Quelab, the local maker/hackerspace, had a build night featuring Instamorph -- hand-moldable plastic that can be shaped much like clay.
Instamorph is made pliable by heating in hot water, then shaping. Once cool, it is tough, hard, but not brittle.
I thought it would be fun to make a classic "herbie" or "mousy" junkbot, with most of the bits embedded right into the plastic. The end result is OK -- pretty lumpy -- but certainly unusual looking.
I have not finished wiring the 'bot yet -- I will post final notes photos and video when I have a chance to that in the next few weeks.
Step 1: Gather Materials and Tools
- Hot plate, stovetop, or other method of heating a pot of water
- Thermometer, for checking temperature of water
- Tongs or gloves for handling hot plastic
- Wire strippers
- Soldering iron
- Hot air gun for softening and reworking plastic
- Superglue w/plastic prep (for gluing lego wheels onto motors)
- Instamorph, of course
- LM386 amp IC
- 1k - 4.7k resistor for LED
- Two CDS (photoresistor) cells or IR phototranistors
- 10K resistor or 20k pot (I used a 20k pot)
- 100uf - 470uf capacitor
- modem relay or other small DPDT 5v-9v relay
- 2 small motors
- 3904 or similar NPN transistor
- lever/roller/limit switch for obstacle detection
- on/off switch
- 9v battery plug
- optional lego wheels stolen from your son/daughter/neighbor :)
- optional dead LED for rear "wheel"
Step 2: Soften Instamorph
Instamorph comes in pellet form, about the size of small beans. When hard and cool they are an opaque, milky white. When soft and hot, they are clear.
We used crockpots and thermometers to keep the water at a nice temperature, and added pellets slowly. If you stir the pellets gently when they are in the water, they will clump together in a big lump.
When the pellets are clear, they are ready to pull from the water. We used tongs and gloves -- the water is hotter than the plastic -- and trays to catch water drippings.
We "rolled" and "kneaded" the wet plastic pallets to get the plastic reasonably smooth and to squeeze out the water.
The junkbot lump was a pretty big piece of plastic -- a lot of water needed to be squeezed out of the lump prior to working it.
Step 3: Work the Instamorph -- Basic Body & Motors
Shape the plastic in the rough shape of the robot.
The motors need to be the strongest mount, so embed them first. You may want to solder wires to the motors FIRST, so the wiring can be run through the soft plastic itself. Press the motors into the plastic, molding around the motors as you go.
Work fast and keep a close eye on your plastic -- as it starts to become opaque, it is hardening and will be become impossible to work with. You can use a hot-air gun to soften areas for more work (see next step) but with a piece of Instamorph as large as this junkbot, the center will harden and you will NEVER ever be able to heat the plastic enough from the outside to rework the center.
Once the motors are embedded, angle the motors down a bit and get them reasonably aligned. As noted above, it will be really hard to rework this part after-the-fact.
Step 4: Work the Instamorph - Components and Stalks
After the motors are embedded in the basic shape, turn it over and start shaping the top and adding more embedded components.
I pulled some plastic out as sensor "stalks" and pushed the CDS wires right through the plastic. Support the stalks with toothpicks or wire as they will be floppy till the plastic cools. If you don't like the overall bend/shape of the stalks, wait for the plastic to harden, then hit them with an air-gun and reshape.
Embed the 9v battery -- note that the plastic will shrink a bit, so use a dead battery for this part. The battery will initially need prying out when the plastic cools, but real batteries will "snap" in and out perfectly.
I chose to embed the relay and the power LED into the plastic directly. The rest of the components will be wired to the chassis "dead bug" style.
Embed a lever switch in the front for obstacle detection. If you don't get the angle quite right, soften the plastic with a hot-air gun and rework it.
Step 5: Reshape Small Areas, Add Back "Wheel"
If necessary you can make small adjustments by hitting the plastic with a hot-air gun. On a lump this big, it will not turn "clear", but small areas will -- as you see the plastic clearing, you can rework it a bit with tools suitable for clay -- popsicle sticks, spoons, clay carving tools, etc.
For a tailwheel, embed a dead LED right into the plastic, or shape the plastic into a "nub" that can be the tail dragger itself.
You can also embed a power switch right into the plastic. In my case, I hadn't decided where to put the switch until late in the build; I was able to heat up the back end by the battery quite nicely and push the switch in where I wanted it.
Again, when the Instamorph cools and hardens, it is very strong, and shrinks a tiny bit, so it really holds things tightly.
Step 6: Wire It Up!
I generally build the classic "herbie" junkbot variation by Wilf Rigter, but with CDS cells and the "power/balance" LED wired directly as a power indicator.
So get out the soldering iron and do it!
"Lumpybot" will get wired up in the next few weeks; I'll post photos then.