Discussion in 'Scratch Built' started by lakeroadster, Dec 27, 2018.
Out of curiosity, what is your workflow for Inventor?
Work flow - the sequence you take through Inventor; from concept through fruition, how do you work through Inventor? Your methodology.
I am not a simulator expert at all. I am however guessing that open rocket simulates your three canted Motors as, well, NOT canted. I expect in real life there will be a loss of efficiency of true forward propelling thrust due to the Cant Angle. Will this significantly effect stability?
Thanks for the input fella's.
That was discussed in some of the previous threads. Yes they aren't canted in Open Rocket, and, yes their thrust would need to be looked at as reduced based on their angle from vertical. Also, if all 3 motors in the canted cluster don't fire that too will affect stability.
Lets be bold. I feel I have done my due diligence. At this point lets leave it up to the Gods of Speed and Gravity.
I've used CAD for years and the method used depends on what your designing.
For model rockets, since I am a scratch builder, I typically make a quick model that is one piece part to visually tweek it to what is visually appealing.
Then I'll run the design concept thru Open Rocket to check for stability issues.
Once the Open Rocket simulations are successful I then go back and create a new model rocket in Inventor, one component piece at a time. I build it just as I would build the actual rocket.
That's the beauty of solid modelling programs such as Inventor. You build the rocket in the computer just as you would in real life. If you're experienced enough, problems that would arise in the actual fabrication / construction phase can be caught during the modeling phase.
Being long in the tooth I originally started my career on a drafting board, then designed equipment for decades using 2d cad. But when solid modeling became available it was a godsend.
I agree. Build time!
I would like to amend a previous comment I made... this rocket would look great in a steampunk motif. But it'll be cool in whatever colors.
LOL, eminently reasonable. Basically what I do, except my models (external blade helis and airbrakers) aren’t sim-able, you are already more diligent than I am, so I try to fly them in an empty field where there is no one to around to worry about (or laugh at me.)
Fascinating! Can you simulate physics in Inventor?
It's more geared towards physics of dynamic mechanisms like linkages or geartrains, but yes, Inventor will do dynamic simulations. I've used it to simulate mechanisms for things like strap-on booster attachment points in the past. It will also do Finite Element Analysis based stress analysis, giving you a sense of how complex shapes will respond and possibly fail under loading.
Far and away the biggest utility of Inventor in rocketry though is the ability to go step by step through the physical structure of a rocket in far more detail than Open Rocket could ever do, and produce ready-to-go files for laser cutting or 3d printing if you have access to those tools, or just cut and drill templates if you're doing all parts by hand.
Inventor doesn't do any kind of CFD modeling, so it's not very useful for CP determination, though it wouldn't be hard to rig up a "cardboard cutout style" approximation (it WILL determine your CG very precisely). Solidworks (similar program) has a built in CFD simulator, which I know people have used to determine centers of pressure on aerodynamic bodies like rockets.
What about autodesk CFD?
Don't have any personal experience with that software, but it seems that should be possible.
Also reading further up this thread for your motivations in asking this question, Inventor dynamic simulation can also definitely apply a time-variant force at each motor mirroring the motor curve to get a sense of the behavior of the canted motors and how they would react, either in a vacuum, or with some approximation of the aerodynamic corrective force applied after deriving it from CFD.
Trying to force Inventor/CFD to do all these simulations is kind of overkill though. Open Rocket is much better for quick approximate functional checks, and Inventor shines in planning out the detailed mechanical structure and fabrication procedures. With hobby products and tools there are always dozens of unknown variables which mean that adding in a good chunk of safety factor is often much more helpful than any increase in simulation quality -- heck, that's true most places in real engineering as well. Lakeroadster's workflow matches my own pretty closely.
Thank you for that! Yes, I’m blown away by his Inventor skills; it just seemed silly, after all that work, to not use it to calculate CP (at a MINIMUM).
Yeah, if you want to go to the trouble to CFD it, you can, but for the purposes of our hobby, the output of Open Rocket or similar tends to be good enough. In industry, CFD and mechanical CAD are really in two different domains so it makes since that they're separated out like that. I studied ME in college and never touched CFD, people who majored in aero barely/never touched CAD.
