Chute Release

billdz said:

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

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I've also used ematches (from Wildman) to cut monofilament. It was in a place where placing a nichrome wire would have been a pain.

billdz said:

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.

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Which is not a terrifically useful statement on its own given that the battery in particular will have a significant effect on the power the transistor is dealing with in the event of a short. You ultimately need to know how much current the transistor(s) are capable of passing in a short duration "burst" in their physical configuration (heat sink attached or PCB mount?). That data should be available in the transistor's datasheet.

Chris did not go into detail but he said that, with the 0.1 ohms resistance of a one inch piece of 22 gauge nichrome, current will theoretically be about 7A, which the transistors "should be able to handle for a few seconds".

The KSH122 Darlington transistor and the NTD3055L104-1G MOSFET are mounted on a PCB. I don't see any mention of maximum burst current on the spec sheets.

Broke out the meter and did some experiments.

First tried different lengths of the 36 gauge nichrome, which has a rated resistance of 27 ohms per foot (2.25 ohms per inch). The maximum length where the wire turns red is 1.7 inches. With a 1.7 inch length of nichrome, current is about 0.9 amps and the wire turns red. Anything even a fraction of an inch longer does not change the color of the nichrome. With the nichrome reduced to a 1 inch length, current rises to 1.4 amps and the wire looks hotter, white red in color. With a .35 inch length, current is 2.5 amps, and the nichrome breaks after firing, even without pressure.

Next tried twisting pieces of the 36 gauge wire together to make a one inch piece. Twisting 2 pieces together (about the same diameter as 30 gauge) worked well, wire turned white red and drew around 2.6 amps. Twisting 3 pieces together (similar to 27 gauge diameter) drew about 2.7 amps, and the wire turned red. Twisting 4 pieces together (similar to 24 gauge) also drew around 2.7 amps, and the wire did not change color.

So it seems the length of the nichrome wire is critical and probably explains why the nichrome breaks for me but not for Wallace (he has the brass screws on the corners of the cable tie base, mine are on the sides, about .25" shorter distance). If we want to use heavier nichrome, 30 gauge is probably the heaviest that will safely work with my battery. A higher capacity battery will be needed for heavier nichrome.

I've been looking at Nichrome wire on Amazon the ran across this. An 8-pack of 25' spools of 22-36 gauge Nichrome 80. Once I find the right guage to work I think at 25' od what works will last for awhile. Plus other guages to mess around with.

https://www.amazon.com/gp/product/B07DGJKKSK?ref=em_1p_3_ti&ref_=pe_3780150_435109530

love this supplier, fast service.

https://jacobs-online.biz/nichrome_wire.htm

billdz said:

So it seems the length of the nichrome wire is critical and probably explains why the nichrome breaks for me but not for Wallace (he has the brass screws on the corners of the cable tie base, mine are on the sides, about .25" shorter distance).

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These are some excellent observations; well done!
My first thought is to determine what the length would be if you did have the plastic mount with the corner screws, and curve your wire between the side screws you do have into an S shape or maybe a zigzag. That way, you still use the physical setup you have, but you get the proper length. Another thing to think about is the melting point of the elastic you are cutting. It may not be necessary to get the wire completely red hot. Try wiring in a potentiometer to make your current variable. Start low and monitor the current needed to actually break the cord. From there, add maybe another 0.1 amps just as a little extra assurance of a successful cut, and then call it good at that point.

ebruce1361 said:

These are some excellent observations; well done!
My first thought is to determine what the length would be if you did have the plastic mount with the corner screws, and curve your wire between the side screws you do have into an S shape or maybe a zigzag. That way, you still use the physical setup you have, but you get the proper length. Another thing to think about is the melting point of the elastic you are cutting. It may not be necessary to get the wire completely red hot. Try wiring in a potentiometer to make your current variable. Start low and monitor the current needed to actually break the cord. From there, add maybe another 0.1 amps just as a little extra assurance of a successful cut, and then call it good at that point.

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Thanks for the thoughts.

The nichrome may get hot enough to break the elastic without nichrome turning red, have not tried that, I was thinking it needed to be as hot as possible without breaking. There are several plans on the web for "hot wire styrofoam cutters" -- the wire does not turn red on these, the recommended temperature is 600 degrees. The elastic cord probably needs a higher temperature than styrofoam does, but further testing is needed.

A zig zag or S shape could get my device to the correct current, but there needs to be a way to hold the nichrome taught, so that it maintains a firm contact with the elastic cord. As you mentioned earlier, a ceramic coil form might do the trick. Or I could just move the screws to the corners. I'd have to cut off the ribs and drill two holes, but it would duplicate Wallace's setup.

