#91  
Old 12-09-2018, 09:15 PM
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ericb45696 ericb45696 is offline
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That made my day as well. I salute you sir.
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  #92  
Old 12-09-2018, 10:40 PM
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hiflyer hiflyer is online now
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Your new avatar is majorly apropos Dave.

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  #93  
Old 12-10-2018, 07:43 AM
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joecoin joecoin is offline
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Quote:
Originally Posted by davetherocketguy View Post

There's also another company, Altus Metrum that makes the TeleMega which not only can send its GPS location back to you it also has a tilt detect function on there which can be used to trigger the parachute charge along with a bunch of other stuff. Of course it's pretty salty at $450. I think I'd rather buy a really nice new DG cart than that.
...
You don't need that $450 item. Just get an old furnace thermostat and pull the mercury switch out of it.

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  #94  
Old 12-10-2018, 08:57 AM
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davetherocketguy davetherocketguy is offline
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Originally Posted by joecoin View Post
You don't need that $450 item. Just get an old furnace thermostat and pull the mercury switch out of it.
Ahhh yes the old mercury switch trick. You're a pretty smart fella...you'd fit in well with rocketry folk.

Mercury switches...Short answer: It might work but probably won't do what you want it to when you want to do it so that makes them rather sketchy.

REALLY Long Answer:

Mercury switches rely on the force of gravity to complete a circuit. This circuit will be connected to deployment charge and a battery. Thing is, you want to make absolutely sure that during prep and walking out to the pad that the circuit doesn't complete before flight or you're going to need to clean your undies when the parachute charge pops in close vicinity. As a result, most rocket clubs really frown upon using mercury switches. I do realize you could shunt the circuit or wire up a switch between the two but there are other issues to deal with...

Then there's the little problem of gravity and other forces acting on the rocket. In most rockets a mercury switch will definitely not work well because as soon as the motor burns out the rocket is experiencing weightlessness as it slows. Drag really isn't much of a factor since most rockets are very aerodynamic. So as a result that little ball of mercury may or may not complete the circuit. A good example of what I am talking about is the Vomit Comet that is used to train astronauts for weightlessness. It goes up at a steep angle and cuts the engines just prior to apogee and then begins to fall in a ballistic trajectory thus inducing the relative weightlessness for those on board.

In this case, the FBD&D is very draggy. What will likely happen is as soon as the motor burns out the drag will slow the rocket faster than the pull of gravity and the mercury will complete the circuit as soon as the motor burns out. Not a good thing. That means the chute will deploy at a velocity of around 100-150 mph by my very rough estimation which is a good way to damage the rocket or shred the chute. And that's a pretty big maybe. I don't want my chute deployment to rely on maybe any more. I want more of a sure thing. Ideally, the best time for a parachute to come out on a hobby rocket is when the rocket is horizontal which is at its slowest possible velocity during the flight and will cause the least amount of damage to the airframe.

There's another product out there called the PET2+ made by Missleworks and that is probably what I am going to get for the FBD&D. Not only can it detect tilt (not sure exactly how it does that) but its also a timer. So I can wire up 2 charges to it so one charge goes off based on tilt and the other based on elapsed flight time.

Don't get me wrong joecoin...its a good suggestion but we rocket folk have already explored that option.

-Dave

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Last edited by davetherocketguy; 12-10-2018 at 09:00 AM.
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  #95  
Old 12-10-2018, 09:42 AM
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Quote:
Originally Posted by davetherocketguy View Post
Ahhh yes the old mercury switch trick. You're a pretty smart fella...you'd fit in well with rocketry folk.

Mercury switches...Short answer: It might work but probably won't do what you want it to when you want to do it so that makes them rather sketchy.

REALLY Long Answer:

Mercury switches rely on the force of gravity to complete a circuit. This circuit will be connected to deployment charge and a battery. Thing is, you want to make absolutely sure that during prep and walking out to the pad that the circuit doesn't complete before flight or you're going to need to clean your undies when the parachute charge pops in close vicinity. As a result, most rocket clubs really frown upon using mercury switches. I do realize you could shunt the circuit or wire up a switch between the two but there are other issues to deal with...

Then there's the little problem of gravity and other forces acting on the rocket. In most rockets a mercury switch will definitely not work well because as soon as the motor burns out the rocket is experiencing weightlessness as it slows. Drag really isn't much of a factor since most rockets are very aerodynamic. So as a result that little ball of mercury may or may not complete the circuit. A good example of what I am talking about is the Vomit Comet that is used to train astronauts for weightlessness. It goes up at a steep angle and cuts the engines just prior to apogee and then begins to fall in a ballistic trajectory thus inducing the relative weightlessness for those on board.

In this case, the FBD&D is very draggy. What will likely happen is as soon as the motor burns out the drag will slow the rocket faster than the pull of gravity and the mercury will complete the circuit as soon as the motor burns out. Not a good thing. That means the chute will deploy at a velocity of around 100-150 mph by my very rough estimation which is a good way to damage the rocket or shred the chute. And that's a pretty big maybe. I don't want my chute deployment to rely on maybe any more. I want more of a sure thing. Ideally, the best time for a parachute to come out on a hobby rocket is when the rocket is horizontal which is at its slowest possible velocity during the flight and will cause the least amount of damage to the airframe.

There's another product out there called the PET2+ made by Missleworks and that is probably what I am going to get for the FBD&D. Not only can it detect tilt (not sure exactly how it does that) but its also a timer. So I can wire up 2 charges to it so one charge goes off based on tilt and the other based on elapsed flight time.

Don't get me wrong joecoin...its a good suggestion but we rocket folk have already explored that option.

-Dave
About 10 minutes after I posted that, I thought; well, that rocket might shake a little too much for the mercury to remain quiescent, which could cause the switch to actuate prematurely which could lead to Dave having to clean his undies.

In the late 1960's I would save every cent I could and send it all to Estes mail order warehouse. I bought not only pieces parts, but the technical data sheets ( I forget what they called them), I built a small glider, carefully following all the "rules" and tested that thing every which way I could. Didn't have a wind tunnel though.

Maiden flight of the glider. Got 10 feet off the rod and commenced to doing lots of fancy aerobatics. Had a lot of my older relatives getting really excited . Never thought my old uncle Joe could move so fast.

Also had a Camroc, but never did get a good picture out of it. Here's a guy that resurrected one:

http://www.rcgrabbag.com/archives/estes-camroc-1966

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  #96  
Old 12-10-2018, 03:40 PM
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davetherocketguy davetherocketguy is offline
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And two days removed from the launch and I've already bought the first new part for this beast...a Pet2 timer.

-Dave
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  #97  
Old 12-10-2018, 03:51 PM
Steve West Steve West is offline
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...
I can't stop thinking about how to make a basket that is held up by flames. Even if it is only an illusion, I want it to look just like your avatar.

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  #98  
Old 12-10-2018, 04:46 PM
Lazerface Lazerface is offline
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Dave, you are the man! That is all.

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  #99  
Old 12-11-2018, 09:03 AM
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CaptainAnhyzer CaptainAnhyzer is offline
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  #100  
Old 12-11-2018, 10:34 AM
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joecoin joecoin is offline
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I can't stop thinking about how to make a basket that is held up by flames. Even if it is only an illusion, I want it to look just like your avatar.

LED flame lamps:



https://www.youtube.com/watch?v=yp6VhgQ6s2o
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