Chute Release

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The nichrome did indeed seem to heat up a bit after getting the command. Maybe double check your connections and make sure there isn't somewhere where you're getting excess resistance? Also if the battery is new, try charging it completely, discharge it, then fully recharge it again. Sometimes I've had new batteries act squirrely on their first charge.
 
Nichrome: Whats the C rating of your battery?
Springiness: The bundle looked awfully loose to me. I need to have it much tighter to get a good springy release.
 
I just re-watched Wallace's original video. I also think making the string tighter would help it melt faster, and therefore be in contact with the nichrome as short as possible while it's hot. Maybe that's what broke the wire; the wire momentarily became soft and delicate while hot, and since the elastic hadn't let go yet, it put too much pressure on the wire. It's a bit counter-intuitive, but making the elastic tighter might stress the wire less.
 
Yes, I agree, I thought the elastic cord was good and tight but it needs to be extra tight. I don't see a C rating on the battery, it is 7.4v 450mAh, should be enough (although I'm now curious what Wallace used). Makes sense that pressure on the nichrome while soft and delicate would break it. Also, the resistance of the nichrome is 27 ohms per foot and my run is a little shorter than Wallace's, so perhaps the increased current was a factor.
 
Yes, I agree, I thought the elastic cord was good and tight but it needs to be extra tight. I don't see a C rating on the battery, it is 7.4v 450mAh, should be enough (although I'm now curious what Wallace used). Makes sense that pressure on the nichrome while soft and delicate would break it. Also, the resistance of the nichrome is 27 ohms per foot and my run is a little shorter than Wallace's, so perhaps the increased current was a factor.

So maybe a heavier guage nichrome wire (more resistance) would do the trick.
 
Just the opposite, heavier gauge has less resistance, but good point. I'd prefer to stick with the 36 if possible, since I just bought 100 feet of it (lifetime supply), and even the 36 gauge is finer than hair, hard even to see with my bad eyes. I'm going to try a second test in a few minutes.
 
Just the opposite, heavier gauge has less resistance, but good point. I'd prefer to stick with the 36 if possible, since I just bought 100 feet of it (lifetime supply), and even the 36 gauge is finer than hair, hard even to see with my bad eyes. I'm going to try a second test in a few minutes.

I know about a lifetime supply! :D I shortest amount I can find on Amazon is 250'.

I hope the new test is a success.
 
I know about a lifetime supply! :D I shortest amount I can find on Amazon is 250'.
They sell 25' rolls on eBay but the 100' roll is just 10 cents more.

For the second test, I tied the elastic cord as tightly as possible. This time I did get a good springy release, but again the nichrome wire broke. Not that big a deal, the nichrome is easy to replace, but probably worth experimenting with different lengths and gauges to find a sweet spot where the elastic pops immediately and the nichrome lasts longer.

Also noticed that the 36 gauge nichrome is not that strong, one piece broke when I apparently tightened the brass nut a bit too much.

Finally, if I had to do this over again, I'd get a zip tie base like Wallace's, with the holes in the corners (e.g., https://www.alliedelec.com/product/thomas-betts/mpny-750-9-d/71523884/, rather than the ones now being sold at Lowes and Home Depot, where the screws have to go in at the sides, which blocks the hole and makes it more difficult to thread the nichrome.
 
Someone who knows more about this stuff than me could probably come up with a very durable nichrome-based device. We know from Wallace that a good resistance for the nichrome jumper is around 3 ohms. If we use heavier, stronger nichrome, resistance is less (close to a short) and we risk damaging the Quantum (36 gauge = 27 ohms per foot, 22 gauge = 1 ohm per foot). Maybe the trick is to use heavier nichrome but to not just use a short, straight piece, instead make a coil or other shape that is long enough to get the resistance up to 3 ohms? Or would that require a larger battery?
 
I treat it as expendable. On mine, it doesn’t burn thru every time. I still replace it. I think it’s more brittle after a heat cycle.
 
I treat it as expendable. On mine, it doesn’t burn thru every time. I still replace it. I think it’s more brittle after a heat cycle.
Yes, that makes sense, and that may be all we can do with a small battery for power. There can be long-lasting nichrome wire heating, such as toasters, hair dryers, space heaters, but I don't know if thicker nichrome can be made to work with a small battery.
 
