most common). Used for altitude hold and precision landing.
• 0: Forward. Used for simple object avoidance.
• 24: Up. Used for ceiling-following or indoor flight.

Tuning & Behavior

• Default: 25 (Down).
• Warning: If the orientation is set incorrectly (e.g., set to Forward when pointing Down), the drone may attempt to "climb" to avoid what it thinks is an obstacle in front of it.

Rangefinder Pin (RNGFND1_PIN)

Description

RNGFND1_PIN sets the Analog Input pin used for Analog rangefinders (Type 1).

• -1: Not used.
• 0-9: Analog Pin Number. (e.g. 0 for A0).
• Note: This parameter is only relevant if RNGFND1_TYPE = 1.

Tuning & Behavior

• Default: -1

Rangefinder Power Save Range (RNGFND1_PWRRNG)

Description

RNGFND1_PWRRNG allows the autopilot to turn off the distance sensor when the drone is flying high.

Some Lidar sensors consume significant power. If you are flying a long-range mapping mission at 100m altitude, but your Lidar only works up to 20m, keeping it active is wasteful. This parameter puts the sensor into a low-power "Sleep" state when the estimated terrain clearance exceeds this value.

• 0: Disabled (Sensor is always ON).
• Value (m): Altitude above terrain at which the sensor sleeps.

Tuning & Behavior

• Default: 0.
• Usage: Set to slightly less than your sensor's maximum effective range.
• Note: This requires the sensor driver to support a low-power mode (e.g. Lightware).

Rangefinder Ratiometric Enable (RNGFND1_RMETRIC)

Description

RNGFND1_RMETRIC calibrates the autopilot's ADC (Analog-to-Digital Converter) behavior for Analog distance sensors.

• 1: Yes (Standard). Most simple analog sensors change their output voltage relative to the 5V supply. If the 5V rail drops slightly, the sensor's output drops too. The autopilot compensates for this by comparing the sensor voltage to the rail voltage.
• 0: No. Use this if the sensor has its own internal voltage regulator and outputs a constant voltage regardless of the input power (e.g. some high-end Lightware sensors).

Tuning & Behavior

• Default: 1.
• Recommendation: Leave at 1 unless your sensor's manual explicitly states it has an internal voltage regulator.

Rangefinder Scaling (RNGFND1_SCALING)

Description

RNGFND1_SCALING calibrates Analog rangefinders (Type 1). It defines how many meters of distance correspond to 1.0 Volt of output.

$$ \text{Distance} = (\text{Voltage} \times \text{Scaling}) + \text{Offset} $$

• Example: If 1V = 1m, set Scaling to 1.0.
• Example: Maxbotix EZ4 outputs ~3.3V at 7m. Scaling ≈ 2.12.

Tuning & Behavior

• Default: 3.0
• Calculation: Measure the voltage at a known distance. $Scaling = \frac{\text{Distance}}{\text{Voltage}}$.

Rangefinder Minimum SNR (RNGFND1_SNR_MIN)

Description

RNGFND1_SNR_MIN defines the "Quality Threshold" for your distance sensor.

Digital rangefinders (like those using DroneCAN) often report the strength of the reflection (SNR). In environments with poor reflectivity (e.g. over tall grass or dark surfaces) or at the very edge of the sensor's range, the data can become noisy and unreliable. This parameter tells the autopilot to ignore any distance reading if its quality score falls below this limit.

Tuning & Behavior

• Default: 0 (Trust all data).
• Recommendation: If you see your altitude "flickering" or jumping when the drone is high up or over difficult terrain, increase this value to 10 or 20.
• Note: Setting this too high will cause the rangefinder to "drop out" (status 0) even when it might still be reporting valid data.
• Context: This is primarily used by DroneCAN/UAVCAN rangefinders.

Rangefinder Stop Pin (RNGFND1_STOP_PIN)

Description

RNGFND1_STOP_PIN allows ArduPilot to turn the rangefinder sensor ON and OFF dynamically.

This is primarily used to save battery power or to prevent the sensor from producing noisy signals when the vehicle is flying too high for the sensor to work (Out of Range).

• -1: Disabled (Sensor is always ON).
• 0-103: Physical GPIO pin number used to control the sensor's enable/stop line.

Tuning & Behavior

• Default: -1.
• Usage: If a pin is configured, the autopilot will set the pin HIGH to enable the sensor and LOW to disable it when the estimated altitude is well beyond the sensor's maximum range.

Rangefinder Type (RNGFND1_TYPE)

Description

RNGFND1_TYPE enables the primary altitude/distance sensor.

• 0: None. Disabled.
• 1: Analog. Voltage-based sensors.
• 2: Maxbotix I2C.
• 4: PulsedLight I2C. (LIDAR-Lite).
• 10: MavLink.
• 15: TFmini. (Serial).
• 24: DroneCAN.

