TAO Finless Sustainer Build Thread

Started making parts for Estes Industries Rocket Plan #128 TAO -- thought I'd invite the TRF along for the swearing and fits of digital-fabrication-derangement-syndrome (that is totally a thing) induced rage.

Fin-can + booster first.


The original plans call for 1/8 inch balsa for the fins. I modeled the fins 3mm thick -- which looks really chunky -- but I wasn't sure about the stiffness of the Amazon Basics PTEG, so I stuck with it. I'll add some details of the modeling and printing in subsequent posts. I am thinking about trying again, with thinner fins.



The original plan was to insert wooden dowels at the top and bottom of the hatch, to engage with holes in the bottom of the booster and the inside surface of the sustainer airframe. When I tried that, it turned out to be too hard to get everything lined up flush and secure. So I printed another version (with a lip at the top of the hatch.


Still uses dowels (wooden tooth picks) at the bottom. I switched out the filament for the red PETG because I wanted to see how my kluged-up filament dryer worked. It doesn't -- so I had to drill some blobs out of the holes where the toothpicks will go.



It fits together well enough, but the inner diameter of the fin can is a just little too small for the Estes BT60 coupler I was planning to use.


I think this will cease to be an issue when I cut away the piece for the hatchway.

Since jquavins, mbeels, and neil_w made me feel bad about printing the simplest of simple nosecones (okay, neil_w wasn't actually, but comments from three forum members makes it seem like a mandate) I spent way too much time watching less-than-useful YouTube tutorials and reading long-out-of-date discussion board threads, trying to figure out how to model a spiral fluted elliptical nosecone in F360.

I finally gave up and made the model in Maya



Slic3r didn't like any of the file formats saved directly from Maya, so it took a trip through F360 to be converted to STL. Pro-tip -- it seems as if the origin for the .obj file exported from Maya is NOT the same as the origin F360 uses to land the imported mesh, Every attempt came in translated a few millimeters over in the x-direction.

The flutes on the printed cone weren't reading as well as they did in the 3D renders. Made a taller, pointier version with a 1.5 rotation twist.




Don't guess that the flutes will do much, aerodynamically, so they need to look maximally cool.

jlabrasca said:

Since jquavins, mbeels, and neil_w made me feel bad about printing the simplest of simple nosecones (okay, neil_w wasn't actually, but comments from three forum members makes it seem like a mandate) I spent way too much time watching less-than-useful YouTube tutorials and reading long-out-of-date discussion board threads, trying to figure out how to model a spiral fluted elliptical nosecone in F360.

Click to expand...

Nothing derogatory meant! Those twists look great, that is an eye-catching nose cone. I bet it would really pop with a contrasting paint scheme. Very nice!

I like your additions (technically subtractions) to nose cone. It will be interesting to see if they help maintaining spin on the sustainer.

I like how the TAO combines a few uncommon techniques in one, but I don’t like the finless sustainer. I just have a hard time believing the booster will put enough spin into the second stage to keep it stable. Anyone getting reliable flights from a 100% plan built model probably knows a lot about CGs or is lucky.

Good luck with your attempt with the Tao. Using 3D printed fin can and nosecone look like good improvements on the original design.

I have built a Tao, as a matter of fact it is pictured in my avatar. If you are interested, I discussed it ad nauseum in this thread https://www.rocketryforum.com/threads/is-the-tao-spin-stabilized-2-stage-rocket-stable.55583/

Basic things I learned were that it really needs some nose weight. Also, mine lost its rotational momentum fairly quickly after booster separation, and my thought was that possibly relocating some weight out near the airframe would help. However, I have not rebuilt it... YET

I'll be watching your thread with interest.

Mr Rocket said:

I have built a Tao, as a matter of fact it is pictured in my avatar. If you are interested, I discussed it ad nauseum in this thread https://www.rocketryforum.com/threads/is-the-tao-spin-stabilized-2-stage-rocket-stable.55583/

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Thanks! I read your post just minutes after starting a print on a redesigned fin can (I decided to reduce the thickness of the fins to 1.5 mm since the PETG is stiffer than I'd expected/feared). After looking at the linked thread, I made further modifications; increasing the pitch on the flaps to 11.5°and beveling the leading edge of the fins.
I already had the notion that I'd install tungsten Pinewood Derby weights around the circumference of a disc installed inside the nose cone (as part of the fixture that will connect the NC to the airframe). I will make that the next part of the build.

Increasing the pitch on the flaps made the print significantly more challenging...


Got it on the 4th attempt


Made some progress on the fly-wheel sub-assembly






It will go in, but Its a really tight fit in the nosecone. Pretty sure there will be no second chance if I don''t put everything together straight -- so I will cut another set of bulkheads with a looser tolerance -- but not today.

Looking good, I'll be very curious to see how it goes. I'm curious, are you going for a particular moment of inertia with the fly wheel, or just "something"?

mbeels said:

Looking good, I'll be very curious to see how it goes. I'm curious, are you going for a particular moment of inertia with the fly wheel, or just "something"?