It might be possible to reinforce the strength of the nichrome by wrapping a length of it around something. Obviously, this would have to be a non-conductive and heat resistant material. The first thing that came to mind was ceramics. You could sand down and shape a shard from a broken plate or bowl into a small rod to wrap the wire around, or you could try forming one out of clay and baking it. Anyway, the idea is the ceramic (or whatever) rod would take the structural load of the elastic, so the wire can heat up and cut the elastic without much pressure.
 
I took a look, and I'm using 32 AWG. 10 ohms/foot and I'm using about an inch. Mostly with a Quark, but I have flown it with the Quantum, too.

I played around with different batteries, testing to see just what kind of igniters the Quantum could light. Even though they're all 2S Lipo, there's a big difference between a 20C 200mAH Cox foamy park flier battery (4A) and the 45C 300mAH (13.5A) Turnigy batteries Cris suggests. It's not just the safe discharge rating, it makes a difference in what the battery can dump through the ignition circuit.

And while I've had some strange problem with eggtimers - cooking the outputs hasn't been one of them.
 
You can always use a load resistor, something in the 1W~10W and 1ohm~50ohm range like (these).
I can't see what use a load resistor would be. A load resistor is designed to cope with a nominal load of power ie. current x voltage drop across the resistor ie2. it's made from resistance wire that won't get too hot at the nominated power you're exposing it to.
What you're fundamentally constrained to in this application is current and power available from your (small) battery source - primary due to the internal impedance of the battery. You certainly don't want any further resistance in series with that impedance and the load resistance of your wire cutter and the wire from a wire-wound power resistor will likely be too heavy to heat enough for this app as the cutter itself. Yes, you can chop up the wire within the resistor to reduce its resistance (thereby increasing current through it) but you're probably better off just buying the same gauge resistance wire on its own if that's the intention.
As I see it there are a few avenues to possibly explore like using a small LIPO battery with a very high "C" rating for your power source thereby allowing the use of a thicker resistance wire... or scavenge an old camera flash circuit with the HV cap and use the heat from the flash tube to melt/sever the line... or if money is no issue, maybe you can try one of these.
 
... or if money is no issue, maybe you can try one of these.

I can imagine incorporating a cutting laser into a rocket would make some folks nervous for the safety aspect, but if done correctly with the laser essentially enclosed with nowhere for the light to go except into its own casing, it could certainly be an alternative. Not to mention, there are 450nm blu-ray laser diodes out there that are considerably cheaper and would only require a driver circuit to be built. Those don't have as much wattage as the one you suggested, so the elastic might take longer to cut (and it would work better with black elastic), but it could indeed work.

Dang it! Now I've got even more mad-scientist ideas I want to experiment with! As if I didn't have enough to begin with! :D
 
Thanks for the replies. I'm thinking there is a way to have a permanent nichrome hot wire with a small battery, but it would take someone with more knowledge than me to figure out the details.

Wallace, what battery are you using? Perhaps your nichrome is not breaking but my nichrome is burning through because of a difference in the battery, since everything else is the same.

There are some calculators that can tell you what gauge and length of nichrome is needed for a particular job, but to use them we'd need to know the desired temperature of the wire -- hot enough to cut the cord quickly but not so hot that the nichrome breaks, see https://www.easycalculation.com/engineering/electrical/nichrome-wire-calculator.php and https://www.jacobs-online.biz/nichrome/NichromeCalc.html (600F is recommended for styrofoam hot wire cutters).

@Edison: "It might be possible to reinforce the strength of the nichrome by wrapping a length of it around something." It is definitely the pressure of the cord on the nichrome that is causing my nichrome to break. I've fired it a few times with no cord and the nichrome turns red hot but does not break. Of course, we need substantial pressure to ensure the cord breaks, but Edison's idea to wrap the nichrome around a ceramic support could solve the problem.

