Waterproofing - Page 1
Forum section: electronics / beginners

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 26, 2017, 12:41:39 am
content: hello guys and gals!ive been looking into waterproofing some drone electronics and so far only figured this might be harder than it seemed at firstso i was hoping that some one here might be able to help me, without ending up in too many rabbit holesand maybe ill learn one or two things without being spoiled by half-true "facts"the requirements include:- long lasting waterproofing (more than just 1-2 months)- 100% water protection up to low depths (in case it ends up in a pond or along the coast)- vibration/crash resilient (considering speeds of up to 90-100km/h)- low weight (which is why i havent considered general potting)- maintainable, as in being able to resolder things without having to re-coat every thing- allow heat exchange (since the motor speed controllers can get quite warm/hot)- protect the camera housing without having to coat the electronics and endanger the CCD chip- protect USB, JST, XT60 and board-to-board connectors including LiPo batterythe drones operate at 5-24V with up to 140A (might be more as LiPo's become better)and primarily consist of the following:- power distribution board incl. LiPo- flight controller (which can include barometers)- 1 speed controller per motor incl. motors (which should already be waterproof)- CCD camera (with housing)- a radio and separate video transmitter (with 2 pigtail and 1 cloverleaf antennas)- also possible but not always present are an exposed microphone and buzzerso far i came across the following:- general purpose conformal PCB coating (didnt last very long as it started to crack)- silicone conformal coating (heard from several guys that it also didnt last very long)- nail varnish (skeptic)- corrosion-x (suspect this will only prevent corrosion)- nanoprotech (which made me think i might need to learn some more)regarding the last producthttps://youtu.be/EzEreJfRp8Y(to not link to the distributor directly, in case its phony)i couldnt fully grasp, how it could protect from short circuits but still allow a current flow where it had to beor is this maybe an exaggerated marketing gig?can you help me out, or have a favorite solution/product you know and works in such or similar application?thank you!

author: james_s
author_rank: Super Contributor
timestamp: April 26, 2017, 12:47:44 am
content: I know guys who use a product called CorrosionX and report good luck with it. It's virtually impossible to satisfy all of your requirements though, by far the most effective method is to stay away from water. Foam fixed wing planes will float, multirotors don't.

author: Ian.M
author_rank: Super Contributor
timestamp: April 26, 2017, 12:52:12 am
content: I'd like to see that demo after a pound of salt has been stirred into the tank!Ultrapure Waterhas a resistivity that can be over 18 Meg·cm

author: JanJansen
author_rank: Frequent Contributor
timestamp: April 26, 2017, 02:30:02 pm
content: I would not try that at home with a drill in bath.edit : ok, the movie also says not to try home disclaimer.curious : how many times do you have to spray ?, 1 time or everyday ?, why dont they use that default on everything ?

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 26, 2017, 03:48:01 pm
content: Check the radio control plane websites. The guys that fly float planes have been dealing with this for years. As I recall the solutions generally involve silicon grease to prevent water intrusion in servos and connectors and baggies to protect receivers and ESCs. RTV where the wires enter and leave bags. You have more elx and wires associated with FPV, but the same principals should apply.

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 26, 2017, 05:35:09 pm
content: cheers for all the inputs so far!@james_s - im aware ill probably not find THE 1 product to cover every little thing, but was/am hoping to find a better solution than corrosionxobviously its better not to go and bathe, but unfortunately its not always inevitable - considering we often get rain/snow here and that stuff can also take weeks to dry & if id do wait i might only get 2-4 weeks of flying per year@JanJansen - with the RC version of the product they claim it will give full protection for 1 year and possibly more, not sure about the amount of layers required though (assuming 1)@CatalinaWOW - ill give that area some more research, i kinda doubt the bagging solution will work for the power distribution board and speed controllers very well, since the point of failure is usually where the cables penetrate and thats quite a fewspecially since just heat shrinking already requires things to be un/re-soldered etc + it adds quite a bit of weighta little side question; lets assume id apply a layer of WD40 to some electronic components - how would i go about calculating the insulation properties in different types of water? or would i be better off experimenting with a scrap PCB and see where it catches fire?maybe it will become easier if i fully understand what parameters im dealing with

author: Codebird
author_rank: Regular Contributor
timestamp: April 26, 2017, 05:44:10 pm
content: From personal experience: Not ABS-in-acetone or model-painting lacquer. They both peel off easily.I had middling results with candle wax, but I expect a product purpose-made for the application will be far superior to any improvised substance.

