The "brains" of hubo are this little PC: A mini-ITX board running an 800MHz Pentium-III. Power is drawn from the distribution board shown below, which can run from any DC source.
The hubo computer runs Windows XP; besides being a familiar environment, this feature makes it easy to connect to (USB, serial), move data, and debug with a keyboard and mouse.

These parts make up the testing station. Motors, controllers, IMU's and force sensors interface just like they would on a normal hubo. The 2 small wires (yellow and black) connecting to the ITX board are the CAN interface, which connects the computer to all the peripherals in the system. This begs the question, what is a CAN and why is it used? A good technical summary can be found here (wikipedia). Practically, the advantages are clear: A CAN bus allows many different compatible devices to communicate over the same data lines. Each transmission packet has an overhead of about 6 bytes, and can transmit 0-8 bytes. The extensive header information gives each packet a unique encoding. Devices on the line can then be programmed only to receive or transmit data with a certain address. Wiring topology is thus determined by software, rather than hardware, making it easy to add/change sensors and drivers.


An arm and a leg

The left leg of the Hubo is a sophisticated mix of art, engineering and subtle cleverness. The leg has a total of 6 DOF: 3 in the hip, one at the knee, and two at the ankle. These movements allow the Hubo to have almost human leg articulation. Missing from this picture are the stacks of motor driver boards which power the joints.

The design is a compromise between machining simplicity and compactness. In less critical areas like the leg structure, relatively simple machined plates support all of the parts. In areas such the hip joint (right) and ankle joint(below), the opposite is true.

The hip joint design bypasses belts and pulleys seen on the knee and ankle, and places the servo inside the joint. It attaches directly to the harmonic drive (the end of the motor and encoder is visible in the picture).

The ankle joint combines 2 axes as well, but without resorting to the internal drive arrangement in the hip. Instead, a shaft connects the drive belt/pulley from the motor to the drive on the other side of the joint. The lower belt and motor seen on the assembled leg drives the other joint, which turns on the bearing visible to the left.

The arm (left) is a good example of design with inverse kinematics in mind. A human shoulder, for example, is a ball joint, with muscles attached to pull in various directions. While this allows 1 joint surface to do the work of 3, and simplifies the mechanism, it complicates the control problem immensely. With 3 axes working in parallel, there is no unique series of motions for the muscles to move the arm through a given path.

The Hubo arm uses a series arrangement of joint axes as shown. The first rotates the whole arm, the second swings the arm, and the last rotates the arm around this new axis. since all 3 axes intersect, it acts like a single joint. Since the angular velocity between successive bodies is simple, the inverse kinematics can be easily written.

Each of the shoulder joints, as well as the elbow joint use a sophisticated internal-servo design to save space. Shown to the right is an exploded view of all the parts that make up one joint. the servo attaches to a small harmonic drive body, which then meshes with a gear inside the body of the joint. The 2 bearings allow the motor and inside of the harmonic drive to turn freely wrt the outside. This arrangement allows the outside to turn at a greatly reduced speed wrt the inside.


Starting from scratch - Electronics

The first 2 weeks here have been all about learning the basics of HUBO's construction.
My first lesson was to build a universal F2808 DSP board that the lab uses for microcontroller applications. This small and relatively simple board has all the challenges of proper soldering. Aligning the 2808 chip took 3 or 4 tries, as the slightest misalignment could make very small solder shorts. While the SMD resistors are labeled with a tiny code, the capacitors are differentiable only by size and color. The same size and color chip can be 2 or 3 orders of magnitude difference; if the wrong one is soldered on, it's almost impossible to diagnose afterwards.

The A/D board I built next functioned properly, though this time I had to contend with power components. The large copper area connecting to the DC/DC converter dissipated heat, making it tough to get a clean contact.

Next up was soldering the motor controller board. Lacking PSPICE, I designed a simple Excel sheet to account for all the components off of the schematic. I wrote a few formulas to convert component values to part numbers, which could then be sorted. Soldering all of one component at a time ensured that I missed none, and that only one kind of identical-looking part would be on the table at a time. For the amplifier, a neat little trick to get the MOSFETs to line up properly was to bolt them all to the heatsink first.

Other accomplishments:
  • Obtained copy of HUBO dynamic walking PhD thesis by Dr. Jung-Yup Kim
  • wrote a brief MATLAB simulation of a lab project: the pneumatic pogo-stick
  • Photo tour of important buildings in KAIST
  • Took a photographic sequence showing major steps of leg and arm assembly
  • Rebuilt 2 broken harmonic drives; learned assembly/repair technique for similar drives located throughout the chassis.
  • Assembled a DSP board and IMU A/D board from scratch
  • Assembled a complete motor controller set (controller and amplifier)


Workspace and tools

The main parts bins. For anyone who might be planning a lab in the near future, this is the example to follow. It's hard to see in the pictures, but there is a stock of every part you could ever actually use. Furthermore, all the part bins are labeled, sorted, and logically arranged.

The soldering station where I work is well equipped, if unremarkable. All of the circuit boards, from IMU to motor controller, are custom. As such, they have 10's of different blanks in stock, as well as enough solder to plumb a city. In-house technicians do the majority of the assembly (both mechanical and electrical parts), freeing up some of the students time to focus on design and experiment. The sheer volume of components in even 1 HUBO necessitates this arrangement.

Unfortunately, SMD components are a pain to both store and use. There are 5 or 6 blue trays devoted to standard size resistors, capacitors, LED's, and ICs. Due to the lack of desk space, however, you have to keep shuffling the trays to find what you need. A better approach for common boards is to fill the tray with all the parts necessary for that board. That way, assuming someone keeps inventory, you can work quickly and efficiently.

