I could use just a little guidance

[JimJarvis50]

So I did a little looking and found references to the BBXI spinning at rates of 2Hz and 5Hz, so not sure what I was remembering. My other payload flew on a Terrier Orion, I have that as spinning up to 6.66 rev/s, with roll frequency crossing the vehicle's pitch frequency very rapidly at 1st stage separation [a big drop in inertia perhaps], and then the spin rate stays above the pitch frequency for the rest of the flight. Fins were canted 55 arcminutes. You might want to peruse MIL-HDBK-762 DESIGN OF AERODYNAMICALLY STABILIZED FREE ROCKETS (17 JUL 1990), I recall it seemed pretty thorough.

br/

Tony

So, I have the document. Looks like a nice, light reading!

Jim

 

[JimJarvis50]

Last Airfest, the evening I gave you the "pixie pellets", We went across to trailer and talked to [can't remember name] guy who had the trailer set up for tracking multiple rocket transmitters/gps [up tp 17 of them at once].

That was Chris (Random Flying Object). Unfortunately, he doesn't speak English.

Topic was spin stabilizing, i think you were lazer focused on your high altitude motor ignition issue and may have forgot.
Anyhow I discussed at length how I was going the route of spin stabilizing my full scale Sparrow-Arcus vs your active method.

I was dreaming about pixie pellets and eating some Cajun something-or-another. Spin? Who needs that - I have a system! It just won't fit in this rocket. I thought we might try something new.

Other issue I wanted to conquer wad the interstage, after 1/3 scale success with spinning, wanted to do I//s like the real deal..requiring a pointed I/S that fits into nozzle of sustainer, like the real sounding rocket. Kurt did same. [but we did not realize that till after his flight was made public]
Thinking it may solve any binding problems spinning may induce...once again, no point in re-inventing the wheel, since this is how the full scale version does it.
The problems and solving of them saved for another time, your issue at hand spinning.

I would prefer to control when the parts separate, but I hadn't considered binding.

MY first stage does NOT spin, only upon separation does the sustainer begin spinning...make things a bit simpler for us.

I'm hoping to use electronics that are imune to roll. If you had that, would you spin from the start?

Here is except from my thread on my journey so far that may help;

I have read much of this in the past, but not the entire thread at once. Great documentation as always.

As a matter of fact if this trend follows up-scaling, there is no need to de-spin [yo-yo] for apogee deploy.

Are you thinking about trying that? Would be a cool project.

Also added weight in NC and careful mounting of gear on center axis balanced to aid in spinning..not coning, is needed. Not that difficult at all.

What is significant about added weight in the cone?

At 1.6 seconds booster burns out [at 1.500 ft], stages separate & sustainer immediately spins up to full speed under coast....26-29 rps.
In 5 sec. of coast, sustainer reaches 5,500ft where ignition occurs sending spin rate up to 36-37 rps.

Did you ever do a plot of spin rate versus velocity? Just curious.

Hope this may start your path to "spinning". I think 5-6 eps is too low for you and the harmonics of your large rocket.

I need to learn how to calculate the pitch frequency. Thanks for taking the time to share your experience. I don't know enought about this stuff to do it without help.

Another Jim

 

[UhClem]

I need to learn how to calculate the pitch frequency. Thanks for taking the time to share your experience. I don't know enought about this stuff to do it without help.

Rocksim can plot the natural frequency, both coupled and uncoupled. This depends on air density and velocity so varies a lot. "Topics in Advanced Model Rocketry" covers the math in gory detail.

 

[Random Flying Object]

That was Chris (Random Flying Object). Unfortunately, he doesn't speak English.

54 68 61 6e 6b 73

 

[JimJarvis50]

01001001 00100000 01110010 01100101 01110011 01110100 00100000 01101101 01111001 00100000 01100011 01100001 01110011 01100101 00100001

 

[Random Flying Object]

01001001 00100000 01110010 01100101 01110011 01110100 00100000 01101101 01111001 00100000 01100011 01100001 01110011 01100101 00100001

8 bit ben DuSaQ

 

[Random Flying Object]

De-spin isn’t so bad if you can afford the mass.

 

[JimJarvis50]

De-spin isn’t so bad if you can afford the mass.

I think it would be very difficult to incorporate in the design we have. But nothing is completely ruled out yet.

By the way, Merry Christmas Chris, exist for many years and do well.

Jim

 

[blackjack2564]

Hmmmm..... "I rest my case"? Now you got me in need of de-spinning...lol

Ps sorry I forgot your name Chris, won't happen again.

 

[Random Flying Object]

No worries, didn’t realize blackjack2564 = CJ.

De-spin = figure skating
If you have volume at your FINAL Cg and can accommodate the mass then go for it.

P.S. I’m working on a 100kft+ mod for the TeleMega/EasyMega that would work nicely for de-spin mass deployment and proper drogue delay.

I just did a tumble analysis on my project at 120kft+ and it looks like me trying to do a cartwheel after a six pack. Spin stabilization definitely has my attention.

 

[jderimig]

Here is my yoyo despinner. Sized for a 3" sustainer airframe. Servo operates the release arm trigger by altimeter event signal. May switch to solenoid to eliminate servo board. System built in to the stack of the sustainer electronics package.

 

[JimJarvis50]

De-spin = figure skating
If you have volume at your FINAL Cg and can accommodate the mass then go for it.

Final Cg is 12" below the top of the motor case.

Jim

 

[jderimig]

Why does the despin need to be at the CG?

 

[Random Flying Object]

Final Cg is 12" below the top of the motor case.

Jim

Let’s make sure our FINAL is the same. After burnout with laundry still in and nosecone still attached.