author: mtdoc
author_rank: Super Contributor
timestamp: April 26, 2017, 06:15:12 pm
content: Has anyone ever tried using polyester resin - as in what is used for fiber-glassing and gel-coating boats, etc in a marine environment?I've used it for surfboard repair for years and it's pretty easy to work with. It seems like brushing a thin layer on a pcb might work well for a permanent, light weight waterproofing. Of course later repair or rework would would be a problem.I don't know what it's electrical conductivity is but I'd think it would be very low. Thermal conductivity is likely high enough to allow adequate heat exchange with a thin layer.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 26, 2017, 09:16:00 pm
content: When designing military electronics we never had much success waterproofing at the board level. Even though we did coat boards with stuff you would never want to deal with at home. Things like parylene. The only types that we used there that you might be interested in are the two part polyurethane varieties. They don't come from the dime store. No matter how good the coating is there have to be places to let the electrons through, and there are almost always pinholes and voids. So to keep water out the electronics compartment was sealed.You might want to think of options along those lines. Use food service wrap and a heat gun to seal the whole thing, except for the connector you bring out for battery charging. Silicon grease at the motors. It will be a PITA but TAANSTAAFL.The other thing I recall from the RC guys sealing efforts is that they don't need, or intend to have long duration sealing. If you are going to crash your drone in a lake and then go pick it up next week you are out of luck. The sealing is intended to keep casual water out for the few minutes or maybe tens of minutes until recovery can be effected. When a crash in the water occurs dis-assembly and drying are the rule.

author: DTJ
author_rank: Super Contributor
timestamp: April 27, 2017, 02:59:17 am
content: Despite their absolutely shite website these guys sell a great PCB sealer, its clear and easy to use.http://www.sensongroup.com/senson-tek/productsYou brush or spray it on as thinly or as thickly as you want. It bonds really well and does not peel.It seems to last indefinitely. It can be soldered through or you can quickly strip it from the boards using methylated spirits / IPA.Maybe it would work for what you need.

author: JanJansen
author_rank: Frequent Contributor
timestamp: April 27, 2017, 03:12:41 pm
content: You can always try it on a Hobbyking drone.

author: David Hess
author_rank: Super Contributor
timestamp: April 27, 2017, 06:14:51 pm
content: My experience with waterproof conformal coatings is that surface preparation is very important but the only good experiences I have had were with vacuum potting and I am not sure how you could combine the two economically. If you had a large enough vacuum chamber to dunk the individual boards into the conformable coating, then I expect that it would work very well.I wonder if a heat shrink film could be used to bag the boards.

author: FlyingSquirrel
author_rank: Contributor
timestamp: April 27, 2017, 10:37:48 pm
content: cheers for the inputs every one!@CatalinaWOW - with the resources that the military has, it does give me quite a respect for the topic, regarding they even struggle with itwont the food wrap create electrostatic charges that zapp the components? and yes, id rather not use chemicals that will kill every fish in the pond i accidentally land inbut ill give the polyurethane compounds some researchingalso no, the idea is to have it survive tens of minutes up to maybe an hour and a nice to have would be able to dry it relatively quickly, so i dont necessarily have to leave home directly, in case something happens at a spot that took me half a day or more to reach@DTJ - companies that concentrate in their core business usually tend to have ugly websites (so that can also be a good sign)is it worth spending almost 1k on one of their kits, or would you recommend a specific product?@JanJansen - id rather not support hobbykingeven if it will cost me twice as muchi could also get a cheap 50-100buck drone from the next store, but it also wouldnt be a reliable test comparing a <10W with a >2000W drone@David - wont the vacuum just get rid of bubbles? and wouldnt vibrations achieve the same thing? regarding there woudlnt be several centimeters of coating

