Modeling Maxwell

I put together a simple 3–D model of Maxwell to help visualize and play around with future modifications – before I actually invest the time and $$$ to implement them. Using SketchUp, it was easy to build a dimensionally accurate 3–D model, and to rotate it for viewing from any angle.

Maxwell is based on the Blue Base from Rogue Robotics, and has a Parallax Board of Education (BOE) controller. As I have time, over the next week or so, I’ll flesh out the model adding the controller and other details.

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Why Reinvent The Wheel?

I’ve noticed while doing research on various micromouse designs, that the designers (engineers?) often reference two sources of inspiration. One is an article written quite a while back by David Otten of MIT about how one of the early MITEE micromouse designs evolved. The second source of inspiration is RC model cars.

On most weekends, assuming the weather decides to cooperate, I like to go kickbiking. It’s great conditioning and exercise, and it gets me out of the house for a while. This morning (Sunday) it was extremely cold, but there was no wind, and no rain, so I put on a sweatshirt, muffler, jacket, and cap, and went out to exercise for a while. One of my favorite kickbiking routines is to kick through the local neighborhoods, through the bayside park, and then finally head up towards a major shopping center that has a Starbucks across the street. I buy a paper at the train station kiosk, then an iced cafe mocha grande, and spend the next hour or so relaxing, catching up on the news, and doing some people watching. This particular morning I also stopped by the bookstore and picked up a RC model magazine. I wanted to see what ideas I could find that might be adapted to robot design – especially to micromouse design.

It’s been years, perhaps decades, since I examined a RC model car in any detail. Apparently the technology and design has evolved quite a bit since I was very surprised at some of the models. It was definitely time well spent – a good investment. Here’s a short rundown of things that caught my attention:

Weight distribution – low center of gravity, batteries in the middle, motor to the rear giving more weight (traction) to the rear wheels. Servo controlling the steering is tilted at an angle (most robot designs tend to keep the servo mounting at right angles.)

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Close-up view of the steering servo mounting and linkage.

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Base plate is thin and low to the ground. In this case, it’s actually two separate plates. The base doesn’t have to be symmetrical – notice how the rear plate is offset to provide clearance for the motor gearing..

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Different design but some of the same features.

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Here’s an interesting diagram that explains how some of the steering mechanism works and how it’s controlled by the servo.

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Here’s a very different design – this time with four wheel drive. The motor sits on one side of the chassis and its weight is counter balanced by the patterns on the opposite side. I was really impressed by the cut outs in the the chassis for the batteries and motor. They provide a lot of stability, and allow the center of gravity to be as low as possible. There were several other things about this design that stood out.

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The effective use of cotter pins to secure some parts.

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Here’s a closer look at the chassis cutouts I mentioned above.

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The drive mechanism comes straight up the middle of the chassis.

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This is a top view of the motor, gears, and toothed drive belt.

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Side view of the motor, gears, and belt.

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The drive belt runs almost the whole length of the vehicle.

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It certainly seems possible, even probable, that I will be able to draw on some of these, and other RC model design concepts for my own robot projects.

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Design and Manufacturing Resources – Small quantities and prototypes

Plastic Parts – Laser Cut:

Pololu Corporation -

Provides extremely cost effective laser cutting for most plastics (acrylic, ABS, polycarbonate, acetal, nylon, styrene, gatorfoam, styrofoam, PETG, wood, cloth, and paper. They accept CAD output in several formats including DXF, or even a faxed sketch, and provide you with a PDF estimate of the job.

http://www.pololu.com/laser_cutting.html 

Their website includes quite a few detailed examples of laser cut parts they have made along with details on the design, materials, and piece part costs. Be sure and check out the two examples of the plastic parts used in their own robot kits.

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The five parts shown above are used in their servo driven sumo robot kit. Laser cut from 1/8” acrylic the total cost including cutting, material, and USPS shipping is less than $10.

 

Printed Circuit Boards:

CadSoft Online - CadSoft Online

Developers of the EAGLE circuit board design package. EAGLE stands for Easily Applicable Graphical Layout Editor. The package includes a fully functional layout editor, schematic editor, and autorouter – all integrated and making use of a single user interface so you don’t have any troublesome, error prone conversions between your schematics and layouts. For hobbyists and personal (non-profit) use, CadSoft provides a freeware version – EAGLE Light Edition – that’s fully functional with only a few minor limitations.

