The Bike With 2 Brains
The Beginning
During my first Burning Man experience in 2004, I found myself alone a lot of the time. I found that although I'm pretty good at meeting new people, and good at the art of conversing, that moment of first contact is still a challenge. That moment is much easier if there is a catalyst — a common observation, or a shared activity, for instance.
While I was there, I felt compelled to give something back to the community. I conceived of the idea of creating "The Bike With 2 Brains," a vehicle intended to foster social interaction. The mechanical concept is simple: two riders propel a vehicle by pedaling independent wheels mounted side-by-side, thereby allowing it to be differentially steered like a bulldozer — to go straight, both riders must pedal at the same rate. The rear wheels will pivot freely to allow the front wheels to steer.
Using sight and sound as a lure, I expect it to draw curious individuals. The vehicle will be inviting for someone to explore on their own, and sitting alone next to the empty seat is a catalyst to initiate conversation with others. Also, from this vantage point, they may feel empowered to seek others when they ordinarily would not have done so (i.e. yelling at people.)
The Bike With 2 Brains offers people a unique experience to share. Once two riders are situated, they'll need to determine where they want to go since both riders contribute to travel direction, and therein lies the twist.
If the riders agree on a destination, they will have an experience where their symbiotic behaviors quickly get them to their destination. If they disagree, one rider may concede and help bring the other to their destination as a "gift of work" which cannot be directly reciprocated (the conceding rider needs to find a different individual to help them get to where they wanted to go.) Alternatively, a rider may concede and then be able to experience something they would not have realized otherwise — fostering an experience of exploration.
It will be amusing to watch riders who fail to come to agreement and where neither rider concedes.
Blog Entries
Design Overview
Frame
The frame of the Bike With 2 Brains is made from a combination of bicycle parts, unicycle parts, and steel pipe. The front wheels have a direct-drive crank made from a unicycle. The rear wheels are made from the front bracket and steering mechanism from a bicycle — the bracket is aligned vertically to permit the wheels to freely caster. The rest of the frame consists of bicycle tubing for the parts that are straight and steel "Schedule" pipe (the stuff for water, gas, and old electrical work) for the parts that are bent.
The seat is made from wood covered with cotton cloth and cushioning from a junked futon mattress. It is supposed to give the suggestion of lips.
About the eyes: they are there for two reasons: the obvious aesthetic reason, and also for a little bit of safety. If the vehicle tips over, the eyes will prevent someone from getting seriously injured having their leg pinned between the frame and the ground … At least that's the theory.
Power Source
I had originally considered making a propeller-driven windmill that pivoted to catch the wind on the top of the Bike With 2 Brains for primary power, but after seeing PicoTurbine.com, I realized I could simplify things with a Savonius rotor. The rotor is made from about 10 inches of 5-inch round ductwork cut in half and mounted between a couple 2×4's. A baby stroller wheel from the trash is used as a gear to drive a 1-inch wood spindle mounted on a DC brush motor from a cordless drill (I think) in what ends up being about a 7:1 ratio. The rotor is mounted in a steel frame using a 5/16" shaft (7.98 mm or 0.8% smaller than 8mm) which pivots against inline-skate bearings (which have an expected shaft diameter of 8mm) from Pleasure Tools.
The rotor has a 9.2-inch diameter and will run at about than 30 RPM for every mile-per-hour of wind speed. (The Savonius rotor will generate peak power where the tip speed of the rotor is 80% of the wind speed.) Thus, in a 10 mile-per-hour wind, the rotor will run at 300 RPM causing the generator to run at 2,100 RPM and generate about 20 watts of power (at least in this unverified fantasyland.) In a 75 mile-per-hour gust (which is the anticipated maximum speed) the rotor will run at 2,250 RPM causing the generator to run at 15,750 RPM. The rotor should be able to handle this speed (see also, "unverified fantasyland" comment) and the generator should be able to handle up to 20,000 RPM (ibid.)
The DC brush motor acting as a generator can output up to about 20 watts of power which is run through a shunt regulator (which shunts all power above what is currently used by the rest of the system to a dummy load thereby limiting the rotation speed of the rotor) and supplies 13.8 volts to the battery charging circuit and main power. The output from the generator drives a battery charger to maintain a backup battery (in those rare times when there's no wind) and provide power for the computer, audio system, and lighting.