author: David Hess
author_rank: Super Contributor
timestamp: April 28, 2017, 01:40:13 am
content: Quote from: FlyingSquirrel on April 27, 2017, 10:37:48 pmIt gets rid of the bubbles but it also forces the encapsulant into the surfaces of the board and parts on the board with 14.7psi when the vacuum is removed. The problem which you identified is that you need to dunk the board to apply the encapsulant. Actually you could brush or spray it in a vacuum but that is beyond anything simple.If you went to this much effort, then I would also thoroughly clean and bake out the board before doing the vacuum encapsulation process.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 28, 2017, 03:00:55 am
content: Remember (particularly when dunking boards) to mask/plug/isolate all connectors, sockets, trimmers, test points, switches, relays and the like. It is remarkable how effective conformal coating is at eliminating the function of these devices, even when it is not successful at keeping moisture out.If you are coating under a vacuum be aware that some large plastic IC packages actually have a vent port in them and can have strange behavior when filled with conformal coating. Vacuum makes the masking discussed in paragraph one much more difficult.Troubleshooting these problems is sometimes easy, but often amazingly difficult.Red Squirrel - I don't think the ESD problems from using food service wrap would be any worse that those caused by the plastic bodies these things have. I have only limited experience using this wrap around electronics, but have never had a problem and never drawn a spark with it. I suggested it because a single layer would be waterproof (barring scrapes and the like) and would weigh virtually nothing.There is also virtue in a layered defense. For this type of application multiple pretty good layers or methods could easily be better than one really good one.

author: DTJ
author_rank: Super Contributor
timestamp: April 28, 2017, 05:41:14 am
content: Quote from: FlyingSquirrel on April 27, 2017, 10:37:48 pmYou just need a bottle of the sealant. Probably $30 or so. Freight will probably cost you more than the sealant. Pic attached.There must be a similar product on your country.Regarding the food wrap - I'd be wary of that a voltage potential could be generated as the wrap is unwrapped off the roll or off the device.

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2017, 05:01:57 pm
content: Quote from: CatalinaWOW on April 28, 2017, 03:00:55 amReally? Where does it vent from? The bare die? Where is it and what kind of packages? I'm not challenging your statement, it's just not something I've ever been aware of. That is, aside from things like barometric sensors, speakers and microphones that obviously need an opening.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: April 28, 2017, 07:18:52 pm
content: I've forgotten the specifics, but I believe it was a large Cyprus gate array that we encountered. The port is filled with a grease like substance that matches the package visually. I can only speculate as to why the port was there, it certainly wasn't for measuring atmospheric quantities. One of those fun things you find in a production program that has stopped working.

author: SeanB
author_rank: Super Contributor
timestamp: April 30, 2017, 11:55:45 am
content: That would be a part in a cheaper plastic cap over BGA, which will have a void in it and a vent.Would be careful on that Senson website, it seems to have some very dodgy links in the pages, pointing to payday loans and the such. Might be a good idea not to order online there for a while till that is fixed, perhaps a phone call would be safer to find a local stockist.however, as a user of Parylene and Mesoupolet K, which are really good PCB conformal coats, they really require careful preparation of the board. At a minimum a thorough wash in solvent, a scrub all over, followed by a rinse, then baking for a few hours at elevated temperature( and there the MIL 125C is good, as you do not melt things in the 120C oven), followed by a careful brushing on of multiple coats of the conformal coat, following the directions as to mixing to the letter, a clean brush each time ( brand new, washed a bit in water then solvent and then oven dried, preferably a non painted brush so the paint does not run) and removal of all bubbles, then the baking after final coat. Not fun is the coatings are very aggressive chemicals till mixed, and have a very short shelf life unopened, and an even shorter open pack life, and a really short pot life. however they do work, and in most cases are solder through with good isocyanate fume extraction, or a 120mm fan and a window in our shop.Interesting thing about the Mesopoulet K is that you could drop a board with it as a coat into the boiling TCE ultrasonic cleaner, and leave it there for a half hour, and the coating would be mostly fine and undamaged, though in the interim the majority of the plastic parts ( capacitors, sleeves, the epoxy the board contained, some IC packages and any plastic parts of the board connectors) would either have swollen and burst, or were completely gone. Was very good at stripping the lettering off packages, and cleaned any chassis down a treat, no matter what coated it dirt or paint wise.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 01, 2017, 09:06:43 pm
content: thanks a million for all the inputs every one!think ill try conducting several tests with different ideasspecially applying multiple layers and also see how i can integrate gelatinous sticky tape, to protect the coating against stress without letting the tape cause the stresssince the tape i tested seems to be very resilient to heat (even with 100ºC above my normal-high soldering temperature, right next to the tape)ill also look into the food wrap as an additional coating, since ESD should also be less of an issue on already coated componentsand for now i think ill keep the vacuuming in the back of my head, regarding there are several components that probably wont be compatible with this solutionbetter to ie loose a button to water and replace it, rather than having it inoperable from the startps: a little discovery i made (in case it helps some one)when you coat something, then heat shrink it, you can apply drop by drop of additional coating along the opening/s of the heat shrinkand the coating will wick up throughout the inside of the heat shrinkdepending on the size of the heat shrink etc it might not wick through every little corner (maybe vacuuming might improve this)but it will probably reduce/prevent moisture/water from collecting under the heat shrink

