I made a forum about a switch on rocketryonline and then someome said that I shouldnt shunt the charges because it is just another thing to go wrong. But shunting is ment to make the rocket safer?!?! I will be using one missile works slot switch... is it really that dangerous to shunt? If he ment I might forget to unshunt then i would never (checklist) but are there any dangers with it in other ways besides forgeting to turn the shunt switch off?
shunting?
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rstaff3
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That is because every switch you put in adds a potential failure point. The true minimalists believe in simple twist-wire connections for charges. I saw on an rmr search that one good method used 2 brass bolts separated by an insulator. You thread a bolt through the pair to make/break the connection.
Don't underestimate the ability of a mechanical connection to fail. I worked on a triply redundanct data comm system and the most unreliable part of the data path were the mechanical patch jacks.
Don't underestimate the ability of a mechanical connection to fail. I worked on a triply redundanct data comm system and the most unreliable part of the data path were the mechanical patch jacks.
I was private messaging with someone that used 6 of them.. not problem.... I dont think the failure would be very likely with 2 when it has been done with 6. It is a very reliable switch from what I have heard and I dont think it is very likely.
rstaff3
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I tend to agree it is unlikely. But not impossible. One thing about rocketry (and many things in life) you will always find someone who has successfully done something. The classic is 'my grandma smoked, drank, and ate a fatty diet all her life and she lived to 99, so I don't see why I shouldn't also'. Or, 'why should I eat a healthy diet? I read where it only adds 2 months (stat made up by me) to your life time' Tell that to all the dead people it took to make up for that grandma.
Geesh, sorry, I went overboard. I suspect that you will be just fine using the switches. As for me, I will still direct power my electronics and break the charge lines. And make sure my battery is taped, velcroed, or ty-wrapped to the holder (I KNOW about that failure mode
)
Geesh, sorry, I went overboard. I suspect that you will be just fine using the switches. As for me, I will still direct power my electronics and break the charge lines. And make sure my battery is taped, velcroed, or ty-wrapped to the holder (I KNOW about that failure mode
)
mike_bar
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Dick, do you have a photo or diagram of the brass bolt connection?
Off-Topic: I have a 48-year old friend who is now in the hospital with a blockage to his liver. He is fit, trim and eats healthy (vegan diet). The doctors said it was in his genes, and that his lifestyle did not help or hurt the illness.
Super-size me!
mike_bar
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It sounds like a home-made, minimalist switch, simular in function to the Aerocon PCB mounted Screw Switch.
Aerocon Systems Armored Switches
DynaSoar
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If the choice is between positive safety and possible failure, my choice would be to live to try again. The things that can go wrong by not using one are more numerous and worse than by using one.
If people tell you not to, and don't have experience using one, they're blowing smoke. If they tell you not to and have experienced failure because of that, they're not someone you'd want to learn from.
See the thread about static electricity and igniters for reasons to use one.
rstaff3
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I think where Dyno is coming from is no mater what, ANY components you add will reduce reliability. And he is conservative, believing that no matter how small the risk may be, why take it if you don't have to? I probably fall somewhere in between.
BHP
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Attached is a photo of a homemade screw switch. This photo was taken by and is of friend's altimeter board but I have made and used similar switches on my L3 Big HOrizon upscale. They're a rather rugged switch, easy to make and keep a clean outer airframe. The access holes for the screw double as electronics bay vents as well.
I like rstaff3's saying the "twist and tuck" folks are minimalists. I now consider myself a 'rocket electronics minimalist' as I don't like the idea of too many switches (read "failure points") myself. I have only used screw switches or the "twist and tuck" method on the battery power wire myself. The ejection charge wires I leave unbroken.
After I posted this message I realized I should probably add the following if you plan to make a screw switch yourself:
Use brass strip from the hardware store for the body. It bends easily with needle-nose pliers. Vary the height for whatever length switch you may need for your BT altimeter board distance.
Use a brass nut to solder to the brass strip. Before you do that, however, thread a stainless steel screw into the brass nut to keep the threads clear. The stainless won't become soldered to the brass so you can remove it.
