: Hello Everyone,

: With all the recent problems with GPS's and waterproofness (or lack thereof),
: I have decided to use the rest of this epoxy to make me a waterproof GPS
: case. I mean waterPROOF, as in 40 feet underwater for 30 min, which I plan
: to actually test on a scuba dive. Of course it won't be used underwater,
: but the idea is design for overkill and not have to worry with it. I'm
: open to your input.

: I do some underwater photography, and am basically taking ideas from
: underwater housings available for video and still cameras.

: Step 1: Make a sculpey clay mold around my gps. Sculpt the outside into a
: nice rectangle with rounded edges. Leave a little extra raised area where
: the buttons will be. The front of the clay will be open for the face of
: the GPS, and the edges on the front will be flat.

: Step 2: Cast the sculpey mold in resin, tinted yellow. (personal preference)

: Step 3: Sand the face of the casing flat, and the side where the buttons will
: be (Remember, this was cast slightly raised in that area) will be sanded
: flat.

: Step 4: Cut gaskets out of rubber gasket material to go around the button
: area and face of the unit.

: Step 5: Drill holes that line up with each of the buttons on the unit.

: Step 6: Insert spring-loaded pins into the holes.

: Step 7: Cover the holes with rubber gasket material, and make a plastic rim
: that will screw it down. Drill holes for screws. The end result will be a
: rubber piece on the outside, under which will be a metal spring-loaded pin
: that matches up to your buttons on your GPS.

: Step 8: Make a face out of plexiglass, which will screw down to the front,
: with a rubber gasket. Of course it would be nice to have it hinged and
: have a neat latch system, but for now screws will do. It will just make
: changing the batteries a little harder.

: Step 9: Insert GPS, screw it shut, and mount it to your kayak. (Oh, I forgot
: the part about including mounting points.) Now you can do rolls, thrash
: waves, get rained on, whatever you wish, without fear of ruining your GPS.

: Anyone got any ideas on this? I wanted to use an o-ring system as opposed to
: the rubber gasket on the front, but doggone that complicates things. I may
: try to route a groove for an o-ring. A flat rubber gasket should work
: pretty good. If any of you have ideas please submit them. I am open for
: suggestions.

: QUESTION: Will the casing inhibit the ability to track satellites? How can I
: make it so that it doesn't? I'm not sure how GPS signals work. I mean, it
: can transmit through the case of the unit, but not through some leafy
: trees in the forrest??? I never really understood that. The casing I'm
: planning would be at least 1/8" thick. I realize I could go out and
: buy one of those plastic bag things that covers the GPS, but I want a hard
: case that I can mount to the kayak easily. I don't want an overgrown
: ziplock. Besides, making your own is so much more fun and challenging.
: Isn't that why we made our own kayaks in the first place?

: Thanks,

: Malcolm

Sculpy is nice stuff. But it is fairly expensive, and you don't need it to make a mold from your GPS. Among MANY other possibilities, you can use "Play Dough" instead. That should be available at any toy store. Or, you can make your own from flour, salt and water. You cna use a pasta recipe, (with or without the egs) or jsut try using a couple tablespoons of salt to each cup of flour, and enough water to make a stiff putty-like paste. Knead it a lot and let this sit in a closed plastic bag for at least a few hours before using it. The kneading and salt help the wheat proteins develop a substance called "Gluten" which is what makes this work. Either the commercial version of Play Dough or your home made version can be baked after they air dry -- but you really don't need to.

Once you have your desired shape, cover it with plaster of paris to make a mold into which you can cast resin.

If you plan to cast with your boatbuilding epoxy, reinforce the resin with chopped glass fibers. You can make these by cutting narrow strips of fiberglass cloth (say 1/2 to 1 inch wide) Pull on the long threads and you'll set all those short fibers free.

You could skip the plaster of paris and the playdough/sculpey process, too. Drop your GPS in a plastic bag, greas teh outside of the bag and just slather on a thick layer of glass-filled epoxy resin. When it hardens you pull out the GPS and bag, leaving a perfect mold behind. Machine that to get a flar surface for your case front. Make the resin mix thick enough so that it won't run, and use a fast setting resin mix. If you want a thicker wall on the case, you can add more layers of resin and glass.

If you want to give yourself some clearance for controls for pressing the buttons, place a 1/2 icnh or 3/4 inch spacer over the gps before you put it in the plastic bag.

You can buy a small battery operated bag sealer and use havy freezer bags, or Seal-a-meal bags, and just open the bag when you need to replace the batteries. then reseal the bag. One bag will last for many days that way, and since the bag sealer and the GPS all use AA batteries you should have plenty of power on hand to run the sealer.

If you are plannng to use the GPS uderwater, you might want to try this plastic bag bit first. If the radio spectrum on which the GPS units work is filtered out by the water content of trees, then you certainly won't get any signal when you are 2 or 3 feet under water -- much less 30 feet down.