Experimenting and testing is fun and educational, but at the end of the day it may be best to stick with the single-use configuration, since I have a lifetime supply of nichrome and it only takes a minute to replace the broken piece.

Greg Furtman said:

I've been looking at Nichrome wire on Amazon the ran across this. An 8-pack of 25' spools of 22-36 gauge Nichrome 80. Once I find the right guage to work I think at 25' od what works will last for awhile. Plus other guages to mess around with.

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What kind of battery are you planning to use? If you going to use something like my 7.2v 480mAh, I'd stick with 30 gauge or thinner, unless you can rig it up so the nichrome run is 0.5" or less.

There are now tiny little batteries that appear to have enough juice to heat nichrome. This guy is using a 3.7v Li-ion that is the size of a fingernail:

I wonder how a couple of these would work for chute opener purposes?

I just had another thought on the ceramic coil form idea. What about JB Weld epoxy? According to the wikipedia page for it, "J-B Weld can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes."

You could roll a thin rod of it as it's curing, or maybe even make a flat rectangular backplate for a zig-zagged wire to rest against. There's also the PC-7 "clay" type epoxy or even PC-11 marine epoxy which sets up like the stone-like coating in swimming pools. I couldn't find data on the melting points of these two epoxies, but I'll bet it's similar to JB Weld if not better.

And, you may be right and the best approach is to regard the nichrome as an expendable component considering the cost of the wire per flight has to be a few pennies at most, but I'd hate to see conditions get to where your wire somehow breaks before the elastic does and then you have a complete failure to deploy.

For this application though, you're primarily looking for a high discharge rate and LiPo batteries tend to be preferable for that over Lion even though the latter often provides higher energy densities.
For very high temperature exposures like this, nothing quite shines like ceramics (other than graphite, but that's semi conductive) so personally if I was making up a structure that was in contact with the wire I'd probably favour some type of ceramic or refractory composite - maybe a composite of fibreglass & a sodium silicate based putty (such as some muffler putties). Although the wire is thin and the time is short so I could be over thinking that a touch.

billdz said:

Thanks for the thoughts.

The nichrome may get hot enough to break the elastic without nichrome turning red, have not tried that, I was thinking it needed to be as hot as possible without breaking. There are several plans on the web for "hot wire styrofoam cutters" -- the wire does not turn red on these, the recommended temperature is 600 degrees. The elastic cord probably needs a higher temperature than styrofoam does, but further testing is needed.

A zig zag or S shape could get my device to the correct current, but there needs to be a way to hold the nichrome taught, so that it maintains a firm contact with the elastic cord. As you mentioned earlier, a ceramic coil form might do the trick. Or I could just move the screws to the corners. I'd have to cut off the ribs and drill two holes, but it would duplicate Wallace's setup.

Experimenting and testing is fun and educational, but at the end of the day it may be best to stick with the single-use configuration, since I have a lifetime supply of nichrome and it only takes a minute to replace the broken piece.

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Various binding posts. Only have the first & last connected. That way you can create a longer crossing. Just an idea.

rocket_troy said:

For very high temperature exposures like this, nothing quite shines like ceramics (other than graphite, but that's semi conductive) so personally if I was making up a structure that was in contact with the wire I'd probably favour some type of ceramic or refractory composite - maybe a composite of fibreglass & a sodium silicate based putty (such as some muffler putties).

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What about glass? I could slip a piece of a microscope slide under the nichrome wire and the nichrome would remain flat, even with the elastic cord pressing tightly on it. It's the pressure of the elastic cord on the nichrome that causes the unbacked nichrome to break.

rocket_troy said:

For very high temperature exposures like this, nothing quite shines like ceramics (other than graphite, but that's semi conductive) so personally if I was making up a structure that was in contact with the wire I'd probably favour some type of ceramic or refractory composite - maybe a composite of fibreglass & a sodium silicate based putty (such as some muffler putties).

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What about glass? I could slip a piece of a microscope slide under the nichrome wire and the nichrome would remain flat, even with the elastic cord pressing tightly on it. It's the pressure of the elastic cord on the nichrome that causes the unbacked nichrome to break.

billdz said:

What about glass? I could slip a piece of a microscope slide under the nichrome wire and the nichrome would remain flat, even with the elastic cord pressing tightly on it. It's the pressure of the elastic cord on the nichrome that causes the unbacked nichrome to break.