I use 6-32 nuts and screws of various lengths.
It does take a surprisingly large amount of solder to complete the connection. Don't be overly concerned with that - it'll work.
The most dificult part is measuring and deciding where to put the access/vent holes in the airframe. I haven't done enough of them to offer any advice here - you're on your own.
Good luck!
I like rstaff3's saying the "twist and tuck" folks are minimalists. I now consider myself a 'rocket electronics minimalist' as I don't like the idea of too many switches (read "failure points") myself. I have only used screw switches or the "twist and tuck" method on the battery power wire myself. The ejection charge wires I leave unbroken.
After I posted this message I realized I should probably add the following if you plan to make a screw switch yourself:
Use brass strip from the hardware store for the body. It bends easily with needle-nose pliers. Vary the height for whatever length switch you may need for your BT altimeter board distance.
Use a brass nut to solder to the brass strip. Before you do that, however, thread a stainless steel screw into the brass nut to keep the threads clear. The stainless won't become soldered to the brass so you can remove it.
I use 6-32 nuts and screws of various lengths.
It does take a surprisingly large amount of solder to complete the connection. Don't be overly concerned with that - it'll work.
The most dificult part is measuring and deciding where to put the access/vent holes in the airframe. I haven't done enough of them to offer any advice here - you're on your own.
Good luck!
rstaff3
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Ack, was reading fast on the way to an errand, and oviously didn't parse Dynos post. I AM an advocate of protecting the ematches. I am NOT an advocate of most switches to power up the unit. An excpetion is the type shown by BHP.
mike_bar
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BHP,
I like your screw switch. I will have to make one of these.
DynaSoar
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A shunt is not a switch to power something up. It is a grounding bus between leads to a critical component, in this case one with a pyro charge. It does not have to be any more complicated than the alligator clip-on-ematch idea, or twisting (in this case, untwisting) two wire ends. The worst that can happen if you forget to unshunt the leads is it'll fail your continuity test before you launch it.
You DO test continuity before launching, right?
(That's a generic "you", rstaff3).
If it needs to be done before you fly and it's not safe if not done, you should be using a "Remove before flight" tag on it, whether it's something to actually remove, or a test to perform and the tag serves only as a reminder.
It is true that any additional steps add complexity. However, inadequate complexity, in being able to launch a rocket in an unsafe condition, is as much a problem.
BHPs idea is a good one.
I was thinking of soldering something like the tail end of a Copperhead to the two sides of the leads, and clamping an alligator clip on it to short them. That can be placed just inside a vent hole where it doesn't stick out but is easy to reach.
DynaSoar
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Here's an idea.
Get a headhpone jack and plug to match it.
Mount the jack in a vent hole. Run the ground side of all circuits needing shunting to the ground side of the jack, the hot leads to the hot side of the jack.
Short the hot and ground leads together inside the plug.
With the plug out, everything works normally. With it in, the firing circuits are all shorted and nothing can fire due to power or static.
There are very few things that can go wrong, and the few possibilities would result in fail to short, not prevent proper operation.
If you're afraid you might forget to remove it before flight, make the vent hole directly in line with your buttons/lugs. With the plug sticking out you can't put it on the rod/rail. The "Remove before flight" tag becomes extraneous, except for the coolness factor. And to help find the plug when you drop it.
Bonus: the mounting hardware for the jack protects and strengthens the vent hole.
If you use a stereo jack/plug, don't forget there are two hot leads on both. Short them together on both jack and plug.
Get a headhpone jack and plug to match it.
Mount the jack in a vent hole. Run the ground side of all circuits needing shunting to the ground side of the jack, the hot leads to the hot side of the jack.
Short the hot and ground leads together inside the plug.
With the plug out, everything works normally. With it in, the firing circuits are all shorted and nothing can fire due to power or static.
There are very few things that can go wrong, and the few possibilities would result in fail to short, not prevent proper operation.
