Thread: New Crawling Skeleton (Part 2)

Tweet

Bottom view of Wing Board



STEP 4: Wiring Motors: The left side motor crank needs to turn COUNTERCLOCKWISE for the skeleton to have forward motion. In turn, the right side motor crank will need to turn CLOCKWISE for forward motion. Twist the two wires of the AC/DC adapter to the left side motor wires. Plug into power and observe which way the crank turns. If it turns CLOCKWISE, just swap the two wires. (Changing the polarity on a DC motor will make it turn in reverse.) Repeat the same steps with the right side motor wires. If the right side motor crank turns COUNTERCLOCKWISE, just swap the two wires. Once everything is correct, solder the wires and use heat shrink or electrical tape to insulate them.

STEP 5: ARM ASSEMBLY
RIGHT ARM----Cut a length of 1/2" diameter PVC pipe 13+1/2" long. Measure 3+1/2" from one end and use a 7/64" drill bit to drill a hole all the way thru the opposite side of the pipe. This will be the end that attaches to the motor crank. Measure 3/4" from this first hole along the side of the pipe and drill another hole. (NOTE: Starting with this hole and all remaining holes -DO NOT DRILL ALL THE WAY THRU THE PIPE TO THE OTHER SIDE, ONLY TO THE MIDDLE.) Now drill as many hole as possible between these first two holes. Then use a dremel tool with a cutting disc to cut out the area between all of the holes. This long cutout needs to be about 1/8" wide all the way across. Mark this side of the PVC pipe as the FRONT side.
Turn the PVC piece to the opposite side using the small hole we drilled all the way thru as a guide. This will be the REAR side. Measure along the pipe 5/8" from this first hole that was previously drilled and drill another hole (be sure not to drill all the way thru the pipe). Like before, drill as many holes as possible between these first two holes then use the dremel to cut out the areas between the holes. Make the gap approximately 1/8" wide again.



These long holes we are making allow the arms to pivot properly as the skeleton makes it's crawling motion while also keeping the arms from slipping off the motor crank carriage bolt.
Cut a short 1" piece of 1/2" diameter wooden dowel rod. Insert it into the motor end of the PVC arm piece about 1/2". Secure it in place with a small screw. This helps to keep the carriage bolt snug against the arm as it rotates.
Cut another 13+1/2" section of PVC and repeat all of STEP 5 for the LEFT arm.




STEP 6: Attaching Arms
Mark the middle of the 1+1/2" hole in the RIGHT WING. Drill a 1/8" pilot hole on each side of the arm hole. Slide the motor end of the right arm onto the motor crank bolt. Slide a 3" piece of coat hanger wire thru the gaps we drilled in the PVC. (This is basically the AXLE for the arm.) Use two #8 flat head screws and flat washers to secure the axle to the right wing.
Repeat STEP 6 to attach the LEFT arm.











STEP 7: Arms/Hands

The easiest way to make the arms is to use the upper and lower arm pieces of a cheap blow-mold skeleton. Cut a hole in each end of the upper and lower arm bones from a Blucky skeleton. Layer each bone with paper mache and then a coat or two of latex paint after drying. NOTE: I use cheap paper towels and two parts Elmer's Glue and one part water for the paper mache mixture. Slide the upper arm bone onto the LEFT arm PVC piece. Use a small screw to secure it in place. Attach a 1/2" PVC 90 degree elbow onto the end of the left arm PVC . Cut a 10" section or 1/2" PVC . This will be the LOWER arm. Slide this piece into the 90 degree connector and then slide the lower arm bone onto it. Again, use a small screw to secure it in place.
Repeat all of the previous steps for the RIGHT arm.
For the hands I used coat hanger wire to shape the fingers and added wads of masking tape for knuckles. Then covered the fingers in more tape (see picture). Paper mache each hand the same way as the arms and then add a coat or two of latex paint. Once finished, cut a slot in the end of the PVC “wrist” and slide the back end of the hand into it and secure it with a screw.
Age the arms and hands as desired at this time.


