Older blog entries for RoboDo (starting at number 2)

RoboDo Control: Revised

One of my design goals in the RoboDo project is to establish "levels" of control which mimic, in some small way, the interactions found in nature.

When you wake up in the morning, what do you do?

I open my eyes and look at my environment. My body tells me I am lying down. My mind then determines that I am in bed in my bedroom. I then mentally review my priorities and decide what to do next. This almost always involves getting out of bed.

Note that most of this is done more or less automatically, and that different "systems" are involved. Note also that some of these systems are under the direction of other systems, but that the "lower level" systems don't need detailed instructions in order to perform their routine tasks. When we decide to walk, for example, we don't need to concentrate on moving each muscle... our legs know how to walk. It's exactly this sort of layering I want to explore.

I now see that I will need more processing power and memory than that provided by the typical microcontroller, so I am looking at a single board computer (SBC) instead.

The new scheme includes a SBC with a 500Mhz processor, 1 gig of RAM, 4 USB ports, 4 com ports, a flash card slot, and fast Ethernet. A 16 channel USB servo controller in the hips will control the legs, while another in the torso will control the arms. A 4 channel USB servo controller will handle the torso bend and torso rotate, as well as the head tilt and pan. The torso will also contain a USB I/O board for the sensors.

Of course, all of this is subject to change. :-)

More to follow...
Humanoid Robot Joints - The Hips

The hip joints of today's popular bipedal robots have many limitations. More articulation in this area would allow much greater range of motions.

After playing around a bit, I have come up with a design which I intend to use in my RoboDo project. Here's a rough picture...

The "stride" servos (the topmost ones) are connected to their respective legs with either chain or gears, which allows us to reduce the 180 degree servo motion to 120 degrees. This will produce a modest gain in power while limiting the travel in this joint to 75 degrees forward and 45 degrees backwards.

The main benefit however, is that this allows us to have the leg joint supported by a solid shaft and 2 bearings.

The leg rotate servos are also supported by 2 bearings. I just don't like the idea of hanging the whole leg off of a single, cantilevered support point.

At first glance, the "leg lift" servos (the lowest ones pictured) may seem redundant, but these servos will allow RoboDo to kick higher when the legs are rotated to their normal walking position, and allow freedom of motion in this area when the legs are rotated to other positions.

More soon...

1 Mar 2008 (updated 17 Mar 2008 at 22:14 UTC) »
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