Altimeter cloud: Flight 1112

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.

999 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.

1 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.

1:1 (50Hz)

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.

12000

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.

8x 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 time

The Lockout time is how long the altimeter should stop making decisions and taking actions if it detects unusual high speed altitude changes that are unexpected.
These false readings can be caused by ejection charges (if the altimeter is in the same compartment as the motor ejection gases) or even when you transition to Mach speeds and can give false readings of altitude changes.

When these events are detected the system enters Lockout for the specified time while it stabalises. This effects things like triggering the output, or calculating other data.

750ms

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.

1.5 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

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.

8.00 °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

Output 1 enabled

Disable or enable the output from being able to turn on or off.

DISABLED

Output 1 trigger

After apogee (altitude)

This method triggers when the altitude drops below the set altitude after apogee is detected.

After apogee (time)

This method triggers the defined seconds after apogee is detected.

After launch (altitude)

This method is activated if/once the altimeter exceeds the set altitude after launch.

After launch (time)

This option triggers the defined seconds after launch is detected.

After burnout (time)

This method triggers the defined seconds after burnout is detected.

After apogee (altitude)

Output 1 time on

This is how long the output should trigger ON state when the rules are met.

2000ms

Output 1 altitude

This is the altitude to trigger at if using a trigger method that works on altitude.

For example if you set this to 75m and After apogee (altitude) for the trigger then the output will turn on at 75m on descent above the launch altitude.

0 meters

Output 1 time

This is the time variable for output triggers that work on time.

For example if you set this to 3 seconds and After apogee (time) as the trigger then the output will turn on 3 seconds after apogee.

0 seconds

Altitude lock

Altitude lock is a safety feature that prevents the output from triggering if the altitude is below this level when the rules are met.

50.00 m

Tilt angle lock

This is another safety feature. It can be used to disable the output if the rocket has gone too far from vertical.

For example if you set the tilt angle lock to 40 degrees then the output will not fire if the rocket is more than 40 degrees from vertical. To disable set this to 0.

0.00 °

Sensor calibration

Calibration offsets used during this flight.

Gyroscope⚠ Gyroscope has not been calibrated

X0.000°

Y0.000°

Z0.000°

Accelerometer

X-29.770 mG

Y-27.110 mG

Z55.880 mG

Device settings

Device TAG

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

Merc8139

Language

The language setting configured on the device.

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.

5 dBm (default)

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)

1000

Ch6 max pulse (µs)

2000

Ch6 frequency

50 Hz

Ch6 angle ON

170.00°

Ch6 angle OFF

10.00°

Ch6 on time

2.00s

Channel 7 mode

ON = HIGH

Ch7 min pulse (µs)

1000

Ch7 max pulse (µs)

2000

Ch7 frequency

50 Hz

Ch7 angle ON

170.00°

Ch7 angle OFF

10.00°

Ch7 on time

2.00s

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.

0.0200 kg

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.

1.000

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.

0.00400 m²

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.

287.05 J/(kg·K)

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.

300.00 m

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.

5.00%

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 1112

The flight, moment by moment

Stability0.1%Poor

About the stability score

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Apogee, adjusted for conditions

FLIGHT 1112

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Apogee, adjusted for conditions

FLIGHT 1112

BURNOUT

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