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2003 BEAM SolarRoller Race Rules & RegulationsRules & Regulations (Same as 2002) Last modified on February 4, 2002

Originally Created by Dr. Mark Tilden
Rules adapted for BEAM/WCRG Games by Dave Hrynkiw

Official PDF Version of the 2002 Rules
1381 Solarengine Rosetta Stone
Flashing LED Solarengine Rosetta Stone

Note: The following is an extract of the official PDF version above. Competitors are strongly suggested to use the above PDF as your guidelines.

Object:

Given a maximum single solar cell size of 806.5 square millimeters (1.25 square inches), make a self-starting 150mm (6") robot dragster to race one meter (3.3 feet) in full sunlight (or 1000 watts of Halogen lighting). Competitors will race each other down parallel 150mm (6") wide lanes. Fastest to finish, or furthest travelled in 3 minutes wins.

Background:

The Solaroller is a deceptively simple device which employs many of the features of small robot creature design. It is valuable in that it introduces the concept of the self-contained, one-motor-neuron Solarengine, the heart of many BEAM competitors. It is an excellent starter project for future roboticists and can be as minimal or complex as desired.

The Solarollers only history is that it is a classic type "1" roving vehicle as described by Valentino Braitenburg in his book "Vehicles" (1984, MIT Press). That is, a vehicle that only moves forward, its speed proportional to the amount of light it receives on an optical sensor. Although simple conceptually, it can be quite difficult to implement because of the solarcell size restriction. 806.5 square millimeters (1.25 square inches) of even the most efficient solar cell is barely enough to turn most motors, let alone take the strain of actually moving the motor, solarcell, and wheels down a racing lane. This is where the designer learns the value of using what is commonly called an electronic "relaxation oscillator". The idea is to accumulate charge in an electronic storage capacitor while the device is at rest, and then to release it into the drive motor suddenly, causing the device to jump forward in steps. The stored energy spent, the capacitor returns to saving energy for the next time. This can be done using many methods from a simple two transistor circuit (detailed later) to a complex sequencer-FET arrangement.

The problem is that most electronics require between 2 to 5 volts to operate, and most commercial solar cells only produce 0.5 volts. Amorphous solar cells are thereby recommended. These are found in many standard solar-cell calculators, and are characterized by a multi-cellular design; stacking 0.7v cells or stripes adjacent to each other to produce a low efficiency, low current 2 to 5 volts, which is exactly what is required.

The rest is innovation, calculation and solder-skills. The immediate advantage of building such devices is that they can be very small and thus very robust (see figure below). Anyone who has worked with space-quality solar cells knows that they are sharp, expensive, and as fragile as a potato chip. The amorphous cells are, although not indestructible, significantly tougher, cheaper, and easy to work with. Not surprisingly, it is also often cheaper and easier to buy and destroy a whole calculator for its solar cell than to buy the cell separately from a science shop.
Small means tough. No battery means that your Solaroller will only have to worry about mechanical wear and natural corrosion. Once a Solarengine is complete, it can be used for more than just racing. Devices from robot Venus-flytraps to self-turning solar Christmas tree ornaments have been successfully constructed, and competed in various competitions.

The Solarengine is a counterintuitive learning machine. Most people have learned the simple idea of putting a battery to a motorized toy and then watch it whiz about. By contrast, the Solarengine is quiet, slow, and sedate. However, a robotic device using a battery must eventually have that battery replaced, much to the detriment of the environment (and the device if the battery leaks). On the other hand, a Solarengine device is slow but persistent, and will continue to work for many years regardless of human intervention. The lifetime is only limited by the years long decay-time of the cell, and the quality of adhesive holding the device together.

The Solaroller teaches designers to deal with micro amperes of power and efficient mechanical designs from the start. In battery powered toys, a shorted wire could lead to smoke, in a Solaroller, even a 100 kilo-ohm current load is a disastrous energy loss (in a battery powered toy, a high impact crash is inevitable. In a Solaroller, it can only happen if it manages to roll off the shelf. A small leash is recommended).

To help out first time Solar Engine builders, the following page is a high-detail "Rosetta Stone" for Solaroller construction. Such a device can be put together using the contents of the cheapest solar-cell calculator, a dead walkman, and possibly a radio. Chances are you (or a friend) have just these items in the back of a junk drawer, and there is much you can learn just by taking them apart.

Solaroller Plan

The Racing Platform:

The racing strip is composed of two side by side 1 meter lanes of clean, smooth, level, white melamine, glass mirror, or painted flat plywood, with 25mm (1") high x 12mm (1/2") wide melamine/arborite walls along both sides of each lane. The lanes will have exactly 150mm (6") between wall surfaces along the full travel length. Competitors start in a 150mm (6") square with their forward edge pushed up to the inside edge of a thin black or white starting line drawn on the walls and mirror surface. Exactly 1 meter away from the start line is the finish line. The finish square is also a 150mm (6") square and has no end wall.

Due to heat distortion, the walls cannot be guaranteed perfectly straight.

The light source for the table will be positioned so that no shadows fall from the sides of the vertical walls. Competitors will race into the light source and must be able to optimize a light source from perfectly vertical (90 degrees) to a late afternoon angle (30 degrees). Light may be limited by a single clear window, but otherwise should be unhampered. Due to the possibility of excessive heat buildup, it is advised competitors not use hot glue, soft, black plastics, or wax to hold their solarollers together. Melting has occurred on occasion, and hot glue has been known to hold a racer in place mid-way down the racetrack.

Solaroller - The Race:

The single-heat race begins when the judge says "go" and lets a charge build up in the two competitors. This is done by the judge lowering the conductive metal rail at the rear of the starting box that is shorting out the circuitry in the competing racers. Care shall be taken to insure that competitors are released fairly and with as little disturbance as possible. In designs where the aforementioned does not work, an alternate method of starting must be worked out with the judges. It is, however, the designers' responsibility to insure that a clean start can be managed, and this is best done by including a pair of shorting wires that fully extend to the rear of the 6" starting box.

Once the contacts are open and the devices allowed to charge, the race has started. To insure the devices follow the "self-starting" rule, competitors must remain immobile for at least 3 seconds following the start of the race. If one or both move within that time, a false start is called and the race is re-run. If it happens again, then that competitor's designer has the option of removing the device for modification to re-race later, or moving the competitor back so that it does not cross the start line before two seconds are up.

Solaroller Starting Gate

The race is run until the frontmost vertical edge of a competitor crosses the finish line at the end of the 1 meter lane, until a designer concedes, or until a full 3 minutes has elapsed (at which point the racer travelling furthest wins).

In the case of the There and Back event, the race is run until the forwardmost vertical edge of the racer crosses the line after tagging the wall at the end of the 1 meter track and returning. The race can also end after a designer concedes, or until a full 6 minutes has elapsed (at which point the racer travelling furthest wins).

During the run, competitors are allowed to touch the surrounding walls as necessary but should not damage or climb the walls. Any competitor that stalls or binds against a wall shall be left untouched until the progress of the other competitor is determined. As soon as the other competitor has caught up without binding, that competitor shall be declared the winner of that heat. In the case of a dual stall, the competitor the farthest down the lane way shall be considered the winner of that heat.

If clear, unobstructed sunlight is available or the halogen light option is used, the times of the individual runs will be kept track of. All running times shall be registered and recorded.