Hey All!
I was signing on to update my Goblin build post and saw this post and got side tracked...LOL
I'm new to rocketry too and am still figuring out Open Rocket as well.
I just updated my OR Goblin file last night to compare actual weight vs OR weight after last coat of primer and before paint. (just painted it last night)
Turns out it's almost 10 ounces heaver than OR is indicating...before final scuffing and before paint.
So, I checked to see if I could alter the finish weight to compensate....couldn't find a way to do it, so I calculated the overall surface area of the body, fins and nose cone, all separately so I can add weight at the right percentage in the right places.
When I get a final weight I will then divide the difference in weight between OR and divide it into tiny little pieces and then add it as a "mass" object, renaming it as "paint" (If anyone has a better easier way please let me know!).
Also I weigh EVERYTHING, I use a gun powder scale for the smaller pieces which weighs to 1/10th of a GRAIN.
That's 1/70,000th of a pound!!! Then I convert to ounces for Open Rocket.
I account for the epoxy by weighing each batch after mixing then weigh the remainder after application, and will apply as a "Mass" object in the proper location (re-named "epoxy") if I cant add the mass on the proper part in the proper place during assembly.
For example the epoxy fillets for the fin tabs to motor tube. I took that weight and added it as mass-centered between the mid and aft centering rings.
The weight wont be perfect because you have some epoxy loss that can't be weighed like on the mixing sticks, and wipe-off from the application sticks, but it will get you in the ball park and I like to round UP in weight on anything BELOW the center of gravity and round DOWN on any weight above.
That way the rocket will tend toward being MORE stabile than shown on Open Rocket instead of less.
It seems like a lot of work...but the saying is "Garbage In = Garbage OUT!
Another example is to weigh the forward motor mount CR and then weigh the chute strap hook that mounts to it and add that weight to that CR.
I'm NOT DONE YET, so it won't match the rocket setting on my table since again, I'm not done with painting, and I haven't added the Jolly Logic Chute release, but take a look and see how I try to make it accurate.
I try to make everything in OR be the proper weight and in the proper place....
Garbage in Garbage OUT!!! LOL