RocSim Question

[sandman]

As I have said before I got RocSim V7.04 last weekend.

Where are all the engines?

I thought I loaded all the engines into my program but the 24mm F21 is missing and the old 29mm G25-15 is not to be found.

OK...maybe it's just that I can't find them.

A little help here, please?

 

[teflonrocketry1]

24mm F21W is under A-Econo and the 29mm G25 is under the Aerotech Mfg. heading. Just click on the word "code" top of the column labled code after selecting Show All engines in the Engine Diameter Display. This will sort the motors a to letter and impulse making it easier to find what you want.

Bruce S. Levison, NAR #69055

 

[sandman]

So...how do I get the engine data from EMRR into my program.

I AM computer illiterate.

 

[rkt2k1]

Sandman,

1. First download the specific engine (.ENG) file from the EMMR archive to your computer. (i.e. AT Econjets - Aerotech_Econjets.eng)

2. Either save or copy the engine file to the Rocksim Data directory which is usually located at C:\Program Files\Apogee\RockSim\DATA.

3. From the Apogee programs menu, run the engine compiler. (Compile Engines)

4. Select all the engine files you want to be able to use in Rocksim and add them to the "to be compiled" window to the right.

5. Press the compile button. Program will display status. When completed you can exit.

6. Launch Rocksim, load the appropriate .RKT design file and load one of the new engines in the list.


I believe this compile process is necessary due to differences in how Rocksim handles the data in the file compared to Wrasp, for which the format was originally designed.

Hope this helps!

 

[joepolicy]

You should have a folder under Rocksim called Data. That is where you want to put all of your engine (.ENG) files. There are already a lot in there.

Once you have done this, find the Program folder (also under the RockSim folder) and find the program called COMPENG.EXE. Double Click it to start it up.

You will see a two paned window. On the left side will be all of your .ENG files. You need to select the ones you want and click the Add button. I generally use the Add All button except when EMRR is doing a contest. Nick creates an .ENG file with all the motors that can be used for a contest. Once you have the engines you want on the right side, click the Compile button.

That's it. The next time you go into RockSim, you will see all of the engines you compiled.

The .ENG files are text based and are editable. I usually combine individual engine data files into a master file to help eliminate duplicate engines showing up in RockSim. There are several "all-in-one" files out there that contain multiple engines from various manufacturers.

Last, the compiler blows out the engine list each time you run it. For instance, say you have every engine loaded. But, you decide to enter the EMRR contest. You would load the virtual5.eng file into your Data folder, run the compiler program and only select virtual5.eng from the left hand side and hit compile. When you go back into RockSim, you will only see the "allowed" engines for the contest.

Hope that help!

 

[rkt2k1]

Sandman,

How'd you make out compiling the engines files into Rocksim?

 

[sandman]

Sorry...been kinda in and out today and haven't had a chance to...busy day...family.

I'll give it a shot tomorrow.

 

[rkt2k1]

Sandman,

No worries! I was just excited about being able to help you out for a change! There was another recent thread on the same topic. A link is posted there to the Apogee newsletter which details the process as well.

 

[sandman]

I don't know what my problem is...maybe it's something I just don't see.

To begin with I cannot save any rock sim files I create into "DESIGNS" file.

I can get to and open saved files from the DESIGNS folder but I can't put any into it.

I can save files in a different folder...but not into DESIGNS.

As to the engine file...I cannot seem to open the engine files in the "save to" menu.

Whenever I go to "Save As" all I get is a folder called "ROCSIM" ,which is the main foulder for rocksim and none other.

I'm lost.

 

[n3tjm]

Which version of Windows are you running it on? Are you trying to run it off a networked drive? Sounds to me that folder only has read only permissions set to it.

The eng files go into the DATA folder. Sounds like you don't see it . It should be there... Try rebooting the computer. Have you ever been able to load motors before?

 

[sandman]

I'm running windows XP

I'm not running on any network.

I got the software last Friday so I have to assume it's the latest.

I have been able to save into the "DESIGNS" file but not any more.

There is one thing I did than may have messed things up a bit.

I created a new Desktop folder and put all the Rocsim stuff into that folder rather than have "The Engine Compiler", "RocSim", "Engine Editor" and "Uninstaller" all on my desktop.

Maybe that's the problem.

 

[n3tjm]

Did you just have the icons in that folder on your desktop? Or did you install Rocksim into that folder?

 

[sandman]

I had the icons on my desktop.

Created a new folder and just dragged them into it.

 

[n3tjm]

Icons would not affect the program... unless you copied over the executables from the Apogee folder by mistake... but I doubt that happened....

 

[sandman]

Once I took the icons out of the folder I can "save to" DESIGNS all the files I've created.

Now...let me see if I can deal with the 24mm F21 issue.

 

[sandman]

Thanks guys!

I got everything working!

 

[Rockaholic]

I have another rock sim question:

Sorry if it's a dumb question:

If you do a "mass override" how do you know what CG to use?

If you are doing this for a tube (say 24"), would it be the middle of the tube?
What about for fins and other components.
thanks in advance.

Dave

 

[teflonrocketry1]

For a tube this would be the half way point; same with a rectagular fin. For more complex shapes like nose cones simulate them as a lone part and use the CG the program predicts. For fins mount them to a body tube of minimal diameter (0.002" OD and 0.001" ID) made of balsa (or mass overide set to 0.001 ounces and CG at half length), then use the CG the program indicates for the fin(s).

Bruce S. Levison, NAR #69055

 

[Rockaholic]

Originally posted by teflonrocketry1
For a tube this would be the half way point; same with a rectagular fin. For more complex shapes like nose cones simulate them as a lone part and use the CG the program predicts. For fins mount them to a body tube of minimal diameter (0.002" OD and 0.001" ID) made of balsa (or mass overide set to 0.001 ounces and CG at half length), then use the CG the program indicates for the fin(s).

Bruce S. Levison, NAR #69055

\



Thanks Bruce for the excellent answer.
One more question, suppose you don't know the exact weight of all the components because the rocket has been completed.

Should you a) guess at all the components weight (assuming most are scratch materials or a modified kit e.g. fiberglassed tube)
Or b) determine the CG of the rocket and input that along with a mass override....and if b) how do you determine CG? balance it somehow?

thanks again!
Dave

 

[teflonrocketry1]

(b)!!! Get a piece of kite string and tie a slip knot type loop in one end; slide the loop over the rockets main body tube and gently pull the loop tight to the rocket. Move the loop along the air frame until the rocket balances horizontally. This horizonatal balance point is the CG. Then weigh the rocket and enter the CG position from the nosecone and the weight into the mass override screen.

The weight can easily be determined by making a simple double pan balance. The rocket is on one side, then fill the pan on the other with water until the beam reaches horizontal again. Measure the amount of water required to balance out the rockets weight using an oral medication syringe. The volume of water in cubic centimeters or milliliters is equivalent (to within 0.5%) to the rockets mass in grams.

Bruce S. Levison, NAR #69055

 

[Rockaholic]

Thanks Bruce! I think I got it now.

FWIW, I picked up a (new) Saltner scale on ebay for less than 20 bucks.
It's amazingly accurate.
You can weigh a tube and then prime it and see a measurable difference.

From now on I plan on weighing all components ahead of time and then seeing where all the added weight is coming from during the build.

Dave