Roof Coffee Cup





Introduction: Roof Coffee Cup

After reading a post on Gizmodo about a researcher who sent a student riding through college campuses dressed as a clown riding on a unicycle, and how he found people who were on cell phones/using electronic devices were 50% less likely to notice anything unusual happening, I got an idea. 

People maintain driving with a cellphone doesn't distract them.  I decided to see if that was true.  I thought and thought about what I could do to prove it.  Then it hit me.  If I put something on my car roof, I could see if people notice.  I decided a coffee cup was the best choice, and after consulting my friends, they said to go with a StarBucks cup w/attached "cup condom".  I did , and the reaction was good enough for me to give the cup its own Twitter feed( ), where I jot down what people do while driving, then Tweet a recap later.  It's hilarious because I can be driving at 65 miles per hour, and people don't consider how a cup could still be on my roof.  When I take turns in front of them, and the cup doesn't move, they still tell me.  Even at stop lights, when people get out of their cars and try to take it off, some people don't figure out it's not real.

With how hard it is to keep a straight face because I'm laughing so hard, I knew I couldn't keep the fun to myself.  I also wanted to see the RoofCoffeeCup spread out from the small area of New Jersey I drive, and go across the country.  Thus, I'm making my first Instructable.  All I ask is that if you do make a RoofCoffeeCup, please tweet what reactions/where your cup is using the #RoofCoffeeCup hash tag, so we can all share the adventures.

Now some "legal" stuff.  Even though the cup weighs 3oz, the magnets used are hard, and could damage should it fly off, and someone is tailgating you.  Check your local laws before attempting.  The magnets I use are stronger than the ones on those "tear-drop" lights some people put on their roofs, and this cup is lighter than those lights, so if those lights are legal, I don't see why this isn't.  I take no responsibility for anything that happens to you if you try this.  I'm only responsible for when I do it with my own car.  I'm not responsible for any damage to your car through possible scratching or dents if you drop it close to the car.  Don't be a hazard to others on the road.  The reason I went with a coffee cup is it's not that out of the ordinary, and it's not a danger to anyone, like if I attached a laptop or something else heavy.  It also will not cause a panic/calls to police, like doing this with a baby carrier or car seat would, which I DO NOT endorse trying. 

Step 1: Materials Needed:

1 Coffee Cup, paper variety
1 Coffee Cup Lid
1 Coffee Cup Condom/holder/ sleeve
3 Hard Disk Drive magnets
1 piece of scrap plastic to mount magnets to
News and/or packing paper

Step 2: Prepping the Cup.

I did not take photos of the original RoofCoffeeCup, but StarBucks uses special cups around the holidays, so we'll use a new cup for this Instructable.  You must first get a cup.  I usually just check the trash cans outside of StarBucks, then take them home and wash them out.  I check to make sure they don't have any writing on them, are in good shape with no leaks/stains, and usually use the medium size.  Make sure you get the lid as well.  Take them home, and give them a quick rinse and wipe them dry.  You don't want them to get wet on the outside, or else you might get a weak point.  Once dry, you are ready to begin.

Step 3: Making the Mount

To mount the magnets, you could just glue them right to the cup.  But most cups have a recessed bottom, so to get the best sticking power, they need to touch the metal.  I accomplish this by mounting the magnets to a piece of plastic, and gluing the plastic to the bottom of the cup.  In order to get the right size, you need to trace around the bottom of the cup on a piece of plastic.  Cut it out, and trim as necessary to make it just barely slide into the bottom of the cup.  The cups taper, so as long as you get it past the bottom, it will have room to move around and adjust.

Step 4: Arranging Your Magnets.

I use magnets salvaged from hard drives for my cups because they are free to me, and very powerful.  Once removed from the drives and their mounts, you simply need to find a configuration that works for you.  The magnets are powerful, so they will try to fly towards each other, so watch your hands.  If you lay them flat, you can usually find a shape they rest well in.  This cup seemed to work with the magnets going around in a circle.  The original RoofCoffeeCup worked better with one magnet facing the opposite way of the others.  It's the second photo in this step.  Just for a reference, that cup with magnets weighs just under 3oz, but can lift and hold a 10lb dumbbell. 