If you're afraid you might forget to remove it before flight, make the vent hole directly in line with your buttons/lugs. With the plug sticking out you can't put it on the rod/rail. The "Remove before flight" tag becomes extraneous, except for the coolness factor. And to help find the plug when you drop it.
Bonus: the mounting hardware for the jack protects and strengthens the vent hole.
If you use a stereo jack/plug, don't forget there are two hot leads on both. Short them together on both jack and plug.
rstaff3
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I understand what a shunt is and I thought I was agreeing with you in principal on that subject. I am almost convinced that a power switch isn't that bad, but not quite. I still don't need to power switch my altimeter. A reset altimeter is as bad as premature ejection. And yes, it is a good idea to verify continuity after the jostling (sp?) on the way to the pad.
PS the screw switch shown should be effective and safe.
rstaff3
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You have to think about the effects of such a momentary failure. My previous example of a power circuit breaking at drogue ejection is a bad thing. A momentary interruption of the circuit to the main charge, at that time, isn't.
DynaSoar
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You wouldn't need 2 plugs. Anything needed shunting could go to one. Unless you chose not to.
A jack would offer very little obstruction to the hole. A 1/4" jack takes a 5/16" or 3/8" hole to mount into. The 1/4" without the plug in it would be essentially still a 1/4" hole. Same with mini-size 3mm jacks. That's the size of the hole that remains, appx 1/8".
Can you guys just tell me if this is correct. The power switch is no problem because I have a capaciter. The only concern is that the shunt switch will flicker momentaraly. This would only happen while the rocket has high G's... so it could flicker during boost and mabye right after it. But the rocket is going very slow around apogee and while under the drogue so why would the switch be shunting accidently at apogee or at main deployment? Please just give an answer and don't give any more examples.
A
Austin
Hey Guys,
I wanted to add a few comments here. For models under 10 lbs, I do not believe shunting is necessary. This doesn't mean it cannot be applied to provide an additional layer of safety, which is why they are used. What it does mean is that these models are smaller in size making it more difficult to incorporate a shunt system. In addition, they do not pose as much of a safety hazard as the larger models due to thier lower mass.
That is where shunting comes in to play and should be used...to help prevent accidental discharge of ejection loads, staging, etc...on larger and heavier models. A true shunt would both remove the connection from the source and short the leads to the load, such as a match or igniter.
This is where a double pole rotary switch would work the best as it could perform both tasks at once. The screw switches are IMHO the most reliable, followed by high detent, high quality rotary switches. If wired correctly, Phone Jacks make a good shunting device for shorting leads and have been used on many models with great success. Note I said used correctly because all switches have their limitations. That is why the die hards still just twist wires together for shunts and powering/arming their electronics.
That is the beauty of our hobby, there are so many ways to accomplish the same end result and although some may be a bit more reliable than others, they all produce the same end result.
Carl
I wanted to add a few comments here. For models under 10 lbs, I do not believe shunting is necessary. This doesn't mean it cannot be applied to provide an additional layer of safety, which is why they are used. What it does mean is that these models are smaller in size making it more difficult to incorporate a shunt system. In addition, they do not pose as much of a safety hazard as the larger models due to thier lower mass.
That is where shunting comes in to play and should be used...to help prevent accidental discharge of ejection loads, staging, etc...on larger and heavier models. A true shunt would both remove the connection from the source and short the leads to the load, such as a match or igniter.
This is where a double pole rotary switch would work the best as it could perform both tasks at once. The screw switches are IMHO the most reliable, followed by high detent, high quality rotary switches. If wired correctly, Phone Jacks make a good shunting device for shorting leads and have been used on many models with great success. Note I said used correctly because all switches have their limitations. That is why the die hards still just twist wires together for shunts and powering/arming their electronics.
That is the beauty of our hobby, there are so many ways to accomplish the same end result and although some may be a bit more reliable than others, they all produce the same end result.
Carl
A
Austin
jraice...
If you use a shunt to short the leads of each e-match in shunt mode and then "open" this short before launch, there is nothing to cause an "intermittent" connection because the circuit is now open. The match wires can remain connected to the altimeter at all times. Vibration will not effect this type of connection.
