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Project Help and Ideas » Model rocket with Nerdkits data loger

November 20, 2016
by scootergarrett
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I got a 3D printer a while back and designed and made a rocket with it capable of caring a micro controller to log data. It tracks acceleration and barometric pressure and stores it on an SD card chip. I have had many launch failures (parachutes burn off, engine nozzle blow out, ...)but finally got everything working and have had 2 successful lunches. Here are the results plotted with the expected result. accel elevation

November 20, 2016
by sask55
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I think this is a very interesting project.

Your first link "rocket" seams to take me to the same image as the second link "chip". I would like to see some images of the rocket itself.

I assume the acceleration spike at the four second mark may be the parachute deploying is that correct? What is the method used to ascertain the altitudes for the launch, GPS, air pressure, radar, visual sightings? Are you using rocket engines that you made or purchasing model rocket engines? What data source did you use to calculate your theoretical data for the launches? Do you have detailed real time thrust/weight data for the rocket engines used? If so where did you get the engine burn data from?

I have done a bit with model rockets in the past. It has been years since I have thought about it. I don't believe this type of technology was available when I and my sons where playing around with it. It looks really neat to me. You have got me thinking I could possibly get my grand kids interested in this, if only they where a bit older I would certainly look into it. There is a wide range of topics and skills that can be explored here. electronics, physics, model design and construction, programing without even considering the somewhat risky business of producing home made rocket engines. Just about everyone liked to see the lift off, even when they failed is some way, it was great fun.

November 22, 2016
by scootergarrett
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Here is the correct link

You are correct about the ejection charge, it seems like it was a second early.

The altitude is from barometric pressure.

I'm using purchased Estes engines.

As for the theoretical data, I wrote my own code that takes published thrust values for the motor and numerically applies Newton's law, the rocket weight doesn't change that much overall during flight so I just assume the weight loss is linear from the initial mass of the engine to the final mass over the entire burn time. I have validated my code with a program called rocket sim (it's a little more advanced at calculating air drag, but the overall error is less than 1%).

November 23, 2016
by sask55
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The theoretical data is quite impressive, closer than I would have guessed was possible. It seams that for some reason the accelerometer zero point has changed by about -2 g's from the before launch steady state to the after touch down steady state. I don't think that there was detailed engine burn thrust vs time data available when I was involved with model rockets , at least I never saw any at the time. Air drag calculations would defiantly be the most challenging part of the theoretical projection data. As I posted earlier there is a tremendous amount of math, physics, coding and hands on rocket construction that can be explored here.

The rocket looks good. thanks for the post.

Darryl

November 23, 2016
by scootergarrett
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My theoretical model assumes the rocket is always pointing directly up, observer frame of reference. In reality after the ejection charge the payload bay is pointing down and moving with constant velocity. Because I zeroed the accelerometer at resting pointing up there is a 2g difference from when it tips over. Also from the acceleration after the rocket lands (spike) there is a constant -1g as the rocket lays on its side.

November 23, 2016
by sask55
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OK! that does explain the reading I am seeing on your charts. I never really gave it much thought. I was thinking about the total value of the three dimensional vector resulting from a three axis accelerometer. Now that I think about it, that would never return a negative number. The fact that the chart indicated periods of negative acceleration is a clear indication that there is a directional component included in the readings.

I have a Keyes-345 3 axis accelerometer that came as part of a CanaKik. I have made a couple of simple setups on a raspberry pi using that accelerometer. It seam to be quite sensitive, robust, easy to use and has very little total mass. It would be an interesting project to try and build my own flight data logger. It could be used on model rockets, drone flights and possibly even air over water propelled plastic pop bottle rockets. My son designed and built a simple but very effective launch pad set up, for water propelled pop bottle launches, the grand kid love it, they design and decorate there own rockets and with a few pumps of the bicycle pump then a pull on the release cord we have a lift off. If I find the time I would like to experiment with building something like you have perhaps centered around a Audrio mini pro.

Did you design and make your data logger board or did you buy it?

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