If you are planning to use the GPS above water, then why not have an external battery supply? Then you won't need to open the case for the duration of the trip. You can make a water tight case for "C" or "D" cells from plastic or chrome-plated brass plumbing parts. just see which size sink drain pipe your batteries fit into, and get a cap for both ends.

While we are shopping in the plumbing dept., why not see if your gps would fit into a 6 inch length of 3 inch or 4 inch schedule 40 pipe. If so, forget the whole plastic casting operation. by the shot section of pipe and two caps. Glue the caps on with the appropriate PVC solvent, and then run the sealed tube through your table saw. Slice about 1/3rd of it off, and the remaining 2/3rds should be a nice neat case for your GPS. The tablesaw cut should have given you a flat surface to cover with your gasket and plexiglass cover. If need be you can improve on this by sanding the part on a piece of sandpaper which sits on a very flat surface, such as a piece of glass. You can glue on additional pieces of PVC to the outside of this to create thick enough areas for holding the bolts for closing the case.

If you don't want to do the sawing, s if your GPS will fit into an off-the-shelf PVC "T" fitting ( 3 inch or 4 inch) If so, then cap the ends and put a plexiglass face over the middle opening. These may be big enough to allow you to insert some "D" cell batteries, too.

If your GPS has an attachment for an external power supply then you just need to connect your atteries to these contacts. If not, then remove the battery cover and set it aside. Since you'll be putting your GPS inside your own housing it won't be needed. Then make two dummy "batteries" from short lengths of 1/4 inch to 3/8th inch dowel. cut the dowels about 1/2 inch shorter than a real battery. dril a pilot hole in one end of each of these dowel sections and partially screw in a 3/4 inch long #6 brass, or brass-plated screw. Leave enough of the screw exposed so that the dowel with the screw in it is as long as a regular AA battery. Solder a wire to the exposed threads on the shaft of the screw using a rosin core solder. If you don't use brass screws you may have a more difficult time soldering on the wire. You'll want to use an acid flux or an acid core solder in that case. If you use acid core solder, wash the joint and wipe it clean after it cools, so you remove any flux residue. Attach the other ends of your wires to your battery pack, and insert the dowels instead of the "AA" batteries.

As for pushing the buttons on the front of the GPS.

With a rigid faceplate you are going to be very restricted in how you punch the buttons. Ikelite, the manufacturer of underwater housings for cameras sells "o"-ring-sealed controls which will perform nicely at more than your 30 foot depth requirement. these are available as spare parts for their existing housings, or can be used and built in to new housing designs.

The basic Ikelite control mechanism is a metal rod about 1/4 inch in diameter which slides inside a "gland" which contains 2 "o" rings. One "o"ring rides around the control rod, allowing you to move the rod in and out, and rotate it freely. The other "o" ring seals the joint between the gland and the case. You can insert the gland into a 3/8th inch diameter hole and hold it on with an internal nut, or you can screw it directly into a threaded hole in the case.

The control rod has one end which is thinned down and which can be easily bent. You would rotate the control shaft and the bent end would press whatever button was under it. If you wanted to control two buttons with one control, you would install it so that it was centered between each, and so that there was enough clearance so that the bent end could be rotated to reach either button.

I didn't see any prices listed for these control arms, but they used to be farily reasonable. even so, you want ot reduce the number of them to a minimum. This reduces the cost, size and weight of your housing, and reduces the possible number of leaks. Try to design things so you can get away with one control.

If you had 6 or 8 buttons in 2 parallel rows, you could pull the rod out, or push it in, as needed, and then rotate it to press any of the buttons.

On my old GPS the buttons were arranged in a roughly circular pattern. If I was to try working those with a single control I'd bend the thin end into a stairstep shape, and mount the control rod in the cetner of the GPS controls. then I could pull the controll rod up 1/4 inch so the bent end was above all the buttons, rotate the control to place the bent end above the button I wanted, and then press in on the control rod.

Hopefully there is a picture attached below. If not you can see one at Ikelite's webpage.

http://www.ikelite.com/web_pages/control_parts.html

If you don't want to go with Ikelite fittings, it is fairly easy to make controls which do not need to go through the housing. Years ago a friend showed me how he had made controls on his underwater housing so that they could be operated by magnets which were on the outside of the housing. He used small DC electric motors and gearboxes from toys on the inside of the housing, running them off of batteries which were also inside. A reed switch, which is a type of switch which is opened or closed by magnetism, turned the motor on when a magnet moved near. the magnets were on the outside of the housing, sliding along a short plastic track which kept them from getting lost. When the magnet was at one end of the track it rested over a reed switch which caused a motor to turn clockwise. At the other end of the tack was a reed switch which was connected to the same motor, but had the battery polarity reversed. this made the motor turn counter clockwise. With the magnet in the middle the motor didn't spin at all. By various linkages 4 little motors focused the lens, changed the aperture, depressed the shutter, and wound the film.

A little long, but I hope this helps.

PGJ