Step 5: Attaching the Magnets

Once you get the right pattern/arrangement, you need to attach the magnets to the plastic.  I use industrial strength hot glue, so when it's on my roof and the wind is flowing by, it doesn't lose any strength because it's cool.  When the magnets are secure, I like to fill all around them to make it almost one piece.  To eliminate any bumps or high points, while the glue is still hot/warm, I take a piece of wax paper, cover the magnets, and stick it to something metal magnet side down.  This flattens the glue, and the wax paper stops it from sticking to the metal.  It also helps you pick it up from one when it's cool.

Once cool, I run a razor over the magnets to make sure there's no glue on them, and cover the whole thing with electrical tape so the magnets aren't directly touching my car, and to reduce scratches .

Step 6: Dry Fit

Once your glue is dry/cool on the magnet mount, dry fit it into the cup, and make any cuts/trims to let it just slide in.  I like it to be able to pop out, so that if something happens, the paper will seperate from the magnet mount, and hopefully the magnets stay attached to your car.

If you intend on using the cup holder/condom/anything else, now is a good time to try it on the cup and make any repairs/fixes.  Mine had a open edge, and to prevent it catching wind, I hot glued the seam to make it nice and smooth.  Once your happy, now we are going to make this disposable cup be able to survive a 65mph trip down the highway!

Step 7: Waterproofing and Making It Tough

I use clear spray lacquer on my cups.  This makes them durable, stops water from soaking into the paper and making it soft, adds some rigidity to them, and keeps them clean.  I give the inside of the cup usually only one coat, but make that coat a little heavy on the bottom to fill in the area where the bottom meets the inside cup walls.  After that's dry, I then give it a minumum of three coats of lacquer on the outside and allow it to dry between each coat.  This step is why you don't want writing on the cup.  The lacquer will make it run and look bad.  The lacquer soaks into the paper and because it's clear, it's hardly noticable until very close up, and makes it strong.  I also coat the paper holder, inside and out at least four times, because it's usually recycled paper, and softens quick when it gets wet.  I use an old spray can to help keep it's shape while it dries.  Once it dries, you're almost done.

Step 8: Finishing Touches

Because it's a paper cup and the magnets are strong, if you didn't shore up the inside, when you go to remove it, you could crush the cup.  I just use newspaper/packing paper to give it some internal strength, while keeping it light. 

Make sure everything is how you like it, because once the next step is done, there's no going back inside.  Dry fit the lid and make sure the lip is not covered by anything.  Run a bead of glue around the lids groove, and slap it on the cup.  My glue was a little too hot when I did this, and the cups lid melted because of it.  But it's on tight, so nothing I can do.  I usually seal the hole in the lid, so no air/wind can get inside and pop the top off or cause drag to possibly blow it off.

Now you need to prepare a little before you attach the magnet mount.  You want to have some more wax paper handy, and a piece of flat metal.  Squirt glue onto the back of the magnet mount, slide it in the cup end(magnets out, of course), lay down your wax paper on the metal, and put it magnets down on the metal.  The magnets will pull towards the metal, and make sure the magnets sit flush with the end of the cup and also that they are as close as they can be to the metal.  The wax paper will stop any glue sticking, should some escape around the edges.   Once dry/cool, apply some extra where you can, to secure it strong.

The last step is to slide on the cup condom, and glue it into it's place.  Between it and the paper inside, it makes that area the strongest to grab onto and use to detach from your roof. 

Step 9: You're Done!

Here is a shot of the old RoofCoffeeCup, and its "cousin from up North", now finished.

When removing the cup from a surface, trying to pick it straight up will not work, as you can see the cup can hold onto a lot of weight.  You want to try and tilt it to one side and then, like Velcro, it will peel right off.

Step 10: In Closing

I hope you enjoyed this Instructable.  If you do try this, bearing in mind the warnings from the front page, let me know/see your cups journey by tweeting about it and including "#RoofCoffeeCup" in your tweet so I and others can search for it.  I usually tweet what reactions I have gotten, and sometimes where the cup is.  If anyone asks, tell them what it's all about.  I had some cheap business cards made up that I hand to people who get out of their cars/come up to my window to explain what it is.  I've had more than one person laugh like crazy when I explain it.



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    A Coca-Cola cup and a happy meal Box / pizza box :-D

    I accidentally left a gallon of milk on my jeep and got half a block down the road before it fell off and exploded all over the street...I had lots of looks in that short distance... you could use white spray paint in an empty gallon jug with the same idea in mind add magnets.

