Chute Release

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I like your experimenting, and I'm following your development process with interest.

Here is an idea, it would add some complication, and may not be necessary, but I'll throw it out there. In order to ensure that the cord breaks, you could use a switch that is held in the on-state by the tension of the cord. Use the output of the Quark to trigger a latch which then remains in the on state indefinitely. The current path for the heater goes through the switch that is held on by the cord tension. Then the heater doesn't turn off until the cord breaks.

It does add a point of failure, if there isn't enough tension to reliable hold the switch on, then the cord will never break.
 
@billdz

According to the Quark user guide on the Eggtimer website, the output in on for one second (page 9, PP4 of the guide), and the heating element takes about two seconds to get fully hot. So, given the warm-up time and an additional two seconds of working "hot" time (like you said, if it doesn't work in two seconds, it's not going to work) I figure four seconds is the maximum run time for the heater. Therefore, the one second output of the Quark won't be sufficient. Honestly, I don't expect it to actually take four seconds to break the cord, but that's the maximum I figure. Maybe a future version could include a 555 timer chip or a capacitor to run the relay for a few seconds and then turn it off whether or not the cord breaks.
 
@mbeels

The lever switch on my design is held closed by the parachute bundle, and the relay is wired to essentially feed itself and thus keep the heating element hot until the elastic cord breaks. Once the parachute is released, the lever switch opens and disconnects the battery from the cigarette lighter board and relay so only the Quark is on. See the video I posted on the previous page.
 
Some more experiments and notes, bottom line is that I'm going to continue using the device as "single use," at least for now.

* Set it up in Wallace's configuration, with the screws on the corners rather than on the sides. It worked, and often the nichrome did not break, as Wallace previously reported. However, it took longer for the elastic to break, and in one instance the elastic did not fully break at all (it hung together by a single tiny thread). I believe there are 2 reasons for this: 1) the higher resistance from the additional 1/4" of nichrome, and 2) the fact that in this configuration the nichrome and the elastic are not entirely perpendicular, which means a longer cut.

* It is important that the elastic cord presses down firmly on the nichrome. It is not enough that the elastic simply lies on the nichrome, there must be substantial tension. But 36 gauge nichrome is not that strong, so if we pull the elastic down too tightly, the nichrome may break. Even turning the nuts down too tightly can break the hair thin 36 gauge nichrome. The system works with 2 pieces of 36 gauge twisted together (which is the same diameter as 30 gauge). A slightly thicker gauge, maybe 30 or 31, may give the nichrome sufficient strength to avoid accidental breakage.

* I tried a piece of 26 gauge nichrome but it did not work, at least not with my battery. The nichrome did not even get warm, even with just a 1/4" length of the 26 gauge nichrome.

* The hot nichrome does slightly burn the base if the nichrome touches the plastic at all. I have not found any way to avoid this, but it does not seem to be hurting anything.

* If you don't mind waiting a few weeks for delivery, you can buy rolls of nichrome wire for less than $1.50 shipped from AliExpress, e.g., https://www.aliexpress.com/item/32855837595.html?spm=a2g0o.detail.1000023.2.aca63e65MdY7Z6

* The most effective setup, at least for me, is to run the nichrome over the top of the base between the 2 screws (see photo), which allows us to create more tension between the nichrome and the elastic. With this setup, the nichrome breaks every time, but I have a lifetime supply and it only takes a minute to install a fresh piece.
homebrew chute opener.jpg
 
billdz said:
Some more experiments and notes, bottom line is that I'm going to continue using the device as "single use," at least for now.

* Set it up in Wallace's configuration, with the screws on the corners rather than on the sides. It worked, and often the nichrome did not break, as Wallace previously reported. However, it took longer for the elastic to break, and in one instance the elastic did not fully break at all (it hung together by a single tiny thread). I believe there are 2 reasons for this: 1) the higher resistance from the additional 1/4" of nichrome, and 2) the fact that in this configuration the nichrome and the elastic are not entirely perpendicular, which means a longer cut.

* It is important that the elastic cord presses down firmly on the nichrome. It is not enough that the elastic simply lies on the nichrome, there must be substantial tension. But 36 gauge nichrome is not that strong, so if we pull the elastic down too tightly, the nichrome may break. Even turning the nuts down too tightly can break the hair thin 36 gauge nichrome. The system works with 2 pieces of 36 gauge twisted together (which is the same diameter as 30 gauge). A slightly thicker gauge, maybe 30 or 31, may give the nichrome sufficient strength to avoid accidental breakage.

* I tried a piece of 26 gauge nichrome but it did not work, at least not with my battery. The nichrome did not even get warm, even with just a 1/4" length of the 26 gauge nichrome.

* The hot nichrome does slightly burn the base if the nichrome touches the plastic at all. I have not found any way to avoid this, but it does not seem to be hurting anything.

