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OpenRocket 0.9.3

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stickershock23

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Has anyone used this freeware?

I am working on a design, and it has 4 canted motors, I cant seem to find a way to do that in the sim..

Anyone have any suggestions. other than Rocsim? LOL

unless there is someone with rocsim that would like to do a sim for me..
 

Handeman

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I haven't used the freeware, but if you provide a link, I would like to.
 

stickershock23

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I haven't used the freeware, but if you provide a link, I would like to.
Micro gave the correct link.

Its a really good program (for free) Not as many toots and whistles as ROCSIM.

If you are just looking to find you CP CG on an unprovved design, or an approx altitude its perfect.
 

stickershock23

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so does anyone know the answer to my first question?

Can you do canted motors? and how..
 

lkal32

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Mark,
I dont think OpenRocket does canted motors and Rocksim will not either (Rocksim Pro, however, will - but itll cost you a thousand bucks...)
 

stickershock23

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Mark,
I dont think OpenRocket does canted motors and Rocksim will not either (Rocksim Pro, however, will - but itll cost you a thousand bucks...)

OUCH. I think my best guess is good enough LOL

I imagine it really wont change stability or CP if I sim them NOT canted, the only difference I might see would be the final altitude and of course if not all 4 motors light.
 

stickershock23

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JAllen

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I don't think you can show the cant angle in RockSim standard, unless you find a way to overlay a 3d model created in another program, in which case, the other model would look better and probably be more detailed anyway negating the need for the RockSim 3D model.
 

bobkrech

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The vertical and horizontal thrust components are obtained by multiplying the measured thrust curves by the cosine and sine of the cant angle respectively.

The vertical thrust correction factors are not large for small cant angles.
5 degrees = 0.996 or -0.4%
10 degrees = 0.985 or -1.4%
15 degrees = 0.966 or -3.4%
20 degrees = 0.940 or -6.0%
25 degrees = 0.907 or -9.3%
30 degrees = 0.866 or -13.4%

For practical purposes, at an angle of 15% or less you can forget about it, and at 20 degrees, it's -1 sigma of the expected deviation of a given motor.

Bob
 

stickershock23

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I don't think you can show the cant angle in RockSim standard, unless you find a way to overlay a 3d model created in another program, in which case, the other model would look better and probably be more detailed anyway negating the need for the RockSim 3D model.

Thats what I was looking for. how to SHOW it. the numbers and calculations are the easy part.
 

KerryQuinn

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I've been working with Openrocket for the past couple weeks. I like the ease of use and flexibility of this program - and I REALLY like the fact that all of the equations behind it, are documented. It is 6-degree-of-freedom so it attempts to account for canted fins, spin, effects of wind and wind turbulence. It does not have tube-fins or other "offset geometry", but does have tools for staging, clustering etc. It is by far the most powerful free tool I've seen.

For comparison, I analyzed a Quest Starhawk on a Quest B-6-4 using Wrasp and Openrocket (when it gets warmer, I'm planning to run some altimeter vs. simulations tests as well - note, that there are a couple of these in the Openrocket documentation already).

My Starhawk is 4FNC, 0.775"dia, 12.7" long and weighs 43g including the motor.

As built in Openrocket, the calculated weight was 40g and the cg was within 0.5" of actual. The differences are (I think) in the plastic "fincan" used on the starhawk which I attempted to simulate using a plastic "tube" in Openrocket.

In Openrocket you choose the actual RMS surface finish in mils (it provides some estimates, such as 2.3 mils is "smooth paint"). I chose "smooth paint" for this comparison. In Wrasp, you instead choose a single Cd value. In the past I've found the best comparison between my A & B motor powered rockets in Wrasp using 0.9 as a Cd so that is what I used here.

Here are the results of these two runs:


OpenRocket___Wrasp (Cd=0.9)
779 ft________796 ft_______max alt.
6.08 sec______6.4 sec______time to peak
319 ft/s_______322 ft/s_____max velocity
929 ft/s-s_____1092 ft/s-s___max accel
749 ft________755 ft________alt at chute deploy
51 ft/s________54 ft/s______vel. at chute deploy
80 ft/s________62.6 ft/s____vel. at launch rod tip


These results seem pretty darn close to each other, to me.

The effect of choosing the Cd in Wrasp is pretty important to peak alt.
For the starhawk....

Openrocket 779 ft
Wrasp (Cd=0.9) 796 ft
Wrasp (Cd=0.8) 844 ft
Wrasp (Cd=0.7) 900 ft

Of course it isn't worth much to say one analysis is close to another analysis - the proof is in how well any analysis matches the real world, but I have a "comfort level" with Wrasp after the past year of flying it against my HowHigh Altim, so it is good to see that Openrocket is giving similar results.

-Kerry
 

stickershock23

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I have to agree Kerry, For the price you can't touch it. it does 99% of what I need.

Of course I am more of a seat of the pants builder / flier, but when you want to know if something is going to be stable. and about high its going to go It seems to do really well!
 

BEC

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I've tried it a little bit. My test case was modeling a Balsa Machining Service School Rocket with the payload section option, carrying a How High altimeter aboard, then comparing results. I was able to fly the rocket and altimeter last weekend with five different engines and can report that the OpenRocket simulations' peak altitudes were within a few percent on the B motors but further off on the As. I need to try to figure out what the difference was. It is pretty good at predicting where ejection will occur for a given delay as well.

I've not used any of the simulators before so don't have a point of comparison, but it appears to be a very useful tool and you surely can't beat the price. I'll be using it with my students next semester when we get to the "design your own rocket" part of my class to weed out the unworkable designs before they commit to cutting parts.
 

