Servo - July 2017

test a left turn circle (counter-clockwise) and slowly slightly adjust R1 clockwise until it follows the turn properly. Then, go back and retest right and left turns.

There is a best balance of pot adjustments which will let the robot track properly right and left. Once you get it dialed in, you can try speeding it up. One of my videos shows that faster speeds come from using higher voltage Li-Ion cells (~4V) compared to the stock 3V alkaline cells (recalibration required). How fast can YOU go?

Sadly, as I write this, RadioShack stores are having their final clearance sales, and I bought a “Running Microbug” kit for $15 (cat #2770353, Figure 8). This minimalist robot kit uses direct drive from two small square motors: no gears, no wheels. The motors tilt down so that their shafts touch the ground, becoming the world’s smallest wheels (Figure 9). Clearly not suitable for carpet, this is a fast robot for a smooth open floor.

While quite functional, the open-frame motors are practically dragging on the floor and easily pick up hairs, dirt, and anything metallic. I found this out the hard way and had to carefully de-gunk two greasy commutators.

I would recommend enclosing the bottom of the motor with a piece of scotch or electrical tape to keep things out.

This must be done carefully to avoid taping the armature in place. Make a convex pocket in the tape and/or make a non-sticky spot on the tape (paper, tape dot) where it might PCB sure makes a classy chassis with part outlines and numbers in red ink. The small fold-out book gives step-by-step instructions.

Construction takes 30-60 minutes with two novel elements. First, the square metal motor cases are fastened to the chassis at oblique angles by solder only. You’ll need a big iron and some attention to detail to mount both motors symmetrically.

Second, the tail roller uses a big fat barrel diode for an axle (LOL). It’s soldered in place for mechanical function only, but I think it would have been clever to use it in the circuit for something.

After a smooth build, I was prepared to be wowed. Straight off the Shack’s website: “This photosensitive microbug follows light and stops in darkness.” To me, that clearly means that it will track towards a light source. Heck, I’ve already done that with two photocells and one servomotor: https://www.youtube.com/watch?v=4CaAq6gQbLY. Surprise, surprise, however. Here are the exact operating

Switch on to play. If you want Microbug to turn and circle left, fully turn the potentiometer on the right. This then dims the LD resistor and stops the motor on the right. To run and circle in the opposite direction, fully turn the left potentiometer. The brighter your surroundings, the faster Microbug runs.

YOU GOTTA BE KIDDING ME! This doesn’t begin to describe or take advantage of this robot’s components or function. This is neither educational nor fun. Where’s the