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Honestly, I wouldn't really know how to start that computation -- and even if I were to make a stab at it (say, if we wanted to stay above some minimum angular momentum until apogee), there would be so many inputs to which I could not put meaningful numbers... so, yeah the objective here is just to make the moment of inertia of the sustainer larger and to get the rocket spinning faster before it stages.

Since I am going to make a new assembly, I penciled out the difference in moment of inertia between the configuration I built, and a flywheel with the masses flipped up on edge.

Mostly I was hoping to impress folks with the fact that I know how to compute the sagitta of an arc given its radius of curvature and the chord it intersects -- I didn't think it would make much difference.

For the 7 gram masses I pulled out of the box, which are just about half as tall as they are wide (4.55 mm high by 9.45 mm in diameter), rotating them on edge like this increases the moment of inertia by about 10% -- so thats how I will build fly-wheel MkII.

Flywheel MkII









The nose-cone and flywheel are only about 0.4 Newtons, but it feels heavy - with more than half the mass right there at the base of the cone.

I am giving serious consideration to building a booster with a 29mm motor mount. This is never going to be a park flier. Need to run some sims with an E16-0 in the booster.

I am a little discouraged to realize that this design wasn't flight-proven before it won the prestigious quarterly design award... and a little bewildered by the prospect of trying to make it workable in time for the next high power launch.

I have a got a nice piece of BT60 scrap with two clean ends, so I am going to increase the length of the sustainer from 9.375 inches (240 mm) to ~ 300 mm.

While trying to figure out a better motor-mount/staging system, I decided to see how the PETG takes glue and paint.


I installed the spare bulk-head in the spare cone with epoxy and urethane glue. It seems to be holding pretty well.

I used Duplicolor adhesion promoter (which just soaked in to the plastic), then a couple of coat of SpazStix metallic silver backer, followed by a couple of coats of SpazStix holographic color changing paint. The rainbows are pretty subtle, and not very photogenic, but it is definitely showing shifting colors.

Interestingly, the print shows the quads from the mesh model. These were not shown in the Slic3r preview, but both cones have a very definite fishnet pattern superposed over the printer layer striations. It is cool enough that I am going to figure out if I can paint the twistier cone to make it even more evident.

Still working on redesign for the MMT and piston. In the meantime, a shot of the spare cone with better lighting. I am going to build a rocket around this, just because I want to take it to a low power launch and show it off. It actually looks much cooler from a distance.

That's beautiful.

New flywheel is aces. Is there any possible downside to having a preponderance of the rotational inertia concentrated at the front of the rocket? Seems like *ideally* it would be evenly distributed to maintain stable rotation, although of course you want things to be nose-heavy for other reasons.

Also that holo paint is pretty cool (although: "SpazStix"? Really?) Have you considered painting the spiral slot a different color so it'll more visibly corkscrew in the air?

neil_w said:

New flywheel is aces. Is there any possible downside to having a preponderance of the rotational inertia concentrated at the front of the rocket? Seems like *ideally* it would be evenly distributed to maintain stable rotation, although of course you want things to be nose-heavy for other reasons.

Also that holo paint is pretty cool (although: "SpazStix"? Really?) Have you considered painting the spiral slot a different color so it'll more visibly corkscrew in the air?

Click to expand...

I’ve wondered if it would work better at the center of mass, too - but haven’t tried to do the math.

neil_w said:

New flywheel is aces. Is there any possible downside to having a preponderance of the rotational inertia concentrated at the front of the rocket? Seems like *ideally* it would be evenly distributed to maintain stable rotation, although of course you want things to be nose-heavy for other reasons.

Click to expand...

Charles_McG said:

I’ve wondered if it would work better at the center of mass, too - but haven’t tried to do the math.

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The sustainer is a rigid body, all parts turning together. The thrust will act parallel to its long dimension, and so will exert no toques about the COM. The weight will act at the COM , and so will exert no torque about the COM. Only the aerodynamic forces will produce a torque about the COM. Moving the flywheel aft will increase the distance from the COP to the COM, increasing the torque acting to change the rotational momentum of the sustainer. This will increase the rate of precession of the sustainer -- it will cone more, and cone faster the further aft the COM moves.



That's my story, and I am sticking to it.

neil_w said:

Also that holo paint is pretty cool (although: "SpazStix"? Really?) Have you considered painting the spiral slot a different color so it'll more visibly corkscrew in the air?

Click to expand...

Yeah, for the Tao cone I am going to break out the paint brushes, and paint the lands and flutes different colors. I am (currently) planning a red/green paint scheme, per the original plans. I am going use Duplicolor anodized colors -- which are pretty desaturated -- so it won't look like too much like a Christmas ornament (fingers crossed).

I take no responsibility for the name of the paint. It was something I saw some YouTube maker apply to a bike helmet, and I thought I'd try it out to make it more obvious that I'd airfoiled the fins on some rocket.

EDIT: BTW, does the COP reported by OR seem correct? Is the lift acting on the cone really that much larger than the aero forces acting on the airframe?

jlabrasca said:

EDIT: BTW, does the COP reported by OR seem correct? Is the lift acting on the cone really that much larger than the aero forces acting on the airframe?

