Projection Mapping Hell Hound

This project has been haunting me since I found this skeleton dog decoration in the clearance bin at my local pharmacy after last Halloween. I had just completed my Projection Mapping Mask and was looking for a more practical way to carry around this mind-blowing illusion. I also had a blast walking with my daughter's stuff dog on a fixed leash on vacation a few years back (pretending to have it pee on poles and sniffing other dogs).

If you haven't figured it out out yet, the dog leash is a length of steel angle bar upon which I have attached a projector near the grip. The geometry is fixed so I was able to map (or trace) each individual bone in a software designed mainly for use in art installations or DJing (HeavyM). I recorded the video as a screen capture, and I play it back on a loop on the projector (which is also an Android "tablet"). Please watch the video for instructions on how to use the software (there is a free version).

I would not say that this was an easy project, as you require some welding equipment and skills as well as access to one of these mini projectors and some software knowledge. But very rewarding, as it created a true one of a kind accessory for Halloween, or any other "demonic canine event".

Items you will need:

1. Pico Projector: Pond Pico Projector which I got from the initial Kickstarter
2. Computer
3. 5 feet of 1/2 inch angle steel bar, 6 inches of 3/4 inch square tubing
4. Skeleton Dog (these are quite common these days, at least two different kinds)
5. Cheap leash
6. Various screws, fishing line, bolt

Tools you will need:

1. Welder
2. Hand drill
3. Scissors
4. Glue gun

The dog skeleton was looking rather forward, and I figured it would look better if I can project onto its face, including the teeth. So after some prying it came right off; so I predrilled the plastic and screwed it right in at the angle I wanted.

Getting the distance is essential with this type of project, because the projector needs to be far enough to get the whole target; but too far and you lose precious lumens. I also played around to get the angle just right, I wanted it to appear that the dog was leading me; but I couldn't go too far back, or I would lose the optimal projection angle. I ended up going around 8 degrees back from the vertical.

A big challenge with projection mapping on a moving object, is that the projector and the target have to be fixed in 3 dimensions and all the angles. I considered several materials and geometries but settled on steel angle bars, for the absolute stiffness. Aluminum would have been lighter, but I don't have the tools to fabricate with Aluminum. It is really important to get your angle right, I did quite a bit of adjustment of positioning to see what were the angles I wanted and how I was going to thread it through the dog. There are only three pieces of steel basically shaped as a "C". The vertical piece goes all the way to the ground which helps provide support. The second piece runs along the inside of the spine. I drilled several holes along the length to fasten it to the dog with screws.

You need to weld these first two pieces together before you thread it through the gap in the dog's back. Once you are happy with this geometry, you can weld on the handle. See the photos, it should be quite self explanatory.

A series of short screws are used to fasten the frame to the dog.

The projector needed to have a slight angle to the support to keep the projection onto the dog. To deal with this, I welded a wedge of square tubing onto the vertical piece. I was quite challenging to get the right angle and keep it from moving while I welded, so I stuck a screw down the wedge to help keep the gap fixed.

The projector is actually magnetically attached with a mount that I have used for several previous projects using magnets harvested from old hard drives: Magnetic Projector Mount.

The lower jaw was already on a hinge, I merely needed a way to pull it closed on command. I drilled a small hole in the top of the head and threaded a fishing line through and tied it to the lower jaw. I was going to make some sort of trigger mechanism in the handle of the rig, this was going to be quite complex. I chose to keep the line free to pull it with the free hand. I wanted a some sort of handle and needed to keep the line ready to use and untangled when not in use. I ended up glue-gunning some Nd-magnets to the pulling end of line, which stays out of the way stuck onto the steel frame.

I bought a cheap leash from the dollar store. I cut off the snap and glue-gunned it along the front edge of the vertical piece and down the back of the handle.

This was a really cool project and is really impressive to the unexpecting passer-by or party-goer. I will update once I get some reactions from Trick-or-Treaters tomorrow.