Older blog entries for NateW (starting at number 22)

It was a bit of a struggle to get bluetooth working right on the Gumstix, and it paid off. The Gumstix forms a bluetooth personal area network with my laptop when the Gumstix boots, so I can SSH into it for administration and monitoring. The laptop can also open a serial connection via bluetooth to send commands to the Gumstix, which forwards them to the servo controller. I don't even have to be in the same room. :-)

The robot is spread out all over my workbench as I write this, but it's almost time to put it back together again.

The biped mechanics are mostly done, other than a bit of fit-and-finish work:

Front View

Rear View

Whoops... That ED-209 link again. My bad.

I've finally started construction on a biped - something I've been wanting to do for years but never quite got around to doing. It's a made of Lynxmotion servo brackets and laser-cut polycarbonate, and the overall shape was inspired by ED-209. However my "ED-1" uses no linear actuators in the legs, and will probably have longer arms, though I haven't yet made up my mind about that. I think I'll be departing from the ED-209 form factor in order to add an extra degree of freedom to the arms.

The legs, hips, and torso are built; the arms should be done by the end of this week, the feet will follow in another week. I have no pictures (as usual) but a couple people took photos at the Seattle Robotics Society meeting yesterday and if those images find their way onto the web I'll link to them from here.

The dead hard drive I mentioned in my last entry turned out to be not much of a tragedy. I booted to Linux, mounted the drive as a file, then copied the raw data to a good drive. Then Googled for "GPL" and "FAT32" and found some tools... After fixing some corrupt data on the boot sector, I was able to recover about 90% of the data from the dead drive - and as far as I can tell, the other 10% was completely unimportant.

Good news: I got my friend's scout walking yesterday.

Bad news: the boot drive on my desktop PC just failed.

I have backups for the really important stuff, but I have a sinking feeling that there's a "long tail" of stuff that wasn't quite important enough to back up religiously... but which, in aggregate, adds up to a lot of lost work. Only time will tell.

Have been learning about Kalman filtering in hopes of providing my robot with a good sense of balance... In case anyone else is interested in learning about Kalman filtering, here are the best links I've found so far. These are not the most in-depth, but they are (far as I can tell) the ones with the best "plain english" description of what all the formulas mean.

This one presents Kalman filtering of scalar values, rather than vectors, which cuts down on the greek notation but preserves the key concepts. The second link explains how the scalar version is extended to work with vectors:


I found the links above to be the most helpful, but these are also pretty good:


After a couple nights of reading these papers, the light bulb suddenly went on... I get it! At least, I think I do. I'll find out soon, as I just ordered a SparkFun 6DOF IMU, so I should soon have some signals to filter.

I have to plug Sparkfun here because this product appeared on their web site just a couple months after I proposed the idea in their online forum. I beg, they build, I buy. I wish more companies worked that way. :-)


Here come the movies and screen shot I promised a while ago... except that instead of my hexapod, this is a MegaRobotics dog, loaned to me by a friend of mine.

moive: side view
movie: front view
screen shot: source code

The software is coming along nicely, but defining a single sequence of operations (for example, the stand-up routeine at the start of each video) is more trouble than it should be. It might be nice to have the state machine system interpolate from one pose to another when transitioning from state to state... I still need to think on that for a while, but it seems promising.

The four-legged heapod took its first steps tonight. As you might guess, it walks with a limp.

Still no photos... Still working on a new web site to host them.

The hexapod is up to four legs now. One of my parrots chewed up the servo leads on three of the servos, so it's going to have to be a quadropod until I replace those.

The leg design I'm using now is built from hand-bent metal rods, and I'm not satisfied with it. Between the inconsistent bending and the interference between the rods and the chassis, I've decided to revise the legs to use straight rods, with another set of laser-cut plastic pieces to get the ends of the rods in the right places. Hard to explain, but I'll post a photo before long.

The control system software is coming reasonably well. Photos to come...

The laser-cut parts arrived from www.pololu.com and the hexapod is taking shape. There were a couple of minor errors in the plans... no show-stoppers, but it's surprisingly hard to use 2D CAD to design flat parts that get assembled in 3D. :-) Only two legs built so far, the rest will probably have to wait until after the holidays. I post some pictures when it starts to look like a robot. :-)

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