Building Electronics and Robots for the Desert

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So you wanna make a robot that is going to survive in the Black Rock desert? The desert is very hard on equipment. This particular desert more than some. We've built a few robots. Maybe we can help.

We welcome additions to this document, contact Lee at Lee dat org.

Contents


Dr. Jon's Guide to Electronics on the Playa

This section by Jon Foote.

Here are hints gleaned from a decade of doing electronics on the playa. Much of this I learned from The Mad Scientists, other things are hard experience learned with SWARM or on my own.

Suggestions/additions/corrections welcome: headrotor@rotorbrain.com

-Jtfoote 04:15, 3 February 2009 (UTC)


Rule Number 1: Playa Eats Solder

There's something in the electrochemistry of wet playa that just destroys solder joints. If solder is exposed, there's enough moisture in morning dew to make it effectively wet. I've seen a lot of projects ruined by disintegrating solder joints: that switch you soldered up may have just nubs of wire after a few days, especially if there's any flexing involved. (Some people say it's the flux rather than the solder that's the problem; I have no evidence for this but it certainly doesn't hurt to de-flux exposed solder joints with alcohol.)

A possible exception is circuit boards where there's no mechanical stress on the joints. We've had reasonable luck with spray-coating PCBs with fixative. Just make sure wires are connected with screw terminals or other mechanical joints (Digi-Key sells great screw terminals on a .1 pitch)


Stuff That Works (usually)

Ammo case enclosures: make sure gasketed lids work. Caulk wire entrances and jacks. If you paint them white or silver they wont get as hot in direct sun (but they will still get hot).

Crimp connectors: Insulated spades and quick-disconnects are your friends. Invest in a quality crimper and know the difference between good and crappy crimps. (Hint: if it doesn't pull out when you yank on it with all your strength, it may be a good crimp...)

Screw terminals are awesome, and make for easy troubleshooting (you can put your meter probe right on the screw) and easy replacement of bad wires, even in a dust storm.

Fanless things like Basic Stamps or Arduinos. (SBC Linux boards worked well for SWARM.)

Die-cast "bud box" gasketed aluminum enclosures. Die-cast aluminum also makes a good heatsink.

E6000 industrial adhesive (or "shoe goo") for sealing wire exits. It dries faster than silicone, it's stronger, it has a better grip on plastic, and the self-leveling looks much neater.

Heatshrink tubing can help protect solder joints, but squirt E6000 or silicone inside before shrinking for extra anal-retentivity.

Gold-plated connectors and connectors with wiping action. .1 inch headers, RJ-11s, RJ-45's, cat 5 are surprisingly OK (but make sure whatever they are attached to is as well).

Unlike Lee (below), I find wire nuts to be reliable and a great way to do quick power connections. Make sure they are sized correctly for your wire and are screwed on TIGHT. Don't even think about them for signal wire thinner than 28 AWG.

What Your Shipment of Fail May Arrive In

Standard extension cords may crap out if playa gets in the contacts. This is pretty much never a problem in the mundane world, but if things stop working and you have extension cords on the playa, consider them a point of failure.

Don't forget you will need to ship your stuff and the vibration from 6+ hours on the road can break solid core wire or chafe insulation. Use stranded wire, tie-wrap anything that may flex, be careful with sharp edges and insulation. Dangling connectors will get stepped on, snag, or get driven over, so bring spares and plan for it.

Consider thermal effects, and read those data sheets. For example, Y5V capacitors lose 1/3 of their capacity at 40C (in other words, playa temperatures). Derate, derate, derate! Night-to-day temperature differences can exceed 60F, so thermal expansion/contraction can be an issue.

IR communication/signaling won't work in the daytime. Yes, even if it's modulated. It's just too bright out there in IR (as well as visible). At night anything depending on reflection will be fooled by dust (think of the "snow" in all those flash photos). Don't count on IR. (Addendum: I have seen installations that successfully used a Kinect at night; I was a little surprised to see that working!)

Computers and laptops need a protected environment. Ditto for things with fans (e.g. computer power supplies). At the very least, bring a ziplock big enough for your laptop and put it inside when you're not using it.

Linear power supplies and voltage regulators may have thermal problems. Derate a huge amount and heatsink even more. A 7805 rated for 1 amp may have trouble with 200 mA in the heat. Switchers work OK, as long as they are fanless and not overloaded. Again, derate conservatively. If they have fans, treat them as computers.

