Building Small Robots: Making One Cubic Inch Micro-Sumo Robots and Smaller

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.

Small Motors
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.

Small Batteries
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.

MATERIALS

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

Comments

[camo888]

in picture #7 where did you get the tracks for that robot
are they custom made or did u buy them ( if so where)

[shawntherobot]

instread of using the wire  bumper switch you could get one from a computer mouse they usually have three switches that arent very big either so they dont take up much space

[Winterz117]

ok do u really need to use the magned wire over normal wire? its really expensive...

[shawntherobot]

if you take apart an electric motor youll find maybe about 10 feeet iof wire from the average size

[mikey77]

You don't have to use magnet wire, but it makes it much easier to make really small robots. Magnet wire is not expensive, you can just take apart a relay and get the magnet wire that way. Generally, the smaller the relay, the thinner the wire.

[dagenius]

The only problem with thin wires like magnet wire is that it is very thin. The thinner the wire, the more resistance and more inductance. this makes it harder to carry sufficient current through the wire, and creates more rf noise.

[Winterz117]

oh ok gotcha. Yeah I was looking for it on digitec and it was like 50$ a spool, so the spools must have held alot of wire. Ok thanks for the reply if inget a mini robot built I'll send u some pics!

[Elliot says]

how much did it cost you for this robot. Or how much would it of costed you if you didnt have any of the parts already?

[Yashknowsbetter]

Hey..im from india..and we dont get picaxe microcontrollers here...so are there any other tiny microcontrollers..preferably which i can program using C(say AVR)???

[raykholo]

yes avr should work provided you can find one with the same pinout, or u will have to change the circuitry around a bit this robot is able to be programmed via ir remote, which is something that only pic microcontrollers can do, so it might also be necesary to change the code... yes its doable, but i would not advise doing this unless u have some free time and advanced skills in electronics good luck

[caboferdy]

well I have a question.. it uses some kind of program? or it just works with the microcontroller?... i mean.. i haven't seen a usb port or something like it?

[mikey77]

Your question has been answered. Read the comments below to find out about the Picaxe microcontroller, where to get it and how it is programmed.

[Erobots]

You live in the US right? I also do , I suggest you look at Jameco . They have a nice selection of electronics. I use them all the time. Cool robot too!

[mikey77]

Yes, Jameco is a good source for robot parts. That is why I put a link to them in step 2. The very small blue on-off switch on this robot is from Jameco. They also have very nice 12 volt gear motors with a 1/4" shaft that are fairly inexpensive and useful for robot arms and grippers.

[Dirk5]

did you use insulated wire or enamel coted wire?