author: Assafl
author_rank: Frequent Contributor
timestamp: May 03, 2017, 06:58:11 am
content: In the navy active sonar transducers are waterproofed (they are usually heavily pre-loaded piezo ceramic rings and cope with over 1000V excitation voltage). One of the major ingress points are cables. So when you epoxy pot or conformally coat a board water will creep along the cable under the coating.So one way to cope with this was to make O-rings of a compatible substance to the potting compound, and put 1-2 orings on each cable near the board. The Orings seals tightly against the cable (preventing creeping) while the other side of the O-ring bonds with the potting compound.It is somewhat tricky as you want the potting compound to bond with the O-ring but don't want it to attack or melt or cause the O-ring to swell. I do not remember what was used by the navy...+1 on board prep before conformal coating. I have never seen conformal coating crack before.... maybe there is too much vibration and needs a shock mount?As I see your needs you have two options:1. Prevent water ingress at any cost - very hard to do!2. Allow some water to ingress - but also enable it to exit quickly without leaving damage.Salt water makes the second choice harder - but using Teflon cable and sealing all the connections (better - solder them and seal) should harden it for salt water.One way to prevent damage is to expose contacts that sense water and disengage a "power disconnect" relay completely disconnecting the battery packs - so that the wet electronics don't fry (no power source) and you can clean the salt water away quickly with IPA and deionized water.

author: DTJ
author_rank: Super Contributor
timestamp: May 03, 2017, 07:14:03 am
content: Quote from: Assafl on May 03, 2017, 06:58:11 amThat's very good idea Assafl. I'll store that one away for when I need it.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2017, 11:27:21 am
content: Quote from: Assafl on May 03, 2017, 06:58:11 amIts for an aerial drone - water sensing and immediate power disconnect is a horrible idea as one raindrop in the wrong place and it will crash hard.OTOH if there's a telemetry link, sending back an alarm condition for water detected would be smart. Also if water is detected, cutting power after one second of zero throttle, or if its possible to detect if the FCB has crashed (does it have a heartbeat signal, or LED?) or on impact (shock sensor?), would go a long way towards keeping the electronics and motors in salvageable condition, especially if combined with a hydrophobic film coating from a reputable manufacturer.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 03, 2017, 03:00:53 pm
content: ill have a look at the orings, hoping ill find some for every gauge of wirewhat ill try before though, is greasing the borders of the coating - since what i know from diving, is that an oring is only as effective as its integrity, which usually requires it to be treated, so that it A doesnt become brittle and B allow a small layer of grease to completely close the gaps that may occur during temporary expansions of the oringand i have to agree with Ian there, although false positives could be minimized with some tricks, the solenoids that can cope with the required amperages are as heavy, if not heavier as the entire drone

author: Assafl
author_rank: Frequent Contributor
timestamp: May 03, 2017, 03:22:20 pm
content: Quote from: FlyingSquirrel on May 03, 2017, 03:00:53 pmAs I stated Oring compatibility is crucial. But companies like Raychem makes these types of system. The wrong lube and your Oring will swell and lose sealing properties.Also, the disconnect doesn't have to be a contactor - but the idea is to limit the current draw that would destroy sensitive electronics. So perhaps it is not possible to disconnect the motor and driver - but just the entire control electronics. Of course control signals have to be opto isolated.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 03, 2017, 03:37:46 pm
content: good point, reducing the amount of components that are fried is already a partial successbut id have to look into efficiently doing this, with the amount of connections that lead to the less power hungry partsie the flight controller usually has a minimum of 6 connections (not counting ground)and how would i ideally go about calculating the remaining current, if lets say the main power shorts (through the water) to another component?since, to reach a safe current i would have to drop from 140 to 1A, in extreme cases 0.5A (assuming a short without any resistance ofc)

