Using thrustcurve.org to create new motors

MetricRocketeer

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Hi TRF colleagues,

I have a question pertaining to the most recent issue of Apogee’s Peak of Flight Newsletter (Issue 567, 15 Feb 2022).

Part of that article involves creating a new motor using the EngEdit software that comes bundled with RockSim.

More or less, my RockSim itself works well enough. However, the EngEdit software is quite buggy and the program keeps crashing.

So here is my question, please. Can ThrustCurve.org be used to create a new motor?

Thank you.

Stanley
 
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mikec

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Can ThrustCurve.org be used to create a new motor?
Not really. You can use tctracer to generate a RASP file that can then be uploaded to thrustcurve.

What new motor do you want anyway? For EX, there are other tools that produce RASP files from burn simulations.
 

MetricRocketeer

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Hi @mikec,

Thank you for your response.

I am following the discussion in newsletter article, which requires a very low-thrust engine. Anyway, that's not so much the point of my question. I just wanted to see if I could model any engine without using EngEdit, since that program is causing me so much trouble.
For EX, there are other tools that produce RASP files from burn simulations.

To which tools are you referring, please?

Stanley
 

MetricRocketeer

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The motor file is just a text file that describes the thrust curve. You can create one in any text editor if you follow the format/syntax.
Hi heada,

Well, that's instructive. Could you please give me a reference that shows the correct format and syntax.

Stanley
 

MetricRocketeer

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Hi everyone,

Sorry to be dense, but I still don't understand the last step.

I now understand how to use a text editor to format the data for an engine. You make the header using the correct syntax, and put in the thrust curve using lines of data.

So far, so good.

But then how do I compile -- is that the correct word? -- this data to end up with a motor file to use in OpenRocket?

Thank you.

Stanley
 

heada

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Once you have the file created in the right format and the file is saved as an rse or eng file (check that your OS doesn't automatically add .txt and hide it from you) then you have to load it into the sim software. I've never loaded one into OR but Rocksim has a menu item for it.

And I *think* the major difference between rse and eng files is the eng file can have more data points but its been a very long time since I've compared them.
 

MetricRocketeer

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Hi everyone,

And now I understand that the compiler -- but is that the correct term? -- for the engine data is the EngEdit software that comes bundled with RockSim.

Stanley
 

MetricRocketeer

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Hi everyone,

I now understand that all you have to do is correctly enter the information on the motor file, and you can use any text editor to do that. Then you put tht file into the correct place in OpenRocket. Just as @neil_w states:
The motor files are just text files. If you've entered it all correctly, there's nothing more to do. To get the files into OR: https://www.rocketryforum.com/threads/how-to-add-a-motor-to-openrocket.123622/post-1869147

But RockSim's EngEdit program offers all kinds of enhancements, doesn't it? Things that a simple text file doesn't provide. For example, from the thrust curve, EngEdit automatically calculates all the items that you see right on top of the curve -- average thrust, peak thrust, burn time, total impulse, specific impulse, and mass fraction. There is a lot to be said for that, right?

Or am I waxing too rich about EngEdit?

Thank you for your consideration.

Stanley
 

heada

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If you have the curve, then engedit will do all the work for you for creating the text file. Also, the tools from Thrustcurve.org will do the same. If you don't have the curve, then those tools don't really add much.

If its a certified motor, get the official file/curve and work from that. If it isn't a certified motor, you need to learn how to generate the data points or the curve yourself as part of rocketry research.
 

MetricRocketeer

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You were the one complaining about how buggy it was in the first place.

I'm still not sure what you're trying to do. burnsim, http://www.burnsim.com/ for example, will predict a thrust curve from motor and propellant parameters and output a .ENG file.
Hi @mikec,

First, thank you very much for the burnsim.com reference. I will definitely check it out.

Second, you are correct. I did complain about EngEdit's bugginess, which it does have. However, now that I have learned a lot in the last few days about getting motor files into simulation programs, I have come to appreciate EngEdit quite a lot. To be sure, nonetheless, I wish that it worked more smoothly.

Stanley
 

mikec

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If you're trying to follow the recipe in https://www.apogeerockets.com/education/downloads/Newsletter567.pdf I have to say that I couldn't even figure out for sure what he was trying to do, and if you have to build a special motor file to simulate something as simple as an air start in Rocksim, that doesn't say anything good about Rocksim IMHO. OR doesn't have those limitations as far as I know.
 

MetricRocketeer

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Hi everyone,

In my Post #18, I wrote the following:

"But RockSim's EngEdit program offers all kinds of enhancements, doesn't it? Things that a simple text file doesn't provide. For example, from the thrust curve, EngEdit automatically calculates all the items that you see right on top of the curve -- average thrust, peak thrust, burn time, total impulse, specific impulse, and mass fraction. There is a lot to be said for that, right?"

In response -- and I appreciate all the responses that TRF colleagues contribute -- @heada said this:
Also, the tools from Thrustcurve.org will do the same.

I am now pondering that statement. Could someone please explain how to make ThrustCurve.org do those things.

Thank you.

Stanley
 

JohnCoker

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ThrustCurve.org is mostly a repository for data files for certified motors. It has some tools that help make those files. In the past, manufacturers included a printed thrust curve with the motor itself, and we needed to create the data from that printout. Now, the certification organizations generally publish data and we create files from that.

Tools like EngEdit and ThrustCurve.org's TCTracer and meant to help with the process of getting from a printed thrust curve to a data file, but once you have the data file they're out of the picture. The whole point of the process is to get the .ENG (RASP) or .RSE (RockSim) data file which can be used to simulate your rocket's flight.

The RASP (.ENG) format is the older one and easier to create. It's the format described on ThrustCurve.org. the RockSim (.RSE) file was introduced by RockSim and can contain more details about the motor, such as the exact decrease in mass during the burn. (The RockSim format is not officially documented, but since it's a text format, specifically XML, the OpenRocket guys figured out how it worked when they added support for it.)

Tim created a video on how to use TCTracer, and it's linked from the page:
 
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