My little Chinese BALLS 2012 Project

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Will this project meet its stated goals? [See slide 2]

Yes
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Not a snowballs chance in hell
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Maybe
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Total votes: 0

Space Mark
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Re: My BALLS 2012 Project

Postby Space Mark » Thu May 10, 2012 12:38 pm

If you do braze directly to the motor mount, could you have the motor pressure tested?
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Re: My BALLS 2012 Project

Postby cryoscum » Thu May 10, 2012 12:41 pm

Mike, if the calc from the spreadsheet is correct, i.e. 1100-ish Psi, I don't think you want to braze that case...
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Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: My BALLS 2012 Project

Postby Passaretti » Thu May 10, 2012 1:24 pm

~800psi sounds about right for a 38mm reload. I seem to remember a guy (forgot name) parked next to me at an MDRA launch earlier this year who was testing 38mm grains all day. We spoke briefly about his GSE, I asked him what he was measuring and how. Pressure was one of the measurements. He had a long tube connected to his pressure sensor (IP65/NEMA4 type) which terminated into a special forward closure on his motors. The tube was partially filled with grease to inhibit the motor gases from damaging the sensor. Anyhow ... I believe he said he was looking for chamber pressures in the 800PSI range...
Mike Passaretti, TRA 5369

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Re: My BALLS 2012 Project

Postby Passaretti » Thu May 10, 2012 1:25 pm

cryoscum wrote:Mike, if the calc from the spreadsheet is correct, i.e. 1100-ish Psi, I don't think you want to braze that case...


:lol:
Mike Passaretti, TRA 5369

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Re: My BALLS 2012 Project

Postby Passaretti » Thu May 10, 2012 1:28 pm

Space Mark wrote:If you do braze directly to the motor mount, could you have the motor pressure tested?


Yea, it's possible I guess. I gave it a little thought, that is to prepare a smaller "motor" the same way I would the 6GXL and then test it to failure. Not sure how I would do this but it would certainly help.

However, it is starting to look like the risks are building against this brazing option ...
Mike Passaretti, TRA 5369

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Re: My BALLS 2012 Project

Postby OverTheTop » Thu May 10, 2012 1:40 pm

I was thinking about pressure testing earlier also. You might be able to rig something up yourself if you have a decent high-pressure washer. I have one for car and concrete washing that goes to 1400psi. The current lot seem to go up to 1900psi or more in some cases. A few machined fittings and a needle valve for pressure relief might do the trick.
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Re: My BALLS 2012 Project

Postby strud » Thu May 10, 2012 3:50 pm

You must Hydrotest to have any confidence, howver make sure there is little to no air/gas in there before testing to minimise stored energy if it lets go.

May have been mentioned before but why not make a composite tube, mill slots in it and then mount and bond Al fins in place with hitemp epoxy fillets (glass filled) ? Then epoxy this to the motor tube with the same hi temp epoxy (wouldn't need much).

Very near impossible to get fins straight, flat and zero angle of attack with any form of thermal welding.

CS

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Re: My BALLS 2012 Project

Postby PK » Sat May 12, 2012 10:15 am

I reckon you could bond the can to the motor with God's jiz. Over that kind of area it'd be rock solid, allow for some expansion, and you could get it off afterwards.

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Re: My BALLS 2012 Project

Postby OverTheTop » Sat May 12, 2012 3:05 pm

I reckon you could bond the can to the motor with God's jiz.


I didn't know you were religious PK :!:
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Re: My BALLS 2012 Project

Postby PK » Sat May 12, 2012 3:17 pm

OverTheTop wrote:
I reckon you could bond the can to the motor with God's jiz.


I didn't know you were religious PK :!:

I am about that stuff!
PK

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Re: My BALLS 2012 Project

Postby strud » Sat May 12, 2012 6:20 pm

Indeed, it is probably the lowest price 'caulk' you can get, but has some awesome relevant properties for rocketry :D

As opposed to Satan's jiz AKA cows milk.....

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Re: My BALLS 2012 Project

Postby cryoscum » Sat May 12, 2012 9:14 pm

Scoop reckons it's not cows milk, but a certain well known elixir. I agree with you, Craig.
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AMRS L3 | NAR L3 | QRS 089 | MDRA 224
AMRS Technical Advisory Group

Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: My BALLS 2012 Project

Postby strud » Sat May 12, 2012 11:05 pm

Yes indeed, cows milk causes me more misery per ml than any alcohol...

