(Yet Another) 100k Attempt

[waltr]

No problem. Glad my drawing made sense.

 

[robopup]

A few general updates:

New booster and second stage fincans are just about finished - they still need a post cure and a paint job. With the disappointment of the E-60HP, I've moved back to my tried and true (and much cheaper!) laminating + filler recipe. Usually I add milled glass and 404 filler but I did make one small change. I wanted to be able to do all four quarters at once, so I'm also adding a little 406 per a recipe I found somewhere from @JimJarvis50. No drips and holds shape!

Final weights, as a percentage by weight of the laminating resin were:
1.0 - laminating resin
0.5 - milled fiberglass
0.02 - 406
0.15 - 404


I finally got tired enough of my wife's vintage national sewing machine (which works well to mend stuff, but not to sew thin chute fabric) and got a refurbished Brother XR9550. I hadn't really realized how awesome and how relatively cheap (at least compared to the cost of parachutes) modern sewing machines are.

EDIT: Meant to add a picture of a few of the cool stitches this thing can do. Has a library of 100 or so, including a few checkerboard patterns (not shown) which make it much easier to get a ton of stitches through thin kevlar shroud lines.


Here is the second pair of main parachutes - both torroidal, 30 in for the second stage and 40 in for the booster, next to a 38mm AT aft closure.


And have my final nose tips turned. A buddy has a cnc'd lathe so the tips also get a von karmen shape!




Finally, I've decided to move forward with head end ignition and think I have a design I feel can be safe. The electronics sled still bolts to the forward closure, but now on an integrated aluminum platform rather than a 3d printed part. One side of this platform will be cut off so I still have access with snap ring pliers. The igniter shooters wire will pass through a 1/4-20 bolt potted with JB Weld, similar to @FredA's description here. Several friends have been successful with similar methods and I don't want to reinvent the wheel... The goal is to:

1. have the FC and electronics prepped beforehand, along with the igniter
2. at the pad, do the full up test with all wires connected
3. insert FC and snap ring, unchanged from the full up test
4. Bolt airframe to the top of the ebay and shear pin the prepped nosecone

 

[robopup]

Camera window

I had a little extra time and wasn't quite happy with my first try at the payload tube with the camera hole so I took another shot at it. Original goal which worked on round two was to have the window and not use any screws to hold things together. This ended up being harder than I expected and I didn't find many detailed pictures showing how others did there windows so figured I'd throw these here.

Mount for the window is 3d printed and glues into a section of body + coupler tube:


Window is held by a lip in the above picture, and by the blue press fit piece below which will be siliconed in place:


Coupler glued into body tube. I didn't want any glue lip on the inside so I only put epoxy on the coupler. Both the coupler tube and airframe tube got masking tape to keep things clean:


Epoxy cured and (rough) camera hole drilled. Parts printed:


Mount epoxied in place. This was sanded smooth and got primered and painted along with the rest of the tube. Last step will be to insert the glass window and silicone the press piece into place:


Here's the glass I decided to use (20mm) - thanks for the help earlier on!
https://www.esslinger.com/watch-cry...P6kwSPVEe6wAXkbAc9ObonvfuRALEilhoC5hQQAvD_BwE

 

[robopup]

Head end ignition

Final design ended up being very similar to the CAD and method posted above on this page. The idea is that all electronics, closure, igniter and wiring can be fully assembled and turned on to test at the pad. Then, without disassembling (but obviously with electronics off again), can be inserted into the motor and snap ringed in place.

Closure - Camera and staging electronics mount on the top hat. The hole on the bottom left is tapped 1/4-20, where a bolt with the igniter will pass through.


1/4 20 bolt with 1/8 in hole drilled out of the center. Igniter wire will pass through here and be potted in epoxy:


And with electronics mounted:


And, with a fair amount of consternation documented here, I got the final second stage moonburner grains cast a couple weeks ago:

 

[OzHybrid]

I ran into this website a while back (somebody else here found it) and bookmarked it. I suggest you do the same .

https://www.esslinger.com/watch-min...rved-rectangular-1-5mm-thickness-for-cutting/
Great for curved camera windows for airframes.