Avoid electrical tape. The adhesive melts, leaving a black sticky mess. It's also useless to apply in a dust storm. Leave it at home. Use self-vulcanizing rubber tape instead.

Hot melt glue does exactly that. Use silicone or E6000.

Solderless breadboards. Dangling wires and tiny holes are asking for trouble.

Switches, pots, anything with moving parts that can get dust inside. Usually not a problem, but sealed versions help guarantee that Murphy won't bite. We have been reduced to begging for condoms to playa-proof exposed switches.

Tips and Workarounds

These Gardner Bender strippers are awesome. Get some: http://www.kk.org/cooltools/archives/003777.php

If you can't get at it, you can't fix it and Murphy's Law practically ensures it will break. Make everything accessible, modular, and replaceable. Don't pot or encapsulate electronics unless you have spares, because you can't fix it. Use screw terminals so it's easy to find and replace bad modules and wires. Bring spares of everything.

Between heat, dust, dehydration, and whatever else you've been up to, you will basically lose 50+ IQ points on the playa. This can make it challenging to troubleshoot and fix things when they get playafied (and they will). Make it easy for yourself ahead of time: color-code wires, clearly label connectors, power supplies, etc. Print out documents/schematics and put inside your enclosure: you are not going to want to look stuff up on the computer. A good trick is to use different connectors so you literally can't plug things in wrong. Make it easy enough a chimp could figure it out, because that chimp is likely to be you.

Generators are subject to brown-outs and frequently running out of gas. Make sure your circuits & PSUs are OK with this.

Video projectors: build an airtight box with a window. For small projectors, put a large furnace air filter on one side. For big or hot projectors, put in a gnarly filtered exhaust fan and put a shop-vac air filter on the box air intake. Caulk all cable inlets/exits and weatherstrip box lid.

The same trick will help with computers, but for ultimate reliability consider putting them in a van or RV and run extension cables out the window. If you are some kind of mod god, you can do liquid-cooling with the heat exchanger outside an ammo case.

Test test test. In heat. In dust. In wind. In the dark. In combination. Consider going up early (Fourth of Ju'playa) for a dry run.



How to Build Robots for Adverse Conditions

This section by Lee Sonko 22:52, 17 March 2009 (UTC)

This is gleaned from several years of working on projects like SWARM and The Serpent Mother. Comments and additions are welcome.

Laptops and full size computers have a rough time with heat and dust. Daytime temperatures can reach 110 degrees. The heat is multiplied when computers are placed in small containers with poor ventilation. And that is exactly where people end up putting them in a valiant attempt to seal them against dust. Here are some ways to keep them cool:

  • Consider putting the computer in a mini-refrigerator. This will also keep the dust out, and a lock on the fridge can help with security at unattended installations. This was successfully run at PlaySoundGround at Burning Man 2008. A Mac Mini was kept completely cool (36 degrees) by a regular mini-fridge. The system fails safe: if power fails, both the fridge and computer will stop. A fridge draws about 150 watts and can usually cool about 400 watts of component generated heat. We're considering applying for a patent as a "Method and Apparatus for Maintaining Operating Temperatures of a Computing Device in Adverse Performance Conditions by Use of a Heat Pump Mechanism," i.e. computer in a mini-fridge :-)
  • Make a box with liberal use of furnace filters. Maybe add an external fan, maybe made out of plywood... you get the idea. If you use a fan, make sure the fan intake is at least 2 feet off the ground. And you should probably put the fan -inside- the box to protect it from the elements as well. It might need cleaning after each dust storm.


Unprotected electrical switches will fail in dust storms. The high winds blow dust into the cracks that cover the contacts inside the switch. When you go to flip the switch, contact isn't made any more. Most small electric switches will fail this way. The best way to protect them is to seal them completely with rubber gaskets and the like. In 2007, a switch on the computerized LED lighting system on the Flaming Lotus Girls Serpent Mother failed in a dust storm. In 2008, a dust storm knocked out power switches on 4 of the 6 SWARM robots. After swapping out the destroyed switches with spares (don't forget to bring spares!), we made some fine ad-hoc switch seals by putting condoms over the switches. The dry air gave the latex a useful life of just 2 days before tearing but it's ok, people usually have lots of condoms on the playa :-)


Dust and dirt get into electrical connectors. When covered in dust, friction between parts increases, making it more difficult to get connectors on and off. Connectors are more likely to arc and not make perfect contact because they are covered with a very thin layer of insulating dust. Solutions include: keep the dust out, blow the dust off, simply be aware that connectors might need more wiggling and blowing on than when in the default world. In SWARM's experience, some of our 24 volt 10 amp molex connectors had to be replaced after a few months of (rather pretty) sparking use but nothing has failed suddenly on us.


