Introduction: Levitating Phantasm Sentinel Sphere

About: I'm an industrial designer and inventor. I make furniture, decorative boxes, and other fun stuff in my free time.

Hello Instructables! This one's a little obscure, but if you're a fan of VHS-era horror movies from the 80's you're in luck. Now since this is related to a horror movie, please be aware that if you go looking up the source material you're likely to find violent, gory, and possibly sexual imagery related to the film.

In the film and its sequels, there's a mysterious bad guy who has this floating ball of death that has blades and drills and all kinds of other nasty implements that emerge from its seamless chrome shell. The story isn't amazing, but I really liked the second film where there's a cool A-team style improvised weapon building montage before they head off to take on the big bad. There's even a sword fight with chainsaws! I digress :)

The display consists of several elements:

1. A 100mm or 4 inch clear plastic ball. $10.99 (pack of 10)

2. An electromagnetic levitation display stand with permanent magnet puck. $79.99 (I paid $47.99 in July 2017)

3. A 3D printed chassis that goes inside the ball and holds all the parts together.

4. A pair of blades cut from sheet plastic.

5. Fabric, stuffing, and tassels to make cheesy Victorian/funeral parlor looking pillow.

6. Some wood squares to raise up the magnetic stand.

7. A card to cover the LED lights in the base once you've got everything balanced correctly.

8. Glue, spray-paint, sand paper, body filler. $12.99 / $9.80

Step 1: The Build

The levitating platform really does all the heavy-lifting (heh...) of this build and doesn't require and modifications. The hardest part of the whole project is actually getting a nice mirrored-chrome looking paint job in your home shop. I used the instructions I found at the following YouTube link and it worked out pretty well. In my experience however I couldn't get the base coat of black paint to 'flow' and get me a super smooth surface. Every microscopic imperfection is magnified a hundredfold with this silver, so I wet-sanded it after the first coat with 2000 grit paper. That's the death-star looking photo in my garage - it was a very cool effect.

So print the chassis STL part file on your own or upload it to someplace like Shapeways and get them to do it for you. The material isn't super important as long as it's light and won't interfere with the magnets. I don't have a still photo of the ball before painting it, but in the video below you can catch a glimpse of how I placed the split between the two halves of the ball. I didn't want it to show up in a place you'd expect like right on the equator just in case any imperfections showed through the paint.

Take the permanent magnet puck and glue it in place with the lower half of the ball and 3D printed chassis. Then stick on the upper half and cut out the slits that hold the blades. Make these edges as neat as you can so you can avoid fixing the mistakes you make here with automotive body filler later on.

Cut out the blade profiles or 3D print them as well. I've provided an STL file, but don't have the original 2D drawings for them. I beveled the sharp parts of the blades as best I could but the fine edges and points get pretty fragile.

The blades aren't held in place with anything besides friction, but you could use some of that gummy blue poster-tack stuff. It's the prop maker's secret weapon ;)

Sand and fill and sand and fill and sand and primer and sand and primer and sand and primer until you get sick of it and then move onto the black base coat of paint. I left several days of drying time in the summer heat for that to cure before messing with the silver layer. As I said earlier, I ended up sanding nearly all of that first coat off when I saw so many blemishes. Even with 2000 grit paper the silver layer came off with a very gentle touch. The final coat was put on pretty thickly but it dries so fast I didn't get any runs.

Allow more time to dry in the heat before handling the ball. It's got a weird and heavy center of gravity due to the magnetic puck and any iron filings or dust from steel-wool will stick to it, so make sure to keep it clean. For the base, I wanted it to look like a magical curio in my home office sci-fi arsenal, so I decided to hide the base in a velvet pillow with golden tassels on the corners. Now I'm no seamstress, but it's not too hard to sew three sides of square. Most the afternoon I spent on this part was struggling to figure out how to thread the sewing machine at my local makerspace. Just sew everything inside-out and leave one side of the square open to insert the levitation base.

Once I had a pillow that looked good, I played around with the stuffing, but found the levitation base was very short, so I added a wooden spacer to its underside and held everything together with masking tape. Getting the sphere to hover correctly is a bit of an art, but the base I have gives a little feedback with the four corner lights to show you when you've got the right positioning. These lights kill the magic of a ball floating above a pillow, so I put a thick card inside the pillow and just shifted it around to cover the lights when I got the ball floating.

That's it! Let me know if anyone finds a better way of making chrome at home.

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