3 EasyMotor needs to be rigidly attached in the airframe, and the
4 long axis of the circuit board needs to be aligned with the axis
5 of flight. By default, the round beeper on the board should be
6 “up” towards the nose cone, and the screw terminal strips should
7 be “down” towards the fins and motor nozzle end of the rocket.
9 === Power Switch and Battery
11 In addition to the circuit board itself, EasyMotor needs
12 a power switch and battery to operate. Unlike most other
13 Altus Metrum products, EasyMotor does not work with
14 single-cell LiPo batteries. That's because commonly
15 available inexpensive pressure sensors need 5V, which is
16 more than a single-cell LiPo provides. Any battery that
17 provides from 6.5 to about 15 volts should work. Good
18 choices are the common 9V alkaline battery, or the very
19 small and light A23 12V alkaline batteries.
21 Because he often mounts EasyMotor to the motor's forward
22 bulkhead instead of to the airframe itself, Bdale often
23 uses a length of “shooter wire” from an e-match or used
24 motor igniter as a power switch, routing the wire out of
25 the typical fin can vent hole and using “twist and tape”
26 to power up the board. Whatever works!
30 The primary motivation for designing EasyMotor was to have
31 a reliable way of recording motor chamber pressure during
32 flight. To that end, EasyMotor supports attachment of a
33 low-cost analog pressure sensor. The board provides 5V
34 to power the sensor, and an input for measuring and
35 logging the output voltage from the sensor.
37 The kind of sensor EasyMotor is designed to work with
38 takes 5V in and has a linear analog output that ranges
39 from 0.5V at 0 to 4.5V at the maximum pressure supported
40 by the sensor. Very inexpensive sensors that have a
41 “1/8 NPT” threaded input, a “Buick-style” 3-pin connector,
42 and typically ship with a short cable and mating
43 connector, are readily available on eBay and AliExpress.
45 To log in-flight chamber pressure, a typical approach
46 might be to drill a 1/8" sampling hole all the way
47 through the center of the motor's forward closure, then
48 drill and tap partially through the closure with a “1/8
49 NPT” pipe tap. Fill the touch hole with grease, screw in
50 the pressure sensor, and attach the sensor leads to