Kinetic Sculpture Engineering Pointers

One of my major hobbies for the past 15 years has been Kinetic Sculpture building and racing.

Probably the most important thing I've learned over the years is to limit the amount of planning and thinking about a project, and to get off my duff and actually make and try something. You can get stuck forever in the planning process and never accomplish anything. It is better to try to make something that can be modified and/or fixed cheaply and easily than to make a gold plated marvel that never breaks yet doesn't work.

Here are a couple of pointers:

• Two wheels are always faster than three or more, but balance can be a problem at low speeds, in mud and up sand dunes.
• Regardless of the number of wheels, make sure that as much of the vehicle's weight as is possible is supported by the drive wheels. This gives you traction. Balance fore and aft is a different problem that can be solved in a variety of ways, but traction is a major issue that is best solved by proper weight distribution.
• Lighter, more fragile vehicles are generally better than heavy durable vehicles. For an unadorned vehicle try to keep the weight per pilot to less than 80 pounds. You'll be a lot happier racing a lighter vehicle with a bit of performance than a slug, especially up hills.
• Steel is cheap and makes for a good bearing surface, but it is generally heavy and rusts easily. Aluminum is expensive and makes for a poor bearing surface, but it is generally light and doesn't corrode. Stainless steel is great, especially for salt water applications, but very expensive and harder to work with. Wood can be cheap and easy to work with, but it can also be heavy and hard to preserve. Fiberglass and foam can be used with great success for making water impervious curved surfaces and, with care, it can be used for load bearing applications.
• Durable inflatable pontoons can be made "at home" using 18 oz. truck vinyl coated nylon material (available from tent and awning stores) and heavy duty thread and inflatable boat valves. The holes from sewing can be sealed quite well with "inflatable boat sealant", available from many boating stores.
• Styrofoam is an excellent alternative to inflatables, and don't leak. However, unless you form it into hollow hulls, it generally gets quite a bit heavier than inflatables for larger volumes.
• Plan to have at least 50% more flotation than you absolutely need. This will enable you to carry heavier pilots, and have some margin for error if your vehicle puts on extra weight. If you are using inflatable flotation, then I'd recommend at least twice the flotation, so if you lose one pontoon (say, out of two pontoons total), you won't lose the vehicle.
• Try to keep your drive chains out of the sand/mud/water. They will last longer and won't fail as easily in those environments.
• Triangular support structures are good. Try to keep away from using cantilevers as much as possible.
• Remember that vehicles, especially with riders on board, are heavy. Make sure that you:
  • have good brakes that can be used *anywhere*
  • have a good way to deploy flotation upon water entry
  • have a good way to transport your vehicle to and from races
  • have a steering mechanism that is reliable
  • use adequate axles, wheels and wheel bearings
  • have adequately low gears for the hills. 3 inch gears (one crank rotation for 9 inches of forward travel for 3+wheel vehicles, 20 inches of travel for bikes) work pretty well in practice.
• Big wide soft tires are good for soft surfaces, but narrow hard ones are best for hard surfaces. You can make wheels with both characteristics, or with careful design, swap wheels when changing terrain. Swapping wheels takes time, however.
• Bike parts are cheap and readily available. However, they will break if you place enough torque on them. In drive trains you can get heavy duty chains and gears from your local bearing stores, or from catalogs. Go kart stores are another good source for parts. http://www.azusaeng.com/catalog/dwnld/azdwnld.html has been recommended by others as a good source for parts.
• Paddle wheels will work in all soft surfaces, including water of any depth. Props are good only in water that is adequately deep and free of weeds or other obstructions. Oars are typically difficult to use in most of the sculptures I have seen, but they can be effective.

Be creative. Sometimes the best ideas are the ones that sound the wackiest at first. Also, sometimes it is not as important that the vehicle actually makes it over the course without pushing or breakdown as it is that the vehicle and pilots look really cool. If it can do both, great!

Of course, the most important thing is to have fun.

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