1/8 inch usually can take 750# of force. That is from another site I buy from.
Rethinking my AV Bay designs
- Thread starter Issus
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When you say you can't run any threaded rod, remember that it doesn't have to go through the middle of the bay. A single allthread rod (you could go even as small as #12 or #10) run below the sled, offset to one side, with an eyenut on each end would eliminate any stress from the sled or bay. And yes, even small light rockets can have extreme deployment shocks, especially if you have a short harness. How much length are you planning? You should be ok with the 1/8" kev, but if you've got the room, 1/4" will take the beating easily.
Looking forward to some more pix. What are you using for CAD? Solidworks or ? What kind of CNC gear does your school have?
-Ken
Looking forward to some more pix. What are you using for CAD? Solidworks or ? What kind of CNC gear does your school have?
-Ken
Issus
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I'm using 2m of kevlar on each section, i thought I had some in my box of bits so only ordered a small amount which has left me with fairly short lines (I'm a big fan of more-is-better). The problem with putting rod in is that there isn't much in the way of area that has clearance for it - with the two 10mm holes in the end plates plus two 6.3mm holes - if i put another hole between these it's likely to be the weak point and not hold the stress. I'm not aware of a local supplier that sells eye bolts, we have enough trouble getting threaded rod in smaller sizes that isn't terrible steel.
I'm using Solidworks '12. Even though '13 is coming out soon (if it isnt out already), we've just recently upgraded to it from '10 as I was able to get a good deal on the licenses i need for my staff - I threw in an extra license for myself so i've been learning to use it (I come from a EE/Software background).
I Finished school 10 years ago
The CNC gear is my own, I can mill a 1000x550x200 envelope (takes a standard 1200x600 sheet of wood) - it's setup for wood/aluminium. I can only cut aluminium on the weekends though as the compressor (to blow swarf out) and vacuum (to hold it down) are too loud to run after work. I'm also in the process of converting my lathe to CNC and have a 3D printer.
I'm using Solidworks '12. Even though '13 is coming out soon (if it isnt out already), we've just recently upgraded to it from '10 as I was able to get a good deal on the licenses i need for my staff - I threw in an extra license for myself so i've been learning to use it (I come from a EE/Software background).
I Finished school 10 years ago
The CNC gear is my own, I can mill a 1000x550x200 envelope (takes a standard 1200x600 sheet of wood) - it's setup for wood/aluminium. I can only cut aluminium on the weekends though as the compressor (to blow swarf out) and vacuum (to hold it down) are too loud to run after work. I'm also in the process of converting my lathe to CNC and have a 3D printer.
Issus
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I picked up some new PVC pipes to replace the vacuum reservoirs I crushed last weekend last night, as well as the correct bolts for this. I should be able to get the bolts in place tonight and glass tomorrow morning to see how strong it will be.
If the wood works out to be too weak, I have some 316SS M5 bolts that have far smaller heads and will handle all the load the eye bolts can transfer.
There are no eye nuts or bolts at the local hardware store chains it seems, so as I don't have time to order some in from overseas I won't be able to try putting a threaded rod in anywhere. I'll leave that for another rocket build.
If the wood works out to be too weak, I have some 316SS M5 bolts that have far smaller heads and will handle all the load the eye bolts can transfer.
There are no eye nuts or bolts at the local hardware store chains it seems, so as I don't have time to order some in from overseas I won't be able to try putting a threaded rod in anywhere. I'll leave that for another rocket build.
Issus
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Progress!
Last night I CF'ed and glassed the plywood sled. I haven't glassed something in quite this fashion before, with bolts embedded in the layup so it was pretty fun to do.
First up, prepare all the parts for lamination.
All my cloth is cut to size, pop sticks made handy and 3 layers of gloves installed on my hands (one layer per side, one layer to stop bleed through and for setting up the vacuum with - nitrile gloves are too hard/expensive to come by here.)
First on goes the carbon with the weave spread out using a closed pair of scissors. Some of the fibres were damaged by doing this which was unexpected but overall seems to have worked out quite well. I had to put nuts on the bolts to ensure they would stay level, which I had not planned on. The nuts have packing tape over them so the epoxy won't stick. There are extra strands of carbon on the two weak sections on the outside of the bolt pairs, and a couple over the section behind the switch. I'm assured by a mech. engineer that this will help carry strain, however I'm doubtful. Either way it's no extra effort so I figured I might as well.
At this point my hands are too epoxied to be handling expensive cameras, so no more pictures. I added two layers of glass to the side, and then put the peel ply on/wet it out and then flipped the whole thing over.
With the slight gap between the bolt and the wood, I was expecting to be able to get some JB weld down the gap. Having not used it for 6 or so months I had forgotten how thick it was. In the future, I need to apply JB weld or other epoxy to the bolts BEFORE application of carbon/glass on that side, not try and do it all from one side. Oh well, lesson learnt
Once the JB weld was on the bolts and squished through as much as possible to the other side, the same layup for carbon glass glass peelply followed.
I added two layers of regular cleanup cloth on either side of the assembly as breather and then pulled a slight vacuum on it. Yes, its a polyethelene lunch bag, with some blutac as sealant - don't knock it, it works wonders on small parts!
