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Steven88

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Hello. I am trying to get my Loc Big Nuke 3E data entered correctly into Open Rocket before I fly it. I did get the file for my Nuke sent from Loc but of course it is different in weight from how my Rocket ended up being. For example, my avbay has three lipo batteries and two altimeters and is heavy, over two pounds in itself. I was told that instead of inputting EVERY item (such as every screw, battery etc) into the program I could just weigh each section of the rocket, booster, avbay and main and input it into Open Rocket as a unit. However, I don’t see a way to do that. Open Rocket wants to break each piece down individually. Can someone lend me some advice as the best and yet not complicated way of correctly entering my data is so that I can know that my rocket is flight worthy? Thanks in advance
 

Charles_McG

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In the parts tree, if you click on the top most item - might be ‘rocket’ or the name of the rocket - and edit it, you’ll find the mass and Cg overrides.
 

T-Rex

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Since you have the drawing, all OR really needs is total mass and the CG (flight ready with no motor). At that point it will do all the work when you enter a motor. The overrides are as Charles stated above.
 

neil_w

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I was told that instead of inputting EVERY item (such as every screw, battery etc) into the program I could just weigh each section of the rocket, booster, avbay and main and input it into Open Rocket as a unit. However, I don’t see a way to do that. Open Rocket wants to break each piece down individually.
As others mentioned above, you can override the mass and CG of each entire stage, which for a single-stage rocket is a single number.

However, even if you chose not to do that, you still don't need to enter "every screw, battery, etc.". No one does that. Instead, you would enter the avbay as a single "mass object", and enter its total mass.
 

thzero

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However, even if you chose not to do that, you still don't need to enter "every screw, battery, etc.". No one does that.
I do, as I collect the parts. At least that way I have an idea of how much min. it will weigh. As I build it, I weight different build components, and override section weight, cg, etc.
 

neil_w

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I do, as I collect the parts. At least that way I have an idea of how much min. it will weigh. As I build it, I weight different build components, and override section weight, cg, etc.
Well I stand corrected then. :)

I wouldn't guess that is common practice, though; more likely to lump all the avbay parts into a single mass object. In any case, you don't *have* to enter every part like that, but you certainly can if you're happy with the process that way.
 

thzero

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Well I stand corrected then. :)

I wouldn't guess that is common practice, though; more likely to lump all the avbay parts into a single mass object. In any case, you don't *have* to enter every part like that, but you certainly can if you're happy with the process that way.
I would tend to agree tat its likely uncommon practice... :)
 

jrap330

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Does anyone believe RockSim, is easier than open rocket and if yes WHY? Because whe I tried it..I could not find a way to undo a mod I made to an establish design since the SW did not do it correctly. Can you "undo" a change as we use to say with a Windows Program. I keep on getting out and in of the program..not saving changes...a pain and time waste
 

neil_w

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In my brief trial of Rocksim I found it confusing compared to OR... but then again I'm really *accustomed* to the OR way of doing things, so not sure it was fair.
 

caveduck

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If I just want an altitude estimate for motor selection, I just use thrustcurve.org. If I'm going to build an OR sim, I usually put in the major parts accurately and add a couple of mass components for epoxy in the fin can, the avbay (as a single unit), and the tracker bay in the nose. If you're interested in behavior in a crosswind at liftoff (and I am for anything large), you need the moments of inertia to be in the ballpark. Doing a whole-vehicle mass/CG override completely neuters the inertia calcs.
 

jrap330

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Can you input a change.....and SW does not do what you wanted and you need to undo the change without exiting out of the design. I tried modifying an existing Estes File but SW is not implementing the way I want and I cannot undo the change. So I can try again. I have a Estes Sizzler that I made longer , I want to add another body tube. I can add the tube but the fins or motor mounts get move ahead to front of rocket.
 

neil_w

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Can you not reposition the tube to be in front of the other tube? In OR you can do that with a drag and drop.
 

jrap330

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Can you not reposition the tube to be in front of the other tube? In OR you can do that with a drag and drop.
Do know...I tried a drag and drop "ala" windows programs...no drag...no drop.
 

