[Discuss] Near-space balloon: Foam ball located and purchased

Laura Harris EMAIL HIDDEN
Mon Oct 31 14:35:59 PDT 2011


We can use nylon all-thread for the central support rod, if we go that route. Long velcro-enabled straps would be reusable and strong though a bit heavier that zipties (but not by much). If we used a net, we'd still want to secure the halves together (unless you were thinking of drawing the net up into a tight neck at the top . . .). I'm leaning towards the nylon all thread center support rod approach, personally.


As for the interior construction, the interior walls, floors, and ribbing are 5mm foam-core. I was thinking of using gold mylar film for the reflective insulation, but we can go without it and fill dead areas with extra foam. 


Reasoning behind a partial hard-shell was assuming the ball will land bottom down so a full shell could be avoided to save weight. Still, it would definitely make it a tougher rig- more likely to survive for reuse. I was thinking of using fiberglass with epoxy resin for the hard shell.

Idea for paint scheme: paint the bottom 3rd black and the rest red. Black so it is easier to see on the way up (against the sky) and red so it stands out on the ground. Also, a fluorescent colored parachute. 


We can use 1-watt LEDs for strobes. With the short duty cycle a strobe requires, we won't need heat-sinks for the LEDs and they are bright enough to be easily seen in daylight. A simple 555 timer driving a FET switch is all we'd need for a driver. Another thing we can do is hang a strobe from the tether. That way its weight is not considered part of the 6lb payload limit (if I understand the FAA regs correctly). One of those little waterproof xenon strobes doesn't weigh much, either.



________________________________
From: Rick Osgood <EMAIL HIDDEN>
To: Laura Harris <EMAIL HIDDEN>
Cc: Ben Hallert <EMAIL HIDDEN>; "EMAIL HIDDEN" <EMAIL HIDDEN>
Sent: Monday, October 31, 2011 1:58 PM
Subject: Re: [Discuss] Near-space balloon: Foam ball located and purchased


I just had another thought about the design of the chassis that we didn't bring up at our meeting yesterday.  We need to be careful about the material the payload is made of as well as the GPS placement.  The eTrex doesn't have an external antenna so we need to make sure it can get an accurate GPS lock from inside the payload.  So any metal above it would be a bad idea.  So the chassis needs to be insulated but with material that the GPS radio signals can get through.


On Mon, Oct 31, 2011 at 1:51 PM, Rick Osgood <EMAIL HIDDEN> wrote:

Ben, so your idea would be to have the cord come through the sphere via a hole in the top and then attach to the inside of the bottom half?  I want to make sure I understand your idea correctly.  That sounds like it could definitely work and I like that it would remove the requirement for extra reinforcement on the top half.  Only downside would be having the rope going through the payload where it could get in the way of the electronics.
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>Laura, I think the zip ties idea could be cheap, simple, and effective.  It would be nice to have something that didn't require cutting and replacing the zip ties every time we open and close it though.
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>The last balloon I did, we just had a threaded rod going all the way through the center of the payload vertically.  There was a washer and a nut on each side to hold the two pieces tightly together.  Then a small horizontal hole was drilled through the threaded rod at the top so we could stick a sort of hook through it where the line was attached.  The threaded rod was nice and strong but it will add more weight and then you have a metal rod going all the way through the center of the payload which can make the inside electronics layout more difficult.  You can see it in some of the photos from this site: http://www.toddfun.com/2011/02/20/high-altitude-balloon-launch-2/ .  Here is one example photo:
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>On Mon, Oct 31, 2011 at 1:29 PM, Laura Harris <EMAIL HIDDEN> wrote:
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>Ohh- that looks good, Ben. 
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>>One idea for holding the halves together is to use a pair of extra-long nylon zip ties running longitudinally at 90 degrees to each other- grooves formed in the surface would keep them from sliding off. They're strong and light and they avoid the need for any hardware.
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>>________________________________
>>From: Ben Hallert <EMAIL HIDDEN>
>>To: Laura Harris <EMAIL HIDDEN>
>>Cc: Rick Osgood <EMAIL HIDDEN>; "EMAIL HIDDEN" <EMAIL HIDDEN>
>>Sent: Monday, October 31, 2011 1:12 PM
>>
>>Subject: Re: [Discuss] Near-space balloon: Foam ball located and purchased
>>
>>
>>May I suggest that instead of attaching the cord to the top, we run it
>>down and attach it to where the battery bay is?  This way the whole
>>thing is 'sitting' on the cord and we can cut any weight created by
>>reinforcements that would reach to the top of the sphere.  Namely, the
>>only 'strength' needed would be at the bottom where it's already
>>planned to exist.  This also reduces risk of retrieving just the top
>>of the sphere.  :)  I've attached a modified version of the drawing.
>>
>>- Ben
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>>On Mon, Oct 31, 2011 at 12:51 P.M, Laura Harris <EMAIL HIDDEN> wrote:
>>> The ball comes split in half so it's just a matter of holding it together in
>>> flight. I've attached a pic of a sketch showing a preliminary idea for
>>> construction.
>>>
>>> ________________________________
>>> From: Rick Osgood
 <EMAIL HIDDEN>
>>> To: Laura Harris <EMAIL HIDDEN>
>>> Cc: "EMAIL HIDDEN"
>>> <EMAIL HIDDEN>
>>> Sent: Monday, October 31, 2011 10:54 AM
>>> Subject: Re: [Discuss] Near-space balloon: Foam ball located and purchased
>>>
>>> Sweet!  Do you plan to mold something around the sphere?  I'm curious to see
>>> your final design and how we will be able to open it up and
 mount
>>> everything.
>>>
>>> On Mon, Oct 31, 2011 at 9:53 AM, Laura Harris <EMAIL HIDDEN> wrote:
>>>
>>> I found a 12" dia hollow polystyrene foam ball and purchased one. Should be
>>> here in a few days. This is it:
>>> http://www.plasteelcorp.com/mm5/merchant.mvc?
>>> This dramatically accelerates the build progress. :)
>>> L
>>>
>>>
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