 

[Random Flying Object]

Why does the despin need to be at the CG?

Just seems like yo-yo could become a real mess off Cg with unknown tumble vectors and center of gyration.

 

[JimJarvis50]

Let’s make sure our FINAL is the same. After burnout with laundry still in and nosecone still attached.

Yes, the motor is quite long.

Jim

 

[jderimig]

Just seems like yo-yo could become a real mess off Cg with unknown tumble vectors and center of gyration.

Yes I see that now. I was thinking the yo-yo lines would cancel out any lateral forces but that's only true if the lines stay co-linear while they unwind.

 

[Random Flying Object]

Yes, the motor is quite long.

JimView attachment 369592

Well, looks like your stuck with an active hydrogen peroxide thruster system for despin.

 

[jderimig]

Well, looks like your stuck with an active hydrogen peroxide thruster system for despin.

Reaction wheel!

 

[Random Flying Object]

Reaction wheel!

Wouldn’t that be very heavy?

 

[jderimig]

Wouldn’t that be very heavy?

Not if you can spin it really fast, high kv outrunner motor and dump all of lipo batteries energy into it. Probably single use on the motor, it will hard to keep it cool with no air moving through it.

Probably won't work. Haven't done the math.

 

[OverTheTop]

Can of WD-40 driving a set of cold-gas thrusters?

 

[TonyL]

A tough part with the stored energy approaches [yo-yo and reaction wheel], is knowing how much angular momentum you need to accommodate. Since Jim has flight data, about 2x the amount of angular momentum it had last time would be a reasonable starting point. The part about needing enough battery to drive the wheel is an important point, along with the need to compensate for friction losses [usually means velocity creep], so the longer you want it to not spin, the more momentum it takes. Spinning up the wheel and then ejecting it would also solve the friction loss problem.


br/

Tony

 

[VernK]

The reaction wheel sounds like it would be a really fun project. Wish I had the time to work on it. A closed loop system could be designed to spin-up the air frame to a desired RPM and hold it there. Then de-spin near apogee. Probably a pretty significant weight plenty though....

 

[Random Flying Object]

A tough part with the stored energy approaches [yo-yo and reaction wheel], is knowing how much angular momentum you need to accommodate. Since Jim has flight data, about 2x the amount of angular momentum it had last time would be a reasonable starting point. The part about needing enough battery to drive the wheel is an important point, along with the need to compensate for friction losses [usually means velocity creep], so the longer you want it to not spin, the more momentum it takes. Spinning up the wheel and then ejecting it would also solve the friction loss problem.


br/

Tony

Is this the “Tony” from IREC?

 

[jderimig]

A tough part with the stored energy approaches [yo-yo and reaction wheel], is knowing how much angular momentum you need to accommodate.

Tony

For the yoyo despin all you need to know is the moment of inertia of the rocket if the goal to reduce to the spin to 0. Only if you want a non-zero spin result is the starting spin rate needed.

https://apps.dtic.mil/dtic/tr/fulltext/u2/260758.pdf

 

[jderimig]

The reaction wheel sounds like it would be a really fun project. Wish I had the time to work on it. A closed loop system could be designed to spin-up the air frame to a desired RPM and hold it there. Then de-spin near apogee. Probably a pretty significant weight plenty though....

I was playing with the math on this awhile ago. If you spin the reaction wheel up when on the pad then the rocket already has angular momentum so you don't need to spin the rocket. A pound of steel cylinder will do it.

But there are other gyroscopic issues that come into play during flight. I thought is was a good idea until a wise fellow rocketeer challenged me with the question is why sounding rockets don't do this?

 

[TonyL]

Random Flying Object, no not that Tony I'm afraid.

jderimig, thanks for the link to that paper! It makes sense now that I read it that mass ratio and line length can suffice. Measuring mass moment of inertia is a little tricky, but I've heard good things about using a torsional pendulum that would lend itself to getting the roll axis pretty accurately. A cad program would probably be sufficient with a good model.

As for why sounding rockets don't do reaction wheels? I would speculate that 1. yoyo is simpler [they already measure mass moment of inertia] for de-spin, and 2. canted fins are simpler for spin. Mechanisms are generally to be avoided if there is a simpler, more robust solution. The gyro effects seem like they would apply whether it is the body or just an inner wheel spinning. An issue for a reaction wheel for generating spin in flight is that the fins will fight it and absorb energy, making it less efficient that using the fins themselves.

WFF does have an attitude control system module that does fin-steered guidance on a spinning Black Brant XI, and then does static attitude after it is de-spun [yo-yo] and exo-atmospheric, but I forget if it is reaction wheels or cold gas.

For HPR de-spin one could run two counter-rotating wheels, spun up from an external supply and then just brake the appropriate wheel [get fancy and charge a battery with it to buy back some energy to spin it back up]. I kind of like that one for compactness.

br/

Tony

 

[0011001100]

I thought is was a good idea until a wise fellow rocketeer challenged me with the question is why sounding rockets don't do this?

Spinning the whole rocket doesn't require extra mass and length unlike using an internal gyroscope that's why.

 

[jderimig]

As for why sounding rockets don't do reaction wheels?

Tony

If you have a non-spinning rocket with angular momentum provided with a spinning mass (gyro) in the axis of the rocket (z-axis), a moment applied about the x-axis will cause a rotation in the y-axis. Gyroscopic effect.

This could happen with off-centered thrust or other unbalanced aerodynamic forces on the airframe. Not sure if this is the reason or not but this is where I left off when analyzing such a system.

You may need 3 reaction wheels to keep the rocket pointed where you want it to.