Devilish Project (Go Devil 38 kit bash)

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OverTheTop
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Devilish Project (Go Devil 38 kit bash)

Postby OverTheTop » Thu Dec 07, 2017 6:13 pm

Devilish Project (Go Devil 38 kit bash)
Purchased a Go Devil 38 at the Black Friday sales in 2016 from Madcow Rocketry. Just got around to opening it up and starting construction. Thinking about how it will hang together and what I can remove for keeping the mass down….

BATH
Step one was washing all the parts. Everything was washed in water with a drop of dishwashing detergent and about 10% metho. This is to get any mold-release agents (typically waxes) off the parts before my tool or glue gets anywhere near them. Strong epoxy joints please :D

FINS
Next up is beveling the fins. Adjusted my Aldi router table and custom jig, and put the bevels on the three fins.
OriginalFinsResize.JPG


My Dremel went intermittent about six months ago, so this is the first outing for the new one.

The 1.5mm thick G10 fins seemed a little flexible, although they are not that big so it probably doesn’t matter.
After playing around with some sims the speeds were scaring me if I used the supplied fins. So after a brief consideration I grabbed a sheet of 2mm CF plate and marked out the fins. They were cut to size (a little larger than originals as I am really going to push the speed on this and I don’t want the bird going unstable because of CP shift) using a hacksaw (blunted two blades!) and then sanded to size using a handheld belt sander. After careful final filing the fin beveling jig was again brought into play and they were beveled.

Note that I did all this CF work outside, to keep the fine CF dust out of the workshop. The majority goes into the vacuum cleaner. I also did most of the cutting by hand to keep the powder out of the air a bit. Do not breath the dust. Bad for your health. I watered it down on the lawn after I had finished.

FinComparisonResize.JPG

BevelFinsresize.JPG


Final fins were 22g each, and the originals were 17.8g each. Not bad considering each is 50% thicker, a little larger and a ship load stiffer.

Not sure how much I'll get done between now and February as thing are really busy at work :( .

Next up: Probably the fin can. Stay tuned!
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Re: Devilish Project (Go Devil 38 kit bash)

Postby air.command » Sat Dec 09, 2017 7:24 pm

Looking good OTT. How fast are you expecting it go if you needed to upgrade the fins? :D You mentioned you went through a couple of blades when cutting the CF sheet. Is there a preferred cutting blade matrial for CF? I've gone through a few blades as well.
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Re: Devilish Project (Go Devil 38 kit bash)

Postby Oldboy » Sun Dec 10, 2017 10:06 am

When cutting Carbon fibre I use a 5 inch grinder with a 1mm Kronenflex A 60 TZ disc.
Works for me just have to watch the dust
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Re: Devilish Project (Go Devil 38 kit bash)

Postby OverTheTop » Mon Dec 11, 2017 9:19 pm

AirCommand: Looking at about Mach 2+ somewhere. Depends on how much mass I can strip out. I just used high-quality Sutton blades.

Oldboy: I have used a grinder on fiberglass, but I don't want that much CF dust around everywhere, hence using hand tools mostly. I worry about carbon nanoparticles from a health point of view particularly. They are also a bit conductive if they get in the electronics in my workshop.
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Minimalist Tendencies

Postby OverTheTop » Mon Dec 11, 2017 9:27 pm

Motor Mount
I am really trying to get mass out of this thing. I want speed! I had been thinking about the motor mount for quite a while and in the end I had a bit of an epiphany. So, a new motor mount was born.

An offcut of the same fin CF material was roughly chucked in the mill and a disk was cut.
CuttingMM.JPG

MotorMount.JPG


A small aluminium stud was also turned up, and threaded M4 to fit a capscrew.
Here is the new motor mount :) , along with the CTI adaptor.
MountParts.JPG


Total mass for the mount is 4.9g. Not too shabby.

MountAtMotor.JPG


That is a piece of 2mm CF plate. It is actually the bottom of the avionics bay. The avionics bay will be glued into the lower airframe in the correct location, with this lower bulkhead also providing the motor mount and aft avionics closure. This will allow me to shorten the airframe and reduce mass even further.

AvionicsAndMount.JPG


Calculations show it will be more than ample to support the thrust of the gnarliest motor I can find. Yee Haa!

The capscrew allows easy mounting of the motor down through the avionics bay. It is glued into the aluminum stud with JB.
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drew
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Re: Devilish Project (Go Devil 38 kit bash)

Postby drew » Tue Dec 12, 2017 10:27 am

Gotta admit, I'll be mightily impressed if you can break Mach 2 with a 38mm vehicle OTT. My 38s rocket didn't crack Mach 2 on a J510 and it was heavily optimised and used a lighter airframe than what you're using. Still, it's worth a crack!
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Re: Devilish Project (Go Devil 38 kit bash)

Postby OverTheTop » Tue Dec 12, 2017 10:44 am

I won't know till I give it a go! The design will evolve as I progress.

Now the motor mount is integrated with the avionics bay I can shorten the lower airframe :) .

The couplers are of significant mass too. I am looking at shaving them down a little on the inside to lighten the load a little.

Electronics will be a challenge to keep light. Two Ravens and a tracker of some sort. Lots of batteries there :(
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Re: Devilish Project (Go Devil 38 kit bash)

Postby drew » Tue Dec 12, 2017 4:56 pm

Mine was single break / dual deploy with a cable cutter. Raven and TeleGPS in the nose. AeroPac Min Dia Retainer, 3 layer 200GSM airframe, G10 fins with CF over top. Here are the stats from that flight. TeleGPS put my max altitude at 17,507 ft. Max velocity was 2037 ft/s or roughly Mach 1.8. It also pulled nearly 67 Gs.
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Devilish Project (Go Devil 38 kit bash)

Postby OverTheTop » Tue Dec 12, 2017 6:58 pm

Fantastic info there Drew. Thanks for sharing. I am trying to get a feel for what I can do in 38mm. Orange revolution (54mm) got Mach 1.8 but I didn't put any special effort into that one, and the motor was a bit mid-range as well.

I think I have come up with some cleverness for the deployment charges. I'll keep everyone posted how the experiments go. Just building a proof-of-concept currently. Need to see if it actually works. What I am intending could be done a couple of ways.

Also looking at best motors for the flight, particularly calculating mass fraction as a first approximation to speed.
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Re: Devilish Project (Go Devil 38 kit bash)

Postby SpaceManMat » Tue Dec 12, 2017 10:23 pm

Looks good OTT. I especially like the stud, I toyed with the idea of doing away with the eye bolt in the purple parrot, but I figured I actually need the weight to get me up to optimal and it doesn’t take up too much room.

I’ve thought about building a stretched version of the purple parrot, would probably work out much like Drew’s rocket by the sound of it.
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