Quantcast

LiquidFyre Rocketry Switch

The Rocketry Forum

Help Support The Rocketry Forum:

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
I am working on a new safety switch designed specifically for rocketry. Anywhere that your electronics will ignite a motor, and also in some ejection setups this switch is designed to improve safety and prevent accidental firing from mistakes or component failures.

The switch will be a highly vibration/acceleration resistant rotary switch designed to be mounted securely to the tube wall. It will have a universal key that cannot be removed in the first “Safe” position and will have a remove before flight tag. There is an additional “Safe” position in which the key can be removed if necessary, and of course it will be removable in the “Armed” position. There will be a colored indicator displaying the switch state. The switch will be armed after powering your electronics as the last step before flight. I am also considering offering an option with an additional pull pin that can be pulled on a string from a safe distance.

When in the safe position the switch will be shorted on both the altimeter and ignitor sides and there will be no circuit between the altimeter and ignitor. Additionally, when “Safe” there will be a replaceable fuse and buzzer connected to the altimeter. When the electronics are powered on in the case of a faulty altimeter or wiring sending high current to the ignitor the fuse will blow and the buzzer will sound to alert you of the problem. With the fuse blown no connection will be made between the electronics and ignitor. When armed the switch will un-short and connect the altimeter through to the ignitor as normal.

I have already completed a number of tests of the switch circuit with, low current e-matches and high current ignitors, with small single lipos and a 12V 20A wall supply, simulating an altimeter firing before and after armed. In every test the circuit performed as expected, the pyros fired when intended and at no other time.

The switch is being designed to be able to handle 20+ amps but an official spec will need to wait for testing. It should work at any voltage between 3.5-16V (buzzer limited).

Any feedback on this would be greatly appreciated as I continue testing and development.

LFR Switch 1.png
LFR Switch 2.png
 

Cameron Anderson

Well-Known Member
Joined
Sep 14, 2018
Messages
742
Reaction score
302
Location
Reno, NV
Will the switch have some sort of continuity outside the firing circuit when in the "safe" mode to pass initial altimeter power up testing?
I've always assumed (but never confirmed) that if a circuit fails the initial power up test (on a Raven 4, for example), that the failed circuit would not function if a switch was flipped and continuity was achieved after the test.
 

mikec

Well-Known Member
Joined
May 9, 2009
Messages
2,436
Reaction score
345
I've always assumed (but never confirmed) that if a circuit fails the initial power up test (on a Raven 4, for example), that the failed circuit would not function if a switch was flipped and continuity was achieved after the test.
The Raven doesn't work that way. If you power it up with a channel open and subsequently close it, the beeps change, and the channel always tries to fire, open or not. I expect other altimeters work the same way (well, perhaps not the Marsa devices, it's not clear.)
 

Cameron Anderson

Well-Known Member
Joined
Sep 14, 2018
Messages
742
Reaction score
302
Location
Reno, NV
The Raven doesn't work that way. If you power it up with a channel open and subsequently close it, the beeps change, and the channel always tries to fire, open or not. I expect other altimeters work the same way (well, perhaps not the Marsa devices, it's not clear.)
That's very interesting. I want to play with that now and I'll need to test my Marsa now to see how it operates.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
Will the switch have some sort of continuity outside the firing circuit when in the "safe" mode to pass initial altimeter power up testing?
I've always assumed (but never confirmed) that if a circuit fails the initial power up test (on a Raven 4, for example), that the failed circuit would not function if a switch was flipped and continuity was achieved after the test.
The switch shorts the altimeter side in the safe mode so the altimeter would see this as being connected.

Looks neat! Do we want a fuse?
The point of the fuse is to prevent those scenarios when someone powers their electronics and due to a failed component or miswiring a motor lights or an ejection charge blows on the pad. We've all seen it happen. As long as the fuse is rated below your battery amperage capacity it will blow in these situations and the buzzer will sound. Heading back to your table to replace a fuse and investigate a failure is a lot better than the alternative. In the case of everything working normally as long as it's properly sized the fuse will fire your pyrotechnics just fine, in testing I never had a fuse blow while firing the ignitors. Also the automotive style blade fuses should be resistant to G forces and vibration.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
I volunteer for field testing...I'm flying an MD 54mm head end ignition project next year.
Where are you getting your head end ignition hardware? My other new development is a reusable head end ignition closure with built in electrostatic discharge protection circuitry. I'm planning on posting about it soon, but if you want to flight test it as well we should talk. Send me a message here or call me at the number listed on my website.
 

