as yet unnamed
robot number two

Welcome again to bent machine labs.

"bent machine labs: Desire is our one true engine." (TM.)

design notes

Here it is in one piece.

The breadboard there is an area for testing out sensors and circuits.

The robot has two levels. The bottom level holds the batteries, and also some space for expansion. This is what you see when you pull the bottom level off and look at the belly of the robot.

If you find yourself interested in this picture it's because your inner electronics teacher is getting a charge out of how neatly the servo wires have been secured.

Here's that second level I was talking about. The servos get 7.2 volts from 6 NIMH rechargable AA batteries wired in series. These batteries are made by Kodak and will supply around 1500 milli-amp hours (mAh,) which is something like 10 minutes of power at one amp. This is actually pretty good for a AA battery. I haven't really had enough time to check out how long this will last for the robot, but I'm hoping for a couple hours between charges.

Also pictured is a plain old 9 volt battery, which powers the electronics. Fortunately, these won't draw much power.

Optional things that end up making life so much easier.

Without a doubt, it's a good idea put a reset button on a robot and make sure it's easy to get to.

As of this writing, the robot can walk forward, and only forward. Oh, and it can stop, too. I guess that means it's a two-speed robot!

Right now I'm having trouble getting it to go in a straight line (it drifts to the left.) I'm trying to figure out whether this is a software problem or a hardware problem.

Next up is turning, and then backing up. After I get these things worked out, it'll be time to start installing sensors so the thing can operate autonomously.

Other current problems/concerns:

There is no good way to control the speed of the servos with the SSC II, which is essential to goal #3, and I may end up building and programming my own servo controllers.

To operate the robot on carpet, feet of some sort will need to be installed, because the legs just dig right into the pile and then drag.

Here's a diagram of the way the robot walks. There's probably a name for this kind of gait. The diagram reads top to bottom, left to right.

As you can see, the robot only moves one leg at a time while using its other three legs as a tripod (designated by the red lines.) The pink dot is around where the center of gravity is. See the animation below.

This is a simplification, because the legs actually move in an arc and have a longer stride than this, but maybe it will give a better idea.

This is the same gait used by the Sony Aibo and the Lynxmotion quadruped.

More fun to come.

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Everything copyright, 2000 Dave Benz

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