EasyMotor

This board is designed for in-flight characterization of research rocket motors. It records chamber pressure and acceleration to an on-board flash memory chip, the contents of which can be downloaded after flight over USB.

Features

User View

  • Data logger storing motor chamber pressure and acceleration
  • supports inexpensive 5V analog output pressure sensors
  • 3-axis 200-g accelerometer
  • On-board non-volatile memory for flight data storage
  • USB for configuration, and data recovery
  • Designed for use with a battery from 9-12V
  • 1.5 x 0.8 inch board

Example Installations

There are lots of ways to mount an EasyMotor board, but since we've been asked, here are a few photos from snap-ring case forward closures machined by Bdale for test flights of EasyMotor. The sensor bodies are 316 stainless with a 1/8 NPT male boss, so the approach chosen is to drill a 1/8 inch touch hole all the way through the closure, then drill and tap 1/8 NPT female threads part way through the closure thickness. The hole gets filled with grease and the sensor screwed in.

The first example is a 98mm snap-ring closure, with the sensor and electronics mounted off-center so a 3/8" all-thread could be used in the center for motor retention in a minimum-diameter-ish airframe. This motor had a small gap between the last propellant grain and the forward closure, so having the pressure sampling port off-center wasn't a problem. The mounting bracket for the electronics was bent from a bit of 1/16" aluminum sheet and screwed to the forward closure with two short 4-40 screws into tapped and drilled mounting holes. Note the use of an A23 12v alkaline battery in a holder on the bracket with the EasyMotor prototype. These batteries are fine for a flight or two, and both they and the little holders for them are cheap on Amazon and make installations like this fairly easy to put together:

This second example is on a 75mm snap-ring closure, and was Bdale's first attempt using 16-gauge steel to bend a mounting bracket that could also be used for recovery harness attachment. Another A23 and holder are taped on the other side of the sensor not visible in this photo:

This example is a refinement of the 16-gauge steel strap used to form a mounting bracket and harness retention point, this time for a 54mm snap-ring closure.
Bdale has flown this setup several times now, and the only down-side is that it obvious takes up a few extra inches of airframe length. Note also the quik-link wrapped in electrical tape to make sure it doesn't flop down and short against any of the electronics in flight. Note also a long piece of shooter wire that gets fed through a vent hole in the airframe as a twist-n-tape power switch.

Artifacts

The firmware for this product is part of the AltOS suite.

This board was designed using lepton-eda and pcb-rnd.

The hardware design files are available from git.gag.com in the project hw/easymotor.

Availability

Prototypes of v2 were built and successfully flown. The initial production run is back from our surface-mount assembler, and testing is underway. We hope to have these available for sale by February 2021.