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. Like many Altus
13 Metrum products, EasyMotor requires a single-cell LiPo
14 battery, and has an on-board charging circuit. The 5V
15 needed for inexpensive pressure sensors is generated
16 onboard using a switching regulator to boost the voltage.
18 Because he often mounts EasyMotor to the motor's forward
19 bulkhead instead of to the airframe itself, Bdale often
20 uses a length of “shooter wire” from an e-match or used
21 motor igniter as a power switch, routing the wire out of
22 the typical fin can vent hole and using “twist and tape”
23 to power up the board. Whatever works!
27 The primary motivation for designing EasyMotor was to have
28 a reliable way of recording motor chamber pressure during
29 flight. To that end, EasyMotor supports attachment of a
30 low-cost analog pressure sensor. The board provides 5V
31 to power the sensor, and an input for measuring and
32 logging the output voltage from the sensor.
34 The kind of sensor EasyMotor is designed to work with
35 takes 5V in and has a linear analog output that ranges
36 from 0.5V at 0 to 4.5V at the maximum pressure supported
37 by the sensor. Very inexpensive sensors that have a
38 “1/8 NPT” threaded input, a “Buick-style” 3-pin connector,
39 and typically ship with a short cable and mating
40 connector, are readily available through various vendors
41 including Amazon, eBay, and AliExpress.
43 To log in-flight chamber pressure, a typical approach
44 might be to drill a 1/8" sampling hole all the way
45 through the center of the motor's forward closure, then
46 drill and tap partially through the closure with a “1/8
47 NPT” pipe tap. Fill the touch hole with grease, screw in
48 the pressure sensor, and attach the sensor leads to
51 If you aren't up for machining closures yourself,
52 link:http://lokiresearch.com[Loki Research] sells
53 54mm and 75mm "experimental bulkheads" with threaded
54 sensor ports that can be used with snap ring cases.