Marlin523

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Tim Van Milligan is GREAT about answering questions about the Rocksim program. Check the contact us button on the Apogee website and ask him your question.
 

JDcluster

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Unless you are flying a spool rocket, your CD will be far lower than 0.9
I've back tracked a number of rockets down to around 0.40 or so... Rockets ranging in size from 3" to 5.5" over the course of 10 flights or so.


I've played with Open Rocket, nice program. I just hope they don't get in trouble for copyright infringement; it looks allot like RockSim.



JD



I've been working with Openrocket for the past couple weeks. I like the ease of use and flexibility of this program - and I REALLY like the fact that all of the equations behind it, are documented. It is 6-degree-of-freedom so it attempts to account for canted fins, spin, effects of wind and wind turbulence. It does not have tube-fins or other "offset geometry", but does have tools for staging, clustering etc. It is by far the most powerful free tool I've seen.

For comparison, I analyzed a Quest Starhawk on a Quest B-6-4 using Wrasp and Openrocket (when it gets warmer, I'm planning to run some altimeter vs. simulations tests as well - note, that there are a couple of these in the Openrocket documentation already).

My Starhawk is 4FNC, 0.775"dia, 12.7" long and weighs 43g including the motor.

As built in Openrocket, the calculated weight was 40g and the cg was within 0.5" of actual. The differences are (I think) in the plastic "fincan" used on the starhawk which I attempted to simulate using a plastic "tube" in Openrocket.

In Openrocket you choose the actual RMS surface finish in mils (it provides some estimates, such as 2.3 mils is "smooth paint"). I chose "smooth paint" for this comparison. In Wrasp, you instead choose a single Cd value. In the past I've found the best comparison between my A & B motor powered rockets in Wrasp using 0.9 as a Cd so that is what I used here.

Here are the results of these two runs:


OpenRocket___Wrasp (Cd=0.9)
779 ft________796 ft_______max alt.
6.08 sec______6.4 sec______time to peak
319 ft/s_______322 ft/s_____max velocity
929 ft/s-s_____1092 ft/s-s___max accel
749 ft________755 ft________alt at chute deploy
51 ft/s________54 ft/s______vel. at chute deploy
80 ft/s________62.6 ft/s____vel. at launch rod tip


These results seem pretty darn close to each other, to me.

The effect of choosing the Cd in Wrasp is pretty important to peak alt.
For the starhawk....

Openrocket 779 ft
Wrasp (Cd=0.9) 796 ft
Wrasp (Cd=0.8) 844 ft
Wrasp (Cd=0.7) 900 ft

Of course it isn't worth much to say one analysis is close to another analysis - the proof is in how well any analysis matches the real world, but I have a "comfort level" with Wrasp after the past year of flying it against my HowHigh Altim, so it is good to see that Openrocket is giving similar results.

-Kerry
 

GuyNoir

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I can't seem to find a way to get motors into this program. The limited documentation at SourceForge says to put RASP files into the "datafiles/thrustcurves/" directory.

I can't find that directory.

Can someone point me to it?
 

Solomoriah

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I've played with OpenRocket 0.9.5; it works pretty well for my purposes at present (stability checking, mainly). I've made some suggestions on the related Sourceforge forum... I wish I knew Java better. If it were in Python, I'd be all over it. I'd even relearn C.
 

slogfilet

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You simply cant using a standard rocket program.
Did anyone else love this slight typo? Not poking fun at you lkal, this is quite the linguistic anomaly! :D

In an effort to avoid the appearance of a total hijacking... I've started using the program, and it's pretty promising. It's about as intuitive as RockSim, but without the entire feature set.
 

RocketsNorth

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After reading this thread yesterday I downloaded the latest version. I'm impressed! :) and tired - I was up until 3 this morning "playing" :caffeine:
It's a single Java Runtime file, which runs very well on my WIN7 Centrinio 2 Laptop.
It's pretty basic but powerful from what I've seen so far. It does have a similar look and feel to Rocksim but how much can you really do with a designer/simulator for model rockets???
As others pointed out it's still beta, which means it will only get better. It's open source, which is never a bad thing. And most important for the price (free) you really can't beat it, for doing basic rocket designs (3FNC, 4FNC, or 10FNC). More complex projects are out of it's league for now. :2:
 
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stantonjtroy

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Downloaded/updated to the latest version just the other day. Man I love this. It would be cool if they add a template print feature. :roll:
 

RocketsNorth

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I decided to try a complete design using Openrocket.
I have to say that the basic design was easy once I got the correct dimensions for the NC it was very much like working with an older version of Rocksim or SpaceCAD.

Here's some screen captures of the rocket I'm working on....



:cheers:
 

stantonjtroy

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Good looking design. I used it to model my TLP Standard ARM for the mods I had in mind. The only complaint I could see (and I'm picking serious nits here) is the lack of a comercial parts database. This is no real problem though as nearly all part dimentions are published on the web through numerous sources. This works for me as I frequiently roll my own tubes and scratch fins and cones. Here's the capture of the TLP Standard ARM.

Untitled-1.jpg
 

RocketsNorth

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Good looking design. I used it to model my TLP Standard ARM for the mods I had in mind. The only complaint I could see (and I'm picking serious nits here) is the lack of a comercial parts database. This is no real problem though as nearly all part dimentions are published on the web through numerous sources. This works for me as I frequiently roll my own tubes and scratch fins and cones. Here's the capture of the TLP Standard ARM.
Thanks Troy, I really like your work. And I agree with you on both points regarding the parts database. I'm sure this will be addressed in a future version once it's out of beta.
 
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