* If you don't mind waiting a few weeks for delivery, you can buy rolls of nichrome wire for less than $1.50 shipped from AliExpress, e.g., https://www.aliexpress.com/item/32855837595.html?spm=a2g0o.detail.1000023.2.aca63e65MdY7Z6

* The most effective setup, at least for me, is to run the nichrome over the top of the base between the 2 screws (see photo), which allows us to create more tension between the nichrome and the elastic. With this setup, the nichrome breaks every time, but I have a lifetime supply and it only takes a minute to install a fresh piece.
View attachment 396099
Click to expand...
Also, be very careful about your setup. That hot wire burns really big holes in nylon chutes real quick. Ask me how I know...
 
Hey, thought I'd pitch in some thoughts in case they help.

1. Your binding posts are conducting some amount of heat away from the nichrome
2. Silicone is cheap, elastic, and conducts heat poorly (many kitchen products can be used as raw materials)
3. It would be nice to eliminate the mechanical stress on the nichrome

So—and just spitballing here, take this all with a grain of salt, I'm just thinking about this for the first time—consider the following setup as at least a thought experiment:
  • A silicone base with a hump in the middle (either from the silicone itself or a mounded base underneath it, but not flat)
  • Lay nichrome across the hump connected to the electrical leads (does not need to be tight or in tension)
  • Use the least amount of mass necessary to connect the leads to the nichrome (I would suggest tiny crimp connectors rather than binding posts which suck up a lot of the heat you're trying to produce)
  • Place the chute cable across the nichrome a right angle
  • When you tighten the chute cable, the nichrome will be clamped between the cable and the silicone hump
  • The resilience of the silicon will actually give you a little mutual circumferential wrap (say, 100 degrees) instead of just a point contact, which is beneficial because it concentrates heat on the cut line, as opposed to your diagonal example which spread heat more along the length of the line and diluted its effect at the cut line
  • While the nichrome will be pressed into the silicone, it won't be stressed by the tension in the line. In fact, the nichrome should be slack to some extent before starting
  • The nichrome will probably be somewhat more reusable in this setup (isolated from mechanical stress, at least, even though you can still burn it out if you're not careful, but that limit is testable to a large extent)
My thoughts, for what they're worth.
 
@John Beans I wondered if you were going to peek in here with a bunch of us essentially trying to reinvent your wheel! :D (seriously though, all kinds of props to your JL gear; but I love a technical challenge)

I do like your high-temperature silicone idea. It would give the added structural support like with the ceramic rod idea I had, but it would likely be lighter weight and easier to make and replace if damaged. Another thought I had was maybe the elastic is a bit too much because of what @billdz said about the elastic hanging on by a thread. What about using some clear elastic cord frequently used in bead bracelets? It's a single filament so if it breaks at all, it breaks completely; and it has similar strength as the thin elastic cord we've been experimenting with thus far.

As for my setup with the electric lighter bit, I haven't had the opportunity to work on it for the last couple of weeks due to family health issues, but those should be clearing up here soon. Hopefully I can get back to the workbench and get an improved version out soon.
 
Many of you are using the Eggtimer Quantum. I just finished up mine. I love the WiFi interface. But can the flight data be downloaded via the WiFi? Can you get real time data via WiFi? Thanks.
 
ebruce1361 said:
@John BeansAnother thought I had was maybe the elastic is a bit too much because of what @billdz said about the elastic hanging on by a thread. What about using some clear elastic cord frequently used in bead bracelets? It's a single filament so if it breaks at all, it breaks completely; and it has similar strength as the thin elastic cord we've been experimenting with thus far.
Click to expand...

The cord in this case for this approach doesn't actually have to be elastic. Probably better if it's not, and monofilament might be a great choice. Braided nylon cord does melt (it's how we trim tethers lately), but I don't know how much energy it takes to melt each type of cord. A good experiment to do. Hang a weight from each type over the edge of a table to simulate the same load and time it.

Chute Release uses elastic cords specifically to limit load on the mechanism, not because elastic is a better type of thing to use on a chute bundle (in fact, it can sometimes be worse in several ways).

As I mentioned in one of my NARCON talks, there's always a final break though concept which completes the viability of a design for me, and in Chute Release's case it was using elastic bands to limit tension. Otherwise people would crank them down tight and break them, it's a natural tendency to think "tighter is better."

True story, one university team took all three of their Chute Releases and very diligently measured the tension that would cause the devices to fail. They charted that data out nicely, then contacted me because the Chute Releases no longer could hold a pin. They weren't the first people to wonder what the ultimate strength of the devices were (people are curious), but they were the only ones to do destructive testing on all of their units to figure it out. The solution? I refurbished their pins and catches, and advised them to use the bands as tension-limiters and worry more about other aspects of deployment.
 
Kudos to them for going through the trouble to generate that kind of failure data, and to you for refurbishing their CRs! Talk about a win-win.

John Beans said:
Chute Release uses elastic cords specifically to limit load on the mechanism, not because elastic is a better type of thing to use on a chute bundle (in fact, it can sometimes be worse in several ways).
Click to expand...

When I imagine a release device holding a parachute bundle that isn't in a canister of some kind, I figure an elastic binding would be ideal because any forces of drag, momentum, etc would work to pull the parachute out of its bundle, and a rigid cord of a fixed length seems like it could more readily fail than an elastic one that could allow some flex, but then return. You say that in some cases, an elastic cord is actually worse. In what ways?
 