Tuning & Behavior

• Default: 0
• Reboot Required: Yes.
• Setup: After setting the type, you must reboot, then configure RNGFND1_MIN_CM and RNGFND1_MAX_CM.

Wasp-LRF Multi-Pulse Average (RNGFND1_WSP_AVG)

Description

RNGFND1_WSP_AVG improves the accuracy of the Wasp-LRF laser rangefinder.

In this mode, the sensor fires a quick sequence of laser pulses and averages the results before sending a single distance value to the autopilot. This helps filter out "Outliers" or noise caused by dust, rain, or difficult surfaces.

• Higher Value: More accurate, but reduces the effective update frequency.
• Lower Value: Faster updates, but more sensitive to noise.

Tuning & Behavior

• Default: 2.
• Recommendation: Leave at 2 for general flight. Increase to 5 or 10 if you are performing slow-speed precision tasks (like automatic docking) where accuracy is more important than speed.
• Dependency: Only active if RNGFND1_TYPE is set to 18 (WASP-LRF).

Wasp-LRF Baud Rate (RNGFND1_WSP_BAUD)

Description

RNGFND1_WSP_BAUD sets the UART speed for the Wasp-LRF laser sensor.

• 0: Low Speed (115200). Standard for most telemetry ports.
• 1: High Speed (921600). Required if you are using extremely high update frequencies (>1000 Hz).

Wasp-LRF Measurement Frequency (RNGFND1_WSP_FRQ)

Description

RNGFND1_WSP_FRQ controls how many times per second the Wasp-LRF laser rangefinder takes a distance measurement.

This is a hardware-specific parameter for the WASP-LRF sensor. A higher frequency provides more data for the autopilot to filter, which is useful for high-speed terrain following.

Tuning & Behavior

• Default: 20 Hz.
• Maximum: Up to 10,000 Hz (if supported by the sensor and communication baud rate).
• Dependency: Only active if RNGFND1_TYPE is set to 18 (WASP-LRF).

Wasp-LRF Moving Average (RNGFND1_WSP_MAVG)

Description

RNGFND1_WSP_MAVG defines the window size for a smoothing filter inside the Wasp-LRF sensor driver.

A higher number of samples in the average leads to more stable altitude readings but introduces a small amount of latency (lag) as the drone moves vertically.

Wasp-LRF Median Filter (RNGFND1_WSP_MEDF)

Description

RNGFND1_WSP_MEDF enables a Median Filter, which is excellent at removing "Spikes" from the data.

Unlike a standard average, a median filter picks the middle value in a set. This ensures that a single bad reading (e.g., a laser reflection from a leaf or a piece of dust) doesn't cause the altitude estimate to jump.

Wasp-LRF Sensitivity Threshold (RNGFND1_WSP_THR)

Description

RNGFND1_WSP_THR controls the "Gain" of the laser receiver.

• Higher Value: Higher sensitivity. Can see farther or over darker surfaces, but more prone to false readings from fog or dust.
• -1: Automatic threshold adjustment.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Bus address of sensor

Note: This parameter functions identically to RNGFND1_ADDR.

Rangefinder function

Note: This parameter functions identically to RNGFND1_FUNCTION.

rangefinder offset

Note: This parameter functions identically to RNGFND1_OFFSET.

Rangefinder orientation

Note: This parameter functions identically to RNGFND1_ORIENT.

Rangefinder pin

Note: This parameter functions identically to RNGFND1_PIN.

Powersave range

Note: This parameter functions identically to RNGFND1_PWRRNG.

Ratiometric

Note: This parameter functions identically to RNGFND1_RMETRIC.

Rangefinder scaling

Note: This parameter functions identically to RNGFND1_SCALING.

Rangefinder stop pin

Note: This parameter functions identically to RNGFND1_STOP_PIN.

Rangefinder type

Note: This parameter functions identically to RNGFND1_TYPE.

Rangefinder Low-Pass Filter (RNGFND_FILT)

Description

RNGFND_FILT smooths the "Jitter" from your distance sensor.

Many rangefinders (especially ultrasonic or low-cost Lidars) produce noisy data that can bounce around by several centimeters even when the drone is stationary. This filter removes that high-frequency noise to provide a stable altitude for the flight controller.

• Higher Frequency: More responsive to rapid terrain changes, but more "jittery" altitude hold.
• Lower Frequency: Very smooth altitude, but the drone might react slowly to a sudden obstacle or drop in terrain.

Tuning & Behavior

• Default: 0.5 Hz.
• Recommendation: Leave at 0.5 Hz for most sensors. If your drone is "bobbing" up and down rapidly while using the rangefinder, try lowering this to 0.25 Hz.
• Disabled: Setting this to 0 disables the filter (raw data is used directly).

Distance (in cm) from the range finder to the ground

Note: This parameter functions identically to RNGFND1_GNDCLEAR.