Cameron Anderson

Well-Known Member
Joined
Sep 14, 2018
Messages
742
Reaction score
302
Location
Reno, NV
Where are you getting your head end ignition hardware? My other new development is a reusable head end ignition closure with built in electrostatic discharge protection circuitry. I'm planning on posting about it soon, but if you want to flight test it as well we should talk. Send me a message here or call me at the number listed on my website.
Message sent!
 

Kelly

Usually remembers to get the pointy end up
Joined
Apr 26, 2010
Messages
375
Reaction score
258
Location
Oregon
My altimeters check for continuity on start-up. How will that work if this device is used?
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,339
Reaction score
1,570
Location
Melbourne Australia
Be careful with fuse selection. Fuses work but they are quite agricultural. They have very wide tolerances and also need a lot more than their rated current to blow typically. For instance, a 7.5A fuse will likely take 30 seconds to blow at double the current (15A). The time comes down as the current goes up, but most fuses will not blow quickly at any current near the rating. Getting and reading the data sheets can be quite instructive, and is essential if you are trying to use a fuse value close to the maximum available current.
 

Kelly

Usually remembers to get the pointy end up
Joined
Apr 26, 2010
Messages
375
Reaction score
258
Location
Oregon
The switch shorts the altimeter side in the safe mode so the altimeter would see this as being connected.
So if the switch shorts the altimeter, then the altimeter is NOT checking my igniters for continuity.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
Any dimensions on this? I think it would be perfect for HEI.
Ask and ye shall receive (the thickness will vary a little by diameter this is for a 2" airframe):

Switch Dims.PNG



Be careful with fuse selection. Fuses work but they are quite agricultural. They have very wide tolerances and also need a lot more than their rated current to blow typically. For instance, a 7.5A fuse will likely take 30 seconds to blow at double the current (15A). The time comes down as the current goes up, but most fuses will not blow quickly at any current near the rating. Getting and reading the data sheets can be quite instructive, and is essential if you are trying to use a fuse value close to the maximum available current.
You are correct, though I think with proper sizing this will not be an issue for most systems as long as the battery can supply enough current the fuse will blow quickly. I probably wouldn't suggest using this with a 9V alkaline for example, though I wouldn't suggest lighting a second stage with one either. The primary thing with fuses that most people don't understand is they have different response rate ratings, not just current rating. Here is the datasheet for the fuses I am testing with:

Blade Fuse Datasheet

So if the switch shorts the altimeter, then the altimeter is NOT checking my igniters for continuity.
You are correct, until the switch is armed the continuity will not be measuring your igniters and will show as good. My understanding, as noted in the replies above, is that most altimeters won't have an issue with this. Without this short you lose the fusing ability and the switch would be no safer than any other setup. I will contact as many of the altimeter manufacturers as I can and verify their behavior. This will allow me to provide a list of altimeters that will be compatible.
 

phyzzld

Well-Known Member
TRF Supporter
Joined
Aug 19, 2017
Messages
76
Reaction score
16
Altimeters such as a Telemega has six pyros so clusters can have multiple air starts. Is there any chance to support more than one pyro channel with one key?
 

boatgeek

Well-Known Member
Joined
Dec 27, 2014
Messages
2,907
Reaction score
1,340
Disclaimer: I’m unlikely to be a customer for this switch.

That said, I like the form factor and the two safe positions. I think the feature of connecting the inputs with a fuse when the switch is safed really limits your market. If the input terminals are an open circuit in the safe position, you can use the switch for altimeter power too. That doubles (or more) your market. Also, for people using WiFi devices like the Egg Quantum or Proton and the switch in the output side, you’d want the switch to be open when powering up the altimeter so you don’t get a good continuity reading and go on with the launch. Yes, there’s a remove before flight tag, but that is still another source of failures.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
Altimeters such as a Telemega has six pyros so clusters can have multiple air starts. Is there any chance to support more than one pyro channel with one key?
At first no, but eventually this could be expanded to multiple channels pretty easily. It would probably get bigger though.

Fuses: Ematches will ignite before any fuse will open.
The fuse is meant to blow when while the switch if safed. At that point the charge is disconnected and the altimeter is shorted that way if a faulty altimeter is sending current when it's powered on the fuse blows. When the switch is armed the now blown fuse is in line with the charge preventing it from immediately firing.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
Disclaimer: I’m unlikely to be a customer for this switch.