    I think i had the bests was real...I stay in a condo block where the rubbish bins are located next to the condo exit. Most people would just walk there and dispose their my case I was lazy...I place my garbage on top of my car, drive to the exit and dispose it...One day I took the garbage ,placed it on top of my car and drove away, forgetting to stop to!!! can you imagine what happen!! I didn't realize it until i reached my school....THE WHOLE WORLD WAS LOOKING AT ME!!! What an embarrassment !!!!

    once i left a no fall band on the step for a car and i drove for about 1hour and nothing happend it stayed there

    I made one of these years ago, and was amazed by the kind of reactions I got from people. You would think that a flat tire, a headlight out, a midget axe murderer hanging onto the back of your car, etc would garner a lot of attention. You'd be wrong.

    A coffee/soda cup on the top of your car will drive other people absolutely bat-crap insane. I had people follow me for miles, honking and waving to get my attention, just to tell me I had a bit of styrofoam on my roof.

    I made one of these with great results. A few of my friends and I came up with a few variations that would work great as well. The first one is for the ladies. Get a cheap thrift store purse, best if it looks expensive, and put the magnets in it. The other would require designing a strong but light weight electromagnet with a push button switch so that as you are driving you can take it down act like you are taking a drink then put it right back on top.

    I like the magnets I get from dismantling discarded microwave ovens. There are two big, strong round ones on the magnetron that might just fit inside the cup.

    3 replies

    BE REALLY CAREFUL ! Microwaves have a large capacitor that boosts the voltage up to 10,000 volts and much more depending on the wattage of the unit . A repair technician was instantly killed when he grounded himself to that capacitor. They can be discharged easily. But I don't recommend messing around inside a microwave unless you are a profesionally trained technician. FYI.

    Yep. I collect those too. Discharge with a screwdriver;however, most are dead and I suspect an underlying cause of the demise of the Nuker.

    Well, it's a lot easier for me to get the magnets from hard drives. I can buy old ones from the flea market for ~$1. Plus, if you need to literally destroy a HDD, there is no better way than handling the platters, then scratching them with a awl or something.

    But I will keep my eye out for an old microwave for exactly this reason, and see if they are stronger than the HDD magnets.  As it is, even a small HDD magnet can hold up at least 2.5 lbs, as shown in the pictures of a RoofCellPhone.  The picture with the weight is only being supported by one of the magnets.  I didn't go heavier because those magnets were just attached with plain Elmer's Glue.


    I did this years ago! A guy followed me till I stopped. Then he got out and told me I had a cup of coffee on my roof of my truck. I showed him the magnet inside. He got so angry that we almost got into a punch-out! Guess he had no sense of humor! So beware, this can cause strange reactions in humans.

    If you think this is cool, I created an entire game out of this. I try to see how many points I can get by people idiotically pointing at the cup on top of my car. Greatly named, Car Cup.

    Rookies...Years ago we had an old gas pump handle with about 8" of ragged hose connected. We drove around with that hanging out of the filler neck all the time.

    The best is when we would start yelling at the Circle K clerk and burnout - hoping he/she saw the nozzle hanging from the truck.

    A coffee cup is cool, but do you know what would be EPIC? A BABY CRADLE!!! Some with no sense of humor might not see the comedy in that however.

    the day i get my car im doing this :D
    it could be kind of entertaining to do with say, a cell phone, but perhaps have it "resting" on the edge of the trunk lid :3
    id do it with a dummy phone though, you never know if someone would be "courteous" and walk off with your $250 smartphone.

    nonetheless, i LOVED reading this. just think of all the things you could up ontop (or maybe even on the side) of your car!

    PS: you could do it with a laptop if you took all the internals out and just used the shell ;)


    I live around the NY/NJ area, and saw a car with a coffee cup on top the other day. I reached out to see if it was stuck on there with magnets. It wasn't, and then the guy who's coffee it was walked up behind me and said "What are you doing?". Quite embarrassing! Great 'ible, though!

    3 replies

    Oh man , I would have thanked you , I hate it when I leave a cup on the roof .

    That's so sad! I always thank people for letting me know and the cup usually says thank you to people who try to save him.