WDG
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- Dec 25, 2009
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I made a 2 stage rocket (4" Talon with home made 2-stage similar to how Wildman is doing his Eagle Claw 2-stage). I was pretty happy with how it worked, but I used a timer for second stage ignition. I like the timer in that it can easily light 3 e-matches off a single channel (and has 3 channels) and timing is virtually infinite (from .3 seconds to something like 2 days). It was also small, inexpensive and well built. However, setting the time portion is a pita. To do so you have to press and hold a momentary position button for the desired time. (I started to make a device using the output of another industrial timer in flicker mode to set it, but still have not finished that.) Besides being a pita to set, the timer has some built in problems. It initiates via a g-switch. So my set time has to equal to my booster (first motor) burn time and then coast time. Well, that whole +/- 20% burn time most commercial motor mfg's publish and hand setting the timer can be a little iffy. But it worked well on my 2 stage. Going to a 3 stage I certainly don't want to use a timer initiated at lift off to light the third stage - way too many variables in there.
One idea I had was to stick with the timer (but finish my device for accurately setting it). For the middle stage the timer initiated by the g-switch at lift off would light the second motor. I could use one of the other channels to power up the sustainer timer. So now I still have the same guessed timing thing for each stage but not compounded from second to third stage.
The other idea I have is to simply use a break wire-ish technique for the booster and sustainer. On my 2-stage I used a Molex connector with the barb removed for electrical connection between sections of the rocket. I am happy with how that worked. So I could have a 2 wire connector that pulls apart between booster and second stage. That connector would be providing "coil" voltage to a solid state relay that has Normally Open (NO) contacts going to the power supply to that igniter. So at separation NO becomes NC and poof. I would do the same thing between the second stage and the sustainer. The only delays I would have would be the time for the motors to come up to pressure.
A third idea would simply be a modification to the second idea. Instead of the break wires letting a set of relay contacts close to the igniter they would initiate a timer. Then I could add some delay. For second stage I don't really want to push it on the delay and am OK with no delay. But on the sustainer, that thing will be moving pretty quickly. I almost have to have some delay in there.
Now, besides the basics I just covered, I want to ensure safe operation. That means each altimeter must be able to do its thing regardless of the conditions. (I don't want the 2nd or 3rd stage to light while I am recovering the rocket.) I don't want any of them to light if the thing is not going vertically upward. I have thought about mercury switches. Has anyone used a mercury switch for a safety kill switch on something like this? If I used something like that I would have it power a latching relay to hold it in the desired (open to igniter) state. But what does a mercury switch do at high G acceleration? I'd hate to have a really hard hitting first stage and get nothing out of the next stages because the switches splashed at take off. Whatever I do, I will certainly need to do some safe, but in air testing. Maybe I will try a mercury switch and have it set to stop a clock or fire a smoke grain at apogee or something benign in another rocket.
BTW, right now I am not worried about redundancy of staging ignition. If it works it works. But if it doesn't work, I want all my chutes to come out, etc. So no one gets hurt and so I can try again. The first stage will not go supersonic, but the second and third stage will. So mach lock and what happens if a stage fails to light and the second and third altimeters are still in mach block mode is a big concern. I guess a way to get a little more time for an event in a failure mode is to have at least one redundant altimeter set with a very low main event. I have seen rockets coming in ballistically only to have the main pop out at a couple hundred feet before impact. I think as far as bad crashes go, that is worse than a straight in lawn dart (because now you have a rocket landing flat at 600 mph rather than straight in). As far as safety goes it just plain sucks. Remote emergency charges may be in order.
I may not respond right away to any comments, but I will certainly read any/all comments made. This is also a project that is mostly n the , "I wonder..." stage. Family, work and other things in life tend to limit my time available for rocketry.
Thanks,
One idea I had was to stick with the timer (but finish my device for accurately setting it). For the middle stage the timer initiated by the g-switch at lift off would light the second motor. I could use one of the other channels to power up the sustainer timer. So now I still have the same guessed timing thing for each stage but not compounded from second to third stage.
The other idea I have is to simply use a break wire-ish technique for the booster and sustainer. On my 2-stage I used a Molex connector with the barb removed for electrical connection between sections of the rocket. I am happy with how that worked. So I could have a 2 wire connector that pulls apart between booster and second stage. That connector would be providing "coil" voltage to a solid state relay that has Normally Open (NO) contacts going to the power supply to that igniter. So at separation NO becomes NC and poof. I would do the same thing between the second stage and the sustainer. The only delays I would have would be the time for the motors to come up to pressure.
A third idea would simply be a modification to the second idea. Instead of the break wires letting a set of relay contacts close to the igniter they would initiate a timer. Then I could add some delay. For second stage I don't really want to push it on the delay and am OK with no delay. But on the sustainer, that thing will be moving pretty quickly. I almost have to have some delay in there.
Now, besides the basics I just covered, I want to ensure safe operation. That means each altimeter must be able to do its thing regardless of the conditions. (I don't want the 2nd or 3rd stage to light while I am recovering the rocket.) I don't want any of them to light if the thing is not going vertically upward. I have thought about mercury switches. Has anyone used a mercury switch for a safety kill switch on something like this? If I used something like that I would have it power a latching relay to hold it in the desired (open to igniter) state. But what does a mercury switch do at high G acceleration? I'd hate to have a really hard hitting first stage and get nothing out of the next stages because the switches splashed at take off. Whatever I do, I will certainly need to do some safe, but in air testing. Maybe I will try a mercury switch and have it set to stop a clock or fire a smoke grain at apogee or something benign in another rocket.
BTW, right now I am not worried about redundancy of staging ignition. If it works it works. But if it doesn't work, I want all my chutes to come out, etc. So no one gets hurt and so I can try again. The first stage will not go supersonic, but the second and third stage will. So mach lock and what happens if a stage fails to light and the second and third altimeters are still in mach block mode is a big concern. I guess a way to get a little more time for an event in a failure mode is to have at least one redundant altimeter set with a very low main event. I have seen rockets coming in ballistically only to have the main pop out at a couple hundred feet before impact. I think as far as bad crashes go, that is worse than a straight in lawn dart (because now you have a rocket landing flat at 600 mph rather than straight in). As far as safety goes it just plain sucks. Remote emergency charges may be in order.
I may not respond right away to any comments, but I will certainly read any/all comments made. This is also a project that is mostly n the , "I wonder..." stage. Family, work and other things in life tend to limit my time available for rocketry.
Thanks,
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