STEP 8: RIB CAGE

Cut a piece of ¾” diameter PVC 16” long for a backbone. Drill eleven small holes thru the side of it at approximately one inch intervals. I used a 3/32" drill bit for the small holes. Place the PVC section on top of the motor mount board, against the right side motor mount hole. Mark the spot where a hole can be drilled for a #10 X 2" Machine Screw to go through PVC. Drill the mounting hole approx. 3/16" in diameter all the way thru the PVC. I then added a 1/4" nut between the backbone and the motor mount hole in order to center the backbone. Mount backbone with the bolt and secure it temporarily with nuts. Slide lengths of coat hanger wire through small holes and bend each side up and then around and curve under to make each rib (see picture). Use the width of the chassis as a guide to conform your ribs to the shape of the skeleton. It takes some patience to get the overall shape of a rib cage. Take your time. To give each rib some thickness I then slid sections of 3/8” clear tubing over each rib.
Paper mache the ribs and backbone and cover with one or two coats of latex paint. Age the rib cage as desired at this time.



STEP 9: Skull and NECK

I used a full size styrofoam skull and separated the lower jaw from the upper skull part. I then used an exacto blade to cut out some of the teeth and also thin out the area behind the teeth. Use some thin wire on each side of the jaw to re-attach it to the skull. Let it hang down loose, with the mouth open, to make it look more menacing. After that I used various colors of acrylic paint to color the eye sockets, nose, teeth and any other highlights you desire.

For the neck, cut a section of ¾ “ PVC about 8” in length. Use a 45 degree angle PVC connector on the top end of the rib cage PVC pipe to connect the neck piece to the rib cage "backbone". (You may have to cut out a small section on the bottom of the elbow piece to allow it to slide over the board that the rib cage is mounted to.) To attach the head to the PVC neck you can use a section of pool noodle inside the skull and just slide the PVC pipe into it.
Or , as an option you can screw a small plastic pulley (from a dishwasher) onto the bottom of the skull. I then took another 45 degree PVC elbow and cut out a squared section at the top of it with a dremel tool. Use a small piece of 3/4" PVC pipe to connect the two 45 degree angle elbows together. I then used the dremel to shave the sides of the plastic pulley so it would slide into and fit snugly in the top PVC elbow. This way you can turn the head and change it's position if desired.





STEP 10: Final Assembly
Run the DC Adapter wires along the center board and out the back of the skeleton. Tape or tie wrap the wire along the way, making sure it won't snag on any moving parts. Keep in mind the skeleton pulls the adapter along as it crawls, so put a knot in the wire somewhere and use a wood screw to secure it to the center board. (This will prevent yanking the wires out of the motor housings.)
Plug in the skeleton and allow the arms to rotate until one arm is just touching the ground. Rotate the PVC connector at the elbow clockwise a bit until the hand is about an inch or so off the ground. Repeat this step for the other arm. The skeleton seems to crawl better when adjusted like this. I also hot glued some "Creepy Cloth" to hang at the wrists and elbows.
Lastly, I use a wireless key fob type remote control (Lowe's carries them) so I can start and stop the skeleton as desired.

THAT'S IT !!

So neat! This little demon could be used all year! Thanks so much Dave

Thanks, Terra!
We could probably add this as a future project for the Prop Building Group since these parts are readily available now.

I really, really, really want to do this!!!!! A Prop Building Group would be WONDERFUL!!
Your tutorial is great Dave, but I'm sure I'll be p.m.'ing you. (remember I'm Blonde. lol)

Thanks for the compliments, Cathy. Yes, don't be afraid to ask any question. I'm happy to help.
I'll probably be building another one myself soon. If I discover an easier/better way to perform any of the steps I'll update it here.
Good luck with your build!

are there two adaptors needed, one for each motor, i see 2 wires on each motor, but the adaptor only has two...?

Thanx

Wayne

Just one 500 milliamp (or larger) power adapter is needed. I found it easier to solder about six inches of wire to each of the two motor power terminals and re-assemble the motor housing. I then solder those wires to the power adapter wires.
So each of the two power adapter wires will have two motor wires soldered to it. (One from each motor.)

NOTE: One step I forgot to add to the tutorial. After completing STEP 3 (Making the Wing Boards) use a dremel tool with a sanding attachment to round off the INSIDE of the round hole where the arm will go through. The arm won't rotate correctly without doing this.

That is a very awesome prop!

Great work dave, looks very cool.