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Sure, I was thinking in terms of composites that could be formed/laid up/moulded/whatever into the geometry that suited the application, but glass should be fine. Even a plaster composite should be fine.

First flight test today, it worked! This is the basic version of the device, same as Wallace's except with the screws on the sides instead of the corners. Hope I'll have time soon to experiment with the suggested improvements, thanks to all for the ideas.

As mentioned, I have a lifetime supply of 2mm elastic cord and 36 gauge nichrome wire. If anyone would like to try building one of these, send me $1 and a s.a.s.e. and I'll send you 3 feet of each.

billdz said:

First flight test today, it worked! This is the basic version of the device, same as Wallace's except with the screws on the sides instead of the corners. Hope I'll have time soon to experiment with the suggested improvements, thanks to all for the ideas.

As mentioned, I have a lifetime supply of 2mm elastic cord and 36 gauge nichrome wire. If anyone would like to try building one of these, send me $1 and a s.a.s.e. and I'll send you 3 feet of each.
View attachment 394139 View attachment 394140 View attachment 394141

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Congrats! A job well done.
I ordered some of those cable tie mounting plates from Amazon, the same Part # that Wallace used. They can be used with screws in the corners.

Thanks! Yes, I picked up a bag of the mounting plates with holes in the corners at Home Depot and like them better. They are easier to use because the holes aren't partially blocked by the screws. And resistance will be higher so like Wallace you may be able to re-use the nichrome.

Did you also order elastic cord? Wallace says he tried several types and the 2mm worked best, and it does work fine for me, but I'm guessing that 1.5mm or even 1mm would work even better. And what type of battery and altimeter will you use?

billdz said:

Thanks! Yes, I picked up a bag of the mounting plates with holes in the corners at Home Depot and like them better. They are easier to use because the holes aren't partially blocked by the screws. And resistance will be higher so like Wallace you may be able to re-use the nichrome.

Did you also order elastic cord? Wallace says he tried several types and the 2mm worked best, and it does work fine for me, but I'm guessing that 1.5mm or even 1mm would work even better. And what type of battery and altimeter will you use?

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I haven't ordered either the nichrome or elastic cord yet. I might send you $1 & a SASE.
I'll probable go with either the Eggtimer Quark or Quantum. I have to look into this a little more, but I do like that you can program the Quantum with a smartphone & browser.

OK, good luck. Any dual deploy altimeter will work, the Quantum is great with its remote control feature, the Quark is basic but cheaper and smaller. Different batteries may lead to different results, think about a higher capacity battery if you are interested in using thicker nichrome.

billdz said:

OK, good luck. Any dual deploy altimeter will work, the Quantum is great with its remote control feature, the Quark is basic but cheaper and smaller. Different batteries may lead to different results, think about a higher capacity battery if you are interested in using thicker nichrome.

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So what are you using? A Quantum?

Greg Furtman said:

So what are you using? A Quantum?

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Yes, a Quantum. The Quantum and all Eggtimers are sold as kits that require some experience with soldering small surface mount components.

billdz said:

Yes, a Quantum. The Quantum and all Eggtimers are sold as kits that require some experience with soldering small surface mount components.

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I built their TRS/GPS and the LCD Receiver. Tiny, tiny parts.

Tried two experiments today:
1) noticed that the mounting plate smoked a bit at the points where it contacted the nichrome, so I filed down the ridge to prevent contact. Seems to have stopped the smoking.
2) Tried slipping a piece of glass under the nichrome. I had hoped this would inhibit the nichrome from getting stretched by the elastic cord and breaking, but this was a fail. The wire turned red as usual but the elastic cord did not break. I suppose the glass absorbed some of the heat and prevented the cord from getting hot enough.

First HPR test with homebrew chute opener, LOC EZI65 on an H283, apogee 920', chute released at 500', no issues.

billdz said:

First HPR test with homebrew chute opener, LOC EZI65 on an H283, apogee 920', chute released at 500', no issues.

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Can you post a pic or two of your final setup?

Made some progress over the weekend on my design, and discovered some issues. The biggest problem is I neglected to account for charging the second battery (only one is needed to run the cigarette lighter, but both in series run the Quark.)

It looks like I will have to do a complete tear-down and redesign to accommodate the proper charging system. Additionally, I'm wondering if I can save some weight and space by eliminating the majority of the cigarette lighter circuit board and have the heating element connected directly to the relay and thus the battery. The heating element is run off just one 3.7v battery, so I don't think it would be a good idea to have both batteries power it, hence why I'm not letting the full 7.4v running the Quark go through the main parachute output directly into the heater. One other option is to run the output from the Quark through a voltage regulator so the coil only gets 3.7v. I can try giving the coil a full 7.4v and see if it survives, but it already gets plenty red-yellow hot as it is on just 3.7, so I don't think it would be necessary or ideal.