@Charles: "I took a look, and I'm using 32 AWG. 10 ohms/foot and I'm using about an inch. Mostly with a Quark, but I have flown it with the Quantum, too." Good to know that 32 gauge works, it is substantially more durable than my 36.

@Tobor: "You can always use a load resistor, something in the 1W~10W and 1ohm~50ohm range." I don't think the nichrome will get hot if a resistor is in series.

@rocket troy and Charles: "there are a few avenues to possibly explore like using a small LIPO battery with a very high "C" rating for your power source thereby allowing the use of a thicker resistance wire." Agree that the C rating is critical, wish I knew what the rating is on my battery.

One guy made a durable electric cigarette lighter with 27 gauge nichrome and a pair of 3.7v Li-Ion batteries, although his batteries are quite large, see https://www.instructables.com/id/DIY-Homemade-Electric-Lighter/
 
I was actually thinking that if you have a high C battery now, maybe a low C battery would heat the wire more slowly.

Just what battery do you have?

And I still think you should just treat the wire as single use. 100' at 1-2"/flight is a lot of flights.
 
Someone who knows more about this stuff than me could probably come up with a very durable nichrome-based device. We know from Wallace that a good resistance for the nichrome jumper is around 3 ohms. If we use heavier, stronger nichrome, resistance is less (close to a short) and we risk damaging the Quantum (36 gauge = 27 ohms per foot, 22 gauge = 1 ohm per foot). Maybe the trick is to use heavier nichrome but to not just use a short, straight piece, instead make a coil or other shape that is long enough to get the resistance up to 3 ohms? Or would that require a larger battery?

You can always use a load resistor, something in the 1W~10W and 1ohm~50ohm range like (these).
....I don't think the nichrome will get hot if a resistor is in series.

Using a load resistor, say 5W at 10ohms, with a thicker gauge of nichrome wire would prevent a short from occurring across the Quantum and still allow more then enough current for the nichrome to glow.
 
Thanks for the replies. I'm thinking there is a way to have a permanent nichrome hot wire with a small battery, but it would take someone with more knowledge than me to figure out the details.

Wallace, what battery are you using? Perhaps your nichrome is not breaking but my nichrome is burning through because of a difference in the battery, since everything else is the same.
I've used several different LiPos but most have a C rating around 30. Keeping the elastic tight seems to be critical and making up a dozen or so, once you find the sweet spot, to keep on hand just makes things easier in the field. Personally, i enjoy creating/tinkering with things such as this much more satisfying than buying something.
There are some calculators that can tell you what gauge and length of nichrome is needed for a particular job, but to use them we'd need to know the desired temperature of the wire -- hot enough to cut the cord quickly but not so hot that the nichrome breaks, see https://www.easycalculation.com/engineering/electrical/nichrome-wire-calculator.php and https://www.jacobs-online.biz/nichrome/NichromeCalc.html (600F is recommended for styrofoam hot wire cutters).

@Edison: "It might be possible to reinforce the strength of the nichrome by wrapping a length of it around something." It is definitely the pressure of the cord on the nichrome that is causing my nichrome to break. I've fired it a few times with no cord and the nichrome turns red hot but does not break. Of course, we need substantial pressure to ensure the cord breaks, but Edison's idea to wrap the nichrome around a ceramic support could solve the problem.

@Charles: "I took a look, and I'm using 32 AWG. 10 ohms/foot and I'm using about an inch. Mostly with a Quark, but I have flown it with the Quantum, too." Good to know that 32 gauge works, it is substantially more durable than my 36.

@Tobor: "You can always use a load resistor, something in the 1W~10W and 1ohm~50ohm range." I don't think the nichrome will get hot if a resistor is in series.

@rocket troy and Charles: "there are a few avenues to possibly explore like using a small LIPO battery with a very high "C" rating for your power source thereby allowing the use of a thicker resistance wire." Agree that the C rating is critical, wish I knew what the rating is on my battery.

One guy made a durable electric cigarette lighter with 27 gauge nichrome and a pair of 3.7v Li-Ion batteries, although his batteries are quite large, see https://www.instructables.com/id/DIY-Homemade-Electric-Lighter/
 
Using a load resistor, say 5W at 10ohms, with a thicker gauge of nichrome wire would prevent a short from occurring across the Quantum and still allow more then enough current for the nichrome to glow.
Hope you are right, that would make it very simple to use long-lasting, thick nichrome. I'll try to find an appropriate resistor and report the results.

