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Registered Member #179
Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287
A lathe is one thing I don't have A solid wood projectile is a great idea but it may be too heavy. My great stuff rocket weighs 199g. Maybe a light weight wood like cork or balsa but stronger. I'm not sure what qualifies though...
I have my current ring screwed to a piece of plastic using three counter sunk screws, and then the plastic is screwed into the center of the rocket which is a pine core. It held up well except for the cupped ring.
My new coil has an extra coat of epoxy on it...I thought about plastic or even cardboard but that would reduce the magnetic coupling by quite a bit due to inverse square law...those pesky laws always get ya
I haven't launched anything for a few days...today's weather is great so I'm going to see about testing some things.
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
Yeah, you want the disk to be as close as possible for max coupling but if your using mag wire I dont think 1/8" away will make very much difference, though I dont have effeciency and velocity measurements so I could be wrong, On my previous HV launcher setup I need 1/8" anyhow to keep it from arcing to the projectile and bypassing the coil. I just used regular insulated wire to prevent this rather than mag wire, but mainly because it was alot cheaper. When I start doing it again, especially with low V I'll be using mag wire. I have a small spool of #13 wire which I'll use on my electrolytic setup.
As far as the wood being to heavy... well its only too heavy if your needing some kinda minimum speed. But to be honest, using smaller disks (3.5") a peice of round wood 3.5" diameter and say 6" long will not weigh very much. I would even put money on it saying with the proposed bullet shape wood would go faster and higher than a flat disk alone. As shown on my website and in other posts I have launched a much larger peice of wood before, not aerodynamic at all, just to see what the extra weight would do. In my particular setup the efficiency had to be several times greater with the chunk of wood atop the disk. I dont have numbers, but launching straight up in the sky, if something goes 1/2 the hieght yet ways 5 times more, it is alot more efficient. I attributed this to the extra weight holding the disk down longer in the magnetic field. I am assuming the disk alone flies off the coil long before the peak pulse power is reached. Like I said I dont have any measured data but with my setup it all makes sense atleast. There is some light wood I have, I think its basswood maybe but I dont have a big enough peice to turn to 3.5" although I could probably get some as it came from a tree in my parents backyard. But I will just use pine, or whatever I can get cheap thats light and turns well. I dont mind the extra weight. You could even cut it in half and hollow it slightly, as long as you leave about 2" thick base I would think it would hold up... Got to get some diodes so I can start experimenting again!
Registered Member #179
Joined: Thu Feb 16 2006, 02:08AM
Location: Hagerstown, Maryland - Close to Prime Outlets
Posts: 287
You're right about the weight helping sometimes...I think I'll glue two 2x4s together and manually shape them into a cylinder and then sharpen it. I may cut it in half and hollow it a bit...perhaps add a payload, such as an egg and foam to see if it survives Then again it may shatter into a shower of splinters...
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
Well dont forget 4"x4"s are easy to come by if you dont want to mess with putting 2 2"x4"s together. Then again maybe that would make a convenient way to open it to put in or remove cargo. If you dont have a wood lathe and dont want to sacrafice hours and hours I wouldnt worry about trying to shape it into a round nose, I bet a chisel cut on every edge would nearly as aerodynamic. I dont know the geometric term but it would look like a 4 sided pyramid for the tip. I myself would use a table saw or compount miter saw (if its big enough) set maybe to 30 degrees for a leading edge. Or if you were really good on a bandsaw you could follow the dome shape on each edge, that would give you a rounded pyramid shape whatever the heck that is called. I might have to find that out.
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new caps & basic launcher testing rig
A solid wood projectile is a great idea but it may be too heavy. My great stuff rocket weighs 199g. Maybe a light weight wood like cork or balsa but stronger. I'm not sure what qualifies though...
