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Wireless Rocket Motor Analyzer

Wireless load cell powered device for measuring and analyzing rocket motor performance.

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This project stems from my High Power Experimental Rocket Platform project (https://hackaday.io/project/6381-high-power-experimental-rocket-platform) and allows for accurate measurement and analysis of homemade experimental research motors.

This project is more than just a load cell test set, it measures the thrust of a static motor test and provides numerous details and insight into the functionality of the design.

The microcontroller monitors the current thrust, detects motor ignition and starts logging the data until the burn is complete.

After the static test, information such as burn time, sample statistics, average thrust, total impulse, peak thrust and a motor designation is given immediately without having to be placed into a spread sheet for further post processing.

The individual samples are displayed where they can be copied into Excel to produce thrust graphs with amazing simplicity.

There is now a wireless ignition channel!

  • 1 × Microcontroller Hackaday.io Trinket Pro 5V
  • 1 × HX711 Load Cell Amplifier/ADC
  • 4 × Half Bridge Weight Sensor 50Kg Load Cell
  • 2 × APC220 70cm Wireless Transceiver
  • 1 × 12 Ohm Resistor Current limiter for super capacitor charging
  • 1 × 1N4148 Discrete Semiconductors / Diodes and Rectifier
  • 1 × 5V 1F Super Capacitor For wireless ignition channel
  • 1 × NPN Transistor BC130 Transistor

  • Test Video

    J. M. Hopkins03/22/2016 at 02:45 0 comments

    Here's the video of one of my last static tests, recorded by a local club member.

  • Video Overview

    J. M. Hopkins03/13/2016 at 22:19 0 comments

  • Iteration Two

    J. M. Hopkins10/19/2015 at 01:31 0 comments

    This board is utilizing an INA125P instrument grade opamp. I'm feeding this into a microcontroller with data rates up to 1,000 samples a second. The wireless data rate can't quite keep up if I want to utilize two channels (pressure transducer), so I'll limit it down, and it helps with noise as well.

    Speaking of noise, I'm still not quite happy, really only getting 10bits of good data off the ADC. I might get a dedicated ADC for this reason.

    PCB design won't be finalized until I'm happy with the design.

  • PCB Parts Selection

    J. M. Hopkins10/14/2015 at 23:13 1 comment

    Due to the interest in this project across amateur experimental rocketry community I have decided to create a PCB for this project that others can use for their own wireless analyzers. There are a couple of common questions and suggestions that I'll answer and list below.

    • Wireless Transceiver choices - Some people are not licensed for 70cm work or have their own transceivers they wish to use. I'll insure that the APC220 can be attached or swapped to another transceiver of choice via headers/serial out connections.
    • Adjustable gain - if you want more resolution at smaller thrust levels, adjustable gain will allow this. The drawback is recalibration after a change to gain. This will be via a potentiometer on the PCB.
    • Faster sampling - I'll be utilizing a better microcontroller that will be a 12-bit resolution, but at much faster sampling rate.
    • Choice of excitation voltage - Not all load cells are 5V. A choice of voltages via jumpers will be available.
    • No surface mount components - This is one I don't like, but do understand. Through hole components are way easier to solder. I will insure this is the case for ease of assembly across the community.
    • Open Design - People want to be able to modify and look at everything. I will create the PCBs, and provide schematics as well as source code. This is a project for the community. The boards will be reasonably priced. I will offer to assemble some for reasonable prices as well.

    Parts list looks like this at the moment:

    • INA125P - Instrumentation Amplifier
    • Teensy LC - Microcontroller/ADC
    • APC220 - 70cm Transceiver
    • Capacitors - Decoupling, filtering, and a super capacitor for ignition channel
    • Resistors - Multiple values
    • Transistors - NPN for ignition channel
    • Connectors
    • Power supplies
    • LEDs for power/visual indicators

  • 5 Grain Mid Power Test

    J. M. Hopkins10/14/2015 at 02:57 0 comments

    This motor was my first try at tiny BATES grains for a 3/4" motor. It was 5 x 1.25" grains which from the thrust curve looks like had some initial ignition issues. I'm going to try and develop a decent F class motor for MPR launches.