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OR has always given CP very far forward when there are no fins. I don't know if that's just a natural result of the equations or what. My intuition says it should be roughly at the middle of the rocket, but I've been told that it's correct all the way up front, or at least OR is working properly.

I'm afraid I must disclaim any proper understanding of the situation here.

That's my story, and I am sticking to it.

Click to expand...

Who am I to argue with such a pretty diagram!

neil_w said:

OR has always given CP very far forward when there are no fins. I don't know if that's just a natural result of the equations or what. My intuition says it should be roughly at the middle of the rocket, but I've been told that it's correct all the way up front, or at least OR is working properly.

I'm afraid I must disclaim any proper understanding of the situation here.


Who am I to argue with such a pretty diagram!

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I think finless makes Cp more sensitive to angle of attack. So if you graphed it, it would move backward quickly (and body lift would increase)

So, how do you simulate the additional degrees of freedom on OR?

Charles_McG said:

I think finless makes Cp more sensitive to angle of attack. So if you graphed it, it would move backward quickly (and body lift would increase)

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Is it correct, though, to show CP of a finless rocket in the nose cone? Seems like a degenerate case of some sort.

neil_w said:

Is it correct, though, to show CP of a finless rocket in the nose cone? Seems like a degenerate case of some sort.

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Alan15578 said:

So, how do you simulate the additional degrees of freedom on OR?

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Not sure what you are asking. There is the component analysis dialog (tools>component analysis), which will give you some numbers as a function of angle of attack

Charles_McG said:

un-labled axes

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>smile<

Is the independent variable AOA?

jlabrasca said:

Not sure what you are asking. There is the component analysis dialog (tools>component analysis), which will give you some numbers as a function of angle of attack

Click to expand...

Sorry, I looked at your posts too quickly. When I saw the complexity, and your "flywheel" terminology, I though you had a rotating bearing in there. I see things more clearly now, although it is pretty, it is much less interesting.

Alan

jlabrasca said:

I am giving serious consideration to building a booster with a 29mm motor mount. This is never going to be a park flier. Need to run some sims with an E16-0 in the booster.

Click to expand...

I am going to build the booster longer, to accommodate an E12-0. According to OR, a D12/A8 version will stage at about 90 meters at which point the roll rate is reported as 1800°/s (30 rpm). An E12/A8 will stage at 175 m with a roll rate of about 3500°/s (about 60 rpm). That represents about a 300% increase in rotational KE.

I want it to stage low enough that we'll be able to see what it does up there. 175m is going to be at the edge of resolution for my old eyes.

I looked at the E16, but there wouldn't be room for a parachute in the booster, so I decided not to pursue it.



I need to make a new recovery hatch for the booster.

edit: because I wrote 3X instead of 300% and that was wrong

Alan15578 said:

I see things more clearly now, although it is pretty, it is much less interesting.

Alan

Click to expand...

>smile<

jlabrasca said:

I want it to stage low enough that we'll be able to see what it does up there. 175m is going to be at the edge of resolution for my old eyes.

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Is there a straightforward way to just make the whole thing heavier, while still meeting weight limits for the E12?

neil_w said:

Is there a straightforward way to just make the whole thing heavier, while still meeting weight limits for the E12?

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Heavier would mean less angular speed. Increasing the cant of the flaps would increase the roll rate (meaning more angular momentum, meaning -- hopefully -- less squirreliness after staging) and also less altitude at staging -- but I don't want to print another fin can. Plus which I suspect that this design is already WAY into the weeds for the OR sim.

I am just going to build it now, I am on the clock here.

@Alan15578, after reading the flight report posted by @Mr Rocket, where it was noted that the rocket stopped spinning after staging (presumably due to drag), I considered putting the flywheel on a bearing. I just couldn't figure out any simple-to-fabricate clutch that would release the flywheel to turn freely inside the sustainer after the rocket staged.

I also thought for a long time about whether to call the "circumferentially arranged masses" a flywheel. If it were a problem set for my students, I'd almost certainly call it a "rigid rotator" -- but that seemed likely to invite snickering, especially since the way the lips of the flutes protrude gives the nose cone -- from certain angles -- the appearance of having a "reservoir tip"

With the hatch deployment of the parachute I question whether the parachute Mass may be asymmetric relative to the longitudinal core axis of the rocket. If so, this eccentric Mass may play havoc with a rapidly rotating rocket

Can't do much until I get the new hatch printed -- 2 hours to go. Decided that no version of the red/green paint scheme was worth the environmental damage. If it spins fast enough, orange + blue will make pink. Since the rocket will spend most of the time NOT spinning, I think that this will be just fine.

BABAR said:

With the hatch deployment of the parachute I question whether the parachute Mass may be asymmetric relative to the longitudinal core axis of the rocket. If so, this eccentric Mass may play havoc with a rapidly rotating rocket

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There are so many other ways that this can go wrong, but I might stuff a sheet of mylar into the booster on the side opposite the hatch. Just for luck.