Our camera can record up to 60 minutes, so we will trigger the burnwire once the camera stops recording.
Then how long does it take for the burn wire to burn through and release the camera once it’s triggered?
Also, I don’t know what the field of view is on your camera, but were you planning to orient it with the dome facing downward? If horizontal, it might be cool to add a tiny thruster to cause the bottle to pan.
I think it should happen as quickly as possible. You are trying to melt the wire (and possibly trying to minimize the energy expenditure on doing so).
The same could be accomplished with an internal reaction wheel (maybe less efficiently).
From my testing, I found that when running about 60A through a 32AWG nichrome wire, it melted and released in 30-50 ms. Ideally, as Jacob mentioned, you want this to occur as quickly as possible. In our dropcam, orientation is not a concern since it has a 360-degree camera but if you are using a normal camera and want it to be facing the same direction all the time, you could add a “fin” to orient it by using the current.
Hi Ivan, we are a bit crazy with the release mechanism of the dropcam. We are developing the burnwire using a relay (11.5V) driven by the Arduino MKR 1010 (3.3V), and we have a big issue: the Arduino can activate the relay when the its power come from an USB. However, it can’t when it is powered with a LiPo 3.7V 2500mA. The pin out of the Arduino MKR has very low amperage and it can’t work.
Did you fixe the issue you had with the burnwire? Any idea how to drive the relay with extremely low amperage?
Pau and Rafa
Hello Rafa,
Thank you for your message! Please see my previous post within this thread, you’ll need to use a transistor in order to activate the relay. Additionally, please make sure that your relay is rated to a high enough amperage, I’d recommend a 20A relay as the bare minimum for our burnwire configuration. Please let me know if you have any other questions.
Im late to this conversation, and maybe I missed something, but I think the simple answer to your question about controlling a relay using an Arduino (or any other micro-controller) pin is in one of your previous posts up above where you show two different schematics. The second schematic is a correct way to control a relay with a micro. The micro controls the transistor, and the transistor controls the higher current of the relay coil.
Note that the relay coil does not have to use the same power supply as the Arduino (as it is shown in your diagram), it can be a different voltage to suit what the relay is rated for.
I would not use the method in the first schematic, most micros are not intended to drive a relay directly.
Thank you so much for these tips, we’ll work on that today.
Thank you Ivan. By the way, in your experience, whats the maximum temperature that you can have inside your dropcam without compromising it.
Yes, our dome will face down and the camera has an angle of 45 degrees.
The only component that significantly heats up without cooling in our dropcam is the gear360 camera. If not cooled, it will go past 50 degrees Celsius and will cause it to stop recording. This should have no impact on the function of the burnwire as these systems are independent.
Thank you! And we fixed the issue of the circuit to activate the relay. We are feeding it with the same 11.5V of the LiPo battery and the transistor makes it work. It is simple but we were doing a big mistake putting the transistor before and not after the coil. Now, all our electronics work and it is time to do more testing about temperature inside the enclosure.
We have a humidity and temperature sensor and we are looking into ways to measure condensation.
Hi Ivan, we have a new challenge and need your insights. Now that the Arduino-controlled electronic circuit that activates the burn wire works well, the issue is that the wire doesn’t burn when tested inside water. We did a few tests with salt water (tap water with a couple of spoons of salt, it could had salt in 300 ppt) and the nichrome wire doesn’t burn. Are we missing something?
Dear @rjehangir, @WorkshopScience and all, we are ready to test our drop cam (now named Blue Eye) and the only thing that doesn’t work is the burnwire. Our circuit gets activated and the wire gets a lot of current but it doesn’t get burned as the one I can see in @WorkshopScience 's video. In the meantime, we will use a reel to recover the camera but this is not what we want.
Any clue? Suggestion?
Hello Pau,
Have you tried activating the burnwire in freshwater? If it works under these conditions then the most likely cause behind the error you mention is too much exposed metal on either side of the wire’s connection points. This leads to most of the current flowing through the saltwater rather than through the wire. We encountered this error when using large metal thumb screws and switching to plastic-ended ones seemed to have solved the issue. If the burnwire doesn’t work in freshwater either then the it is most likely just not receiving enough current. Can I confirm what the capacity and discharge rating of the battery is?
Kind regards,
Ivan
Thank you Ivan. Yes, we tried in freshwater and it didn’t work, but I was optimistic about salt water because of its electric conductivity. I understand your point about too much metal exposed to water. I will share pictures of our burnwire later, and will rethink how to make it using less metal.
Dear @WorkshopScience and @rjehangir, we did several tests of our drop cam, named “Blue Eye”, in Menorca, and it was really great. The burn-wire is not working properly but we believe we can fix it, and the only thing that is pending (for next summer!) is to do some tests in the deep sea. It was impossible to arrange a trip to the deep sea. We did drop the camera in several places, between 25 and 45 m depth, and it worked very well. We are sharing some pictures and videos of the experiments. Now, in addition to fix the burn-wire, we want to refine the design of the enclosure and the mechanism to attach the lights.
In this video, you can see the footage of the camera while it is landing into the seabed.
In these videos, you can see some footage of the drop-cam:
We will make everything open source during the Fall.
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@Paucam - Awesome! Excellent first dive. I’m excited to see more!
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Dear @rjehangir and @WorkshopScience, please see a short video to describe our project and work in progress so far
Still more work to do to fix the burn wire and we plan to make everything open source in GitHub.
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Hello Pau,
Thank you so much for sharing, it is awesome to see your work and the footage looks great! The burn wire is definitely quite a tricky aspect to properly refine, in early trials we attached the entire drop-cam to a fishing line in order to have an emergency option of recovering it. If you are planning on trying it out at great depths where a fishing line wouldn’t be appropriate, I’d definitely recommend you take a look into galvanic releases as those are a cheap and easy method to guarantee a release if all else fails (albeit somewhat inconsistent timing-wise). I really look forward to seeing where you take this project and please let me know if these is anything I can help you with!
Kind regards,
Ivan