83 lines
3.5 KiB
HTML
83 lines
3.5 KiB
HTML
== Installation
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[WARNING]
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Firmware versions prior to 1.9.13 used acceleration to detect
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launch. Starting with 1.9.13, the firmware switched to using
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pressure to trigger recording. Altus Metrum strongly recommends
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upgrading all EasyMotor boards to current firmware, the
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behavior of which is described here.
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EasyMotor needs to be rigidly attached in the airframe, in any
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convenient orientation.
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=== Trigger to Start Recording
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Starting with firmware version 1.9.13, a pressure sensor must
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be attached, and pressure change is used to initiate and conclude
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data recording. Pressure and 3 axes of acceleration are recorded
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for later analysis.
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EasyMotor looks for a 50 psi rise in pressure from ambient to
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start recording. Recording stops when the pressure drops
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below 50 psi and shows variation of less than 30 psi for at
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least 10 seconds. These conditions are intended to capture all
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actual burn data including anomalies such as "chuffs".
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=== Power Switch and Battery
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In addition to the circuit board itself, EasyMotor needs
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a power switch and battery to operate. Like many Altus
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Metrum products, EasyMotor requires a single-cell LiPo
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battery, and has an on-board charging circuit. The 5V
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needed for inexpensive pressure sensors is generated
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onboard using a switching regulator to boost the voltage.
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Because he often mounts EasyMotor to the motor's forward
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bulkhead instead of to the airframe itself, Bdale often
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uses a length of “shooter wire” from an e-match or used
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motor igniter as a power switch, routing the wire out of
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the typical fin can vent hole and using “twist and tape”
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to power up the board. Whatever works!
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=== Pressure Sensor
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The primary motivation for designing EasyMotor was to have
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a reliable way of recording motor chamber pressure during
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flight. To that end, EasyMotor supports attachment of a
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low-cost analog pressure sensor. The board provides 5V
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to power the sensor, and an input for measuring and
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logging the output voltage from the sensor.
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The kind of sensor EasyMotor is designed to work with
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takes 5V in and has a linear analog output that ranges
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from 0.5V at 0 to 4.5V at the maximum pressure supported
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by the sensor. Very inexpensive sensors that have a
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“1/8 NPT” threaded input, a “Buick-style” 3-pin connector,
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and typically ship with a short cable and mating
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connector, are readily available through various vendors
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including Amazon, eBay, and AliExpress.
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These pressure sensors have three wires and sometimes a
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shield around those wires. The colors of the wires can vary,
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but typically are red for power, black for ground, and green
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for the analog output. Hook red to '+5', green to 'PRES', and
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black to one of the two 'GND' screws on the board. The other
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'GND' screw is available for connecting the shield if one is
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present. This is mostly relevant if you're using the product
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for static testing on the ground with a longer than usual
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cable.
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To log in-flight chamber pressure, a typical approach
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might be to drill a 1/8" sampling hole all the way
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through the center of the motor's forward closure, then
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drill and tap partially through the closure with a “1/8
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NPT” pipe tap. Fill the touch hole with grease, screw in
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the pressure sensor, and attach the sensor leads to
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EasyMotor.
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If you aren't up for machining closures yourself,
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link:http://lokiresearch.com[Loki Research] sells
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54mm and 75mm "experimental bulkheads" with threaded
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sensor ports that can be used with snap ring cases,
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and other related mechanical bits and pieces.
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