== Installation
- EasyMotor needs to be rigidly attached in the airframe, and the
- long axis of the circuit board needs to be aligned with the axis
- of flight. By default, the round beeper on the board should be
- "up" towards the nose cone, and the screw terminal strips should
- be "down" towards the fins and motor nozzle end of the rocket.
+ [WARNING]
+ Firmware versions prior to 1.9.13 used acceleration to detect
+ launch. Starting with 1.9.13, the firmware switched to using
+ pressure to trigger recording. Altus Metrum strongly recommends
+ upgrading all EasyMotor boards to current firmware, the
+ behavior of which is described here.
+
+ EasyMotor needs to be rigidly attached in the airframe, in any
+ convenient orientation.
+
+ === Trigger to Start Recording
+
+ Starting with firmware version 1.9.13, a pressure sensor must
+ be attached, and pressure change is used to initiate and conclude
+ data recording. Pressure and 3 axes of acceleration are recorded
+ for later analysis.
+
+ EasyMotor looks for a 50 psi rise in pressure from ambient to
+ start recording. Recording stops when the pressure drops
+ below 50 psi and shows variation of less than 30 psi for at
+ least 10 seconds. These conditions are intended to capture all
+ actual burn data including anomalies such as "chuffs".
=== Power Switch and Battery
- In addition to the circuit board itself, EasyMotor needs
- a power switch and battery to operate. Unlike most other
- Altus Metrum products, EasyMotor does not work with
- single-cell LiPo batteries. That's because commonly
- available inexpensive pressure sensors need 5V, which is
- more than a single-cell LiPo provides. Any battery that
- provides from 6.5 to about 15 volts should work. Good
- choices are the common 9V alkaline battery, or the very
- small and light A23 12V alkaline batteries.
-
- Because he often mounts EasyMotor to the motor's forward
- bulkhead instead of to the airframe itself, Bdale often
- uses a length of "shooter wire" from an e-match or used
- motor igniter as a power switch, routing the wire out of
- the typical fin can vent hole and using "twist and tape"
- to power up the board. Whatever works!
+ In addition to the circuit board itself, EasyMotor needs
+ a power switch and battery to operate. Like many Altus
+ Metrum products, EasyMotor requires a single-cell LiPo
+ battery, and has an on-board charging circuit. The 5V
+ needed for inexpensive pressure sensors is generated
+ onboard using a switching regulator to boost the voltage.
+
+ Because he often mounts EasyMotor to the motor's forward
+ bulkhead instead of to the airframe itself, Bdale often
+ uses a length of “shooter wire” from an e-match or used
+ motor igniter as a power switch, routing the wire out of
+ the typical fin can vent hole and using “twist and tape”
+ to power up the board. Whatever works!
=== Pressure Sensor
The primary motivation for designing EasyMotor was to have
a reliable way of recording motor chamber pressure during
- flight. To that end, EasyMotor supports attachment of a
- low-cost analog pressure sensor. The board provides 5V
- to power the sensor, and an input for measuring and
+ flight. To that end, EasyMotor supports attachment of a
+ low-cost analog pressure sensor. The board provides 5V
+ to power the sensor, and an input for measuring and
logging the output voltage from the sensor.
The kind of sensor EasyMotor is designed to work with
takes 5V in and has a linear analog output that ranges
from 0.5V at 0 to 4.5V at the maximum pressure supported
- by the sensor. Very inexpensive sensors that have a
- "1/8 NPT" threaded input, a "Buick-style" 3-pin connector,
- and typically ship with a short cable and mating
- connector, are readily available on eBay and AliExpress.
+ by the sensor. Very inexpensive sensors that have a
+ “1/8 NPT” threaded input, a “Buick-style” 3-pin connector,
+ and typically ship with a short cable and mating
+ connector, are readily available through various vendors
+ including Amazon, eBay, and AliExpress.
+
+ These pressure sensors have three wires and sometimes a
+ shield around those wires. The colors of the wires can vary,
+ but typically are red for power, black for ground, and green
+ for the analog output. Hook red to '+5', green to 'PRES', and
+ black to one of the two 'GND' screws on the board. The other
+ 'GND' screw is available for connecting the shield if one is
+ present. This is mostly relevant if you're using the product
+ for static testing on the ground with a longer than usual
+ cable.
To log in-flight chamber pressure, a typical approach
- might be to drill a 1/8" sampling hole all the way
+ might be to drill a 1/8" sampling hole all the way
through the center of the motor's forward closure, then
- drill and tap partially through the closure with a "1/8
- NPT" pipe tap. Fill the touch hole with grease, screw in
- the pressure sensor, and attach the sensor leads to
+ drill and tap partially through the closure with a “1/8
+ NPT” pipe tap. Fill the touch hole with grease, screw in
+ the pressure sensor, and attach the sensor leads to
EasyMotor.
+
+ If you aren't up for machining closures yourself,
+ link:http://lokiresearch.com[Loki Research] sells
+ 54mm and 75mm "experimental bulkheads" with threaded
+ sensor ports that can be used with snap ring cases,
+ and other related mechanical bits and pieces.
projects / fw / altos / blobdiff