@Wallace - Thanks for the reply, guess we can rule our battery differences for why my nichrome burns through and yours does not.

I was going to try the first flight test today of the new device but it's too windy.
 
NiChrome wire is a resister. Same same. A resister (as in say a 1k) will get hot under load, that is what we desire. Don't overthink it. As long as your electronics of choice can handle the load it will work.
 
Point being, you "could" replace the NiChrome wire with an actual resistor and as long as it heats up hot and fast enough it will (has been done) work. Might be more repeatable but would probably cost more in the end..There's a point of diminishing returns. I'd suggest keeping it simple.
 
He's basically suggesting to put a high power rated resistor in series to save you from frying the driving FET/Transistor in your favourite altimeter/whatever ie. increasing the resistance in the circuit thereby reducing the current flow.
For me, putting a resistor in series is the very last option I would take. If the driving FET can't handle a current *burst* of that magnitude, then the 1st thing I'd be looking at doing is replacing the FET with something that will, thereby allowing me to maximise my current flow, thereby allowing me to utilise a heavier gauge of nichrome wire, which will not only provide more durability, but more reliability with the cut as more power is being delivered to the cut.
Or use a 2nd FET or relay to drive the current burst.
This is an application where you really want the maximum current available from your battery and not fiddle-arse around with hair thickness wires that *might* work some of the time.
 
I think Wallace is saying that resistance is resistance. A low wattage resistor will heat up like nichrome.

Recall, billdz wants to spare wear and tear on his nichrome (it is a bit of a pain to replace all the time - especially if you’re trying to pull off multiple flights in a day) as long as it gets hot enough to melt the elastic. One option is to dial back the current by increasing the resistance. Another is to get heavier gauge wire - but that lowers the resistance.

Another option yet is to limit the battery. A 200mah 20C battery is going to deliver less current (qualitative experimental data) even if it isn’t strictly a quarter the current of his 450mah 35C battery.
 
I noticed that the Quantum manual says "We've intentionally dead-shorted the Quantum's outputs in testing, with no harm to the Quantum at all," except the processor may reset. I PMed Chris, who thinks the transistors can handle even the minimal 0.1 ohms resistance of 22 gauge nichrome, which should be very durable. Chris would know best, although it seems counter-intuitive to allow a near short on the output of a transistor.

Until I saw this thread, I had never really heard of nichrome wire. Poking around the web a bit more (mainly on vaping-related sites), it seems nichrome is just one of several types of heating resistance wire that may worth testing for rocketry chute opener purposes. For example, there's kanthal, which is said to be more durable and have higher resistance than nichrome. See, e.g., https://www.misthub.com/blogs/vape-...anium-vs-kanthal-vs-stainless-steel-vape-wire.

I like the split-tube configuration in the article cited by Kelly. That guy used igniters (the ultimate in single-use) rather than nichrome.

For now, I'm just going to use the 38 gauge nichrome as a single-use device. Perhaps later I'll have more time to experiment with different types of wires and different configurations, in search of a reliable, safe, multi-use chute opener.
 
For example, there's kanthal, which is said to be more durable and have higher resistance than nichrome. See, e.g., https://www.misthub.com/blogs/vape-...anium-vs-kanthal-vs-stainless-steel-vape-wire

I just read through this, and I wonder if this kanthal wire would also be a better option for home-made igniters and ematches. I frequently see at club launches where a beefy 12V system dumps enough current for clusters and the bigger stuff, but the newer clear/white tip Estes igniters will burn their nichrome completely apart before the tip gets hot enough to actually start the motor. Sorry to divert the topic there, I've just had some issues with those igniters and this has me thinking.

Back to the chute release stuff, I have been slow on my build with the cigarette lighter (sorry), but I just got some relays in the mail from Electronic Goldmine, and I hope to have a basic prototype working soon for you all. I have a club launch this Saturday, so I will probably not work on it until Sunday.
 
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