  • Useable board area is limited to 4 x 3.2 inches (100 x 80 mm)
  • Only two signal layers can be used (top and bottom)
  • The schematic editor can only create one sheet

Even with those limitations, the EAGLE Light Edition has more than enough power to handle almost all robot hobbyist design needs. They even reference a complex 68HC12 board that was completely designed using the freeware version. And, if for some reason, you really need all the power of the EAGLE Standard Edition they sell a fully functional non-profit, single user license at a discounted price.

http://www.cadsoft.de/index.htm
 

Spark Fun Electronics -

Produces custom PCBs from your design files for $2.50 per square inch. No hidden fees, no gimmicks, no minimum sizes or quantities. They even provide free shipping within the US. PCBs are 2–layer with white silk screen, green solder mask, no limit on the number of vias, no limit on the number of pads or components, and are routed not sheared. Minimum size is 1”x1” and the maximum is 10”x15”.

Their site has detailed instructions on the file format and information required.

http://www.sparkfun.com/shop/index.php?shop=1&cat=86

Small Parts, Gears, Tools, and Materials:

Small Parts, Inc -

Anything and everything – you name it, there’s a good chance they stock it. Materials like stainless steel, brass, copper, ABS, acrylic, ceramics, … Components like plastic tubing, connectors, o-rings, wire, cable, screws, fasteners, washers, gears, … Tools, including machine tools, hand tools, calipers, screw drivers, gauges, loupes, drills, taps, dies, … They bill themselves as “The Hardware Store for Researchers and Developers”.

http://www.smallparts.com

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Machined Parts:

eMachineShop –

Enables you to design your own part using free, down-loadable software, does manufacturability checking to keep you from designing something that can’t be machined, gives you pricing, and allows you to order online. Current capabilities include milling, turning, laser cutting, water-jet cutting, wire EDM, tapping, bending, blanking, punching, plastic extrusion, thermoforming, and injection molding.

http://www.emachineshop.com/index.html

Download the CAD/CAM package, install it, then start designing. Here’s a simple block with four holes:

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Do a 3D visualization complete with interactive, real-time rotation:

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Analyze your part for manufacturability. The software flags problems with your design and where ever possible suggests corrective actions. Once you get the part to pass the analysis, then the software enables you to check the estimated price and delivery for various quantities:

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It even suggests potential cost reductions. In this particular case it pointed out that a smaller stock size would reduce the machining cost and time, and that changing the material selection would allow the part to be manufactured on a different machine tool.

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Re: Dancing Robots

In response to a comment by Ollie:

Yes, they are pretty amazing.

Of course, their price/cost is pretty amazing too. And, they're not autonomous. I've seen a lot of demonstrations of Asimo and other advanced robots here at trade shows, and they still have the 'Wizard of Oz' feeling with a staff of people behind the curtain controlling things. That will improve over time.

If you go through the auto factories, the robots and mechanisms in use are extremely fast and accurate. So the big difference with robots like ORIO and Asimo is their bipedal design - i.e. their ability to mimic human movements.

Frankly, I think it's the typical first generation approach. We tend to design new technology mimicking what we are familiar with. The first cars were horse-less carriages, for example. It took a couple of decades of trial and error and evolution before the body was lowered below the axles and cars were designed as cars rather than carriages. We're seeing the same thing today with computers - the Mac Mini is a great example, though there are lots of others.

I expect robots will evolve along the same lines. We'll spend a decade or two (one human generation?) doing designs that have their roots in older technology. Robots will be designed to do things that humans already do, and to do them as humans do them. Then we'll start to see totally new and creative designs that really apply robotics in ways we can't begin to imagine today. New robots designed to do things in a totally neo-robotic fashion. A solution to a problem that we couldn’t conceive of because we didn’t have the technology, experience or the mindset to think of it from a neo-robotic perspective.

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Dancing Robots

Here’s a link to a video of the Sony QRIO robots doing a traditional Japanese dance, complete with fans. Pretty amazing.

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Living Machines

Excellent paper by Brosl Hasslacher and Mark Tilden titled “Living Machines” – http://cipres.cec.uchile.cl/~rbeam/living_machines.pdf

The paper appears to be undated - at least I don’t know how to recover the date from the internals of the pdf file, but must have been done while Tilden was with Los Alamos.

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