Sliding friction between parts increase because of dust. Wherever 2 pieces of metal slide against one another, dust will get in and make the friction much greater. This can cause mechanical parts to seize up. Adding grease or oil helps. Washing the parts off with a rag or water helps. Sealing the mechanism so that dust can't get in at all is the best. You've probably had this experience with your bicycle. As the week goes on, dust gets onto the chain and bearings, making you ride slower and slower, and onto the derailer system, making shifting more and more difficult. I once remedied a seized-up extendable pole on an RV by pouring water into the cracks.


Electronics can be eaten by the alkali dust. We haven't had a failure like this but I trust the hearsay. You should seal all electronics into reasonably airtight boxes with rubber seals. If you can't seal electronics in an airtight box, consider painting it with Krylon UV Resistant Clear Matte finish acrylic coating;It's Krylon # 1309 (the UV resistant thing is very important) (try finding it at Pearl Art or Flax). More details


Parts of your robot can receive some pretty harsh vibration. Consider sealing electronic components that will receive very rough service in epoxy. I've heard that dousing your electronics and such with hot glue works as well against vibration and banging around, with the benefit that you can still solder connections through the hot glue! Just poke your hot soldering iron through the glue and get to it! Though watch out because a sealed box in the sun can get hot enough to make the hot glue gooey.


Avoid self-adhesive tape whenever possible. Heat, daily temperature swings, dust, and rough service can make using adhesives like duct tape, electrical tape and packing tape a bother. Tape usually works ok but it's better not to have to trust it for important things.


Hot glue can fail. If your project is in a box in the sun, the interior temperature can reach the melting point of the hot glue. I heard first-hand of an artist who hot glued speakers to the inside of a plywood dome; on the first day in the sun, all of the speakers unstuck themselves, wrecking the project.


Don't trust electrical tape for anything. It can fail in the high heat of the desert, leaving a gooey mess. Wire nuts will get dusty and may become unreliable and may come loose due to vibration. What works to connect wires: solder, crimp connectors, butt connectors, screwed-down spade connectors, standard size molex connectors. IDC connectors can get iffy if they get knocked around in the wind and get dusty. But in general they work.

Rick L says that Liquid Electrical Tape works well for exposed solder joints and wires. It comes in a tube or a can and is applied like a liquid. Once dry, liquid electrical tape seals out moisture, dirt, and playa dust. Liquid electrical tape does remain flexible and can be removed with a knife. Unlike regular electrical tape, it will not melt in the desert heat. Manufacturers link here: [1]

How to Clean Dusty Electronics

This wisdom collected from the DorkbotSF-Blabber list, Sepember 2009 and Lee Sonko

So your robot/electronics/machine/computer got all dusty and now you're back in the world. What to do?

First off, playa is generally bad for metal and electronics. when it dries, its conductive, about 600ohms/inch. It's a strong alkali and, combined with moisture, corrodes metal and some plastics. You really should get it off all your nice stuff.

Start washing not with water but with high pressure air. Go outside for this, it's going to get messy.

As long as everything is turned off, when electronics get wet it's not the water that causes trouble, it's whatever is dissolved in the water that stays behind after the water evaporates that might be bad. Almost all electronics go thru a water wash during the final assembly.

If you really like them, and want them to last, open them up, and water+vinegar+toothbrush every little nook and cranny. Then re-oil the appropriate parts.

One option is to rinse thoroughly in distilled water and let dry thoroughly. Maybe put the item in a sunlit space for a day or two or in the oven on warm for an hour but watch out, hot spots in ovens can easily melt plastic.

I don't recommend alcohol or acetone because they can damage things like the conformal coatings on motor armatures, the grease in your bearings, gears and switches.

For larger jobs, a pressure washer can help as long as the equipment you're cleaning can take it. Adding some vinegar to the water can help. Borax cleaner is also claimed to help.

You'll be amazed at how a coating of playa dust will stick to things even after you've scrubbed and scrubbed. Try washing a small section and look at it after it's dried before you get all smug about how clean you got your nice stuff. Diamonds decompose in a billion years or so but playa dust is forever!


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