Jon's Place

Sunday, December 3, 2006


MicroRaptor will have 20 AX-12 actuators, in the following configuration:

7 for each leg - 3 at the hip, one at the knee, one at the ankle, and two at the foot
4 for the neck/head
2 for the tail

Ideally I would add one or two more to the tail, but I'll have to see how it all works out first.

It will be powered by an 8-cell, AA NiMh battery pack, which provides 9.6 volts. The battery will be slung vertically under a backbone that I will have to machine (probably out of aluminum). The legs will be fastened to each side of the backbone, keeping in mind that the backbone on a velociraptor is more or less horizontal. The neck servos will be fastened to the front end of the backbone, and the tail to the back end, behind the legs.

The gumstix/robostix will be attached to one side of the battery, and the other side will have an electronics box which will hold the six-axis IMU/compass and a couple of switching voltage regulators (5 volts and 3.3 volts).

Each sensor or sensor group in this robot will be on the main bus, just like the AX-12 actuators. The IMU/compass will be treated as a single bus sensor. The three range finder sonars in the head, along with the bump sensor, will also be a single bus sensor. Each of these "bus sensors" will have their own dedicated micro-controller, most likely an AVR ATMega8, to communicate on the bus.

The camera is not going to be on the bus, simply because of the high volume of data the robot will be receiving from it. It will have its own dedicated serial port on the gumstix, and I will either be writing or using a vision package to do interesting things with it. One package I have my eye on is EmbedCV, since it is being written for exactly the type of hardware I am using.

One of the things I plan on doing with this robot, after it can walk in a reasonable fashion, is to have it compete in the firefighting competition. I will build a ducted fan "actuator" that will sit on its back, that the robot can turn on and off over the bus. It will push air through a flexible hose that will run along the robot's neck and through the head, to a custom nozzle that will spray the air out at high pressure. The camera will be used for landmark based navigation, and for finding the candle, and ensuring that it gets blown out.

First though, the robot has to learn how to walk. I will be doing a bunch of work in the beginning to give it a reasonable walking gait, but after that the robot will use evolutionary techniques to improve both the smoothness of the gait and its efficiency (in terms of power usage).

I think one of the main problems with most walking robots today is that they don't walk right. If you look at any of the Robo-One type robots, and any of the high-end research bipeds that I have seen video of, they all share one common trait - the body of the robot sways back and forth as they walk. If you were to mount a video camera on a tripod, and stick it on a busy sidewalk, I guarantee that you won't see that kind of body sway in most people. When you watch people walk, you see their heads bob up and down, but the don't sway from side to side at all. This is the reason, in my opinion, why robots have such a hard time walking smoothly, and I'm pretty sure I have come up with a way to avoid it. Time will tell of course, since I haven't ever built a biped, but I have spent considerable time thinking about this problem. I'm not going to say any more on this topic until after I have tried my technique, but of course at that time I will post the results here...


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