Real-time measuring and logging of thrust and rotational speed of a rocket engin

Projects General Guidance
1

Real-time measuring and logging of thrust and rotational speed of a rocket engine with Arduino Uno

Hello

I am a mechanical engineering student from Poland working on (hopefully) my graduation paper and, after doing research on the web and in libraries, I decided I need to delve into electronics in order to take measurements which otherwise I could not take.

Being very new to the electronics and on a budget, I have turned my eyes towards Arduino which I have followed before as a great initiative.

The Project

I am building a portable device for which I need a cheap, disposable source of impulse power (which will be translated to linear and rotational motions), and after much consideration I have selected to use a “rocket engine” in form of rechargeable liquid gas reservoir with a nozzle :slight_smile:
I have designed the device, now I need to engineer it - I need to know the values of forces I can achieve with this kind of power source and to plot its function in time (a short time, as the liquid gas has to last only for a few seconds).

What I want to measure:

  1. Thrust derived from force applied to an electronic weigh scale (or just a strain sensor) with frequency of multiple readings per second (the more, the better)
  2. Revolutions per Minute on a thin diameter (2-3mm, shaft like) and a wide one (40mm) with frequency of multiple readings per second
  3. Additionally at one point I will substitute in tests the rocket engine with an electric engine for rotary movement, as I will need sustained and controllable speeds; I will need to control/measure it’s rpm and a/v draw

How I want to measure:

As a base for all this I plan to buy:
-Arduino Uno
-USB A/B cable to send data to PC
-breadboard with cable connectors

  1. One of two:
    -An electronic weigh scale Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
    -or a force sensor Force Sensitive Resistor 0.5" - SEN-09375 - SparkFun Electronics

  2. Hall Effect sensors with neodymium magnets

  3. Brushless Motor with peripherals (brushed ones as easier to control, but I will need a brushless one at later stages of the project):
    -motor Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
    -Electronic Speed Control Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
    -Programming Card http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=2169
    -Lithium-Polymer battery Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
    -Battery Alarm Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
    -Servo Tester Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking

Questions:

  1. Is Arduino Uno able to send recived signals in real time to a log file on my pc trough the USB cable, or do I need to log the file locally on an memory card like with this shield: Adafruit Assembled Data Logging shield for Arduino : ID 1141 : $13.95 : Adafruit Industries, Unique & fun DIY electronics and kits ?
  2. Will Hall Effect sensor give me multiple readings per second?
  3. Will electronic weigh scale/force sensor give me multiple readings per second?
  4. How to measure rpm of a thin shaft (2-3) with hall sensor?
  5. Is my shopping list complete as far as electronics are considered? Wire, soldering equipment and test stand materials(wood, bolts etc) I can acquire locally.

Thank you very much for all the help and guidance I can get :slight_smile:

2

When I think of rocket engines I think of very high rotational speeds - 30,000rpm - 100,000rpm etc.

At those speeds you need a fast counter to measure RPM. By contrast thrust would be child's play.

Before you decide on an Arduino you need to figure out the highest possible frequency reading that you will need.

Also, if you want to measure high RPM you will need to do it with the Arduino's digital pins because the analogue - to - digital conversions are much slower.

You may also find yourself running into problems with data storage - an Uno might not have enough memory. I don't know how fast an Arduino can write to an SD card, but it is quite slow transferring data to a PC.

...R

3

Robin2:
When I think of rocket engines I think of very high rotational speeds - 30,000rpm - 100,000rpm etc.

I understand, but as I have put my "rocket engine" in quotation marks, so are my desired, humble, quantitative values: about 1.000-2.000rpm and about 2 Newtons. I’ll need 15.000rpm ceiling to measure rpm of the electric motor.

Why so low? There will be no combustion chamber, just liquid, technical, nontoxic gasses (n2o,co2...) expanding from liquid to normal pressure- it’s enough for my needs.

Robin2:
Before you decide on an Arduino you need to figure out the highest possible frequency reading that you will need.

All I really need is to see the shape of curve and how it reacts to changes, say different nozzle; hHz, as for hectoHertz would be awesome, or even daHz as for decaHertz :smiley:

4

I'm not sure from your reply whether you have estimated how much data you will need to collect per second in order to decide if the Arduino is capable of doing the job.

...R