The box is what started this whole project off. I spotted it in a second hand store on sale for a few dollars. Designed to look like a book the box was meant for holding casual curiousities. Flipping the lid up and down it reminded me of the the scene in Harry Potter where one of his textbooks, The Monster Book of Monsters, attacks him from under the bed. I could picture this box being turned into a snazzy motorized attacking monster with a bit of work. Best of all I could give it the look I wanted.
Eyeballing the size I determined that it would be large enough to hold the required motors, arduino, and battery pack that would be needed to bring it to life.
For the motors I used a couple of mid sized DC motors and wheels I had lying around from a previous project. As a quick test I mounted to box on the motors with a bit of duct tape and wood pieces to make sure it would be powerful enough. The weight of the box plus components meant I couldn't just toss a toy motor kit into it. Switching on the battery pack the box plowed straight into the wall with a thump, the motors would be sufficient.
Now it was time to start installing the components.
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Step 1: Bring the Speed
For the motors I decided to mount them to a thin piece of wood to give it more structural support than the cardboard box could do on it's own. Mounting was a fairly straight forward process of measurements and drilling holes for the motor mount using nuts and bolts. A lot of nuts went into this project.
With the motors secured to the wood base it was centered into box, outlines were drawn for where the wheels would stick out, and mounting spots marked for the bolts that would securing the wood base to the cardboard box. I used the cordless drill to make holes for the bolts and starting points for cutting out the wheel holes. To cut out the rectangular holes for the wheels I used the saw blade on my multi tool. Not the cleanest cuts but quick and easy. Four nuts and bolts later and the motors were firmly locked in place within the box.
For the back wheel I added simple roller wheel that would run smooth but a little wonky to give a funky movement while allowing for tight twirls. I ended up cutting a whole in the bottom of the box and mounting it from the inside so that it had the same height clearance as the front wheels.
With all the wheels mounted I powered it up with 12 volts of battery goodness and watched it shoot across the room straight into the wall with a resounding thud. Time to add some brains to my monster and wire in the Arduino.
Step 2: Monster Brains
I'm a big fan of the Arduinos for simple electronic and robotic projects. They're fairly inexpensive, have a strong community behind them, and reasonably easy to program. With the diffent modules available I had the option of controlling it with my smartphone using bluetooth, a tv remote using IR, or a RC remote.
The main reason I went with the bluetooth and smartphone combo was that I had one pre-assembled from a previous robotics project, no reason to start from scratch. When you build stuff for fun there isn't always a right or wrong way to do things. Many times it comes down to personal curiosity and what parts are on hand.
For the Arduino setup I used the tutorial by caqiomoraes at How to control and arduino car via Bluetooth (for beginners) and highly recommend it. It's uncomplicated and easy for a beginner like myself to follow.
It was pretty straight forward since it would just be controlling the two motors. I have plans to add a couple servos and LEDs later but for the moment am keeping it simple. Using an Arduino Uno I attached a motor shield onto it simply by snapping it into place. The bluetooth module needed to be soldered to the board.
From past experience I made it so that I could uncouple the power from the bluetooth module easily. Because it uses the Tx and Rx pins it interferes with the USB serial comm and uploading scripts through the USB. The easy workaround is to unplug the bluetooth module when updating the programming.
As a simple guy I like simple scripts and kept the controls to the basics of forward, back, left, and right. Luckily there are wonderful libraries for both the motor shield and bluetooth module keeping the amount of typing to a minimum. I've attached a copy of the script I ended up using.
With the components in place and program running I gave the beast a quick spin and twirl to make sure everything was working. No thud against the wall this time so it was onto fancying my box up.
Step 3: Give It a Pretty Smile
For the teeth and eyes I decided to whip up a batch of tried and true oogoo. Oogoo is a very cool moldable rubbery material made from 2 parts 100% silicon caulk and 1 part corn starch mixed together. Work outside or in a well ventilated area this stuff stinks and the vinigar smell will linger for awhile. For a great tutorial check out the Instructable at https://www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute
For the eyes I wanted to go big and bold. The original plan was to go with some large glass marbles but that didn't have the effect I was looking for so I molded my own out of oogoo. To create the mold I went hunting vending machines selling small toys packaged in plastic shells. It was the shells I was looking for and when the right size was found three were purchased, one for testing and two for the eye molds.
For the mix I added a dash of dark green acrylic paint and a pinch of sparkles. To keep the color and thickness consistent I made enough of the goop for both eyes. Filling the plastic shells with the green sparkly I capped them with a giant marble to create an open space at the base of the eyes.
The teeth required a bit more creativity to create the monsterous looking teeth. Luckily I found a second hand toy with a great set of dino teeth that would make fantastic molds. After removing the teeth from the toy I pressed them into a wad of molding clay to make a decent indentation. Then a glob of white oogoo (no paint added) was pressed into the clay mold. A chopstick from take-away was used to scratch in a bit of texture on the back of the teeth.
Once the teeth had set they were carefully pulled out of the mold and cleaned up with a sharp knife and scissors.
Now it was time for some spooky zombie gums to hold the teeth.
This time I added some fleshy pink acrylic paint to the mix and poured it onto a plastic container where I could start molding into the size and shape I wanted. Once a general shape was achived the teeth were pressed in and using my trusty chopstick the look was tweeked to get the creepy textured look I wanted.
After about an hour the chompers were ready to be mounted to the book. A bit of platic was cut and glued to the back of the teeth to form a stable base. A hole was drilled for a bold with a matching nut placed and glued under the plastic. A short piece of flexible nylon coated galvanized strapping was bolted into it and bent in preparation for being attached to the book.
Two thin slots were cut into the book box to let the galvanized strapping slide in. The pieces were secured with a bend and a bit of duct tape leaving it a bit loose so the teeth would wobble when racing around.
Now it was time to skin the beast.
Step 4: Let the Fur Fly
The skin of the book was going to make or break the look so I took a bit of time figuring out what I was going to do.
For some tentacles I cut up a rubber snake I picked up at the dollar store and glued the pieces to the box. No real animals were harmed in the making of this monster.
To achieve the look I wanted for the body I went with two types of fake fur. A dark one for the face area and a lighter extra fuzzy fur for the body area. The darker fur came from a old side cushion and the light fur from a trip to the fabric store.
A piece of dark fur was cut to size and secured with some double sided velcro tape. The velcro ensured I could remove it as needed, something I ended up doing a lot while fussing over the look. Once the fur was laid out how I wanted it two slits were cut into it and the eyes pressed through.
For the body a larger piece of the light fur was cut to cover the top cover and spine. A triangular hole was cut out for where the face would show through. Double sided velcro tape was used to secure the body fur down. Minor adjustments and some ruffling of the fur completed the look.
Time to let the beast off it's leash.