As for charging the batteries, it would make more sense to have the batteries connected in parallel to charge, so I will probably have to set up the dip switches to have a "run mode" and a "charge mode" that changes the batteries from series to parallel. From there, all I need to add is a 3.7v voltage regulator to take the 5v from the USB plug down to what the batteries can actually take.

Thus far, I've put in $20 for the Quark, another $18 for two lighters, and while I've ordered a few $20 (approx.) lots of miscellaneous parts online, (relay, dip switches, prototyping board, etc.) I'm ultimately using only one or two parts per lot, so I figure maybe another $10 worth of other parts. Include a plastic casing and a spool of elastic cord, and I think this version still comes in under $60; a bit under half of the JLCR cost.

Video:

Greg Furtman said:

Can you post a pic or two of your final setup?

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Have not changed anything, same setup as in post #60 above. Still treating the nichrome as single use, takes less than a minute to put on a fresh piece. Time permitting, I'll continue experimenting for a multi-use solution.

ebruce1361 said:

As for charging the batteries, it would make more sense to have the batteries connected in parallel to charge, so I will probably have to set up the dip switches to have a "run mode" and a "charge mode" that changes the batteries from series to parallel. From there, all I need to add is a 3.7v voltage regulator to take the 5v from the USB plug down to what the batteries can actually take.

Thus far, I've put in $20 for the Quark, another $18 for two lighters, and while I've ordered a few $20 (approx.) lots of miscellaneous parts online, (relay, dip switches, prototyping board, etc.) I'm ultimately using only one or two parts per lot, so I figure maybe another $10 worth of other parts. Include a plastic casing and a spool of elastic cord, and I think this version still comes in under $60; a bit under half of the JLCR cost.

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Good luck, looks good so far. What would happen if you just placed the lighter's heating element across the output of the Quark (perhaps with a voltage regulator in series if the heating element can't take 7.2v)?

There are numerous cheap 3.7v "mini heating elements" available in various shapes -- tubular, discs, squares, etc. It might be fun to experiment with some of these, e.g.:
https://www.alibaba.com/product-det...pm=a2700.7724857.normalList.31.706459c9AHeotH

The main reason I don't power the heating element right off the Quark is while the Quark can function on 3.7v, it works better with both batteries giving it 7.4v, but I'm worried that much voltage could damage the heater. There's a secondary reason too, I want the heater to stay hot until the elastic cord breaks. If it doesn't break immediately, the Quark could switch the output off and the parachute will stay bundled. I'm using a double pole relay so one side can trigger the lighter power, and the other connects the battery directly to the relay's own coil. The idea is once the relay is activated, it keeps itself on even after the Quark switches off its output. Then, once the parachute is relased, the lever switch that is held closed by the parachute bundle opens and disconnects the battery.

There's another development that just came up today. My charging woes may be remedied with a voltage booster that will take the 3.7v up to 5v to feed the Quark, but the rest of the chute release would still run on 3.7v. That way, I only need the one battery, and so no fandangled switching sysem to charge two batteries. Also, one less battery is less weight, so that's a plus.

Stay tuned!

ebruce1361 said:

The main reason I don't power the heating element right off the Quark is while the Quark can function on 3.7v, it works better with both batteries giving it 7.4v, but I'm worried that much voltage could damage the heater. There's a secondary reason too, I want the heater to stay hot until the elastic cord breaks. If it doesn't break immediately, the Quark could switch the output off and the parachute will stay bundled. I'm using a double pole relay so one side can trigger the lighter power, and the other connects the battery directly to the relay's own coil. The idea is once the relay is activated, it keeps itself on even after the Quark switches off its output. Then, once the parachute is relased, the lever switch that is held closed by the parachute bundle opens and disconnects the battery.

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I've been wondering about the pros and cons of your relay system since you first mentioned it. We certainly want the heater to stay hot until the cord breaks. With the Quantum, we can adjust the "on" time from 1 to 10 seconds but I don't think the Quark has that feature. How long does the Quark keep the heater hot? Is it so short that you need the added security of the relay, enough additional security to warrant the additional weight and complications of the relay system? Perhaps the heating element from your cigarette lighter takes longer to get hot than the nichrome wire on mine, which breaks the elastic cord almost immediately. I have the Quantum set to fire for 2 seconds, which is more than enough, if the cord has not broken after 2 seconds it never will.