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2017, 04:09:29 pm
content: You woudn't use a solenoid to disconnect - that's a job for a fuse and crowbar circuit or for a electrically triggered pyro-fuse. You could also use a MOSFET based disconnect, with gate circuit power drawn from the load side so that you have to connect an auxiliary battery to its output to reset it, on a potted or epoxy coated PCB so leakage cant cause it to reconnect.If you cant disconnect the motor feed, you risk loosing all your ESCs to water damage - so solving the low mass high current disconnect problem is well worth doing. Even a few tens of mA can cause significant board damage in under an hour - it only needs about 3000 Coulombs to electrolytically dissolve a gramme of copper, or slightly over one Coulomb per square mm of 1oz copper track, so anything other than a total disconnect is unacceptable.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 03, 2017, 09:27:03 pm
content: hmm so if i understand you correctly, id use 5 (1 per ESC and 1 for the flight controller) N channel MOSFETs (ie IRF4104SPbF, or is this overspeced?)and without a pull down, allow an initial impulse to power on the circuit/sthen common the gates and allow "intruding" water to create a short to the ground, which would power off the MOSFETswhat ive been wondering:- could i also connect the gates to the carbon frame? (as far as i remember it has a resistance of roughly 30ohms)- should an additional short exist to a power rail, wouldnt that basically short the battery? so id also have to add a 140+A fuse to the batteryand could i also use a P channel MOSFET (without pull up) instead? to power off when any short occurs and use a switch or reverse diode to discharge it once the short is clearedor is the N type scenario more reliable?

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2017, 02:27:18 am
content: Ideally, you'd want to cut all power as close to the battery as possible, so you'd have a single power cutoff module the main battery connector plugs into. You'd also need to do the best you can to waterproof the battery itself, especially to prevent water penetration into the pack and to keep the balance connector dry.I'd be reluctant to include the capability for the module to initially turn on on battery pack connection or turn back on without an external power source as it increases the risk that shock and immersion will cause it to fail to cut off or later to turn itself back on. Having to apply external power to a pair of contacts to activate it isn't unreasonable - just touch them with a 9V PP3 battery. I suppose you *could* do something with a hall sensor and a magnet . . . .

author: Assafl
author_rank: Frequent Contributor
timestamp: May 04, 2017, 06:43:13 am
content: Reed switches is what's used in encapsulated electronics (even in heart pacers they use a reed switch). Cheaper and far more reliable than Hall Effect Switches (and don't need power to operate).I was looking for high power reeds to see if it is possible for the reed to disconnect the battery - but none seem to be over 5A carry currents. There is a safety reed from telemechanique that seems to be 100A rating - but it is big and red and over 100$. Maybe it has a relay inside?So it can control a very low Ron FET, or it may be possible to use a reed switch as a "use once" fuse (replaced every time it falls into the ocean). Even then, having that type of current through a 5A rated switch is too much (even for me).Sealing techniques:Another "sealing" technique, one favored by linesmen, is vaving an inverted "can" or "box", open only at the bottom. Sensitive electronics is inserted from the bottom, and cables are arranged to be "scattered" so that wicking of water up cables is limited (or coated in that yucky hydrophobic grease). In your case, that would mean the copter should only crash upright (which I don't know if doable) and should never tip inverted.The best sealing technique, that one we used most often in the navy, was waterproof aluminum boxes that had waterproof glands. We used Bendix/Amp really expensive glands, but there are cheap plastic ones available. Now the key to using such a box is that the gland has an Oring that is a perfect fit to the cable. Another Oring sealed the gland to the box (or it was a flat profile O-Ring). Sometimes, the connector itself was the gland (REALLY EXPENSIVE!!! - but may find NOS on ebay). We used specified lubrication to ensure the Oring was seated properly.The trick is the cable. The cable has to be round. Not fairly round - absolutely round. It has to have a surface that is sealable like PVC, and more importantly, needs to be sealed at both terminated sides - or you must use a cable that sealed against water ingress. The latter cables are injected with hydrophobic grease that is substantially more annoying than silicon or petroleum grease. Otherwise water would wick up the cable into the box.As examples:For systems like active sonar, the cables were a core of individual transducer HV pairs, each core sealed. The area between pairs was fabric strands with the yucky grease. this core was overmolded in real tough thermoplastic. Above that two alternating direction layers of steel cabling was wrapped (to carry the tons of weight of the transducer array). These were carefully terminated to large load carrying terminations.Smaller side scan sonars use a substantially smaller version of same, and newer generations put a lot of the electronics in the transducer. In an active SONAR that is impossible since the amplifiers are huge.I don't think any of this is necessary. Just conformal coating and getting rid of the potential energy of the battery upon impact should be enough. BTW - What about the motors? If salt water gets into the motors I assume that would destroy the bearings?

