Yes, that thinking was incorrect.
LPR Idea: 12V Rocket Launch System Schematic Using Transistors Configured as Darlington Pair; Also MOSFET-based Circuit
- Thread starter brockrwood
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If a series igniter fails, the launch fails. Fix it, launch again. If a parallel ignitor fails the rocket can go sideways. Really. you cannot see the difference ....
I've seen a series string of igniters fail only lightning 2 motors out of 4.
Did the ignitors fail? Or did they not manage to light the motor? Were they all in properly? Which ignitors? Were they all tested beforehand? How old were the motors? What were the motors? Was there a mix of motor composition types?
There are more things that can go wrong with a cluster.
If you say that you need...
a match that will fire
Positioned at the correct position in the motot and will stay there as all motors get lit.
augmentation of that to initiate motor(diped etc)
Motor composition that will ignite( white lightning has a high chuff on the pad history)
So 4 things that have to go in your favour when you perss the button. 2 motors 4x4=16 things 3 motors 4x4x4 at 4 motors you may be able to have a single failure and a safe flight......
As Aerotech has stated, (on the dedicated Aerotech thread here) their ignitors are NOT SUITABLE for clusters. I expect Estes would say the same. They are not matched. Electrically or performance-wise.
All initiaton matches etc, should be tested to ensure they are matched, and should all be identical.
If you intend to fire clusters, you should use matched electric matches. MJG matches would be suitable. Dipped and enhanced for larger motors as appropriate. I'm not going into that here.
When people don't understand the fundamentals of how pyrotechnics are initiated, the differeing speeds of ignition for different compounds, the performance of an igniter, the difference between a match, igniter, and an initiator, they should probably avoid clusters. Because in practice, they're trickier than they seem in theory.
Short version, you are responsible for what you launch. Including how you light it.
Whatever but 99% I've seen done use parallel ignition including all Estes motors.
So by what you gave as a statistic, 99% of all CLUSTER FAILURES ARE FIRED IN PARALLEL. And the failure you saw when using a series connection, makes all series connections wrong.
Of course, that's true, but not true. But that's the logical fallacy you're proposing elsewhere. ( Fallacy:- A fallacy, also known as paralogia in modern psychology, is the use of invalid or otherwise faulty reasoning in the construction of an argument that may appear to be well-reasoned if unnoticed)
I never said series connected igniters are wrong. I'm saying both are not 100% full proof.
Furthermore I don't need to read about your theories or analysis. Keep that crap to yourself.
Furthermore I don't need to read about your theories or analysis. Keep that crap to yourself.
I resemble that remark! ;-)
I am currently using a relay. But it is an automotive relay and requires a separate 12V power supply to make it go. I figured I could use transistors and it would dispense with the separate power supply. I figured transistors would be like a solid state relay.
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Use dipped ematches instead of Estes igniters for clusters. MJG sells some skinny ones for lighting Estes motors, a light coat of QuickBurst Procast will 100% guarantee that they light instantly, and draw a relatively low amount of current doing so.
I agree with just using relays, unless you are looking to learn more about MOSFETs by making a project. Just use the same 12V source for everything. This makes the system very simple. Keep the 12V battery out at the pad so it's close to the relays. The launch controller box needs one wire back from the pad to supply it with 12V, then a return wire for each relay coil. Add an additional relay as a master relay to kill power to the launch relays as a safety device (activated by a separate switch or key). The same 12V used to drive the relays works VERY well on igniters, especially Estes igniters. No more press the button and wait a couple counts... with 12V they go NOW.
That is what I use when flying all my various incarnations/upscales of the NCR Cluster Duck with black powder motors. I have always used them in series, MJG specifically calls out that either will work: https://electricmatch.com/rocketry/see/23/6/bp-rocket-starters
If you want to use a 12 v relay, use one of the up down converters to supply the voltage for the relay. Then you can use any appropriate power supply in the range 4v to 35v as a power source for firing and the relay coil will get 12v The relay coil would require a back emf diode across the coil.
https://www.ebay.com.au/itm/191736124198? I use these a lot just because of the any in, any out(up to 26v) properties.
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In post #24 there is a fault LED introduced to detect if the MOSFET has become a dead short. Unfortunately, as drawn I *think* the LED2 continuity check no longer works. The green LED lights whether there is a good igniter circuit or not. Great for testing the green LED is good, but no good for checking continuity because there is a power path through the red LED1 even with no igniter connected.
That was noted in the post that both LEDs will illuminate without an igniter connected. It's not a design fault. When an igniter is properly connected only the green LED will light when the button is pressed
That was noted in the post that both LEDs will illuminate without an igniter connected.
It's not a design fault. When an igniter is properly connected only the green LED will light when the button is pressed
Yes, I thought that was the intention. I also agree both will light without an igniter connected.
What I don't get (I'll wire this up so I can really "get it") is how we're preventing the green LED from lighting with a bad igniter connected. I thought that would be the same as no igniter connected, and we know it lights up then. <shrug>
What am I missing?
It's not a design fault. When an igniter is properly connected only the green LED will light when the button is pressed
Yes, I thought that was the intention. I also agree both will light without an igniter connected.
What I don't get (I'll wire this up so I can really "get it") is how we're preventing the green LED from lighting with a bad igniter connected. I thought that would be the same as no igniter connected, and we know it lights up then. <shrug>
What am I missing?
In this design it won't prevent that although both will be less bright. It's all in the interpretation of the status of the LEDs.