Buckeye

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Does anyone believe RockSim, is easier than open rocket and if yes WHY?
In my brief trial of Rocksim I found it confusing compared to OR... but then again I'm really *accustomed* to the OR way of doing things, so not sure it was fair.
OR essentially copied the look and feel of Rocksim, so I would consider both to be equivalent. They do 90% of the same stuff.
 

Steven88

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As others mentioned above, you can override the mass and CG of each entire stage, which for a single-stage rocket is a single number.

However, even if you chose not to do that, you still don't need to enter "every screw, battery, etc.". No one does that. Instead, you would enter the avbay as a single "mass object", and enter its total mass.
I am trying to figure out if I need to add nose weight to my Loc 3E for flying certain motors. If I just weigh and add each section of rocket individually into OR and don’t specify (such as inside the avbay exactly where the three lipo batteries are located, top or bottom of avbay) won’t my sim be somewhat inaccurate in assessing if I need added nose weight or not? Couldn’t the difference between having batteries in the top versus bottom of the avbay make all the difference on nose weight? I’m not looking to go to lots of extra work, but just something I’ve wondered about? If a few washers mounted to the nose cone make a difference on stability, doesn’t OR need to know where all the other items of reasonable weight are mounted?
 

Nytrunner

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If a few washers mounted to the nose cone make a difference on stability, doesn’t OR need to know where all the other items of reasonable weight are mounted?
Yes, but reasonable approximations can be made. For example, you can simulate your ebay as a Coupler. But when you go to override that coupler, you give it the mass of your whole ebay, and adjust its CG same as the real ebay. Presto, the weight distribution of your ebay is now assessed in the sim.
 

Steven88

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Yes, but reasonable approximations can be made. For example, you can simulate your ebay as a Coupler. But when you go to override that coupler, you give it the mass of your whole ebay, and adjust its CG same as the real ebay. Presto, the weight distribution of your ebay is now assessed in the sim.
Ok how do I find the CG of my actual ebay? Balance it from a string and enter that point of measurement into OR?
 

Nytrunner

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Ok how do I find the CG of my actual ebay? Balance it from a string and enter that point of measurement into OR?
I'd use something like the spine of a piece of angle iron/aluminum.

Or a ruler if it's a small bay like BT 60 or something like that
 

Handeman

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I usually finish the rocket. Load it up flight ready, minus the motor and get the weight and CG of that. I then over ride the whole rocket a with weight and CG and then look at stability with the smallest and largest motor that will fit in it. If needed, add any nose weight from there and you can fly anything.

Trying to do individual parts or assemblies is just too much trouble and too susceptible to errors IMO.
 

rklapp

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Is there an ebay in RS that’s not in OR?

My understanding is that the CG of the ebay is not unimportant if the CG and weight of the entire rocket is entered.

Weighing each component is important during the design phase but unnecessary after assembly since it extremely difficult to unglue parts.
 

Steven88

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Not sure what I’m doing wrong on OR. My rocket ready to fly with out the motor will weigh around 6532 grams. My CG comes in at 127 cm. However, when I override the mass and stick an L850 engine in it, it shows that for it to be stable, I’d have to add enough weight to the nose to move the CG to 112 cm. Even if I add a whole lb of weight to the rocket and override it again it only helps move the CG back by one cm. That can’t be right. That will take a ton of nose weight to accomplish that. Any ideas on what I’m doing wrong?
 

Steven88

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The above is for a stability margin of 1
 

Steven88

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OR shows that the way I have my Big Nuke 3E built it is only stable with a J motor at close to 1 cal without changing the CG or adding weight
 

neil_w

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As always: posting the file will help us help you. My guess is it's the exact way you're adding weight and overriding is not quite right.
 

Steven88

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Ok. I’ll send the file over in a minute if I can figure how :)
 

neil_w

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Just attach the file to your reply.
1594604400279.png
 

neil_w

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Suggest you save it as an ORK file if you have any motors configured for it.

I'll take a look in the morning.

My expectation is that you're trying to change nose weight while the entire rocket is overridden... in that case, it'll not have any effect. Tomorrow I'll show you how to deal with this correctly if someone else hasn't already jumped in before then.
 

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