Activating/deactivating a switch without piercing the body tube

[Zeus-cat]

Does anyone have a good way to activate and deactivate a switch for an altimeter that doesn't require sticking something through the sdie of the body tube? I have a small rocket that I would like to set up for dual deploy, but I don't want to use a switch that requires a probe or a screwdriver through the side of the rocket.

Trying to get everything properly aligned in a body tube that is less than 1.5 inches in diameter is a nightmare. I would like to use something like a magnetic switch. Does anyone know where I can get something like this? There is an altimeter vendor on the forum that has magnetic switches for his altimeters, but they are not for sale as stand alone items.

 

[WillMarchant]

Adrian is doing magnetic arm switches at https://www.featherweightaltimeters.com/Av-Bay_Components.php. Is that who you were talking about?

 

[edwinshap1]

i just ran the arming wires through the bulkhead and sealed with hot glue. then i twist them together and put some tape on. then i put the coupler back into the tube and it works fine if i need to disarm i just take the coupler out and pull the wires apart.

 

[troj]

Adrian's magnetic switches should be available soon. Sounds like they're exactly what you're looking for.

-Kevin

 

[Zeus-cat]

Adrian's switches would be great, but the availabilty ststus has not changed in months. Does anyone have an alterrnative idea?

 

[BartDoe]

I think what you're looking for is a "Normally Open" magnetic (reed) switch - see what they have at Jameco - https://www.jameco.com/webapp/wcs/s...ch_type=jamecoall&freeText=magnetic+switch+NO .

The way I understand it, while the two halves of the switch are in contact, the switch is "open" (off). When the 2nd half is removed, the switch is closed (on). To use this in an E-bay, you'd need to have one side of the switch on the inside of the tube, very near to the surface. The 2nd part would be on the external surface directly above the 1st part. This will keep the switch open until you're ready to launch, when you'd simply remove the outside part.

You'd probably have to do some serious googling to find the right one for your purpose, but jameco, digikey, and mouser are good place to find stuff like this. Good luck.

DISCLAIMER: I've never used this method but I may try it now as it sounds intriguing.

 

[troj]

I'm not so sure I'd trust a reed switch in a rocket -- they're too susceptible to bounce.

-Kevin

 

[bobkrech]

I would think that you would want 2 magnetic switches: one to powerup the electronics and a second to powerdown, similar to the start and stop switchs on a drill press or similar contactor powered motor device.

If so, you can probabably use reed switches to set a latching flip-flop or similar electronic switch. If you require the reed switch to be on for several seconds before a state change, switch bounce should not be an issue.

Bob

 

[troj]

I would think that you would want 2 magnetic switches: one to powerup the electronics and a second to powerdown, similar to the start and stop switchs on a drill press or similar contactor powered motor device.

If so, you can probabably use reed switches to set a latching flip-flop or similar electronic switch. If you require the reed switch to be on for several seconds before a state change, switch bounce should not be an issue.

If you use a solid state switch of some sort that's triggered by the reed switch, sure.

But reed switches don't like the rather...aggressive...movements of rockets. I learned that the hard way when I had a G-powered rocket with a reed-switch activated strobe in the nose. I learned the hard way that it had the reed switch (and yes, I should've checked before flying it).

Needless to say, no way, no how would I ever use a reed switch to power electronics, nor would I approve one as RSO -- you come to me with a rocket armed via reed switch, and you've got an uphill battle to convince me it's not going to lose contact at the wrong time.

-Kevin

 

[crossfire]

I would guess your having vent holes in the ebay section of rocket. Just bring your 2 switch wires out of vent holes give them the old twist and go put a little tape on wires and push them back into hole. No mess no fuss no bad switch worries. its old school way.
works everytime.

 

[jms]

Just google for Hall effect sensors. Disruptions in the magnetic field, as opposed to full-on switches (which are mechanical and have obvious problems listed above).

There's obviously the photovoltaic option too. Piece of black tape over a light sensing hole, pull the tape off when you're ready to arm.

 

[G2Rockets]

I would guess your having vent holes in the ebay section of rocket. Just bring your 2 switch wires out of vent holes give them the old twist and go put a little tape on wires and push them back into hole. No mess no fuss no bad switch worries. its old school way.
works everytime.

The only problem I have seen with the twist and tuck method is disarming. you have to completely open the av-bay to disarm. there is a risk of a charge going off while disarming.

John

 

[rocketsmith]

So don't tuck, just twist the pair and tape to the outside of the airframe. It works for me every time.

 

[georgegassaway]

The only problem I have seen with the twist and tuck method is disarming. you have to completely open the av-bay to disarm. there is a risk of a charge going off while disarming.

I agree, I was going to post the same myself.