Even with the inventory on hand, assembling a board is laborious. To properly solder a microprocessor, for instance, you have to carefully line up all of the pins, tack a few in place without disturbing the chip, then heat and solder the rest. Since there are no flux pens, they coat all of the pins in an unsightly wad of solder, and remove the extra with the iron and a lot of paste flux. You get a clean joint, though you pay the price in harsh headache from the fumes. Small components like transistors, caps, and resistors are much simpler, but you still have to properly solder every joint, which means close inspection, eyestrain and...you guessed it...pounding headache after an hour or so.

The technicians make production possible; without them, students would spend hours assembling and checking PCBs. Even more so than HUBO, DASL can't afford that tradeoff without technicians. While we must have the ability to quickly repair and refurbish a damaged board, we still need to buy finished boards whenever possible to save time.

The part to the left is the perfect example of why you need the right tool for the job. To disassemble this harmonic drive, I had to remove the sun gear deep in the body. 6 heavily thread-locked cap screws held it in place. Lacking T-handle hex drivers, the technician suggested using the ball-end allen key. I couldn't communicate my doubt, since he spoke little English, but he demonstrated by removing 4 of the screws without incident. When he torqued the remaining two, however, the heads stripped. My satisfaction was brief, though, since now I had to remove two partially stripped screws from a very expensive part. After finding a bench grinder, I ground the ball off an old key. In that time, he had painstakingly drilled and chipped out one of the screws. The second one popped loose after a nervous twist of my modified key. Simply having a $30 set of T-handle hex drivers would have saved the fuss and the subsequent retapping of damaged threads.


Life at the lab (in pictures)

This is my office space, and a shot of the wall jacks that everything connects to. Despite the goofy appearance of the sockets, they make much more sense. The structure makes the plug more secure when it's plugged in, and the round pins are harder to bend.

Chairs in Korea are ridiculously comfortable, and mine is no different. American chairs feel like park benches by comparison.

The living space: bed, shower, washroom, kitchen, microwave, TV...It's like a college apartment with a commute of about 10 feet. Unfortunately, that washing machine takes 3-4 hours to wash a small load, and doesn't fully dry heavy things like pants. Still, it's way better than nothing.

Each bag contains 100+ packets of instant coffee mix. Though I'm sure the coffee snobs would turn up their noses, the stuff is surprisingly good. The brown sugar is about a year old.


First day at KAIST (6-19)

We visited Hyundai Heavy Industries today, where they presented yet another video (a better one, though). Their shipbuilding operations are world class, and we could see many tankers and cargo ships being assembled from our bus tour. They had a cute little gimmick where they made an industrial robot "dance" to a midi version of Livin' la Vida Loca. Random, yes, but they're Hyundai.

We finally managed to finish The King and The Clown on the bus ride. Without spoiling too much of the plot, it's a story of two minstrels who play for a Joseon king. Due to their "treasonous" material, they are forced by a court to either make the king laugh, or die. Laugh he does, and the king takes them on as part of the court. A lot of executions ensue; it's worth seeing if you can find it.

At the Taejon toll gate, I met with 2 students from the HUBO lab. Since my dorm wouldn't be ready until Friday night, I would use the sleeping area in the lab. This rooms was outfitted with a double shower, AC, an LCD TV, and personal lockers. The complete lack of windows and other light-leaking cracks means that it can be made very dark and quiet at night. As such, it's ideal for sleeping as much as one's body needs. It would be my home for the next 5 days.

A bit of structural change to come: my updates from now on will be mostly particular topics, not necessarily in strict chronological order.

Industry tour

Over the next 1.3 days, we visited 3 industrial sites that are the pride of modern Korean Industry. The POSCO steel plant in Pohang was our first stop. Some of the staff at the main office warmly greeted us at the door, leading us to a presentation room to deliver...an introductory video! My eyes were rolling like someone had let go of a window shade.

The model of the plant they showed us next was accurate and detailed. LEDs indicated which parts performed basic smelting, casting, steelmaking, and rolling. Our tour took us around most of the process by bus, but we were allowed to see the rolling mills in person. Even from 100 ft. away, we could feel the heat from the red-hot ingot as it passed through the mills. The jet of hot steam as coolant water poured on the ingot was almost deafening.

After we left for the nuclear power plant, Julie had the idea (bless her heart) to stop at the beach for a quick break. Within 10 minutes:
  • Jon and Margie got soaked up to the knees due to a wave
  • I responded to an unprovoked splash
  • The ensuing skirmish ended in stalemate due to MAD of each other's shoes
At the nuclear plant, Erica translated for the first part of the tour, explaining how the HWR worked. We even got to see Chernekov radiation first hand, as they deposited spent fuel in the holding tank. Oh, and they also showed us a video. I hate management speak so much. here's just a few of the meaningless terms they threw around in these videos:
  1. 'Future-oriented management' - Duh...any other kind of management is known as mismanagement.
  2. 'Strategic development initiatives' - as opposed to 'arbitrary development'? Why is this news? Did they just abandon plans for a sticker factory or something?
  3. 'Customer-oriented company' - yeah, and the other kind of company is called 'bankrupt'
  4. 'value-added' - buy raw materials cheap, make something with them, sell result at a higher price...otherwise known as the basis for every industry ever. Again, why is that novel enough to mention in a 5 minute pitch?
I don't understand who this sort of jargon is supposed to impress, and I'm saddened that such American bullshit has been successfully exported.

The evening ended on a high note, since Mr. Kilsu Park generously sponsored a round of Noraebong at the hotel. After more drinking in front of the hotel, some of us visited a 'foreigners-only' casino. John's winnings bought some expensive liquor for this who played, while the rest of us ended up heading back early to pack for the morning departure.