Development of a Micro Sumo Robot
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Introduction

I've been working for many months to develop a small but powerful mechanical platform for micro sumo robots, for use with our new Lil'PICcy controller board.

Micro sumo is a new class of sumo robot that is restricted to a cube 5 cm on a side and a maximum weight of 100 grams. This is very much harder to create than a mini sumo robot, which can be up to 10 cm wide and long, has no height limit, and can weigh up to 500 grams (nearly a pound).

The drive train is a critical component, as is the power supply. As for the drive train, the first two attempts were based on small, surplus gearhead motors.

Lil'PICcy One first attempt - "Lil'PICcy One"

SD Lilliputian second attempt - the "SD Lilliputian"

Lil'PICcy Too third time's a charm! - "Lil'PICcy Too"

One set of motors were one-of-a-kind found at Wacky Willy's. They were hard to use, as they were long and thin. They had to be mounted side by side to fit the envelope of 5cm cubed, but this placed their output shafts significantly out of alignment. Thus, idler gears were needed to couple the motors to wheels which could sthen be aligned. This required a complex 3D structure to hold the motors, wheel shafts, and idlers in proper alignment. Unfortunately, this was rather bulky and left little room for batteries. And I don't know where to get more of those motors!

The second attempt was pioneered by PARTS' own Steve Davee, using Apple Mac floppy eject gearhead motors available from All Tronics. Steve discovered that they fit together quite easily back to back, but did require gears to be glued to their output shafts which then would drive gears directly coupled to the wheels. Unfortunately, these gearhead motors are also rather bulky, and left little room, save for pockets of space here and there, for batteries -- not enough room for anything standard. N sized batteries fit within these pockets, but do not have enough capacity to drive the Lil'PICcy board and the two current-hungry motors. Steve's solution was to take about certain brands of 9v batteries and wire the small cells from them into smaller stacks that fit within the pockets. He may still make it work, but I've decided to move on.

The third attempt is very successful, but more expensive. This design relies on the tried-and-true robotics idea of hacking a model airplane servo for continuous rotation. It also relies on an idea shown off at a recent PARTS meeting to save space by leaving the back covers off the servos and nestling them back-to-back.

See GWS PicoBB Hack for details of hacking the servo.

Pictures and Notes

The base plate and scoop were originally prototyped with cardboard, but have since been replaced with hobby brass.

The wheels are hand made from 1/8" plexiglass. They were cut with a 1-1/4" hole saw, then the groove was cut into them by mounting them using a bolt into the chuck of a drill press, then using a rotating drill press vise to swing a small file into place to etch the groove with.

The batteries are Duracell DL2/3A, 3v 1,350mAH lithium cells. They are normally around $8 each, but I got them from Wacky Willy's a long time ago for $0.25 a cell! Lil'PICcy Too has run for a long time on the original set of batteries.

The LEDs for the Sharp IS471Fs were mounted under the PCB to make it easier to block direct IR leakage back into the sensors. A small piece of electrical tape is all that is needed.

The line sensor is the Linediviner.

The robot measures 49 mm wide, 49 mm high, and 49 mm long, and weights only 65 grams.

front view back view

left view bottom view

 

Last Updated December 10, 2003