One of the worst-ever examples of this was a guy in the mid 1990's who had his altimeter inside the main body tube. So, to arm and disarm he put his arm inside of the tube. One day, something went wrong at launch, perhaps it was only one motor of a cluster ignited, or something like that. Anyway, it crashed a few hundred feet away. So, he goes to dis-arm it, sticks his arm into the tube, and "Boom", the altimeter fires the ejection because of the pressure changes inside the tube when he stuck his arm into it. He suffered burns to his hand, arm, and face, one of the most serious ground-ejection accidents I've ever heard of. Also one of the most preventable, and frankly most stupid “accident waiting to happen” design ideas, ever.

I also do not trust magnetic switches either.

The SAFEST WAY is to use some sort of switch that is activated MANUALLY from the OUTSIDE of the rocket.

And actually for a lot of rockets, two switches should exist. One to turn on the system, and one to "Arm" the pyros (ejection, upper stage, whatever). So you turn the system on first. Ideally with a piezo beeper or LED, or something, so you can know the system is turned on properly. And finally, the "Arm" switch, which should be the LAST THING that you do at the pad before getting away from the pad seconds later.

Lots and lots of ground accidental firings have occurred due to not doing that.

Always assume the thing is going to go off by accident........

One project I did, involved two R/C Rocket Boosted Gliders, One (2X SkyDart) riding on piggyback of a larger winged booster. When the booster glider burned out then I flipped a switch on my transmitter to ignite the engine in the 2X SkyDart, for staging. A big concern was accidentally having the upper stage fire while on the ground. So, the “arm” switch for the glider was this simple: The igniter had a plug soldered to it, to fit into a socket in the larger winged booster. The ignitor plug was not put in until shortly before launch, the last thing done before leaving the pad, with liftoff normally 1-2 minutes later.

I am attaching a photo of one of my space shuttle models. This photo shows where the "Power" and "Arm" switches are located (Power to turn on the flight computer, and arming as final arm of the ejection charges). Now, you won't SEE the switches, but that is indeed the point. I'll make another posting later to show where they really are and how they are used.

- George Gassaway

 

[georgegassaway]

What I did with the shuttle was to mount two lever switches inside of the hollow ET nose cone.


SPDT type lever switches. Wired so when the lever was pressed (pin in place), the switch was off, and lever not pressed (pin removed), switch was on.


I did make sure the levers were oriented sideways, so neither liftoff nor deceleration forces could move the arms either way



The switches were mounted in such a way that they could be pressed by 1/32" diameter pins, inserted thru the nose cone's side.



I camouflaged the holes by locating them in-between a conduit tray and pipe that run down the side, in the area inside the red circle of this copy of the first photo:

Of the attached photos below, the first two show the lever switch assembly, with one "remove before flight" pin inserted.

The third pic shows the two holes in the ET nose, before the assembly was glued in place inside of it.

Final pic, the model on pad with the "remove before flight" pins in place. Two (pink) for the ET's Power and Arm switches, and one (orange) for the Orbiter's similar internal lever switch for power for the R/C system.

- George Gassaway

 

[kramer714]

jumping on the band wagon, I think I would have a hard time buying off a reed switch or magnetic switch as RSO unless it used some type of latching relay to turn things off and back on.

Having said all that, it isn't that hard to line up stuff in small rockets, I have a minimum diameter RATTWorks H80, 29mm. I made a battery / altimeter / switch sled that uses an o ring to seal itself in, think a plunger in a syringe where the syringe is the body tube. I started with a delrin rod and pocketed everything out. It slides in and is held in place by a bonded in piece of coupler (keeps it from going too far up) and the nose cone screws into it (keeps it from going too far back) using a short piece of threaded rod (10-24). I use a wood dowel or chop stick to schtup it in there. The screw switch is behind the vent hole. I have a mark on the sled and on the body tube, just line them up as you are pushing it in and the vent hits the screw hole. Simple and if anything goes wrong (read BOOM) I'm never touching or looking at the charge.

Originally, I was going to use a modified Mic plug and push a metal pin in to short the two leads, use a plastic one to push out the metal (turn on and off) the screw switch was simpler.

I can send pictures if you want, I just need to dig it out of the mess I brought back with me from NSL2011.

 

[troj]

One of the worst-ever examples of this was a guy in the mid 1990's who had his altimeter inside the main body tube. So, to arm and disarm he put his arm inside of the tube. One day, something went wrong at launch, perhaps it was only one motor of a cluster ignited, or something like that. Anyway, it crashed a few hundred feet away. So, he goes to dis-arm it, sticks his arm into the tube, and "Boom", the altimeter fires the ejection because of the pressure changes inside the tube when he stuck his arm into it. He suffered burns to his hand, arm, and face, one of the most serious ground-ejection accidents I've ever heard of. Also one of the most preventable, and frankly most stupid “accident waiting to happen” design ideas, ever.

First alt bay I ever put in a rocket was close to that bad, but not quite -- I made the mistake of following direction from someone else, without thinking it through. After I had flown it a few times, I realized it was a really bad idea to be sticking my arm into a tube alongside a live charge. I've not flown it since (yep, it's been a hangar queen for quite a while!) and won't, until I get around to fixing that design flaw.

