Questions about OpenRocket (and Rocksim) Simulator

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slothead

Slothead Tom
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I'm not really a beginner in rocketry, but I am a beginner with these simulations. Just to answer the question before it gets asked: I am using OpenRocket because I am too cheap to buy Rocksim.

Now for my questions:
1. I am currently building a Madcow Super DX3 (cardboard version), but I don't see it in the database that comes with the software. Is there a place I can get a model and use it in OpenRocket? And maybe it is there, but I don't know how to fid it in the database.

2. I also don't see all the rocket motors that I would like to "experiment" with (in simulation). Is there a way to get other motor models?

3. Do the OpenRocket and Rocksim applications use the same file formats for rocket models?

Thanks guys.

Tom
 
I'm not really a beginner in rocketry, but I am a beginner with these simulations. Just to answer the question before it gets asked: I am using OpenRocket because I am too cheap to buy Rocksim.

Now for my questions:
1. I am currently building a Madcow Super DX3 (cardboard version), but I don't see it in the database that comes with the software. Is there a place I can get a model and use it in OpenRocket? And maybe it is there, but I don't know how to fid it in the database.

You might find a sim that someone worked up over on rocketreviews (www.rocketreviews.com). However, there's no quality control, and sims I've found there can have some really horrendous errors. Even the worst of them still may be a good foundation to start from (instead of having to work everything up from scratch). My rule of thumb when going there is "Don't Trust... And Verify (everything)". Important thing to remember... Complex shapes are made up from simpler shapes, this is very important for things like nosecones shapes. Break the shapes down into their components and you can get some really incredible results.


Looks like Madcow does offer Rocksim files of the kit on their (https://www.madcowrocketry.com/4-super-dx3/). OpenRocket can open them and save them, but graphics don't save.


2. I also don't see all the rocket motors that I would like to "experiment" with (in simulation). Is there a way to get other motor models?

That's outside of my realm of knowledge. Sorry, I'm no help there.

3. Do the OpenRocket and Rocksim applications use the same file formats for rocket models?

No... OR can open Rocksim and save .rkt files, but the reverse cannot be said.

Thanks guys.

Tom

Not a problem...

Pointy Side Up!
Jim
 
You can always do quick and dirty simulations on https://thrustcurve.org if you don't want the fun of doing the design yourself.

If you want to do the design, measure and weigh all your parts. Design accordingly. The CP estimate will be good if you got the dimensions right; but the CG will need to be measured after you build your rocket, since you will obviously not be weighing things like epoxy, paint, etc. So once it is built, get the actual CG by balancing it, and then override the design.
 
2. I also don't see all the rocket motors that I would like to "experiment" with (in simulation). Is there a way to get other motor models?

Tom
You can add the motors by going to thrustcurve and downloading the motor file and putting it into a directory that OR looks at when it starts up. The directory can be found in the settings of OR.
 
Thanks Jim. I just examined the Madcow Rocksim model and it is way off of what my model looks like. It may have to do with the 29mm motor mount tube (I have a 54mm tube). The MMT is way too short and the coupler tube is also way too short, both of which push the CG much farther forward. I can't use it for my simulation.
 
You can always do quick and dirty simulations on https://thrustcurve.org if you don't want the fun of doing the design yourself.

If you want to do the design, measure and weigh all your parts. Design accordingly. The CP estimate will be good if you got the dimensions right; but the CG will need to be measured after you build your rocket, since you will obviously not be weighing things like epoxy, paint, etc. So once it is built, get the actual CG by balancing it, and then override the design.
Thanks John, that makes a lot of sense.
Where in MD are you?
 
Thanks Jim. I just examined the Madcow Rocksim model and it is way off of what my model looks like. It may have to do with the 29mm motor mount tube (I have a 54mm tube). The MMT is way too short and the coupler tube is also way too short, both of which push the CG much farther forward. I can't use it for my simulation.

Just go to those specific parts and modify the dimensions. You'll likely need to go to the fin set and modify the tab dimensions as well.
 
I'm not really a beginner in rocketry, but I am a beginner with these simulations. Just to answer the question before it gets asked: I am using OpenRocket because I am too cheap to buy Rocksim.

Now for my questions:
1. I am currently building a Madcow Super DX3 (cardboard version), but I don't see it in the database that comes with the software. Is there a place I can get a model and use it in OpenRocket? And maybe it is there, but I don't know how to fid it in the database.

2. I also don't see all the rocket motors that I would like to "experiment" with (in simulation). Is there a way to get other motor models?

3. Do the OpenRocket and Rocksim applications use the same file formats for rocket models?

Thanks guys.

Tom

As far as #1, you can easily build your own rockets in OR or RockSim using the parts databases which are included.
 
Just go to those specific parts and modify the dimensions. You'll likely need to go to the fin set and modify the tab dimensions as well.

If someone can get me a scan of the fins (with a ruler) and other details, I might be able to whip something up (come Sunday (your time), Monday my time (I'm still in the PRC)).
 
If someone can get me a scan of the fins (with a ruler) and other details...
The fins in the model are fairly accurate, it's just the tabs that need to be resized.

What motors are missing from OR? The database should be pretty up to date.
 
The fins in the model are fairly accurate, it's just the tabs that need to be resized.

What motors are missing from OR? The database should be pretty up to date.
I don't recall at the moment. If you really want to know, I can send you what I can't find as I am looking. One of my limitations is that I don't have any certs (and I'm not quite ready to try), so there are a number of the smaller impulse sizes that I am limited to and some of those I didn't see in the database.

Thanks Mike.

Tom
 
For most everything it's a lot easier to just use thrustcurve and not mess with OR at all, as John S mentioned upthread.
 
there is a user's guide to open rocket https://wiki.openrocket.info/User's_Guide
I suggest measuring each part even though Madcow has rocksim files, I've found without exception they are pretty bad. Plus your paint job, glue up, electronics ect will be different then theirs.

Importing motors is easy, download the file from thrustcurve.org and copy it into a folder as described on this page.

https://wiki.openrocket.info/FAQ#How_do_I_add_motors_to_the_database.3F

the folders are C:\Documents and Settings\username\Application Data\OpenRocket\ThrustCurves\ or C:\Users\username\AppData\Roaming\OpenRocket\ThrustCurves depending on which version of windows you have
 
For most everything it's a lot easier to just use thrustcurve and not mess with OR at all, as John S mentioned upthread.

Yes.

Keep in mind that OR and RS are primarily small-scale CAD programs. You need to design the model as the first step. This does enable more advanced physics in the simulator for finer analysis. However, thrustcurve is good enough for most decision making: approximate altitude, picking a safe motor, picking a delay, etc.
 
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