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Wednesday, June 3, 2009

Inside the $400 Colony Scout: Robot on a Budget

Now that I posted some videos of the Colony Scout in action, I’ll discuss the platform in a little more detail.

The basics: It’s a compact (4.75”x6”), four wheel-drive robot equipped with an array of IR distance sensors, automatic recharging capability, and other features yet to come. The current talk is to use an ARM7 based board running at 40MHz, paired with an unspecified ATMega for additional I/O.

Some background: The goal of the Colony project at the CMU Robotics Club is to develop a low cost swarm robotics platform capable of structured coordination to carry out tasks too difficult for a single machine.

Colony has been around for several years and has made great strides with a few robot upgrades along the way. The team is prepping the Scout as a potential replacement for the current ATMega 128L based robots.

The goal: The Scout is a deviation from the 2-wheel differential drive robots used in the past. While a common and versatile form factor, the two wheeled platform balked at any non-level terrain. Even driving up ramps or over wires can become an issue. Scout is designed to expand the exploration options beyond level and rectangular environments.

What’s new? Faster processors and an efficient code base will permit the Scout to actively respond to a complex environment. The new sensor array extends the current 5 IR sensors to 7 for additional range and cliff detection. A bump switch returns for the front bumper to detect obstacle collision (useful when purposely pushing objects).

Each of the Pololu wheels comes equipped with a quadrature encoder that gives ~3mm linear accuracy. The 10x12mm micro metal gearmotors are lighter, faster, and stronger than the Solarbotics GM8s on the current robots. Using four motors does draw more current, so the battery is upped from a 6V 2200mAh NiMH pack to a beefy 7.2V 4000mAh Li-Ion pack.

Conclusion: The Colony Scout is a tough little machine that can cross rough terrain while employing a multitude of sensors, all for a sub-$400 cost per robot. Plans are in place to make the robots “smarter” than ever before, and able to respond to the environment faster and in a more coordinated manner.

Summer 2009 is all about prototype testing – learning about the platform and its capabilities and limitations, so stay tuned – More videos and posts will be coming your way!

What do you think? What types of functionality, from line sensing to 3D mapping, do you think a cheap robot should have?

See http://www.danshope.com/blog/2009/05/putting-colony-scout-robot-through-its.html for more pics and vids on the Colony Scout.

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Sunday, May 31, 2009

Putting the Colony Scout robot through its paces

The new Colony Scout platform was up and running for a few hours today as I continued testing the AWD system. Scout is a prototype platform for swarm robotics at the Carnegie Mellon Robotics Club.

We remade the baseplate out of 6061 aluminum on the CNC mill as the previous handcut plate was too soft and imprecise. I wanted the alignment of all the motors/wheels to be as consistent as possible for straight tracking with minimal correction from software.

The headers you see sticking up beside each wheel are for quadrature encoders - the encoders give the robot about 3mm linear resolution, which is decent for a vehicle of this size.

Another exciting component added today was the rocker, which allows the front and rear axles to swivel (vertically). This allows all four wheels to contact the ground during most terrain crossing, improving traction. The updated platform outperforms the Scout of two days ago, which featured a rigid baseplate.

The new components have a high degree of polish accomplished by good design and machining practices. Our club machine shop allows us to turn out quality parts and have a fast turn around time from concept to prototype.

Click through to http://www.youtube.com/watch?v=ePaPGyjW2uk to watch the video in HD.

There's also some great tests on http://www.youtube.com/watch?v=fyRmg570KJw from a few days ago.

Keep tuned for more updates this week!

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Monday, April 6, 2009

That's Just Boulderdash!

The Carnegie Mellon team participated at the 2009 ASME Mars Rocks competition in Dayton, OH a few weekends ago. You can watch our robot, Boulderdash here http://www.youtube.com/watch?v=oY4gXETGdrw or see a competition recap at http://www.youtube.com/watch?v=nQIlcrWNil0.

