THE DEVELOPMENT OF THE CLOCKWORK RADIOINITIAL IDEASWhilst watching a television programme in September 1991 about the spread of AIDS in Africa, Trevor Baylis hadthe inspirational idea for the clockwork radio. The programme highlighted the problem that in remote villages therewas no electricity, and the cost of batteries was prohibitive. As a result, the health messages about AIDS were notgetting through to the population.

Trevor Baylis started by experimenting with ideas in his garden shed that evening. Hisinitial idea was based on the old style windup gramophone. The turntable was driven by asimple spring. His idea was to use this principal to build a spring-driven radio.

The first prototype was made from an old radio and an electric motor taken from a guitartuner. He attached a hand drill and by turning the drill he was able to power the radio.Essentially he was using an electric motor as a dynamo to generate electricity.

Trevor Baylis experimented with a number of springs andarrangements of gears to generate the power. The mainproblem was that the logarithmic spring did not provide a constant energy source asit unwound and would get significantly weaker towards the end of the period. Evenwith the best gears to reduce the friction he could not get the generator to lastlonger than four minutes.

A trip to the shops in his car gave him the breakthrough inspiration for the design.Whilst he put his seat belt on he realised that the seatbelt mechanism spring couldprovide an answer to his design problem.

Seatbelt mechanisms (and retractable steel rulers) use constant force spring. This is a coil of steel that has beenformed in one direction. When the spring is turned in the opposite direction it stores energy. Since the springwants to return to its original shape, when it is released it uncoils and in doing so it releases its energy. Theconstant force spring allowed Trevor Baylis to increase the sound output to fourteen minutes. Trevor patented hisradio design in November 1991.

DEVELOPMENTIt took Trevor Baylis a further two years to get his design accepted forcommercial production. During this time he had many disappointing rejectionletters, some claiming that his idea could not possibly work.

His appearance on the Tomorrow’s World programme in April 1994 providedhim with the break he needed. Watching the programme was ChristopherStaines. He thought the radio was an excellent idea that was worth developingand manufacturing. Together with Rory Stear they set up Baygen PowerCompany. (Baygen is short for Balylis Generators).

Before the radio could be manufactured, each component was tested and improved. Engineers at Bristol Universityredesigned the gearbox. The gears were made from plastic and the number of bearings and axles were reduced.They also found that there was insufficient power to drive the electronics properly, so they increased the originalconstant force spring to double its original size.

It took nearly four years from initial idea until production. The testing, evaluating and improving were essential toimprove the prototype and make a radio that worked efficiently.

PRODUCTIONThe clockwork radio now sells over 100,000 per month from its manufacturing base in Cape Town, South Africa. Itis distributed throughout the world by agencies like the United Nations and the Red Cross. In 1999 50,000 radioswere distributed to refugees from Kosovo to help them trace family members and keep up with developments inthe war.

THE FUTUREA number of designers are looking at extending the range of clockwork energy powered devices. Prototypes have been developed for powering water purification devices, lap-top computers, CD players and global positioning systems.

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HOW IT WORKSAll the Freeplay products share a similar power generation configuration. The diagram below shows a cutawaysection through the Lantern, which was introduced in November 1997.

ENERGY TRANSFERThe energy is transformed by the mechanism. By winding upthe mechanism kinetic energy is converted into potentialenergy stored in the spring. When the spring uncoils itconverts the potential energy back to kinetic energy thatdrives the dynamo which generates electricity.

The constant force spring is made from textured steel.When this is deformed by winding it against its natural shape it will try to revert to its natural shape. By windingthe spring from one spool to another, energy is stored. As the spring returns to its original position, it releases itsenergy and applies a rotational torque to a transmission.

These diagrams show the principal. In the diagram above,the constant force spring is wound against its curvaturefrom the storage spool onto the torque spool. Once fullywound and released the spring then returns from thetorque spool to the storage spool, thereby producing aconstant force on the torque spool as it unwinds. Thespring has an end stop for over wind protection.

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Storage spool Torque spool

Storage spool Torque spool

GEARSThe torque from the spring is transferred via a compound gear train to the dynamo. The compound gearboxspeeds up the speed of rotation from one to one thousand in a three-stage gear system. The gearbox then drivesa dynamo (a small DC motor in reverse) that produces about 100 watts. For sixty winds of the crank handle, thespring will generate around thirty minutes of airtime.

The spring in the radio is designed to operate for10,000 windings. This will allow approximately threehours use each day, for five years. The spring will thengradually weaken and reduce in efficiency. The radiowill still work, however, its batteries will need to becharged from an external power source.