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Re: My BALLS 2012 Project

Postby Passaretti » Sun May 13, 2012 8:49 am

Sumo310 wrote:Mike, have you looked at using Durafix to attach the fins? I'm not sure what difference it'd make, but might be worth a look?


Ok, Simon ... You can play for my team!

Was planning on glassing the mock-up "motor casing," this morning but then the postman dropped off the Durafix rods ...

First thing I tried to do was patch a few small 1/4" punched holes in an aluminum redbull can.... that was pretty easy. Next thing I tried to do was butt join two pieces of 0.25" thick 6061-T6 plate. I thoroughly sanded all sides of the plates with 220grit sandpaper, clamped them together, hit the fillet areas with a wire brush and then wiped with acetone.

Fire up the torch and then took a few minutes to get a feel for how much heat I needed to dump into the pieces. It was a lot more than I expected... Nonetheless, I worked up the temperature gradually. The only indication of temperature I had (besides the hair on my hands burning) was the melting of the Durafix rod. Might have to get my hands on some of those crayons ... I noticed the rod start to weaken and break off in small chunks at first. Once I got past that this was somewhat normal, I started to push the rod into the metal and got a pool to form. From there it was like trying to make a big solder joint. The first joint turned out pretty fat, while the other one turned out pretty skimpy. This was largely due to the fact that the molten metal was running off the end of the fillet like water and pooling beneath.

One thing I noticed that could be pesky is that creating two fillet joints on either side of a fin may cause the previous joint to re-flow. I noticed this today, but perhaps I should have let the piece cool completely before attempting the second joint.

While these first two joints were far from perfected, I felt I had something good enough to test. How strong was this joint? Well I found out soon enough. I started to drag a sledgehammer out but then decided to take a slightly more scientific approach. I'll let the pictures below do the talking.

Roughly speaking, I was able to create approx 74 Nm of torque (55 ft-lb or 755 kg-cm) on the joint. Total deflection of the plate at that load was approx. 1mm. I have to admit I was pretty damn surprised ... These joints were far from perfect but they held up to a substantial load without even breaking a sweat ... I did not test to failure, but I would venture to guess the aluminum would have yielded before the joint popped.

Going to mess around some more with the rods, but then the next test will be a piece of fin material (0.189"T" in a but joint to a 0.1-0.125"T piece of plate which should represent the final fin-can.

Mike
Attachments
IMG_6200_.jpg
Close-up of one of the joints (post loading). No noticeable effects from the test.
IMG_6199_.jpg
Close-up of one of the joints (post loading). No noticeable effects from the test.
IMG_6185_.jpg
All of the Olympic weights I had ...
IMG_6150_.jpg
What's the worst that could happen? One end of the barbell is sitting on a bench and is constrained in one axis. This allowed the other end of the barbell to move up and down with respect to the ground. The wire rope is attached to the barbell as close to the plates as possible.
IMG_6147_.jpg
Bolted the piece to a 4x4 and clamped to an overhead i-beam. The point piece of aluminum plate on the bottom is fixed point / indicator to measure deflection in the cantilevered plate under load.
2012-05-12 13.41.11_.jpg
Skinny joint
2012-05-12 13.34.11_.jpg
Fatty joint
2012-05-12 13.27.34_.jpg
2012-05-12 13.27.34_.jpg (203.46 KiB) Viewed 790 times
2012-05-12 13.18.49_.jpg
2012-05-12 13.16.31_.jpg
2012-05-12 12.38.48_.jpg
2012-05-12 12.38.19_.jpg
1lb of Durafix, approx 21 rods. With shipping the cost works out to about $2 per rod.
Mike Passaretti, TRA 5369

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Re: My BALLS 2012 Project

Postby PK » Sun May 13, 2012 9:07 am

Two tips for using that stuff:

1: Preheat.
Maybe mount a heat gun/hairdryer somewhere, or use your boyfriends hair straightening wand (seriously those things have perfect cartridge heaters in them) to get the whole show up to >70-80 deg C before you start. It'll make a huge difference to the amount of heat you need and the time you have to work the joint.

2: Deal with the oxide layer
about 100mS after you rough the metal up with sandpaper, it starts forming a new oxide layer.
See if you can grab a small (think toothbrush) stainless wire brush.
Clean it, then put it into the braze pool while it's molten and scrub the oxide layer off the aluminium. you'll get a much better bond.

PK


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