The unit from magic fire is considered one time use but we have recovered
several and when tested they still work. For safety I suggest you never
reuse them in something that is so safety critical.
Larry

At 11:49 AM 6/2/02 -0700, you wrote:
>Hi Ash
>
>>Now that sounds like a great fun project :)
>
>Not really but someone has to do it ;-]
>
>>I'm working on a timer for use in Amateur Rockets, you can get 30Gs or more
>>on the initial firing of a large motor..
>
>I helped with an altimeter for a friends hi-powered "lawn dart" They are
>getting those
>things 10-15K off of the pad. It's amazing they get that high with only a
>few seconds
>burn time on the motors. I'm not sure what the actual G load is on these
>guns but it should
>be 100G plus. The altimeter was just thru hole with coating and it worked
>fine.
>
>>I'm going to be using SMT components because of size and weight.. And
>>because of F=MA, the smaller the mass, the less force acting on the
>>component. However my timers are (hopefully) reused.. :)
>
>The SMT seems to be the way to go.  It would cut the size and mass way down.
>
>I'm not quite energetic enough to try and find something the size of a quarter
>buried in snow somewhere on the side of a mountain ;-]
>
>>Also, I've heard (but have no evidence) that crystals are much more
>>sensitive to acceleration then resonators.. so be careful how you do your
>>oscillator. Maybe use the internal R/C oscillator and a special pre-trim
>>step prior to launch. Feed the PIC a known frequency so it can compute the
>>appropriate calibration value.. This would have to be done at ambient
>>temperature just before launch I would guess.
>
>The hardest part about doing this is the "operators" in my case. It would
>have to occur without user intervention. The guys using these are not techies,
>are generally cold, wearing gloves and could care less (from what I've seen)
>If I can figure out how to do this without them having to take off the
>gloves they
>would do it. ;-]
>
>>  Perhaps the cheapest way to do this is with a
>>thin wire loop through which a clip is inserted and a length of string ties
>>the clip to the back of the barrel. This is assuming that your launcher is
>>air powered..
>The lanyard is how they want to do it. Its pretty simple, cheap and reliable.
>All of this has to function reliably in some fairly harsh conditions.
>
>>You also need to think very carefully about safely arming and disarming the
>>device. You definitely don't what this going off in the gun or near you!
>Well right now I'm working with 4 distinct steps to arm or disarm.
>Reversing any of the
>4 would stop the fuse easily. Even with one of the small charges (about
>4lbs I think)
>you have to run pretty damn fast to escape the blast radius. Currently they
>are doing
>this with burning fuses. so the only safety is to fire it or yank it apart.
>
>Dave
>
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Larry G. Nelson Sr.
mailto:L.Nelson@ieee.org
http://www.ultranet.com/~nr

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