The engineers faced new problems with the design ofthe Freeplay lantern. The lantern uses an energyefficient bulb and high quality lens, yet the clockworkmechanism can still only provide five minutes of light.

Research established that torches are used forapproximately four minutes each time. To ensure thatthe torch is capable of shining for longer than fiveminutes, it has a facility to transfer the mechanicalenergy stored in the spring into a battery store. Thebattery store is capable of holding up to two hoursworth of energy. Three windings of the spring willgenerate enough energy to power the torch for fifteenminutes.

Views of the compound gear train and spring

STORING ENERGYIn addition to the spring and gearbox for providing power, the Freeplay 360 radio uses a high performanceamorphous thin film solar panel, with a 3V 50mA output, to boost the charge to the batteries.

The panel generates electricity when exposed to sunlight. In direct sunlight,the radio will run off the solar panel alone, while as the exposure tosunlight decreases, the radio will automatically compensate by drawingfrom the spring to maintain power.

The batteries can also be charged from an external power source via thejack plug. This needs an input between 3-12V 100mA.

Further technical details on either the radio or the lantern can be obtained from the Freeplay web site at thefollowing address:www.freeplay.com

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GEARS, MECHANISMS AND BEARINGSGears are wheels that have a number of teeth evenly spacedaround their perimeter and they are designed to transmit rotarymotion and force. Gears mesh together when their teeth interlockwith each other. A gear transmits force when its teeth lever theteeth of a connecting gear. When two gears mesh, the larger gearis called the wheel and the smaller gear is called the pinion. Whena series of gears mesh together they are called a gear train.

The diagram to the right shows a small gear train. If the wheelturns anticlockwise, the pinion will turn clockwise. Since the gearsare of different size, they will rotate at different speeds. Thedifference in their speeds is called the Velocity ratio, and can becalculated using the following:

A third gearwheel called the idler can be placed betweenthe two gears to make them rotate in the samedirection. The idler gear has no influence on the speedof the other two gears. An example of an idler gear isshown in the diagram to the left.

To achieve a large velocity ratio a compound gear trainis used. A compound gear train combines two or moresimple gear trains by mounting them on the same shaft.

To calculate the combined velocity ratio, you have toestablish the velocity ratio of each pair:

BEARINGSBearings are used to reduce friction on rotating shafts and togive support.

The simplest bearing is a bush bearing. As the shaft rotates inthe bearing, it rubs against the sides. The friction between therubbing surfaces is reduced by using materials, which slideeasily against each other.

Bush bearings are frequently made from nylon or brass. Thetype of material used for the bearing depends upon the force itis designed to hold.

Nylon is generally used for bearingsthat are designed to support smallloads. They are inexpensive andeasy to manufacture.

The bearings shown in the diagramto the left are designed to take bothradial and axial loads.

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VR= No. of teeth on driven gearNo. of teeth on driver gear

Radial bearing

Axial bearing

VR1= 2:1 VR2= 8:1 VR3= 4:1VRT= VR1 x VR2 x VR3VRT= 2:1 x 8:1 x 4:1VRT= 64:1

QUESTIONS HISTORY1. What was Trevor Baylis’s inspiration for the design of the

clockwork radio? What did he make his first prototype from?

2. Why was it necessary to change the prototype before it wentinto production?

3. Find out what was unique about the production line for theclockwork radio in South Africa? How many radios do theyproduce each month?

4. Compression and Tension are two types of spring:a. Draw a simple diagram of each spring.b. Describe two uses for each type of spring.

5. Describe with notes and sketches, the production method used for manufacturing the case for the clockworkradio and lantern.

GEARS1. What is the term given to when two gears are interlocked?

2. What is the name given to the small gear that is placed between twolarger gears in order to achieve the same direction of rotation?

3. What is the collective name given to a series of gears working together?

4. What do the inner and outer circles represent on the symbol used byengineers to represent a gear on drawings?

5. The diagram to the right shows two gears meshing. The driver gear has80 teeth and the driven gear has 12 teeth.If the driver gear is rotating at 900rpm, what is the output speed?

6. The diagram to theleft shows acompound gear train.Calculate the totalvelocity ratio.

7. If the driven gear isrotating at 500rpm,what is the speed ofthe driver gear?

NEW PRODUCTS1. As part of their continued development , Freeplay are looking for a range of new applications using the

clockwork mechanism. a. Suggest a range of products that could be powered by a clockwork mechanism.b. From your list of products, sketch a series of ideas for how the clockwork mechanism could be

incorporated.

2. Find out about the work of the Freeplay Foundation at www.freeplay.org.uk

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Driver 80 teeth

Driven 12 teeth

A Driver 60 teeth

B 12 teeth

C 60 teeth

D 15 teeth