Both LEDs ON indicates there both good and no igniter is connected.
I can design the circuit to isolate the two LEDs but it involves more circuitry. Trying to keep it simple without any electronics.
I don't use a switch in my controller to confirm continuity. When the battery is connected and both LEDs light up that tells me everything is OK. Connect igniter and red LED goes OFF, green LED stays ON, meaning all is good.
In addition I can monitor the status of the igniter continuously.
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Thanks, @sghioto , that's what I was hoping was the answer. It's a matter of carefully choosing resistor values and getting used to what a good vs bad indication looks like. Fair enough.
What I threw together is more complex, and loses the green LED test. In exchange, the LEDs are definitely all on or all off -- in bright light I might need that.
I added a momentary Test button. Pressing that will confirm the red LED is good and also tell me if I have igniter continuity. If not pressed, a red LED says the MOSFET is shorted, and the green is always off.
J3 is the igniter leads connector.
With an un-pressed switch:
- D6 has 12V and is monitoring DS for a short.
- D7 is disconnected.
When you press the switch:
- The 12V is removed from the igniter/Drain net (pink in the drawing). Instead the 12V flows through D6 to ground, confirming it is good.
- D7 is switched into the igniter/Drain junction. There's now no 12V on there. D7 will light only if there is good continuity through the igniter wires (remember DS is not conducting).
It's worth noting the igniter has to be armed (I have an automotive relay isolating the igniter positive wire from power until you've connected everything) to check continuity.
There's no such requirement for checking the MOSFET and D6. You can check that before arming the igniter (which is good, since a shorted DS may cause an unintended launch).
What I threw together is more complex, and loses the green LED test. In exchange, the LEDs are definitely all on or all off -- in bright light I might need that.
I added a momentary Test button. Pressing that will confirm the red LED is good and also tell me if I have igniter continuity. If not pressed, a red LED says the MOSFET is shorted, and the green is always off.
J3 is the igniter leads connector.
With an un-pressed switch:
- D6 has 12V and is monitoring DS for a short.
- D7 is disconnected.
When you press the switch:
- The 12V is removed from the igniter/Drain net (pink in the drawing). Instead the 12V flows through D6 to ground, confirming it is good.
- D7 is switched into the igniter/Drain junction. There's now no 12V on there. D7 will light only if there is good continuity through the igniter wires (remember DS is not conducting).
It's worth noting the igniter has to be armed (I have an automotive relay isolating the igniter positive wire from power until you've connected everything) to check continuity.
There's no such requirement for checking the MOSFET and D6. You can check that before arming the igniter (which is good, since a shorted DS may cause an unintended launch).
Another version isolating the LEDs using a LM393 dual comparator chip.
No test button(s) required. As long as the voltages on the + inputs (pins 3,5) of each comparator are higher then the - inputs (pins2,6) both LEDs are OFF
When an igniter is connected - pin2 becomes higher in voltage then + pin3 and turns ON LED2.
LED3 is activated when the ignition button is pressed activating Q1 causing the voltage on +pin5 to be less then -pin6 or if Q1 is defective.
Voltages shown are without igniter connected and Q1 not activated or defective.
No test button(s) required. As long as the voltages on the + inputs (pins 3,5) of each comparator are higher then the - inputs (pins2,6) both LEDs are OFF
When an igniter is connected - pin2 becomes higher in voltage then + pin3 and turns ON LED2.
LED3 is activated when the ignition button is pressed activating Q1 causing the voltage on +pin5 to be less then -pin6 or if Q1 is defective.
Voltages shown are without igniter connected and Q1 not activated or defective.
So, was this launch system ever built? What does it look like? How well did it perform? I'm gathering information and supplies to build one for me and my grandson to use on our local fields.
Not sure which system you mean. I have bench tested all circuits on a breadboard. Personally I would replace Q1 with a relay.
Still working on it. Between my day job and the puppy, so little time to dedicate to hobbies. :-(
Electronics are easy in theory. In a practical world, you have to put a bunch of protection systems in place for
Reverse polarity connection
Overvoltage protection, both battery supply and static voltages.
Input protection, to ensure no input voltage is above or below operational limits
And current protection.
You also have to understand what you're working with. A 12v battery is NEVER 12v. Almost never.
Electromechanical devices like relays, are less operationally sensitive. You can overvoltage a coil by a significant amount and it will survive.
With transistors and mosfets you only need to be a millivolt above a limit and you can let the smoke out without actually seeing it go....phut...
Reverse polarity connection
Overvoltage protection, both battery supply and static voltages.
Input protection, to ensure no input voltage is above or below operational limits
And current protection.
You also have to understand what you're working with. A 12v battery is NEVER 12v. Almost never.
Electromechanical devices like relays, are less operationally sensitive. You can overvoltage a coil by a significant amount and it will survive.
With transistors and mosfets you only need to be a millivolt above a limit and you can let the smoke out without actually seeing it go....phut...
Well, I could finish it. But I spend a lot of time on TRF. ;-)
Thanks for the update. Sometimes projects fizzle with no conclusion. Sometimes the project is a success and the OP just forgets to update the discussion. So at least now I know. Again thanks. Good luck and I’ll keep watching.
Sooner or later I will get it done. My hobby projects proceed at the speed of life.
The plan is to build @sghioto ‘s circuit in post no. 24. If you want to leap frog me I think that is the one to build.
Or the slightly simpler circuit by @sghioto in post number 19.
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