Hi Dave,

Now that sounds like a great fun project :)

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'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.. :)

If you were to arrange the PCB so the axis of acceleration goes through the
surface and "pushes" the components onto the board, I'd assume that you
wouldn't have any problems..

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 will be determining when the unit is "fired" from the
cannon. You can get G-Switches but they aren't all that cheap.. Perhaps you
can arrange a "pull fuse" which is tethered so that it pulls out of the
timer half way along the cannon barrel - that way it won't affect the
accuracy of the projectile. 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..

Another alternative might be a light sensor - arrange a ring of bright
lights at the end of the barrel and a sensor on your board detects the pulse
of light as it passes.. Or even the dark to bright transition from the
daylight as the projectile exits the barrel..

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!

Good Luck!
Cheers,
Ash.

---
Ashley Roll
Digital Nemesis Pty Ltd
www.digitalnemesis.com
Mobile: +61 (0)417 705 718




> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Dave King
> Sent: Sunday, 2 June 2002 6:56 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE] [OT]
>
>
> At 10:25 PM 01/06/02 +0200, you wrote:
> > > What is the maximum vibration level and/or G force standard smt or
> >thruhole
> > > will tolerate ?
> >
> >Wouldn't it make sense to regard the whole detonator as
> use-once? I guess
> >the price of a 12c508 would not add much to the total cost.
> >
> >Wouter van Ooijen
>
> It definitely is a use once ;-]  They shoot the charges
> 4-12km and each
> shot costs
> at least $75+. The idea is to allow an air burst so the full
> concussive
> force hits the
> snow. Its more effective than the standard fusing which
> simply hits and
> buries into
> the snow and explodes. The snow actually dampens the force
> enough to be
> noticeable.
>
> This would be a secondary fusing system so that if it was set right it
> would go off just
> above the snow but if it failed it will have the standard
> fusing. If it
> works right they can
> reduce the size of the charges or have to make fewer shots
> and more than
> pay for the
> pic.

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