Enable Rangefinder (Phase Specific) (RNGFND_LANDING)

Description

RNGFND_LANDING is the master switch for integrating distance sensor data into the Plane and QuadPlane flight logic.

Even if a rangefinder is configured and reporting data, ArduPilot will not use it for altitude control during landing or takeoff unless this parameter is set. This provides an safety layer, allowing pilots to verify sensor health before trusting it for critical landing maneuvers.

• 0: Disabled. Rangefinder data is logged but ignored for flight control.
• 1: Enabled. Used for landing approach, final flare, and VTOL assist.

Tuning & Behavior

• Default: 0.
• Safety: Only enable this after verifying that your rangefinder reports accurate distances and doesn't "glitch" or drop out while the vehicle is in motion.

Rangefinder Landing Orientation (RNGFND_LND_ORNT)

Description

RNGFND_LND_ORNT tells the landing controller which way the "Ground" sensor is facing.

• Standard Plane/Copter: Set to 25 (Pitch 270 / Down).
• Tailsitter (Landing on tail): Set to 4 (Back).

Tuning & Behavior

• Default: 25 (Down).
• Significance: If you have multiple rangefinders (e.g. one pointing forward for obstacle avoidance and one pointing down for landing), this parameter ensures the landing logic only listens to the downward-facing one.

RNGFND_MAX_CM: Rangefinder maximum distance

Description

Maximum distance in centimeters that rangefinder can reliably read.

Values

• Units: cm
• Increment: 1
• Default: 700

Description

This parameter defines the "Range Limit" for the rangefinder.

• Function: Any reading above this value is ignored. If the sensor reports a value higher than this, ArduPilot treats it as "Out of Range" (e.g., looking into clear sky).
• Usage: Set this to slightly less than the maximum distance listed in your sensor's datasheet to ensure high reliability. If your sensor is rated for 10 meters, setting this to 900 (9m) can prevent the autopilot from acting on weak, noisy signals at the edge of the sensor's capability.
• Altitude Limit: If the drone flies higher than this altitude, the EKF will stop using the rangefinder for terrain following or precision landing and switch back to Barometer/GPS altitude.

Rangefinder Max Update Rate (RNGFND_MAX_RATE)

Description

RNGFND_MAX_RATE acts as a "Data Limiter" for your distance sensor.

While high-end Lidars can report data hundreds of times per second, sending all that data over a CAN or MAVLink network can cause congestion (too much traffic). This parameter ensures that the sensor node only sends a fresh measurement at this maximum frequency, keeping the network efficient.

• 0: No limit (Send as fast as possible).
• 50 (Default): Sufficient for most navigation and landing tasks.

Tuning & Behavior

• Default: 50 Hz.
• Recommendation: Leave at 50 for most setups. If you have multiple distance sensors on a slow CAN bus, you might reduce this to 20 to free up bandwidth.
• Note: This is primarily used on AP_Periph CAN nodes.

RNGFND_MIN_CM: Rangefinder minimum distance

Description

Minimum distance in centimeters that rangefinder can reliably read.

Values

• Units: cm
• Increment: 1
• Default: 20

Description

This parameter defines the "Blind Spot" of your rangefinder.

• Function: Any distance reading reported by the sensor that is less than this value will be ignored by the autopilot and treated as "Out of Range."
• Why it matters: Most Sonar and Lidar sensors have a physical limit where they cannot distinguish between zero distance and a very close object. If this value is set too low, the drone might think it is at ground level while still several inches in the air, leading to a premature motor cut or a hard landing.

Rangefinder Position Offset (RNGFND_POS)

Description

RNGFND_POS (often appearing as RNGFND1_POS_X/Y/Z) tells the autopilot exactly where the sensor is mounted on the frame.

Correctly setting the Z-offset is particularly important for landing. If the sensor is mounted 10cm below the center of gravity but this is set to 0, the EKF will think the drone is 10cm higher than it actually is, potentially causing a hard landing.

• X: Positive = Forward.
• Y: Positive = Right.
• Z: Positive = Down.

Tuning & Behavior

• Default: 0.
• Measurement: Measure from the flight controller (center) to the face of the sensor.

Rangefinder Minimum Signal Quality (RNGFND_SQ_MIN)

Description

RNGFND_SQ_MIN defines the "Certainty Threshold" for your distance measurements.

Many sensors (especially acoustics/sonars used in ArduSub) report a confidence level or signal quality. If the return signal is weak (due to bubbles, silt, or extreme angles), the sensor may report a "Confidence" percentage. This parameter tells the autopilot to reject any measurement if the sensor's own confidence is below this value.

• 0: Trust all data (Default).
• 50: Reject data if the sensor is less than 50% certain.

Tuning & Behavior

• Recommendation: Set to 50% if you find your depth or altitude readings "glitching" in difficult environments.
• Context: This is functionally similar to RNGFND1_SNR_MIN but uses a normalized percentage (0-100) instead of a raw SNR value.