That said, I like the form factor and the two safe positions. I think the feature of connecting the inputs with a fuse when the switch is safed really limits your market. If the input terminals are an open circuit in the safe position, you can use the switch for altimeter power too. That doubles (or more) your market. Also, for people using WiFi devices like the Egg Quantum or Proton and the switch in the output side, you’d want the switch to be open when powering up the altimeter so you don’t get a good continuity reading and go on with the launch. Yes, there’s a remove before flight tag, but that is still another source of failures.
I understand your first point, but this product isn't meant to be used as a power switch it is specifically meant to improve the safety of second stage motors and prevent injury due to failed hardware, faulty wiring, or other accidental means. It has internal circuitry for this purpose it is very much not just a switch. There are already a lot of good products for that. Eventually I would like to make other versions of the switch to be used for power or other purposes which could use the same key setup but be more compact. As for your second point you would check the continuity after arming which would give you the true continuity of your charges.
 

Rob702Martinez

Zip-Tie Oversight Committee
TRF Supporter
Joined
Dec 30, 2015
Messages
1,289
Reaction score
295
Location
Las Vegas
At first no, but eventually this could be expanded to multiple channels pretty easily. It would probably get bigger though.



The fuse is meant to blow when while the switch if safed. At that point the charge is disconnected and the altimeter is shorted that way if a faulty altimeter is sending current when it's powered on the fuse blows. When the switch is armed the now blown fuse is in line with the charge preventing it from immediately firing.
When its on the pad how will you know if the fuse is blown? All things considered that we are arming when on the pad anyways. Or would the blown fuse trigger continuity fails?
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
There is a buzzer that only sounds when there is current and a blown fuse. So assuming you check the fuse before installation the current that blows the fuse will sound the buzzer. Also with the fuse blown I don't believe the buzzer is a low enough resistance to show continuity on the channel, I will have to test.
 

Ravenex

Sponsor
TRF Sponsor
Joined
Aug 13, 2014
Messages
932
Reaction score
40
When its on the pad how will you know if the fuse is blown? All things considered that we are arming when on the pad anyways. Or would the blown fuse trigger continuity fails?
I did some testing with an Eggfinder Quantum, a Perfect Flight Stratologger, and a Missileworks RRC2+. All three altimeters update the continuity continuously, if the continuity changes from good to bad or vice versa the indicators change accordingly.

Both the Quantum and the Stratologger have the same behavior and give the correct response in all cases. In the "Safe" position indicating a blown fuse as bad continuity and a good fuse as good continuity. In the "Armed" position they shown a blown fuse OR bad ignitor as bad continuity and both a good fuse AND good ignitor as good continuity.

The RRC2+ always shows good continuity in the "Safe" position and only shows the status of the ignitor in the "Armed Position". This is because the RRC2+ is sensitive enough that the buzzer completes the circuit regardless of the fuse state. This is still workable by using the buzzer to indicate the fuse state and the altimeter to indicate the ignitor state. If you check the fuse before installation in the rocket and the buzzer doesn't sound in the "Safe" position then the fuse is still good. So the altimeter indication in the "Armed" state would then be enough to tell the ignitor state. Still, I will talk to Jim at missile works to better understand the continuity test threshold and see if I can make some adjustments to improve this behavior.

I can borrow a Featherweight Raven to test with some time soon. I will also contact the other altimeter manufacturers to find out about their continuity tests.
 

Nytrunner

Pop lugs, not drugs
Joined
Oct 15, 2016
Messages
7,155
Reaction score
2,619
Location
Huntsville AL
I think this is a great mechanism for safing/arming a head end ignition system.

Im not sure I'd employ it for general deployment pyros, but for staging I think its great
 

jderimig

Sponsor
TRF Sponsor
Joined
Jan 23, 2009
Messages
3,200
Reaction score
599
You are correct, until the switch is armed the continuity will not be measuring your igniters and will show as good. My understanding, as noted in the replies above, is that most altimeters won't have an issue with this. Without this short you lose the fusing ability and the switch would be no safer than any other setup. I will contact as many of the altimeter manufacturers as I can and verify their behavior. This will allow me to provide a list of altimeters that will be compatible.
For the Marsa altimeters a short detected on a pyro channel will fail the power-on self test with one exception. If the channel is programmed as a Motor-Timer for igniting a motor that channel will always pass because it is assumed that there could be safety opens or shunts in the circuit. Any other event programmed (apogee, altitude or regular timer) will fail if there is a short on the outputs.
 
Top