Altimeter cloud: Flight 1855

General flight settings

Forecast pressure

Set this to your local forecast pressure at sea level. This will offer you slightly improved accuracty for your flight, although it's not 100% essential every little helps!

Xcweather.co.uk is a decent place to grab pressures from for your location and time.

1013.2 mbar

Launch detect

This is the altitude above the launch pad altitude where the altimeter will trigger itself into recording / flight mode.

The altimeter keeps a constant average of the pressure while waiting for launch, it uses a simple algorithm and the pre-flight buffers to do this. The most recent 120 samples (~4 seconds) are ignored so your pre-trigger altitude won't effect the ground baseline.

For almost all uses we suggest keeping this on the 25 Meter (~82 feet) default settings. If you want to test your altimeter by throwing it in the air, or are planning a very low flight you may want to lower the setting.

35 meters

Sample ratio

The altimeter runs at 50Hz however you can record every sample or every X samples in order to extend the log time. For example if you set the ratio to 1 it will save 1:1 samples, or if you set it to 3 it will save 1 in 3 samples.

1:5 (hybrid, reduces after apogee)

Max samples

This is the maximum samples the altimeter will log per flight. When it reaches this amount it will stop and save the recording.

18000

Recording stop

This setting is how the altimeter decides to stop recording. You can choose either 450 (~9s) or 900 (~18s) samples stable or it will record until the max samples limit unless you press the BUTTON in Manual stop mode.

The samples stable method waits for the devices altitude not to change for the set number of samples. This is defined by not changing by more than +/- 1.0 meters for 98% of the samples, it's a reliable method to stop the recording after landing within 8-10 seconds (300 sample) or 16-20 seconds (600 sample).

Auto: 450 samples stable (~9s)

Oversampling

Oversampling is a internal setting of the BMP 390 pressure sensor. It is how many samples are taken for each reading. By taking multiple samples for each pressure reading the altimeter reduces noise and increases the resolution of the output.

The sensor can run at 50 samples per second in 4X mode, so we suggest leaving it in this mode as it will offer the highest accuracy.

16x Oversampling

IIR filter

The IIR filter is another internal sensor for the BMP390 pressure sensor. It is a Infinite impulse response filter used to enhance pressure measurement accuracy by reducing noise. It's primarily for smoothing out rapid pressure changes.

We suggest not setting this too high as it will cause delay to changes in altitude if set very high.

COEFF 7

Pressure filter

This filter is a software Kalman filter that runs on the altimeters processor.

The Kalman filter uses a prediction step based on a system model and then a correction step using new measurements to refine its estimate, it creates accurate most certain results from data with noise in it.

Kalman 2 (default)

Lockout change

This is how we detect a lockout. If the pressure changes by this much in a single sample downwards (pressure increase, lower altitude) then it's likely to be a false reading. Multiply the setting by 32 to get the speed in meters per second that it will trigger at.

0.5 meters

Sync sensors

The filters on the pressure sensor can cause it to lag very slightly behind the Accelerometer and Gyroscope data. The Sync sensors option detects how far out of sync these sensors are. It then corrects the Acceleration and Gyroscope readings to match the pressure sensor.

ENABLED (30 samples / 140.00ms)

Orientation

This is the orientation you intend to install the Altimeter in your rocket. It's needed to ensure completly accurate angles and orientation charts and reports. Check out the Manual for more information on this.

Upwards (text up)

IMU filter

The IMU filter, or fusion filter takes the data from each axis of the Gyroscope and Accelerometer to calculate the Pitch, Roll, Yaw and tilt angle from vertical. These filters can build up some discrepency over time so it's important to calibrate your sensors to minimise this.

Madgwick 6-Axis

Launch ALP

This is prevention against accidental launch detection.

With this disabled the launch is based only on pressure and something that creates a low pressure can trigger the flight by accident. For example pulling your nose cone off can even trigger it.

With this enabled the rocket also needs to have seen 8 samples (0.25 seconds) of acceleration above this setting in the last 3 seconds as well as the pressure drop to trigger. There is a backup trigger of 1.05 seconds of altitude being above the launch detect setting too.

There are very few situations where this option would cause issues, so we suggest leaving it on.

1.4G

Launch lock

When enabled, the altimeter locks out recording for a set period after power on to prevent false triggering during setup.

DISABLED

Static temperature

A fixed temperature value used for altitude calculation when the external temperature sensor is disabled or not connected.

15.00 °C

Temp sensor

If an external MT1 temperature sensor is connected, this controls whether it is used for logging only or also for altitude calculations.

DISABLED

Output settings

Arm switch

When enabled, GP6 is a hardware arm switch — outputs and rules are held off until the switch is closed to ground.

