Jon's Place

Sunday, December 3, 2006


This is my first blog post about my new project. Yeah, it seems like I start a lot of new projects, but this one is a little different. This is my first legged robot, my first biped, and my first attempt at integrating some serious AI into a robot.

This micro-raptor will be based on a Bioloid Kit, which I will order sometime (hopefully) early in the new year. I've ordered a couple of AX-12 servos already, and should get getting those sometime this coming week. Anyways, here's the plan from the hardware side:
  • Bioloid Kit (comes with 18 servos) plus 2 extra servos (total 20 degrees of freedom)
  • gumstix (400 MHz, with bluetooth, running Squeak)
  • robostix (running a program my brother Dave wrote, to interface to the Bioloid bus)
  • 6 axis IMU with compass (made from this and this and this)
  • digital camera (hooked to the gumstix)
  • 3 sonar rangefinders (mounted in the head, forward, left, and right)
  • bump sensor in the nose
That's it for the hardware side. Of course, the real thing that will make this robot different is the software. I've been researching for the past two years a new kind of autonomous controller, which works more like the way I think a person's brain works. This robot will not have enough processing power or storage capability to really push the brain software to the limit, but it should be a good start.

Anyways, I'll talk more about the software in a future post. Right now I'd like to get back to the hardware side. This project has a genesis from two different angles. The first angle is the robot I have been designing to go along with the brain software, which you can see a picture of next to this paragraph. It uses something called "series elastic actuators", which I believe are the best kind of actuators that you can actually get for a robot with limbs. I'll probably go into more detail in a later post about what I like about SEA's. Note that the robot pictured here is not MicroRaptor -- it is what I want to build eventually, but simply can't afford to build at this point.

The second angle for this robot comes from my friend Julian, who is a Smalltalk developer/fanatic like me, is heavy into underwater robotics and a whole bunch of other things that we share in common. We've worked together in the past (professionally), and we hang out a lot, watching Firefly and building robots and doing cool design work on various things. Anyways, Julian saw an advertisement for the RoboNova, and basically went apeshit over it. He's wanted a small biped humanid for a long time, but until recently they haven't been available.

I was looking around at the RoboNova at different sites, for pricing and to see what else was available in the Robo-One category of biped humanoids. I stumbled on a relatively new kit, called the Bioloid, made by a Korean company called Robotis. On the surface, it doesn't look much different than the other servo-driven humanoids, but after reading the specification sheet on the servos, I realized that they are completely different.

The AX-12, which is the custom-made servo that the Bioloid kit uses, is an amazing piece of technology. It is twice as powerful as the standard servo that the RoboNova kit comes with, Instead of using a standard pulse-width modulation signal, they use a serial bus, where each servo has an addressable ID. Using this bus, you can interrogate each servo, and retrieve data from the servo, including the position, real time rotational speed, internal temperature, and (most importantly) torque.

You can set various configuration parameters for each servo, including compliance, which specifies how closely it tries to maintain the position you tell it to go to. With the appropriate settings, you can make these servos work almost exactly like a series elastic actuator (assuming you put the right control software in the computer controlling them).

Once I realized the capabilities of these servos, I realized I could easily build a small velociraptor for a reasonable price, which will allow me to start experimenting with this new "brain" autonomous controller. Thus the MicroRaptor project was born.

I'm going to stop talking here, and save details for a future post...


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