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2017, 06:50:55 am
content: Reed switches frequently don't survive hard impact schocks. Even assuming the glass body is well enough protected and supported not to break, the reeds can bend leaving the switch permanently open or closed.If the battery is disconnected quickly enough (seconds not minutes for salt water), everything else is salvagable if the motors and boards are immersed in clean fresh water as quickly as possible then cleaned and dried within 24H. If you let anything dry without cleaning, the increased salt concentration will almost certainly FUBAR it

author: Raj
author_rank: Frequent Contributor
timestamp: May 04, 2017, 10:20:34 am
content: Silicone dip?

author: Raj
author_rank: Frequent Contributor
timestamp: May 04, 2017, 10:21:49 am
content: Quote from: mtdoc on April 26, 2017, 06:15:12 pmResin isn't shock resistant

author: Ian.M
author_rank: Super Contributor
timestamp: May 04, 2017, 10:59:20 am
content: Also Polyester resin is known to have adhesion problems to Epoxy. Its OK for laminating but is a lousy encapsulant or adhesive. Many marine DIY users and a few companies have found that out the hard way . . . Epoxy resin would be a significantly better choice, but applying a thin enough coating without the use of dilutants that may compromise its water resistance would be difficult.However, I see no reason to use anything other than a modern thin film hydrophobic coating. The extra weight and thermal resistance to ambient are both negligible and as long as there's fume extraction, such coatings don't interfere with rework *EXCEPT* if epoxy PCB repair or other glueing is required.A further thought on the disconnect: If local laws permit amateur pyrotechnics, and the O.P. has access to a lathe, he could make an explosive disconnect similar to an explosive bolt. When fired it would expel the mated male bullet connector in the battery cable from its female end. Construction would basically be: machine a M-F bullet connector extender out of brass rod, with a cavity in the center to hold an electric igniter, and some black powder sealed in place with a wad smeared with electrical grade silicone. The igniter wires would be led out through small 45 deg angled holes in the side of it, sealed with a small blob of silicone inserted before the igniter and the whole assembly insulated with thin silicone tubing. I would expect several to be damaged during development, but once the right powder charge weight has been found, the brass shell should be reusable - just clean and rebuild with a new igniter, powder etc.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 04, 2017, 06:24:28 pm
content: ive ordered some appropriate MOSFETs and will try looking into trying to make an XT60 extension, that will cut the main power upon water contactreg. the initialization with the 9V battery - couldnt an unlucky short also trigger the MOSFET? making sealing these terminals crucialunluckily i have no control over the orientation in which the drone would crash, i usually do my best to have it upright when i anticipate a crashbut ive already had it in every other orientation too - since unlike the typical photography/video drones, these are meant to flip/roll/twerk in every direction (even fly upside down)and i wont be able to legally get access to gunpowder here (maybe 1ce a year when they sell some fireworks), ive even failed purchasing general acids (H2S04, HCl etc) with more than 10% concentration (thats how knobby they are here)but you gave me another idea - maybe i could use a 0.25W resistor as a backup for the MOSFET, designed to fry similar to a fuse