I would recommend using the shunt to parallel your ematch (as just mentioned), where the comments previous and yours appear to be discussing the actual disconnection of the match (series instead of parallel)...I would not use the disconnection method unless you use good detent rotary switches or the screw switch along with the parallel method...they are both test proven in my book. Remember though the purpose of the shunt is to prevent the match from lighting...opened in series does disconnect it from the device, but static electricity across that open lead can still cause the match to fire. But if the leads are shorted (parallel shunt method) they will never light...this is the safer way to do it.
Remember that the whole purpose of the shunt is to add a layer of safety while handling the rocket and prepping it on the pad. Once that is completed, the shunts have done their work and can be removed before the button is pressed. For this reason, they should be designed so they do not add any more problems. If you have any more questions, fire away and I will try to assist.
Carl
If you use a shunt to short the leads of each e-match in shunt mode and then "open" this short before launch, there is nothing to cause an "intermittent" connection because the circuit is now open. The match wires can remain connected to the altimeter at all times. Vibration will not effect this type of connection.
I would recommend using the shunt to parallel your ematch (as just mentioned), where the comments previous and yours appear to be discussing the actual disconnection of the match (series instead of parallel)...I would not use the disconnection method unless you use good detent rotary switches or the screw switch along with the parallel method...they are both test proven in my book. Remember though the purpose of the shunt is to prevent the match from lighting...opened in series does disconnect it from the device, but static electricity across that open lead can still cause the match to fire. But if the leads are shorted (parallel shunt method) they will never light...this is the safer way to do it.
Remember that the whole purpose of the shunt is to add a layer of safety while handling the rocket and prepping it on the pad. Once that is completed, the shunts have done their work and can be removed before the button is pressed. For this reason, they should be designed so they do not add any more problems. If you have any more questions, fire away and I will try to assist.
Carl
UhClem
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I have used a DPDT slide switch from Radio Shack (definitely not on the high end of the quality scale) as a safe/arm switch on several flights with no problems.
The switch is wired so that the two commons go to the e-match. One set of contacts is wired together to short the e-match when the switch is in the safe position. The other set of contacts goes to the altimeter. The dynamics for these flights were not terribly great. (Aerotech Initiator on G64's and such.) The switch was mounted so that motor acceleration would push the slide to the armed postion.
I have also used the same part to switch power to two altimeters (One switch for each altimeter with contacts paralleled.) and also to switch the pyro power on three flights. One of which was my level 3 certification flight. The switches were mounted so that acceleration was 90 degrees from the slide switch action. Everything worked.
Because I am certain that the reliability of electronics is not 100%, I never rely on a single altimeter for deployment. Either motor ejection, a timer, or another altimeter acts as backup.
This whole arguement on shorting e-matches comes down to a struggle between flight safety (you want to deploy the parachute) and ground safety (you don't want it to happen on the ground).
Use the switch to improve ground safety.
Use redundant deployment mechanisms to improve flight safety.
The switch is wired so that the two commons go to the e-match. One set of contacts is wired together to short the e-match when the switch is in the safe position. The other set of contacts goes to the altimeter. The dynamics for these flights were not terribly great. (Aerotech Initiator on G64's and such.) The switch was mounted so that motor acceleration would push the slide to the armed postion.
I have also used the same part to switch power to two altimeters (One switch for each altimeter with contacts paralleled.) and also to switch the pyro power on three flights. One of which was my level 3 certification flight. The switches were mounted so that acceleration was 90 degrees from the slide switch action. Everything worked.
Because I am certain that the reliability of electronics is not 100%, I never rely on a single altimeter for deployment. Either motor ejection, a timer, or another altimeter acts as backup.
This whole arguement on shorting e-matches comes down to a struggle between flight safety (you want to deploy the parachute) and ground safety (you don't want it to happen on the ground).
Use the switch to improve ground safety.
Use redundant deployment mechanisms to improve flight safety.
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