But doing full CAD models of rocket builds has so much utility beyond what you'd get from Open Rocket and the like. I'm currently in the early planning stages of a scale Delta II with nine functional strap-ons (a nice, simple means of returning to the hobby ), and Inventor's been absolutely essential in planning out all the intricate structures and mechanisms involved. The fact that I then have all the parts ready to go for laser cutting without extra work is a sweet bonus on top.
I predict that every one of your threads from here until eternity will attract folks wanting to talk about your CAD work. If you're so inclined might I suggest one day doing a thread over on the Electronics and Software forum showing how you put together a rocket model with Inventor. Then in the future you can just point folks over there whenever it comes up.
I understand it is some effort to do that. Just a thought.
Back on topic: do you have a concrete plan to start building this thing? I am looking forward to this one, and more than usual I'm looking forward to the eventual flight pics and video.
Great idea Neil..
It's snowing here today.. so I should be able to consolidate the various parts lists and order raw materials from BMS.
I'm slow, it took me about 9 months to build the X-wing...
hiking, biking, snowshoeing, and other stuff gets in the way of Rocketman stuff.
It took me 10 years to build my 1st ground up hotrod... '31 Ford Tudor
And 4 years to build the next one.... '27 Ford Roadster Pickup. I designed the frame and suspension on CAD, had the brackets and components NC torch cut at work and then fit-up, assembled and welded (with my buddy Don's help) everything in my garage.
With a few others thrown into the mix during that time frame too.
It's an exhibition, not a competition. Please, no wagering.
So I'm ready to buy parts and stumbled upon a BMS BNC80BBH nose cone...
so I'm asking for Opinions: Better Mercury or Space X
or Space X
I think the Mercury fits better with the jaggedy aesthetic of the whole thing.
Search your true feelings, Master Lake. and feel the force within you. Plus a BT-80 size Mercury capsule is pretty expensive, I imagine. And what's a Mercury capsule without the hand crafted tower? (Hehe).
That thar is a BT60 capsule, not BT80. A (similar? same?) Gemini Titan nose in balsa is cheap from BMS, no more than the elliptic nose.
Ah, right you are Neil! And the Gemini capsule at BMS is considerably cheaper than the one at erockets. However BMS doesn't have the Mercury capsule in that size, but erockets does, although at considerably more than the Gemini.
Thanks for the comments guys.
Your perspective helps. Sometimes when designing pretty much anything.... if a fella looks at it for too long, any change seems better. When in reality, it's just different.
I went with the erocket Gemini capsule and the rest of the pieces parts from Balsa Machining Services.
I didn't buy any motors though.. buying mail order BP motors and shipping them to ka-ka-cold-cold-Colorado in the winter makes me worry about getting a subsequent visit from the Green Hornets side kick and he's not very fond of rockets.
Cool. I shall now await the build.
Spent some more time today massaging the Open Rocket models of The Lifting Rocket... adding extra mass for various components.
An interesting (to me anyway) twist appeared in the worst case scenario simulation.
If only one of the cluster motor fires a message appears, as follows: "An error occurred during the simulation. Large angle of attack encountered."
Which makes sense. A heavy rocket, with inadequate thrust that is off c/l, kicks over during flight.
Logic and Proportion aren't dead after all.....
The bad news.. if this actually happens.. The Lifting Rocket is DOA. The Gods of Speed and Gravity win yet again.
Man, this is a groovey ride!
Cluster: What about going with 2 motors rather than 3? I like the 3-motor look, but 2 motors may be more reliable for ignition?
I live in the RC rocket glider world, so options for removing ejection charges are critical.
Dynasoar Rocketry has an option for an E motor with no ejection charge.
I also have plugged D booster motors with JB Weld, which has worked well. But a plugged motor is illegal at NAR events, so...…"You didn't see ANYTHING"....
Too bad Estes doesn't make these anymore. NAR certified. I wonder if they ever made a plugged 18mm motor.
After pondering all the comments about using plugged motors vs std delay/ejection I like that running all the motors with ejection will minimize the chance of a lawn dart in the event all motors don't fire at ignition.
The body tube on the lifting rocket is stout due to all the internal couplers, centering rings, fins and strut rods. It also has a considerable amount of volume due to it's long length to dissipate the pressure increase in the event multiple ejection charges fire off at the same time.. P1V1 = P2V2
The NAR certification doesn't carry much weight with me. The Estes E9 motors that routinely CATO are/were NAR certified also. I hope the new management at Estes focuses on bringing Quality Assurance back into the fold as a much higher priority.
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