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 06, 2017, 07:31:47 pm
content: heres a little update to the waterproofing its self:so far what i found to be the most robust solution for the ESCs is:- conformal coating; ive done 2 layers of spray and 2 layers by dripping and spreading evenly, without brushing (later after soldering)- self fusing tape; over the entire board and cables, with roughly 5mm of overlap (pressing it closed around the wires)- more conformal coating; where the wires penetrate the self fusing tape (for additional safety)this seems to work perfectly for the ESCs, since the wires all enter on one side and exit on the exact opposite sidebut i doubt that this will work for the FC or PDB (without using countless layers of the self fusing tape), because theres wires and connectors in all directions (so still experimenting here)what ive left out so far mainly for weight reasons, but could be added later (in case the above solution should eventually fail)- o-rings around the individual wires (as Assafl mentioned, but i havent got for all the required gauges yet), to help seal them off- steel/aluminum protective lacquer, which could be added around the tape to help protect against abrasion (be ware of conductivity!)

author: Koen
author_rank: Frequent Contributor
timestamp: May 06, 2017, 07:37:50 pm
content: The hell are these answers ? There's solutions. It's a known and solved issue. Some products are even sold at major electronic distributors for very reasonable prices. Don't over-complicate it, don't try your own mixture of solutions. Look how the pros do it and copy it.

author: FlyingSquirrel
author_rank: Contributor
timestamp: May 06, 2017, 08:21:55 pm
content: and how do the pros do it...?note:- weight and maintainability (so potting wont do)- vibrations and high G-forces- a lot of grime involved (dust, sand, dirt, mud, grass, branches you name it)messing with the chemical integrity of the mentioned substances was never a subjectthe only solutions i found in the sector so far are either unreliable, have to be refreshed very often, are not maintainable or they mainly consisted of marketing (without actual details)ps: as mentioned, the best coating the major electronics distributor in the country recommended finally ended up cracking and delaminating

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 07, 2017, 01:02:03 am
content: I hope this all works well for you. You might want to do some test flying where the parts are easily recoverable. ESCs do tend to be marginal on cooling, and the multilayers of conformal coating haven't done any favors for heat transfer. A lot will depend on your flying style, but the test flights will give you the best chance of learning at the lowest cost.

author: Assafl
author_rank: Frequent Contributor
timestamp: May 07, 2017, 01:02:54 pm
content: Quote from: FlyingSquirrel on May 06, 2017, 07:31:47 pmIf you leave wiring exposed - it will wick (capillary) water under the self amalgamating tape. The tape will then prevent the water from evaporating - causing more damage.You can try to dip the ESC in water and measure resistance - you will find that it rakes it no time to get in.As a rule: 99% waterproof is worse than no waterproofing at all (water resistance being different than waterproofing). Because water will eventually get in - and the lagging will make it stay.

author: Ian.M
author_rank: Super Contributor
timestamp: May 07, 2017, 01:20:25 pm
content: Which is why you either have to start with a brand new freshly cleaned board, use a high adhesion conformal coating, and pull a vacuum on it then release before its started to cure to get good penetration under components to totally seal all exposed metal apart from the off-board connections, or use a hydrophobic nanofilm surface treatment so you don't get large blobs of water on the board and capillary action doesn't wick it under parts.Wrapping it in *anything* other than a foiled pouch hermetically heatsealed round the wiring, containing a dessicant sachet, will make the problem worse. Failure to keep the boards clean will make the problem worse. Unless you fly in rain or fog or over beaches, most of the dirt should be dry and easily cleaned with a soft brush and a vacuum. Don't let it build up, especially if rain is expected.If you've been flying at sea coasts near salt spray, you've got a major problem. As the salt dries, it forms localised pockets of extremely concentrated brine which can cause rapid corrosion anywhere metal is exposed. To prevent problems, either your electronics needs to either be well enough sealed to survive a hoze-down while running without any water penetration (a lot of extra mass) or you need to strip the craft and wash all the boards and motors as soon as possible after the flight then, if there's any sign that the hydrophobic coating is under-performing, wash with IPA, dry thoroughly and reapply the coating.