Bit late to the party... Microscope slides are a cheap source for optical flats. Box of 100 for $14. 1mm thick.

 

[robopup]

With a Sunday departure planned, I'm full on final prep mode now:

I've done four more second stage ground tests, and three more booster ground tests using the concept documented here. I feel much better about consistently getting the main out. So, onto recovery prep...

Charges - all high altitude use @tfish's vinyl tube method (I can't find the awesome picture he has of this floating around here... somewhere). All low altitude use simple glove tips:


Recovery for both boosters and second stages have all Z folds taped on kevlar. I'll install charges and pack chutes later in the week:




All grains for motors are cut, cored, density-checked and the bates grains all have their faces sanded concave (I need to make a fancy trimming tool like Kip's!). Liners are also cut. Plan for today is to get grains glued in and motors built:

 

[tfish]

@robopup

This one? (5/16 ID is good for 3" rockets)


I used glove fingers for many years..I've switched to balloons in the last few years..most of the time a 7" round balloon (walmart) can be turned inside twice which adds some latex tubing effect and better odds that the other near by charges don't get 'set off' before their time (Dollar Tree has 9" round balloons for bigger charge holders.


The above vinyl tube charges are in 3/8" ID tube...for a 6" rocket.
now back to the robopup build....

Tony

 

[robopup]

@tfish That one!

 

[robopup]

It always takes longer than I think it will...

Both full stacks prepped. 6am departure tomorrow.

 

[Adrian A]

Is this for BALLS or an earlier launch?

 

[robopup]

Is this for BALLS or an earlier launch?

XPRS. I’m in a group helping to prep ARLISS rockets so getting in early. Onto the playa today!

 

[robopup]

 

[kjhambrick]

Dang !

I miss playa launches at dawn !

What a beautiful pair of rockets you have there @robopup !

EDIT: I meant to also say: HAVE FUN AND GOOD LUCK !

-- kjh

 

[robopup]

@kjhambrick Thanks! New moon out here too! Life is hard…

 

[Spacedog49Krell]

You are doing it right, build two vehicles to get one back. If you recover both, it's great. Most of the time, for me, it's 50%.

Good luck on your flights.

 

[rharshberger]

Good luck Robo!

 

[cerving]

How is the playa? A lot better than at Burning Man, apparently...

 

[Spacedog49Krell]

How is the playa? A lot better than at Burning Man, apparently...

The two main playas in the area, Black Rock and Smoke Creek to the west, drain very quickly.

 

[robopup]

How is the playa? A lot better than at Burning Man, apparently...

Playa is in great condition from what I’ve seen, haven’t done much exploring yet though. I’ve never driven on it when it’s been this smooth. I’ve also never seen such a mess at burning man.

There was a small amount of standing water to the west just past the 12 mile entrance but nothing after that. Sounds like there’s still water to the north east of the launch site. Seems to be drying out quickly though.

 

[robopup]

I’ll write up a summary in a few days - lots of data to go through - but I went 1 for 2 on the weekend. Successful flight was full recovery to 75k - second stage coned hard.

Stress levels still returning to nominal. Absolutely pumped.





Edit: better GoPro frame

 

[James Keller]

Hell yeah congrats! Looking forward to your write up and what you have for us next!

 

[rharshberger]

Congrats looking forward to your report!

 

[kjhambrick]

Woo Hoo @robopup, Congratulations !

What a beautiful day on the Black Rock Playa for flying your impressive rocket !

Yes, catch your breath and please post when your pulse and blood pressure and respiration rate are back into normal ranges

Thanks !

-- kjh

 

[wclaybaugh2]

I’ll write up a summary in a few days - lots of data to go through - but I went 1 for 2 on the weekend. Successful flight was full recovery to 75k - second stage coned hard.

Stress levels still returning to nominal. Absolutely pumped.

View attachment 604598

View attachment 604599

Edit: better GoPro frame
View attachment 604690

Well done.

