For me, one of the great challenges in electronics is to see just how small a robot I can make. The beautiful thing about electronics is that the components just keep getting smaller and cheaper and more efficient at an incredibly fast pace. Imagine if automobile technology were like that. Unfortunately, mechanical systems at this time, are not advancing nearly as fast as electronics.
This leads to one of the main difficulties in building very small robots: trying to fit in a small space, the mechanical system that moves the robot. The mechanical system and batteries tend to take up most of the volume of a really small robot.
pic1 shows Mr. Cube R-16, a one cubic inch micro-sumo robot that is capable of reacting to its environment with music wire whiskers (bumper switch). It can move and explore the perimeter of a small box. It can be remote controlled using a universal TV infrared remote control that is set up for a Sony TV. It can also have its Picaxe microcontroller pre-programmed with reaction patterns. Details begin on step 1.
Step 1: Components of a One Cubic Inch Robot
Mr cube R-16, is the sixteenth robot that I have built. It is a one cubic inch robot that measures 1"x1"x1". It is capable of autonomous programmable behavior or it can be remote controlled. It is not meant to be anything that is very practical or particularly useful. It is merely a prototype and proof of concept. It is, however, useful in the sense that building a tiny robot allows you to hone your miniaturization skills for robots and other small circuits.
Building Small Robots and Circuits
Keep in mind that building as small as possible means that it may take twice as long as it would normally take to build the same circuit in a larger space. All kinds of clamps are needed to hold the small components and wires in place while soldering or gluing. A bright work light and a good magnifying headset or a fixed magnifying glass are a must.
It turns out that one of the biggest obstacles to making really tiny robots is the gear motor that is required. The control electronics (microcontrollers) just keep getting smaller. However, finding low rpm gear motors that are small enough is not so easy.
Mr. Cube uses tiny pager gear motors that are geared at a 25:1 ratio. At that gearing, the robot is faster than I would like and a little twitchy. To fit the space, the motors had to be offset with one wheel more forward than the other. Even with that, it moves forward, backward, and turns fine. The motors were wired on to the perfboard with 24 gauge wire that was soldered and then glued with contact cement. At the rear of the robot a 4-40 sized nylon bolt was screwed into a tapped hole underneath the bottom circuit board. This smooth plastic bolt head acts as a caster to balance the robot. You can see it in the lower right of pic 4. This gives a wheel clearance at the bottom of the robot of about 1/32".
To mount the wheels, the 3/16" plastic pulleys mounted on the motors were powered up and then, while spinning, were sanded to the right diameter. They were then inserted into a hole in a metal washer that fit inside of a nylon washer and everything was epoxied together. The wheel was then coated with two coats of Liquid Tape rubber to give it traction.
Another problem with the smallest robots is finding small batteries that will last. The gear motors used require fairly high currents (90-115ma) to operate. This results in a small robot that eats batteries for breakfast. The best I could find at the time, were 3-LM44 lithium button cell batteries. The battery life in very small robots of this type, is so short, (a few minutes) that they usually cannot do anything close to practical.
There was only room for three 1.5v batteries, so they ended up powering both the motors and the Picaxe controller. Because of electrical noise which small DC motors can create, one power supply for everything, is usually not a good idea. But so far it is working fine.
The space in this one inch robot was so tight that the thickness of the 28 gauge wire insulation (from ribbon cable) turned out to be a problem. I could barely put the two halves of the robot together. I estimate that about 85% of the volume of the robot is filled with components.
The robot was so small that even an on-off switch was problematic. Eventually, I might replace the crude whiskers with infrared sensors. I have literally run out of easy to use space, so fitting anything more, without resorting to surface mount technology, would be an interesting challenge.
I like to use clamshell construction for really small robots. See Pic 2. This consists of two halves that hook together with .1" strip headers and sockets. This gives easy access to all the components, making it easier to debug the circuits or make changes.
Pic 3 shows the location of some of the major components.
2 GM15 Gear Motors- 25:1 6mm Planetary Gear Pager Motor: http://www.solarbotics.com/motors_accessories/4/
18x Picaxe microcontroller available from: http://www.hvwtech.com/products_list.asp?CatID=90&SubCatID=249&SubSubCatID=250
L293 motor controller DIP IC: http://www.mouser.com
Panasonic PNA4602M infrared detector: http://www.mouser.com
30 AWG Beldsol heat strippable (solderable) magnet wire: http://www.mouser.com
3 LM44 1.5V. Lithium button cell batteries: http://www.mouser.com
Small blue on-off switch: http://www.jameco.com
Thin solder- .015" rosin core solder: http://www.mouser.com
Resistors and a 150 uf tantalum capacitor
.1" fiberglass copper traced perfboard from: http://www.allelectronics.com/cgi-bin/item/ECS-4/455/SOLDERABLE_PERF_BOARD,_LINE_PATTERN_.html
Performix (tm) liquid tape, black-Available at Wal-Mart or http://www.thetapeworks.com/liquid-tape.htm