I'll be posting more about the design of our rock sweeper soon! Until then enjoy the videos. Thanks to Jimmy Bourne for the media editing.

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Monday, February 16, 2009

RobOrchestra Update: Bass Drummin' Bot

This past Friday was quite productive for the RobOrchestra team as two instruments were constructed -- the first two for this year.

A few of the guys got together Friday afternoon and built a hurdy-gurdy prototype. The stringed instrument is constructed from a cardboard box and plywood frame. So far the instrument sounds decent when turned, but needs some work on amplification. Using material other than cardboard should definitely help the acoustics...

Fellow RobOrchestra member Andrew Burks and I spent the better part of Friday night (yay social life) working in the shop on the bass drumming robot (as yet unnamed). Andrew made an awesome SolidWorks model which we used as a reference for the parts.

The basic design uses a Bimba air cylinder limited to ~0.5" stroke under 30psi. The cylinder has pivot points at both ends. The pivot points took a lot of machining as we had some pre-existing components that needed to be modified to allow attachment points. One screw up and we were out those parts and had no spares. Fortunately, everything went off without a hitch.

Once the cylinder has pivots at both ends, one end gets attached to the "shoe" of the pedal, the other end inside our robo-leg. We have some sweet plans for decorating said leg -- but until then...

here's a truly amazing picture of yours truly, oh how flattering :-)

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Monday, November 24, 2008

Snarebot 2008: The Little Drummer "Boy"

The RobOrchestra Snarebot is finding its legs..err arms this year. The project is a few years old and has experienced incremental improvements over its lifetime. This time around we are looking to make a dramatic improvement based on the existing design and input from drumming consultants. We want to make it as realistic at drumming as possible with good dynamics and a pleasing sound.

The old design used two large solenoids pulling on cables to actuate the drum sticks. The wires were connected to specialized rubber holders that had built in compliance to allow the sticks to rebound quickly off the drum surface. These work really well and were one of the biggest components in the success of snarebot 1. What the 'bot lacked was good control over speed and dynamics - since solenoids are either "on" or "off", that's all you could coax out of it. Since there was a single pivot point, it was also impossible to induce different velocities out of the drum strike.

This is the design I envisioned last year - a small, portable device that could fit on any standard size drum. It was actually really neat, and I built a small prototype for the shell and legs. When you rotated the center handle the legs would extend or contract depending on the direction you turned. Since there wouldn't be much force opposing the legs (all downward) they would remain extended and the 'bot would perch happily on the edge of the drum.

This worked pretty well, but only left about an 8 diameter area in which to fit the drum stick mechanism. We found out that short sticks sound really flat since you couldn't get the pleasing resonance you normally hear from a snare drum. The device made had about 4" arm and could hit every 25ms, so speed wasn't an issue.

My sketch for this years' redesign is above. Its larger offset design allows for greater movement and the use of standard drum sticks, so we avoid the resonance issues of the past design. It will incorporate cable drives, solenoids, and servo motors to provide a wide range of speed and dynamics control lacking in Snarebot 1. The drawing isn't exactly to scale as the drum sticks actually stretch across the diameter of the drum, but after taking some measurements I verified the design is doable. Now it's just a matter of finding time to sit down and CAD model it in SolidWorks.

Some people have expressed concerns about latching onto the tuning bolts, but others say we should be fine. I've designed the 'bot this way so that we can eliminate the large clunky stand. It worked out pretty well for Snarebot 1, since you could easily reposition it, but we have something up our sleeves for this design that can accomplish the same thing.

You can't see it from this drawing, but the base will incorporate motorized translation and rotation so the snarebot can target different areas of the drum. Now, we're starting to talk about a lot of motors here, but each RobOrchestra controller board has ~16 outputs, so we should be fine. Hmmm....how about some neon underlighting?

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Daniel Shope is the site owner and moderator of DanShope.com, a portal dedicated to robotics and engineering. Dan is currently a student at Carnegie Mellon University and is pursuing dual degrees in Mechanical and Biomedical engineering.

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