Assuming the wind speed stays above 10 miles-per-hour (which should yield about 20 watts of power from the generator) for 12 hours a day, the generator should produce an average of 10 watts every hour. Thus, if the power consumption of the bike is less than 10 watts per hour, it should never run out of power.
Computer
The computer is a super cool 18F252 PIC 8-bit microcontroller from Microchip bought from SparkFun.com along with a development kit. It runs at 20 MHz and includes 32 kilobytes of flash memory that can hold 16,000 instructions.
Details are still hazy, but the computer has the following inputs and outputs:
- Analog input to check battery charge status.
- Analog output to specify voltage levels for LED level.
- Digital output to select color (red, green, or blue) to apply LED level output.
- Digital output to select LED to light.
- Digital outputs to manipulate MP3 player and to perform a fade-out/soft-mute of audio output.
- Digital input to determine when riders are sitting on the vehicle and when they're pedaling.
Further, it performs the following functions:
- Control MP3 player to select tracks.
- Sequence lighting in a manner compatible with the currently playing track.
- Monitor battery level and revert to emergency lighting if there is no generator power and the battery is running low.
- [Pipe dream:] Keep track of approximate real time and monitor generator output, rider occupancy, and travel distance.
- [Pipe dream:] Add LED headlights on the front wheels that strobe to freeze the wheel spokes.
Lighting
Although electroluminescent wire is really cool looking in most applications, the Bike With 2 Brains lighting uses true-color LED's from LS Diodes. The LED's are housed in a durable (and water-resistant) polyethylene tubing which has a milky-clear appearance. The LED's are spaced approximately one every foot which gives the tubing a soft glow. Each LED is individually addressable and can be assigned unique levels for each of its red, green, and blue component colors.
The LED's have a common cathode (negative terminal) and individual anodes (positive terminals) for each of the three colors (red, green, and blue.) Since each color has its own voltage and current characteristics, resistors are wired to the anodes so a voltage level of 5 volts on the input will cause full-brightness — without overload — in each color. The cathodes are wired individually back to the control computer, and the anodes (well, the resistors) are wired in parallel back to the control computer. Thus, to address an individual color on a particular LED, voltage is supplied between the common color anode and the individual LED's cathode.
Although it is theoretically possible to pulse-width-modulate the light output on the LED's by supplying significantly more than the maximum continuous current to each LED in brief pulses, the Bike With 2 Brains design uses an absurdly more elaborate system. As described prior, each color has a current-limiting resistor at the anode and an addressable cathode that returns to the control computer. In addition, 10 µF capacitors are wired between each of the three colors of an individual LED and the common cathode of that LED. Therefore, by sourcing a high-current pulse to the capacitor, its voltage level can be quickly set and deteriorates about a volt every millisecond (through the 35 mA LED.) Therefore, as long as the computer can update each voltage level in less than that time, the LED can be maintained at full brightness.
Audio
The audio system consists of an MP3 player and an audio amplifier.
The MP3 player is a Digisette Duo-MP3 with 32 MB of on-board flash RAM. Experimentation demonstrated that the player will handle monophonic, variable bit-rate recordings and output "acceptable" fidelity at 56 kilobits per second yielding over an hour of play time. The player supports mechanically-actuated forward, reverse, stop, volume-up, and volume-down buttons. These buttons appear to be able to be emulated using solid-state hardware and wired into the circuitry of the player without difficulty. Thus, the control computer can select tracks to play and theoretically maintain which track is currently playing.
Audio source material comes from several artists in the Rochester, NY area to-be-determined. Thematically, artists were encouraged to comment on one of three ideas: a symbiotic relationship, an antagonistic relationship, and longing for a relationship. The control computer selects which of these kinds of music is to play to represent the mood of the vehicle.
An on-board amplifier drives car-stereo speakers behind an environment-resistant housing. Given an estimated efficiency of 90 dB at 1 watt at one meter, 2 watts per channel output almost 100 dB of sound. While this will not be enough to overpower a thousand-watt rave, it will easily be audible from a great distance in the quiet areas of the playa.
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