Timer vs Altimeter for Single Deploy

[doug_kosty]

So.... I'm thinking that I need some electronics in my rockets. I am using RMS24/40 motors for the most part and would like to be able to tinker with the parachute deployment times easily. (Motor ejection, while simple, seems a little limited and plagued by repeatability issues. I have not had any disasters yet!)

Which way to go - altimeter or timer? The timer is simpler, but of course is open loop. Nonetheless, I sort of like the idea of tipping my toe into the electronics pond, so to speak.

Any strong opinions? I'd probably start off with a smallish rocket and learn the ropes before doing anything crazy. Next stop is dual deployment which just seems like a good idea when you are flying on an ISLAND.

 

[Pantherjon]

I would go with an altimeter..Timers are nice I suppose, but , then you will have to rely on the timer being activated either by the initial engine thrust or some external switch when the rocket launches..With timers you will then be subject to the accuracy of the delay you program it for, IE engine burn time + coast time til apogee = deployment..You can run into the same problems with a timer as with the supplied delay on the motors, too long and you have a lawn dart. Too short and you have a zippered body tube..

Altimeters, especially barometric measuring ones would be the way to go..It will detect when there is no longer any altitude increase and pop your charge for deployment..

How small of rockets are you talking about? 2 good altimeters that are fairly small come to mind: Missile Works RRC2 Mini usually found for $79.95 or the Featherweight Raven which goes for $149.00..The RRC2 Mini is fairly easy to program..And both lend themselves ideally for your next step into doing dual deploy..

 

[kandsrockets]

I agree with Jon about going with a altimeter over a timer. Another good simple alt is a perfectflight hialt45.

 

[DexterLB]

I have both an altimeter and a timer (both homemade), and I've tried them both. The problem with a timer is as Pantherjon described. What i've noticed about altimeters is that you need several vents, and if it's a small rocket the vents can compromise stability. Correct me if I'm wrong, but in that case a timer may be better, although I'd rather use a breakwire instead of G-Switch

 

[Pantherjon]

I don't believe that the vents would cause a stability issue, unless, of course, they are made excessively too large.. I think what COULD come into play with a barometric altimeter is in relation to the placement and orientation of the vent holes. If, for example, you had 2 vent holes 180 degrees apart, a good gust of wind could 'spoof' the altimeter into believeing it is at apogee and it will fire the deployment charge..

I agree, if I were to use a timer, I too, would want to use a breakwire instead of a g-switch.