John Beans said:
The cord in this case for this approach doesn't actually have to be elastic. Probably better if it's not, and monofilament might be a great choice.
Click to expand...

I was just about to chime in with similar feedback. 2mm elastic seems to be way overkill, and very difficult (relatively) to melt. I was going to suggest a thin piece of monofilament for the fusible portion, and then if you need elastic, just tie the end of the mono to a rubber band or section of elastic.

Kelly
 
ebruce1361 said:
You say that in some cases, an elastic cord is actually worse. In what ways?
Click to expand...

Well, for the same reason that it is good for gripping a chute, it doesn't slide great on the inside of fuselages. For instance, in a tight 38mm fuselage, you're better off finding a fabric elastic band (any fabric store) because that will slide out easier. In addition, if you have a puffy bundle, the band can sometimes grip the loose fabric after release, and the band won't spring off completely. It stays buried in folds after the pin releases, and in a calmish jet stream the chute may just land in a loose bundle without inflating.

Hopefully those explanations make sense.
 
Ah! Gotcha. It's the same reason why hair bands aren't usually regular rubber bands (I have two daughters with long hair, so I've had to become a bit of an expert in hair accessories). In the case of either your Chute Release or our hot cord cutters, I was planning on using fabric elastic anyhow, (notwithstanding my idea about the monofilament bracelet cord) but even those can bind around a canopy on a bad day. I had another brainwave yesterday driving home looking at the air freshener on my mirror: that elastic cord is REALLY thin. After a quick google search, I found that it's most likely 0.7mm and is pretty easy to come by. Given its extremely thin diameter, it will likely melt much faster and still have all the benefits of a fabric elastic with less chance of binding inside the body tube or around the canopy after being cut due to its low surface area and low friction with the nylon coating.
 
ebruce1361 said:
Ah! Gotcha. It's the same reason why hair bands aren't usually regular rubber bands (I have two daughters with long hair, so I've had to become a bit of an expert in hair accessories). In the case of either your Chute Release or our hot cord cutters, I was planning on using fabric elastic anyhow, (notwithstanding my idea about the monofilament bracelet cord) but even those can bind around a canopy on a bad day. I had another brainwave yesterday driving home looking at the air freshener on my mirror: that elastic cord is REALLY thin. After a quick google search, I found that it's most likely 0.7mm and is pretty easy to come by. Given its extremely thin diameter, it will likely melt much faster and still have all the benefits of a fabric elastic with less chance of binding inside the body tube or around the canopy after being cut due to its low surface area and low friction with the nylon coating.
Click to expand...

You thinking something like this?

https://www.michaels.com/0.5mm-elastic-cord-by-bead-landing/10442838.html
 
I'd be tempted to see how quickly monofilament fishing line would melt.
963cb061-0e06-40e7-9ab1-eadac2e708cb
 
I use monofilament fishing line in my version. At the recommendation of Cris Erving. Melts easily.

I do like a tight, springy band. It looks like it pops away from the chute better, rather than getting caught up in it.

John’s suggestion that fabric would slide better on the inside of the tube caught my eye, though.
 
I can see fishing line having the benefits of melting easily and not snagging, but having the elastic spring apart when cut seems like it would offer an added benefit. I wonder if there's a way to have our cake and eat it too. Perhaps an elastic cord that has been cut to a specific length so it reaches maybe three quarters of the way around the parachute bundle and release mechanism, and then a short length of fishing line added to connect the ends. The trick would be to find the ideal way of connecting them so it doesn't break. Hair bands either have a small metal crimp holding the ends together, or the ends are partially melted and fused together. Maybe some kind of similar method could be used here.

The release device cuts the fishing line, and the elasti band pulls the whole wrap away from the parachute.
 
Wallace said he experimented with various things, including monofilament, and found that the 2mm elastic worked best. I have the feeling that 1mm elastic would be as good or better, but I have only used the 2mm.

I have not tried a silicon backstop, as John suggested, but I did try a glass backstop, which did not work at all, the elastic cord did not break. Either the glass absorbed some of the heat or the backstop too much lowered the tension between the elastic and the nichrome.
 
ebruce1361 said:
@billdz

According to the Quark user guide on the Eggtimer website, the output in on for one second (page 9, PP4 of the guide), and the heating element takes about two seconds to get fully hot. So, given the warm-up time and an additional two seconds of working "hot" time (like you said, if it doesn't work in two seconds, it's not going to work) I figure four seconds is the maximum run time for the heater. Therefore, the one second output of the Quark won't be sufficient. Honestly, I don't expect it to actually take four seconds to break the cord, but that's the maximum I figure. Maybe a future version could include a 555 timer chip or a capacitor to run the relay for a few seconds and then turn it off whether or not the cord breaks.
Click to expand...
Although I've not tried it, a Quark may not be the best option in this use case.While I'm sure there are a lot of other options out there, a Quantum is tough to beat for the money. I do have a Proton and that should also work well, just have yet to fly it so I can't say for certain. Shoot Cris an eMail, he's always happy to help.
 
And.. be careful when using silicone, it has a grabby/clingy quality that might just cause your recovery to snag.
 

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