Serious robotocists will want to check out White Box Robotics' PC-BOT (Fig. 1). This is a professional mobile platform: expandable, with the horsepower to handle add-ons. It is also something that has a presence, compared to the smaller Lego Mindstorms or iRobot Create. At 21 in. and 55 pounds (24 kg), the PC-BOT is a formidable robot in the pattern of Star Wars' R2-D2.
The big difference between the PC-BOT and most off-the-shelf robots is capacity. It has internal bays for user-developed peripherals. It is controlled by a Mini-ITX motherboard, which provides PC-level compute capacity that can use standard USB peripherals like a global positioning system (GPS) module to enhance its capabilities.
Its heavy-duty motors, wheels and casters are still limited to a relatively flat surface but it does not have to be completely smooth. Carpets will not slow it down, but obviously stairs are more than a challenge. Its pair of 12-V, 9-A sealed lead acid batteries provide plenty of power for the two dc stepper drive motors.
It's not a choice between a truck, sedan, or Ferrari, but the PC-BOT does come in different flavors that will take a different-sized bite out of your pocketbook. The full-up 914 PC-BOT comes in at $4995. This includes all the bells, whistles, motherboard, headlights and plastic case. It is ready to run out of the box and has the look of a professional robot. It is ideal for someone intending to use the PC-BOT in public applications.
The $3995 9-Series Development Platform (Fig. 2) is essentially a naked 914 PC-BOT. Yes, those custom plastic parts are a bit expensive, but not always necessary mdash; especially if you intend to build your own.
The base platform, and of course the 914 PC-BOT, come with a VIA EPIA SP 13000 LVDS Mini-ITX mMotherboard with 1 Gbyte of 400-MHz PC3200 DDR RAM. The system boots from an 80-GB 2.5-in. SATA hard disk or a slimline DVD-ROM/CD-RW drive. External USB ports can be used to temporarily attached more drives or drives can be added internally as well. The 8 half-height 5.25-in. drive bays (Fig. 3) initially house the computer bay speakers and audio interface, along with the DVD/hard disk drive combo.
The two systems comes with a Linksys 802.11g wireless USB adapter. This works with Linux or Windows. Ubuntu Linux and Windows XP Home are included as well. They come configured with VNC remote control support since the unit typically operates in a headless fashion.
Bargain hunters or those with a Mini-ITX motherboard can get away with the $2995 9-Series Basic Unit. This essentially provides all the hardware, including basic electronics. It does not include items like the motherboard, web camera, and USB wireless adapter, but it does include the batteries and power supply. The plastic case is available separately.
Interconnect and Drive System
The PC-BOT has dozens of digital and analog IO, but most will be handled by the USB Machine Management Module (M3). The M3 controls the motors, headlights, and infrared sensors that can be spaced around the PC-BOT. It does not control devices attached directly to the motherboard (like the USB camera) or devices that are added by the user. The M3 does not handle other interfaces built into the mother such as the serial ports.
Combining everything else into one control unit simplifies wiring and software control. M3 drivers are provided for Linux and Windows. The M3 unit is inside the core the PC-BOT, but a pair of plug-in panels can be found at the bottom of the front and rear of the PC-BOT (Fig. 4). Devices like the IR range finders are connected individually to the M3 unit.
The PC-BOT is a hefty system built around a solid metal frame; hence its 55-pound starting weight. Adding a few more heavy peripherals or devices would crush most other platforms, but not the PC-BOT. To move its bulk, the robot has a pair of heavy-duty stepper motors linked to large wheels (Fig. 5) by drive belts.
Power from the two lead acid batteries runs through a pair of Mini-Box M2-ATX power supplies. These are the same ones used in our Car PC (Car PC, Part 2: The Mini-ITX PC, ED Online #14228). One power supply handles the motherboard. The other handles the electrical requirements of the rest of the system.
The robot keeps its balance using a pair of patented self-cleaning roller-ball casters in the front and rear of the robot (Fig. 6). These allow the robot to pivot. Unlike free spinning wheels, the casters don't get caught on obstacles.
Overall, the PC-BOT's drive system is a good compromise between ruggedness and mobility. It does not require extra power when standing that a balancing robot would, and the implementation hefty enough to move its bulk rather quickly and accurately. In fact, the typical limitation on movement is the quality of the environmental sensing system rather than the drive system.
The PC-BOT can go up gentle inclines, roll over small bumps and run on carpet without any problems. Obviously it will not be going up or down stairs but it is quite mobile otherwise.
Quick Access Key To Success
The PC-BOT consists of a set of linked compartments that are all part of a solid metal case comparable to the best PC mini-towers. The M3 control unit, batteries and motor are housed in the lower section, and the central part is laid out in 5.25-in. drive-bay fashion. On either side is a pair of boxes that can flip down (Fig. 7) and then open (Fig. 8) with the twist of a latch. One holds the box up. Another pair keep the lid on the box. The boxes are hinged so they swing down and wires hold the boxes at a right angle, parallel to the ground.
