Coat Hanger Walker:
Bug Report & Troubleshooting Ideas

Leg Mounting Pad Tip: One builder recommended buying several sets of the Leg Mounting Pads from Solarbotics so that you can swap out different leg configurations. Good idea! The pads are cheap.

Changing the Walker's COG: As discussed in the book and on the Shop Talk Building Robots discussions, there are a number of ways to tweak and improve the Walker's gait (see Gait Dampening and Leg Tweaking below). One other solution is to change the bot's center of gravity (COG), by shiting the battery packs towards the back of the servo motor casing. To leave this option open to you, you'll have to scew the packs on during initial assembly (not screw and glue as suggested in the text). You can do a final gluing once you have the COG where you want it.

Switch Clarification: In the book, we were somewhat unclear about figuring out what terminals on a switch you should connect to if the switch has more than two. This should clear things up.

Gait Dampening: If, after you've assembled your Walker, the circuit is too lively, the gait too active -- or, if movement favors one side, eventually making the walker unstable until it falls over, you can constrain the front legs with a rubber band. Just put the rubber band over the front legs, over the control chip, and let it rest just behind the microswitch. We'll try to have a picture or drawing of this soon. Tie knots in the band until you get decent pressure on the front legs. Run the Walker and see if it's enough. If not, tie another knot. Keep adjusting tension until you get the correct back and forth motion in the legs.

Leg Tweaking: Don't forget, the legs on your Walker are bendable. If the height of the Walker makes it unstable, or it slightly favors one side over the other, you can easily fix this by splaying out the legs more, or otherwise changing their shape. Just make sure to hold the gear/leg assemblies tightly as you bend the legs so that the torque you put on them doesn't break anything.

Who the Heck Ever Heard of Zytrex?: When out tech editor Dave Hrynkiw saw the photos of the Walker for Chapter 7, he emailed and asked: "Where the heck did you ever get a Zytrex chip? I hope I didn't send that to you!" He didn't. I'm not sure where it came from. It was just in my parts cabinet. I had a Fairchild Semiconductor 74HCT240, but I munged a pin off of it during the initial breadboarding, trying to pry it out without my chip puller. It's actually a good idea not to use "off brands" like this, but to stick with known companies like Fairchild. Some of these cheapo chips don't perform up to spec or have high failure rates.