1 [[!meta title="EasyMotor"]]
4 This board is designed for in-flight characterization of research rocket
5 motors. It records chamber pressure and acceleration to an on-board flash
6 memory chip, the contents of which can be downloaded after flight over USB.
8 This is what a production v3 board looks like:
10 <a href="v3/top.jpg"> <img src="v3/top-thumb.jpg"></a>
11 <a href="v3/bottom.jpg"> <img src="v3/bottom-thumb.jpg"></a>
17 * Data logger storing motor chamber pressure and acceleration
18 * works with inexpensive 5V analog output pressure sensors
19 * USB for configuration, data recovery, and battery charging
20 * Designed for use with a single-cell LiPo battery
21 * 1.5 x 0.8 inch board
23 ### Developer View ###
26 * [NXP LPC11U14](http://www.nxp.com/products/microcontrollers/cortex_m0_m0/LPC11U14FHI33.html) System-on-Chip
31 * 8 12-bit analog inputs
32 * I2C, SPI, async serial
34 * Analog Devices [ADXL375](https://www.analog.com/en/products/adxl375.html) 3-Axis Digital MEMS Accelerometer
37 * on-board USB-based charger for single-cell LiPo battery
38 * low noise 5V switching regulator to power pressure sensor
39 * precision divider with 0.1% resistors to scale pressure sensor
40 analog output to match SOC analog input voltage range
42 * Written mostly in C with some ARM assembler
43 * Runs from on-chip flash, uses on-chip RAM, stores flight data to serial flash
44 * USB serial emulation for "console" interface
46 * [lepton-eda](https://github.com/lepton-eda/lepton-eda) for schematic capture
47 * [pcb-rnd](http://repo.hu/projects/pcb-rnd/) for PCB layout
49 * The hardware is licensed under the [TAPR](http://www.tapr.org) [Open Hardware License](http://www.tapr.org/ohl.html)
50 * The software is licensed [GPL version 2](http://www.gnu.org/licenses/old-licenses/gpl-2.0.html)
52 ## Example Installations ##
54 There are lots of ways to mount an EasyMotor board, but since we've been
55 asked, here are a few photos from snap-ring case forward closures
56 machined by Bdale for test flights of EasyMotor. For launch detection to
57 work, the board must be mounted so the board's long axis is aligned with the
58 axis of flight, and by default the "beeper end" must be towards the nose.
59 Note that these examples all feature earlier versions of EasyMotor that used
60 a different power supply and battery strategy. Don't be confused by that! The
61 production version of EasyMotor uses our standard Altus Metrum LiPo batteries.
63 The body of the pressure sensors used are 316 stainless with a 1/8 NPT
64 male boss, so Bdale's usual approach is to drill a 1/8 inch "touch hole" or
65 sampling port all the way through the forward closure, then drill and tap
66 1/8 NPT female threads part way through the closure thickness. The hole
67 gets filled with grease, and then the sensor screwed in. Since Bdale usually
68 builds airframes that assume the recovery harness can attach to the motor
69 case, several prototype installations depended on the stainless steel sensor
70 body to act as a bolt to attach a bracket that supported both circuit board
71 mounting and recovery harness attachment.
73 The first example is a 98mm snap-ring closure, with the sensor and
74 electronics mounted off-center so a 3/8" all-thread could be used
75 in the center for motor retention in a minimum-diameter-ish airframe. This
76 motor had a small gap between the forward propellant grain and the forward
77 closure, so having the pressure sampling port off-center wasn't a
78 problem. The mounting bracket for the electronics was bent from a bit of
79 1/16" aluminum sheet and screwed to the forward closure with two short 4-40
80 screws into tapped and drilled mounting holes. Note that this early version
81 of EasyMotor used an A23 12v alkaline battery in a holder on the bracket. Those
82 batteries were fine for a flight or two, but dealing with them was a hassle,
83 which is one of the reasons the production was designed to use a LiPo.
85 <a href="photos/IMG_20200905_112722.jpg"> <img src="photos/IMG_20200905_112722-thumb.jpg"></a>
87 This second example is on a 75mm snap-ring closure, and was Bdale's first
88 attempt using 16-gauge steel to bend a mounting bracket that could also be
89 used for recovery harness attachment. Another A23 and holder are taped on
90 the other side of the sensor not visible in this photo:
92 <a href="photos/IMG_20200907_101910.jpg"> <img src="photos/IMG_20200907_101910-thumb.jpg"></a>
94 This example is a refinement of the 16-gauge steel strap used to form a
95 mounting bracket and harness retention point, this time for a 54mm snap-ring
96 closure. Bdale flew this setup several times, and the only down-side is that
97 it obvious takes up a few extra inches of airframe length. Note the quik-link
98 wrapped in electrical tape to make sure it doesn't flop down and short against
99 any of the electronics in flight. Note also a long piece of shooter wire that
100 gets fed through a vent hole in the airframe as a twist-n-tape power switch.
102 <a href="photos/IMG_20201010_142952.jpg"> <img src="photos/IMG_20201010_142952-thumb.jpg"></a>
106 Motor characterization products from Altus Metrum are documented in a manual
107 available in [html](../AltOS/doc/motortest.html) and
108 [pdf](../AltOS/doc/motortest.pdf) formats.
110 The firmware for this product is part of the [AltOS](../AltOS) suite. Test
111 data can be downloaded, plotted, and exported in CVS form using the altosui
112 ground station executable.
114 The current hardware design files are available from
115 [git.gag.com](http://git.gag.com) in the project
116 [hw/easymotor](http://git.gag.com/?p=hw/easymotor;a=summary).
118 For easy reference, pdf snapshots of the files used for production version 3
121 * [schematic](v3/easymotor-sch.pdf)
122 * [pcb artwork](v3/easymotor-pcb.pdf)
123 * [bill of materials](v3/partslist.csv)
127 Version 3 is in production and available for sale.
projects / web / altusmetrum / blob