PET2 Timer Issues in high drag rockets

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Well-Known Member
Apr 23, 2003
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Just wondering if anyone has had any issues using the PET2 timer with the G-switch launch detection in high drag rockets.

I bought a brand new timer for use in a pyramid rocket. Since I planned on using the lift of detection of the G-switch I decided to ground test the timer and it worked fine. I had built a nice electronics bay for it and loaded it up set for 4 sec's. Flew the rocket on an I motor, plenty of thrust certainly more then my arm swing used on the ground test.

I failed to fire and was still beeping when I got to the rocket. Luckily this rocket was build with ballistic recovery in mind. We checked the timer and reset it and flew it again, this time it passed overhead in an arc, when passing over several people reported hearing the fast beeps meaning it had armed. Still not ejection and when I got to the rocket it was back to the slow beeping which is just the all ready beep.

So, we tried another PET2 timer again the same thing, up down no ejection.

I wrote to Missile Works. My theory is that the high drag rocket causes the timer to disarm on when it decelerates. He thinks this cannot happen and claims once it arms, indicated by fast beeping, it cannot disarm. He then focused on the fact that we could hear a small piezo beeper.

So this last weekend a friend of mine who was familiar with this issue decided to test his PET2 timer, which he has flown over 30 times without problem, in a high drag rocket. He used a sort of spool rocket and flew yet a third timer in a different rocket, same thing no ejection. He did it again using pull pin and it worked fine.

In case you forgot my question after my story. Has anyone else had any issues with PET2 timers using G-switch in high drag rockets?

Sorry not to be able to offer any advice on your timer. I am however interested in building my own tetrahedron rocket and I have a few questions.

It seems as though equilateral tets are fairly common. How do you calculate the CP of a tet? For CG is see you use 1/3 of the way up the sides from the bottom and then just calculate all the interior stuff as normal, but I can't find much on CP.
Interesting theory on the drag stopping it from firing, I had never thought of that for some reason, but I guess it could be why. I can't see why it would do that though.javascript:smilie(':confused:')
I plan on flying the rocket again this week at least two more times on small H motors and plan on testing the G-switch on the other channel of the timer.

And sorry Gregzo, I can't help you on your question

If it worked using the break-wire but fails using the g-switch it sounds like it isn't pulling enough g's to activate the timer.
Funny -- David and Erik Gates recently had the same reaction in a Polecat WOKET powered by a K250, except they were using a BSR Timer2N. The Timer2N has a lower activation threshhold than the PET<sup>2</sup> for sure (long story on that one... maybe another time; let's just say that it involved airstarts, both brands of timers, and lots of skywriting under chute!), and the Woket DEFINITELY moved out on the K motor. It was supposed to airstart three one-grain G motors and then pop the chute... but neither happened. Perhaps it is a G-switch bounce issue? The high acceleration at liftoff seems to be enough, but it is abruptly floated forwards because the rocket almost immediately stops accelerating.

Thoughts? I've been wondering the same thing!
If it worked using the break-wire but fails using the g-switch it sounds like it isn't pulling enough g's to activate the timer.
It is definatly pulling enough g's to activate the timer. I've flown G64s in 3lb rockets with this timer 15 times using the g-switch. This rocket also weighs about 3lbs so it should be enough.
Scott's pyramid rocket was definatly pulling enough g's with his I class sugar motor in it with a >1 second burn.