And actually for a lot of rockets, two switches should exist. One to turn on the system, and one to "Arm" the pyros (ejection, upper stage, whatever). So you turn the system on first. Ideally with a piezo beeper or LED, or something, so you can know the system is turned on properly. And finally, the "Arm" switch, which should be the LAST THING that you do at the pad before getting away from the pad seconds later.

I'm going to disagree with you a little bit on this...

First, I don't like multiple switches, as it's another failure point. But I can live with the introduction of the failure point more than I can live with the idea of arming the charges as the last thing.

Recovery should be armed before the igniter is hooked up. That way, should something go awry with the launch control system and your motor lights as soon as you hook up the leads, then you have an active recovery system.

In my opinion, it should be...

1) Place rocket on pad
2) Raise rocket to launch position
3) Arm recovery electronics
4) Verify launch system is safe
5) Install igniter
6) Connect igniter

The reality? Launch systems are another device, and any device can suffer a failure, which may well make it "hot" when you don't expect it.

-Kevin

 

[bobkrech]

If you use a solid state switch of some sort that's triggered by the reed switch, sure.

But reed switches don't like the rather...aggressive...movements of rockets. I learned that the hard way when I had a G-powered rocket with a reed-switch activated strobe in the nose. I learned the hard way that it had the reed switch (and yes, I should've checked before flying it).

Needless to say, no way, no how would I ever use a reed switch to power electronics, nor would I approve one as RSO -- you come to me with a rocket armed via reed switch, and you've got an uphill battle to convince me it's not going to lose contact at the wrong time.

-Kevin

Kevin

I wouldn't design a rocket with a reed switch either, nor would I use a locking switch. If a rocket lands with failed pyros, I want anyone to be able to safe the charges simply by turning or pushing a switch to the off position.

Bob

 

[Adrian A]

Adrian's switches would be great, but the availabilty ststus has not changed in months. Does anyone have an alterrnative idea?

As an update, my prototype magnetic switch passed its high-current and high voltage tests this morning. I'll be ordering parts this week and I should have production units ready to ship in about 3 weeks.

Here are some specs:

• Battery voltage up to 16 V
• High-side switch handles current up to 20 Amps, with on-resistance of 10 to 20 mOhms
• 100% solid state, surface mounted parts
• Latched switch position with capacitive hold-up to retain state during power outages of several seconds.
• Size: 0.54" x 0.72" x 0.13"
• Battery activation/deactivation range ~ 1" with a small rare-Earth magnet
• 4-40 mounting screw holes designed to be used as wire terminal connections. Wire holes included under the screw heads for wire-wrap security and/or soldered connections.
• 3 wires required for connection: Ground, Arm in + and switched Arm out +.
• Very low standby power: ~2.4 micro-Amps means over a week of standby time even for a tiny 130 mAhr battery

This morning I ran 10 Amps through a 1.2 Ohm resistor and the switch didn't get warm (but the load resistor sure did!). There are a couple more tests that I'm going to run, but there's not much risk of a surprise at this point. I have also hooked this switch up to one of the tiny 130 mAhr li-polymer batteries I like to use, and I only lost a few mV over the course of a week. You'll need to disconnect your battery for long-term storage, but setting up an av-bay a week or two before the launch won't be a problem.

 

[The EGE]

Adrian, those sound really awesome. Keep us updated.

 

[troj]

As an update, my prototype magnetic switch passed its high-current and high voltage tests this morning. I'll be ordering parts this week and I should have production units ready to ship in about 3 weeks.

Excellent news! A friend has been waiting for these -- I'll pass the word along to him.

-Kevin

 

[Trident]

Does anyone have a good way to activate and deactivate a switch for an altimeter that doesn't require sticking something through the sdie of the body tube? I have a small rocket that I would like to set up for dual deploy, but I don't want to use a switch that requires a probe or a screwdriver through the side of the rocket.

You could install a small screw that when tightened down flush, completes the circuit. One way to do this is to have two metal leafs, one solidly anchored, and one that is flexed to be normally open, and is pressed into the closed position by the screw. No bounce, and a nice solid electrical connection.

 

[Blackfly]

Check out "Proxy Sensors"; We use them a lot at work for I/O applications and safety barriers, there are thousands of models; get them as surplus off ebay. Its not too difficult to incorporate such a switch, just make sure you have a buzzer or led to indicate your I/O status.

for similar reasons(aesthetics), I use these on my RC Helis. No problems whatsoever in hundreds, if not thousands of flights.
https://www.hkm-models.com/Emcotec Switches.html

Curiously, if you're running a baro altimeter, why not just use one of your porting holes as a means of accessing your I/O switch? Screw switches from aerocon systems are great and super reliable.

Patrick

PS..... or wait for Adrians Mag switch; sounds like a winner to me!!

 

[Zeus-cat]

Looking forward to checking out your mag switches Adrian! A buddy of mine might be interested in one of them too.