Willing to discuss axisymmetric balance….

Bill

 

[robopup]

Well done.

Willing to discuss axisymmetric balance….

Bill

Thanks Bill. I'm still going through altimeter data and onboard video and at this point I think that the biggest contributor(s) are likely not off axis mass. Having said that, I'm still interested in general on any actionable advice for someone doing this on a shoestring budget in their basement...

 

[wclaybaugh2]

Thanks Bill. I'm still going through altimeter data and onboard video and at this point I think that the biggest contributor(s) are likely not off axis mass. Having said that, I'm still interested in general on any actionable advice for someone doing this on a shoestring budget in their basement...

Assuring that the CG in the pitch and yaw planes is at the same location can be accomplished by static balancing the payload (assuming the rest of the vehicle is axisymmetric in mass). How to do that is discussed here: https://www.rrs.org/2023/03/17/static-balancing-of-a-payload/.

The superior alternative is dynamic balancing. The smallest machine that will do that job cost about $800k; however, folks who own such machines are often willing to rent them. I have been quoted $4000 per day for dynamic balancing a small payload; it is--in my experience--very unlikely it would take more than one day to fully balance a nine inch or smaller diameter payload, even if several feet in length. But given that hobby payloads rarely cost as much as $4K; static balancing may be the lower cost solution.

Bill

 

[James Keller]

Assuring that the CG in the pitch and yaw planes is at the same location can be accomplished by static balancing the payload (assuming the rest of the vehicle is axisymmetric in mass). How to do that is discussed here: https://www.rrs.org/2023/03/17/static-balancing-of-a-payload/.

The superior alternative is dynamic balancing. The smallest machine that will do that job cost about $800k; however, folks who own such machines are often willing to rent them. I have been quoted $4000 per day for dynamic balancing a small payload; it is--in my experience--very unlikely it would take more than one day to fully balance a nine inch or smaller diameter payload, even if several feet in length. But given that hobby payloads rarely cost as much as $4K; static balancing may be the lower cost solution.

Bill

Hey Bill,
That article you linked is really interesting. I'm wondering at what point is this necessary to do? Also perhaps I'm misunderstanding but for smaller rockets can you balance the entire rocket similar to a RC propeller(on a much larger scale)?

Hope you don't mind the slight derailing of your thread robopup.
Thanks,
James

 

[OverTheTop]

Keep in mind that one of the main goals of balancing is to reduce flex over the length of the airframe. Energy loss due to that flexing is one of the driving factors that changes the rotation on the roll axis to end-over-end tumbling (actually the preferred mode for the airframe) once outside the atmosphere. Assuming balance is reasonable, airframes are stiff and fins are not causing the coning, most of the energy loss can come from the usual slip joints we use on the airframe. More serious rockets tend to use radax joints to eliminate the hysteresis that is present in slip joints, thus delaying the tumbling behaviour.

Without external controls a rocket rotating around the roll axis will always degenerate to a rotation around the axis with the highest moment of inertia, so end-over-end.

 

[OverTheTop]

Continued...
Here is a good article with graphs of slip joints and radax joints compared for hysteresis. See figure 3.
https://www.osti.gov/servlets/purl/5007820

 

[wclaybaugh2]

Hey Bill,
That article you linked is really interesting. I'm wondering at what point is this necessary to do? Also perhaps I'm misunderstanding but for smaller rockets can you balance the entire rocket similar to a RC propeller(on a much larger scale)?
View attachment 605223
Hope you don't mind the slight derailing of your thread robopup.
Thanks,

Carefully drilling an off center hole in the back of a bullet will cause it to cone…there is no lower limit to mass imbalance caused coning.

Propellers have the desirable characteristic that much of the mass is far from the axis. Balance is thus much easier to achieve compared to a small rocket. Even getting a two inch rocket dead centered on it’s axis seems like a bit of a challenge.

As a practical matter, I’ve found axisymmetric balance to become an issue at about three inches diameter; below that the vehicle performance—even with staging—is unlikely to care much if it cones some.

Bill