I'm only putting -20in-hg of vac on it, as last week I imploded a vacuum chamber so i'm taking it easy. What the heck is -20in of hg you might ask... and why the hell am I using such an archaic measurement... well thats what the people who make my vacuum gauge decided to use. kPa, Bar, even PSI gauge would have been more sensible - oh well. An in my head calculation puts this at ~0.7kg/cm which is fine for this.
Last night I CF'ed and glassed the plywood sled. I haven't glassed something in quite this fashion before, with bolts embedded in the layup so it was pretty fun to do.
First up, prepare all the parts for lamination.
All my cloth is cut to size, pop sticks made handy and 3 layers of gloves installed on my hands (one layer per side, one layer to stop bleed through and for setting up the vacuum with - nitrile gloves are too hard/expensive to come by here.)
First on goes the carbon with the weave spread out using a closed pair of scissors. Some of the fibres were damaged by doing this which was unexpected but overall seems to have worked out quite well. I had to put nuts on the bolts to ensure they would stay level, which I had not planned on. The nuts have packing tape over them so the epoxy won't stick. There are extra strands of carbon on the two weak sections on the outside of the bolt pairs, and a couple over the section behind the switch. I'm assured by a mech. engineer that this will help carry strain, however I'm doubtful. Either way it's no extra effort so I figured I might as well.
At this point my hands are too epoxied to be handling expensive cameras, so no more pictures. I added two layers of glass to the side, and then put the peel ply on/wet it out and then flipped the whole thing over.
With the slight gap between the bolt and the wood, I was expecting to be able to get some JB weld down the gap. Having not used it for 6 or so months I had forgotten how thick it was. In the future, I need to apply JB weld or other epoxy to the bolts BEFORE application of carbon/glass on that side, not try and do it all from one side. Oh well, lesson learnt
Once the JB weld was on the bolts and squished through as much as possible to the other side, the same layup for carbon glass glass peelply followed.
I added two layers of regular cleanup cloth on either side of the assembly as breather and then pulled a slight vacuum on it. Yes, its a polyethelene lunch bag, with some blutac as sealant - don't knock it, it works wonders on small parts!
I'm only putting -20in-hg of vac on it, as last week I imploded a vacuum chamber so i'm taking it easy. What the heck is -20in of hg you might ask... and why the hell am I using such an archaic measurement... well thats what the people who make my vacuum gauge decided to use. kPa, Bar, even PSI gauge would have been more sensible - oh well. An in my head calculation puts this at ~0.7kg/cm which is fine for this.
Issus
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This morning I pulled the AV Bay sandwich out of the sandwich bag. It looks pretty crappy, but with it still being slightly green I could trim it up with a knife easily.
There are a couple of small air pockets in the glass, so I rubbed on some epoxy before putting it in the oven to go through a cure cycle for several hours. It comes out looking like this:
As carbon is not transparent, I had to print a template to drill the holes through the glass/carbon to the holes in the plywood. It's the same drawing as I use for CAM on the mill so it's nice and easy to line up. I used some double sided tape to hold it in place while drilling on the drill press.
With a light sanding, it comes up looking like this:
Some of the holes look a little rough where I trimmed up some fibres that were not cut by the drill bit. I'm not going to bother doing a week of thin epoxy layers and then sanding them back to get a perfect gloss smoothness, as this is a test AV bay and not a show piece! It looks rough as guts but is extremely solid and appears to be highly functional.
Next I need to wire the switch up and then mount the electronics to make sure everything fits.
The glass and carbon have added quite a bit of weight to this, so I'm interested to see how it's going to compare for weight to an AV bay with threaded rod. If nothing else, I gained some valuable real-estate in the AV bay to fit these stupidly large barrier blocks in!
There are a couple of small air pockets in the glass, so I rubbed on some epoxy before putting it in the oven to go through a cure cycle for several hours. It comes out looking like this:
As carbon is not transparent, I had to print a template to drill the holes through the glass/carbon to the holes in the plywood. It's the same drawing as I use for CAM on the mill so it's nice and easy to line up. I used some double sided tape to hold it in place while drilling on the drill press.
With a light sanding, it comes up looking like this:
Some of the holes look a little rough where I trimmed up some fibres that were not cut by the drill bit. I'm not going to bother doing a week of thin epoxy layers and then sanding them back to get a perfect gloss smoothness, as this is a test AV bay and not a show piece! It looks rough as guts but is extremely solid and appears to be highly functional.
Next I need to wire the switch up and then mount the electronics to make sure everything fits.
The glass and carbon have added quite a bit of weight to this, so I'm interested to see how it's going to compare for weight to an AV bay with threaded rod. If nothing else, I gained some valuable real-estate in the AV bay to fit these stupidly large barrier blocks in!
grouch
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Any update to this Issus? This was one of my all time favorite threads, just curious to see how it panned out.
Issus
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It was too windy on the october launch day, and the weekend after firebans started. We've had 1 day of decent rain so far this since november so its still another 2 months or so before I'll be able to fly unfortunately.
When trying to pack the rocket however, the 6mm ply is too thick for the 54mm body with two altimeters and the batteries I had, it was a real squish to get it in. I need to redesign this before the next launch. As you're interested, i'll update in here when I figure something out
When trying to pack the rocket however, the 6mm ply is too thick for the 54mm body with two altimeters and the batteries I had, it was a real squish to get it in. I need to redesign this before the next launch. As you're interested, i'll update in here when I figure something out
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