DISABLED

Startup lockout

Outputs and rules are blocked for this many seconds after power-on while sensors settle. 0 = off.

None

Launch confirm delay

After launch is detected, outputs and rules won't fire until this many seconds have passed.

—

Altitude floor

Outputs and rules are blocked until the rocket is at least this height above the launch pad.

—

Custom dataset 1

User-defined expression evaluated per sample, available for charting.

—

Custom dataset 2

—

Sensor calibration

Calibration offsets used during this flight.

Gyroscope

X0.210°

Y-0.130°

Z0.130°

Accelerometer

X22.340 mG

Y19.610 mG

Z-4.130 mG

Device settings

Device TAG

A custom name or tag assigned to this device for easy identification.

REDACTED2

Language

The language setting configured on the device.

🇬🇧 English

Shutdown mode

Controls what happens after recording. Standard shuts down normally, Delayed keeps WiFi on for 30 seconds after landing, Stay on keeps the device powered on.

Delayed 30s

LED brightness

The brightness level of the LED indicators on the Mercury. Lower values save battery.

20%

WiFi TX power

WiFi transmit power level. Higher gives better range but uses more battery.

2 dBm (low)

Sleep mode

Controls whether the device enters low-power sleep when idle.

Normal (sleep when idle)

Battery monitor

Monitors battery voltage during the flight.

DISABLED

Cloud group

The cloud group / category this flight is assigned to.

GP6 / GP7 ports

Configuration for the GP6 and GP7 general purpose output ports. These ports can drive pyro channels, servos, or other devices.

Channel 6 mode

ON = HIGH

Ch6 min pulse (µs)

Ch6 max pulse (µs)

Ch6 frequency

0 Hz

Ch6 angle ON

0.00°

Ch6 angle OFF

0.00°

Ch6 on time

0.00s

Channel 7 mode

ON = HIGH

Ch7 min pulse (µs)

Ch7 max pulse (µs)

Ch7 frequency

0 Hz

Ch7 angle ON

0.00°

Ch7 angle OFF

0.00°

Ch7 on time

0.00s

I2C PCA9685 Servo Board

Configuration for the external I2C PCA9685 servo expansion board. This board provides up to 6 additional servo channels.

No I2C servo board was connected for this flight.

Prediction and air brakes

The Mercury can predict apogee while coasting after burnout. These settings control the prediction calculation and optional air brake system.

Dry mass

The total mass of the rocket after motor burnout (dry mass). This is used for the ballistic prediction of apogee altitude. Enter the mass without the motor propellant, or the mass at burnout.

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Drag Cd

The aerodynamic drag coefficient (Cd) of the rocket. This is used with the rocket area to calculate aerodynamic drag during coast. A typical model rocket has a Cd of 0.4 to 0.8. You can find this value from OpenRocket or RockSim simulations.

$tc_not_configured

Reference area

The cross-sectional reference area of the rocket in square meters. This is typically the area of a circle with the body tube diameter. For example a 38mm tube has an area of approximately 0.00113 m².

$tc_not_configured

Gas constant

The specific gas constant for dry air, used in the atmospheric model for altitude and density calculations. The standard value is 287.05 J/(kg·K). You shouldn't need to change this unless you know what you're doing.

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The following settings configure the air brake system.

Air brake enabled

Enables or disables the active air braking system. When enabled, the Mercury will deploy air brakes via the configured servo channel to try and reach the target altitude. Firmware 2.1+ required.

OFF (default)

Servo channel

Which servo output channel the air brake mechanism is connected to. GP6 and GP7 are the two onboard servo headers, I2C channels are for an external servo expander board.

GP6

Deploy speed

The speed at which the air brakes deploy. The Mercury gradually increases the servo angle until the predicted apogee matches the target rather than going full on/off. This setting controls how quickly it ramps up to full braking.

Medium (default)

Target altitude

The target apogee altitude in meters. The air brake system will try to slow the rocket so it reaches this altitude.

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Over shoot %

The percentage over the target altitude to aim for until within 15% of the target. This helps prevent undershooting if the prediction is slightly off early in the coast. For example, with a 1000m target and 5% early adjustment, the Mercury will aim for 1050m until it passes 850m.

$tc_not_configured

Activation altitude

The air brake system activates after burnout, but won't engage until the rocket has reached this percentage of the target altitude. This prevents the brakes from deploying too early when predictions may be less accurate.

20% (default)

Flight 1855

The flight, moment by moment

Stability24.8%Poor

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Apogee, adjusted for conditions

FLIGHT 1855

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Apogee, adjusted for conditions

FLIGHT 1855

BURNOUT

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