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Samoa Hostel Pain in the Axle
"Pain in the Axle" is a bicycle-powered electrical generator that makes use of a modified recumbent exercise bicycle to drive a generator that powers a television and DVD player. "Pain in the Axle" will reside in the common area of the Samoa Hostel for guests to use.
Triad Design created "Pain in the Axle" in cooperation with Danco and the Humboldt Bay Center for Sustainable Living. The device would need to power a TV/DVD player and inspire users to reduce their electricity consumption. The design will be placed in the Samoa Hostel along with a number of other projects designed by engineering students from Humboldt State University. The Samoa Hostel is set to open in the summer of 2011 as a joint effort between Danco Builders and the Humboldt Bay Center for Sustainable Living. It will feature environmentally sound building techniques with the goal of teaching guests how to live more sustainably.
Objective & Criteria
"Pain in the Axle" was designed with a four objectives in mind:
- Educate guests of the hostel about the work required to power common electronics
- Power a television and DVD player with with the clean energy of pedal-power
- Promote healthy living by turning a passive activity (watching television) into something that requires active involvement of the user
- Enrich the community by providing a means of cooperative learning and inspiration
To complete these objectives, Triad Design adhered to seven separate criteria in the design of the unit. The criteria were ranked by importance.
|Safety||10||Electrical and mechanical components of the unit must not be a safety hazard to users|
|Durability||9||The model has to be able to withstand daily use for multiple years with little maintenance|
|Educational Value||9||The design should teach users about power consumption in a hands-on manner|
|Cost||8||The design is under budget|
|Ease of Use||8||The bicycle is comfortable and easy for the average rider to use|
|Power Capacity||7||The device is able to power (at minimum) a television and DVD player|
|Aesthetics||5||The design should be professional in appearance and attract visitors’ attention|
"Pain in the Axle" is designed to work in a similar manner as a typical recumbent exercise bike, as shown in Figure 2. The recumbent bike has been modified to drive a generator, whose output voltage is relative to the pedaling speed of the user. In order to power the TV and DVD player, the user must pedal at a rate that produces at least 10V. A voltmeter allows the rider to see how much voltage is being produced and modify pedaling speed accordingly. If the voltage drops below 10V, a DC/DC converter automatically discontinues power output. This will cause the TV and DVD player to lose power and turn off. The rider must increase their pedaling speed and bring the voltage back up to 10V in order for the TV and DVD player to turn back on.
The Pain in the Axle design is based upon a modified Pro-Form 480 recumbent exercise bicycle. Most of the unnecessary components were removed, including the electronic display, pulse monitor, resistance magnets, and electrical wiring. The simplicity of design of the Pro-Form 480 allowed for easy modification and addition of parts.
- The axle connected to the pedals of the bicycle turn a 9” plastic wheel with multiple grooves along the circumference. These grooves make contact with a ½” wide, six-grooved belt. This belt wraps around both the 9” wheel and a 1 ¾” cast-iron wheel with identical grooves. RPMs are therefore transferred in approximately a 1:5 ratio.
- Attached to the axle of the 1 ¾” wheel is a 7 ¾” cast-iron wheel. Both share the same axle and turn at the same rate. This larger wheel originally served as the resistance flywheel and the circumference is coated in about ¼” of copper. A 3/16” round belt turns a ¾” pulley connected to the shaft of the generator, as shown in Figure 3. RPMs are transferred to this pulley in approximately a 10:1 ratio.
The overall gear ratio is therefore about 50:1. A large ratio is required to reach the desired RPMs of the generator. A visual representation of the components can be seen in Figure 6.
The generator used is a permanent magnet DC motor made by Currie Technologies was originally from an electric scooter. The motor is rated at 24V for 2600 RPM and handles a load of up to 22A. When tested as a generator, however, it behaved slightly differently. Both with and without loads attached, the generator was able to put out a constant 14V at speeds upwards of 1800 RPM. At an average constant pedaling speed of 60 RPMs, the generator will theoretically reach 3000 RPMs. At such high gearing ratios however, frictional losses are expected to be relatively large and not all energy expended by the user will turn into kinetic rotational energy in the generator. Actual pedaling RPMs are expected to be somewhat lower. All wire used in the electric circuitry of the Pain in the Axle is 10g to provide as little resistance as possible for high current. The wire and connectors are insulated to protect users from high amounts of current. Figure 4 is an electrical schematic of this circuit. The unit chosen to regulate voltage is a DC/DC buck-boost converter made by PowerStream Technologies. Voltage output is regulated at 12V DC, and an internal potentiometer allows for tweaking from 11-14V. The buck-boost converter accepts voltages of up to 30V DC and has a number of features benefitting our design including Input polarity protection, low voltage drop-out, and Short circuit protection. The DC/DC buck-boost converter connects to three cigarette-style DC plugs identical to ones found in automotive applications. All DC adapters are fuse-protected for the rated current of the connected device.
The cost of the Pain in the Axle is divided into three different categories: design cost, implementation cost, and maintenance cost.
The design cost of the Pain in the Axle consists of the total number of hours spent designing and building the unit. Figure 7 shows the distribution of the total design hours: 308hr.
The implementation cost of the Pain in the Axle design consists only of the cost of the materials needed to build the display. All labor was performed by Triad Design, and consultation of experts was free. The table lists the materials and their cost to Triad Design as well as the retail cost of each item.
|Material||Quantity||Our Cost||Retail Cost|
|Pro-Form 480 Recumbent Exercise Bike||1||Donation||$299.99|
|24V DC Generator||1||$20.00||$113.99|
|8 amp Fuses (4pk.)||1||$1.99||$1.99|
|Car Power Outlet||1||$17.99||$17.99|
|10 Gage Wire||14||$4.06||$4.06|
|DC Volt Meter||1||$10.89||$10.89|
The Pain in the Axle is designed to last for many years with little maintenance. A weekly wipe down of external components will be necessary to clean the unit of dirt and dust. Since all components are fuse-protected, there is little chance that any of the electrical components will need replacing. However, the fuse protecting the voltage regulator will blow if a load is plugged in that exceeds ten amps. Maintenance costs are therefore expected to be very low, and cost less than $5 annually as shown in the table below.
|Replacement of fuse||30||~$0.50/ea|
|Cleaning of external components||15||$10.00/hr|
For more information visit:
- CCAT pedal powered TV
- Bart Orlando 
- Lonny Grafman
- Sean Armstrong
- Danco Communities
- Marty Reed
- Christian Buesing from Faith Technologies
- John Davis from Solar Hot Water Plus
- Thorin Somers & John Hackett