One box contains the pair of power-supply boards. There is a good deal of extra room in this box, but air flow for cooling is an important consideration. Both boxes have lots of holes specifically designed for cooling.
The other box contains the Mini-ITX motherboard. The external connectors are found on the back of the PC-BOT. There is enough space to add a PCI card parallel to the motherboard with the correct bracket, but mounting something in a rigid fashion will take some work with sheet metal or plastic and some power tools.
The boxes are covered on all sides, but there is a large hold on one side for cabling. This opens into the central area (Fig. 9). This is where the hard disk and DVD drive reside, as well as the M3 control unit access. There is plenty of space for numerous cables; IDE, SATA, USB and power cables are already routed through the area.
I think the flip-down approach is an excellent idea. The only issue I have with the architecture is that the two main front and rear plastic covers must be removed to gain access to the boxes. This is not a problem in general, since hardware tweaking is not something you tend to do once the system is finalized, but most will leave the plastic aside during hardware development.
It is possible to get to some of the interfaces through four small access ports on the plastic skin (Fig. 10). Power switches and charging sockets are readily available, but the one item you cannot access easily is the VGA port on the motherboard. Given the tight confines with the plastic installed, it is also unlikely a cable could be routed to the outside world. In general, this is not an issue, since even in headless mode, most developers will utilize a remote control program using the wireless link; but this does not help much during the boot process. Of course, most developers will likely latch onto a single operating system instead of twiddling the multiple boot feature.
What You See Is What You Avoid
The PC-BOT is capable of handling a wide range of peripherals and sensors, but it comes with two primary sensors. The first is divided into two groups of infrared (IR) range finders. The second is the USB web camera. Neither will do much without the appropriate software support, but the software has direct control over these peripherals.
The M3 system mentioned earlier is used to support the IR range finders. The first group is found around the bottom of the PC-BOT (Fig. 11). They are mounted on a semi-circular metal bracket and there are holes in the plastic cover for these sensors. The bracket and cover have room for 9 sensors. Five are included with the system. Additional sensors can be added as necessary. Coverage of the included five sensors is about the front 250 degrees depending upon the obstacle distance from the PC-BOT. Two of the sensors are for either side. One is aimed directly forward and the remaining pair is off to either side on the front.
A second metal bracket and sensors can be added, but comparable coverage could be obtained with just three additional sensors mirroring the ones in front, since the side sensors would overlap.
The second set of IR sensors is found in the middle of the robot on the front (Fig. 12). These sensors are aimed at the floor at an angle. These are designed to detect the general height of objects, but more importantly they can be used to detect the floor or, more importantly, the lack thereof. A 50-pound hunk of metal and plastic falling down the stairs or rolling over the side of a ledge is not an image most robotocists will want to see. The PC-BOT is rugged...but it isn't indestructible.
The other sensor is the Logitech web camera that is mounted on top and to one side of the PC-BOT (Fig. 13). The ball camera can be aimed in any direction, but typically, "level and forward" will be the direction for most applications. The camera does not pan or tilt, but an adept designer can add this feature. Aimed forward, the camera provides full coverage of the width of the PC-BOT after about two feet.
The camera is suitable for obstacle detection and object identification. Likewise, the processing platform has sufficient horsepower to handle the software that can make it happen. Of course, adding and managing this type of software is a major hurdle, but that is for another article.
A standard Linksys USB-based 802.11g adapter provides a wireless link to the PC-BOT. This will definitely be the way the PC-BOT is programmed and controlled. It has sufficient bandwidth to handle streaming audio and video from the PC-BOT while providing enough headroom for control going in the other direction if necessary. Standard remote control programs like VNC will likely be used to track and control the system, although custom applications can also be used.
The lack of a microphone is the only thing I found missing in the basic PC-BOT architecture, although it is a trivial addition. The motherboard does have an audio input, so it is just a matter of adding the cabling. There are plenty of places to hide it.
One feature I would like to see would be a control panel and input buttons, but this is easy to add even without making major modifications to the plastic cover. There is a removable panel on the top in the rear that is just the right size for such a small control. While the current panel snaps in place, it is not too hard to modify this with a hinge to allow it to flip up; but again, that's another project.
It took a while to get through all of the PC-BOT's hardware features, and it will be even longer to get through the software side because of the flexibility of this platform. I'll be using this to examine robotic software such as Microsoft's Robotics Studio in future articles. The PC-BOT will support almost any PC-based software so there will be a number of articles about the PC-BOT in the near future.
The PC-BOT comes with some sample applications and support for platforms like the Robotics Studio. We had the PC-BOT dancing and chasing the cat as soon as the batteries where charged. Our poor kitty was terrorized as my daughter had the PC-BOT wandering around, saying "Here kitty, kitty...." Now I need to get it ready to be a presenter at our local science fair.