  • Low Power Motor Test

    J. M. Hopkins10/11/2015 at 20:40 0 comments

    This little motor is made in the hopes of getting my MPR going on sugar. You can see the nice immediate thrust and gentle trail off. After the graph ends is about a .5 second tracking smoke burn which was left off as thrust was negligible.

    I'm really enjoying this analyzer!

  • Static Test - 10 October 2015

    J. M. Hopkins10/10/2015 at 23:47 0 comments

    I was able to complete four static tests today at the sod farm at the local monthly club launch (MDRA).

    I tried two shorter, low KN. longer burn motors and two aggressive high KN burns.

    I was able to close the link from a pretty decent range without issue and acquired some great data.

    This is a graph of one of my high KN 1" diameter motors. Just at one second burn time and a very aggressive burn.

    This second graph is from one of my longer burn new motor designs. Initial KN was way low and it didn't come up to pressure fast enough. I didn't think that thrust would be this affected and will change the design to compensate.

    Overall I'm really impressed with the data.

  • New Mobile Stand and Ignition Channel

    J. M. Hopkins10/10/2015 at 14:53 0 comments

    I made this mobile static test stand for this weekend's club launch for testing a few new motor designs with the new electronics.

    The analyzer now accepts input commands add well. On power on the analyzer goes into calibration mode where for 10 seconds averages the load cell data. It uses this data to set zero and noise values.

    At this point I can send a serial command of "ARM 123456" with the appropriate pin and the unit will arm, ready for the ignition channel to activate.

    I can then ignite with the command "1" (for pyro channel 1) where the motor will light and data from the burn will be streamed to the base station.

    I can also give the "SAFE" command to de-arm the unit.

    The electronics for the ignition channel uses a super capacitor to separate the ignition high current draw from the main electronics and avoids brown outs. The super capacitor is charged through a diode and current limiting resistor and controlled via an NPN transistor.

    An update after this weekend's club launch will follow.

  • Pressure Transducer

    J. M. Hopkins10/08/2015 at 09:12 0 comments

    I recently found a viable source for a 1000PSI pressure transducer that will integrated into this analyzer. This will allow for real-time pressure monitoring and logging simultaneously with thrust. It is shipping from China right now and should be here towards the end of this month.

    This will greatly increase my capability to characterize and design my motors.

    Due to increased interest among the amateur rocket enthusiasts in this project I will probably make a small batch of PCBs and sell kits and/or pre-assembled analyzers for those who are interested for reasonable compensation.

  • First Static Motor Measurement

    J. M. Hopkins10/07/2015 at 02:40 0 comments

    I was able to do an initial test with a real motor. The motor itself sustained an erosive nozzle anomaly (widening the diameter of the choke by twice the original), but it actually showed in the graph which is pretty awesome.

    You can see clearly where the failure occurred.

    Data was available for review literally right after the burn on my cell phone (remote logged into my computer inside) which is just amazing.

    I need to alter the impulse and burn time measurement algorithms, but overall I'm very impressed.

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Discussions

J. M. Hopkins wrote 07/27/2016 at 03:31 point

Thanks!

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petter.olofsson wrote 07/24/2016 at 09:48 point

Beautiful :) Nice idea to display the noise level too

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ArsenioDev wrote 10/07/2015 at 16:04 point

Any time estimate on when the code, schematics and hardware designs will be uploaded? 

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J. M. Hopkins wrote 10/07/2015 at 16:16 point

I've been getting quite a bit of interest from people who want to create one of these.

A bit more adjustment to some of the code is necessary, and then I'll be posting some more details.
As far as the hardware goes I'm going to be adding an onboard ignition channel as well. 
Time frame will be probably next weekend as this weekend's time is already spoken for.
I'll probably be making a PCB with minimal components if interest continues. I'll sell at reasonable price already calibrated for those less able to recreate the project as well.

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ArsenioDev wrote 10/07/2015 at 16:24 point

Well you have one very interested hacker here, I've got a need to test custom engines that i've mixed up and get data from a bunker

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J. M. Hopkins wrote 10/07/2015 at 16:28 point

I've had another individual who needs this up to 5000lbs... If I end up making that one for them I'll have to use a hydraulic press to calibrate it :)

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