Power antennas are great. You can make them go up, and, well, down, and... well, they make the radio work. The radio's important so that you can listen to, uh, well, sometimes there's good music. Anyway, they're fun to watch, and I want to keep mine working.

When Nissan (or whoever Nissan handed the specs to) designed this specific antenna, they didn't bother to weatherproof it. Sure, the mechanism has a little spout at the bottom to let the rain out (which, if I lived in Seattle, or Florida, would be all it needed), but around here, moisture will pool in the housing during the day, then freeze at night. Then the nylon gear rack inside the antenna breaks into pieces and I have to tear it apart again.

So I got to thinking, and then to hacking. Here's what I came up with: the pop-bottle cap antenna protector. (Also my first instructable! And entered in the Transform It! challenge.)

(Disclaimer: Cut metal has sharp edges, and wire has a way of whipping around and poking you in the eye if you aren't careful. Bits of wire sometimes take flight when you cut them off. Work carefully.)

Check out the vid:

Edit: I'm totally blown away by the great response/comments I've been getting on this. Thanks all!

Step 1: What You Need

You need:

A bottle cap or two (beer caps are more fun to look at, I used an Izzie cap because it matched the truck)
The motor from a wind-up toy car (we need the steel spring inside; just hit it with a hammer and it'll come apart)
Epoxy
Duct Tape
Wire (I used a tangle of aluminum wire I found beside the road; avoid wire that will rust)
(Optional) Turtle Wax and a rag

Tools:

Tin snips
Pliers
Something to mix the epoxy on, and with

Step 2: Prepare the Cap

Using the tin snips, carefully cut two slits into the ribbed sides of the cap. I spaced mine about three corrugations apart. The tab that this creates will be our hinge.

On the other side of the cap, splay the metal out a little bit. If your cap was pried unceremoniously from its bottle with a church key (or a car key) and it's already all bent up, you may not need to do this. The only purpose for this is to prevent the metal knob on top of the antenna from binding up on the edge of the cap.

Step 3: Create the Hinge

With the pliers, carefully flatten the flap we just created so that it sits more or less level with the face of the cap. If your pliers mar the painted surface, slip some cardboard or inner tube or something between the metal and the pliers.

Then, again with the pliers, carefully roll the tab into a tube. It doesn't have to close completely, so long as it'll keep a wire in it. (If you can't get it to come out right, you could also create the hinge by punching two little holes in the sides of an uncut cap, like the adventure badges in Up.)

Slide the wire through it and make sure it rotates freely. If it doesn't, mess with it until it does.

Step 4: Make the Bracket

The bracket is the wire piece between the cap and the antenna fitting. This bit will take up a few steps due to its comparative complexity, and its execution will vary with your taste and application.

Cut seven inches or so (more than you think you'll need) of wire. If it's bent up, try to get it as straight as possible with your fingers/pliers (this will make it look nicer later). Then thread the wire through the hinge in the cap.

With the pliers, bend a 90 degree angle (or an acute angle, if you want to make it look fancy) near the middle of the wire. Push the cap right up against this bend, and bend the wire on the other side to match. Try to bend it as close to the cap as possible. If the wire bends inside the hinge and binds, mess around with it a bit. It took me a while to get this bit to work right. (If you lose your patience, try bending the wire, then clipping the hinge onto it.)

Got the cap swinging freely? Then you're ready to move on.

Step 5: Make the Spine of the Bracket

Pictures are better than words here, but here's an approximation. This is the part that will vary considerably with the design of your car.

Bend the two wire legs so that they curve down, meet, and turn around. Then bend the remaining legs outwards, like arms outstretched to hug the antenna post (which they will). Test fit it, and bend it around as needed until you like the look and the cap is more or less centered over the hole. Wire's pretty forgiving.

If you're using steel wire, feel free to solder up the spine. This will make the bracket stronger, but also decrease your margin for error, so make sure it's right where you want it before you plug in the iron.

Step 6: Make the Spring Return and Clips

This is where the wind-up car spring comes in handy. If you haven't yet, smash the wind-up motor (or pry it apart if you want the little gears inside) and harvest the spring. Be careful with it; it is a spring, and it is under a bit of tension.

We need to make three parts from this spring. One of them will spring-load the cap, and the other two will hold the spring to the bracket. Again, pictures are the best guide, and your design may vary with your application. The important thing is that you have something to keep the cap in place.

I put a little upward bend in the end of the spring so that it wouldn't grab the cap and scratch the paint. A little bead of epoxy putty, or plastic, or something else that slides easily would work just fine. (The spring doesn't attach to the cap, it only slides against it.)

Step 7: Attach the Spring to the Bracket

Clip the small spring bits over the spine, slip the hold-down spring under them, and crimp them in place. If they don't want to stay in place, you can use a bit of glue here. (Use superglue to hold it down, then slop some epoxy on it; that way you don't have to hold it while it cures.) I recommend leaving it loose for now, so that you can adjust it if needed.

Spring tension depends on application. You don't want it too terribly powerful, or the antenna will have trouble pulling the knob at the top past the cap's lip; if it's too weak it may flap around while you drive. The spring steel is pretty easy to adjust; in my application I could just slide it up or down in its clips. If you want it to be pretty, try to center the end of the spring steel on the cap. (I had to tweak the spine and the hinge arms.)

Step 8: Fit and Test

Remember the hugging wire arms? Bend one of them around the little wart that the antenna hides in. Then, crimp it to the other side. If needed, repeat with the other side; if not, just clip the other arm off. Mess with the loop and bracket until it fits pretty well.

This is where the duct tape comes in handy. Position the bracket where you want it, hold your breath, and turn the radio on. (Best to do this on the antenna side of the car, with the window down, so that you can reach both radio and cap in case something goes wrong.)

Did it go up okay? You aren't out of the woods yet. Turn your radio off to retract the antenna. If the knob on the antenna hangs up on the cap, you've got a little more shaping to do on the lip of the cap; you may even need to hook a little spiral of spring steel to the lip to ease it over the knob.

(If it won't go up, check that the cap moves freely, and that the antenna isn't hitting anything else. If the antenna encounters enough resistance, it'll stop trying.)

If it all works, you're ready to sling epoxy.

Step 9: Glue It!

If you're sloppy, put some newspaper over the paint around the antenna, and wad a little tape into the hole so you can't drip epoxy into the mechanism. If you're competent with epoxy, don't bother.

Mix up a dab of epoxy. (Don't use super glue for this, it's too brittle and doesn't give you time to position the bracket.) You don't need massive globs of it. I mixed too much, and used the excess to "repair" a rock hole in a headlight.

Pull the assembly off of the antenna. Carefully, using a toothpick or a nail or something, dab a little epoxy onto the wire wherever it touches the antenna housing. Try to avoid getting it where it'll show.

Then set it back where it was, re-apply the duct tape, and leave it alone while it cures.

Step 10: Finishing Touches

That should do the trick! Once the epoxy's cured, test the antenna again, just to make sure that everything's working. Adjust the hinge and bracket if they're out of whack. Finally, spray a little turtle wax on a rag and wipe down the cap and bracket to protect them from rust and to shine them up a bit.

With that, you're done. Go cruising in the snow, with the radio on, like a boss.

(You should still let the car warm up a bit before you turn on the radio, just in case. Your new cover will help keep moisture out, but it's not perfect, and nothing on a car works as well when it's cold.)

If you live in an area where you have to dig your car out of the snow before you drive it, try not to smack the cover with the broom. It's not designed to be broom resistant.