99-0755 Clockwork Radio/Lanter

THE DEVELOPMENT OF THE
CLOCKWORK RADIO
INITIAL IDEAS
Whilst watching a television programme in September 1991 about the spread of AIDS in Africa, Trevor Baylis had
the inspirational idea for the clockwork radio. The programme highlighted the problem that in remote villages there
was no electricity, and the cost of batteries was prohibitive. As a result, the health messages about AIDS were not
getting through to the population.
Trevor Baylis started by experimenting with ideas in his garden shed that evening. His
initial idea was based on the old style windup gramophone. The turntable was driven by a
simple 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 guitar
tuner. 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 and
arrangements of gears to generate the power. The main
problem was that the logarithmic spring did not provide a constant energy source as
it unwound and would get significantly weaker towards the end of the period. Even
with the best gears to reduce the friction he could not get the generator to last
longer 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 could
provide an answer to his design problem.
Seatbelt mechanisms (and retractable steel rulers) use constant force spring. This is a coil of steel that has been
formed in one direction. When the spring is turned in the opposite direction it stores energy. Since the spring
wants to return to its original shape, when it is released it uncoils and in doing so it releases its energy. The
constant force spring allowed Trevor Baylis to increase the sound output to fourteen minutes. Trevor patented his
radio design in November 1991.
DEVELOPMENT
It took Trevor Baylis a further two years to get his design accepted for
commercial production. During this time he had many disappointing rejection
letters, some claiming that his idea could not possibly work.
His appearance on the Tomorrow’s World programme in April 1994 provided
him with the break he needed. Watching the programme was Christopher
Staines. He thought the radio was an excellent idea that was worth developing
and manufacturing. Together with Rory Stear they set up Baygen Power
Company. (Baygen is short for Balylis Generators).
Before the radio could be manufactured, each component was tested and improved. Engineers at Bristol University
redesigned 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 original
constant force spring to double its original size.
It took nearly four years from initial idea until production. The testing, evaluating and improving were essential to
improve the prototype and make a radio that worked efficiently.
PRODUCTION
The clockwork radio now sells over 100,000 per month from its manufacturing base in Cape Town, South Africa. It
is distributed throughout the world by agencies like the United Nations and the Red Cross. In 1999 50,000 radios
were distributed to refugees from Kosovo to help them trace family members and keep up with developments in
the war.
THE FUTURE
A 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 WORKS
All the Freeplay products share a similar power generation configuration. The diagram below shows a cutaway
section through the Lantern, which was introduced in November 1997.
ENERGY TRANSFER
Storage spool
Torque spool
The energy is transformed by the mechanism. By winding up
the mechanism kinetic energy is converted into potential
energy stored in the spring. When the spring uncoils it
converts the potential energy back to kinetic energy that
drives 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 winding
the spring from one spool to another, energy is stored. As the spring returns to its original position, it releases its
energy and applies a rotational torque to a transmission.
Storage spool
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Torque spool
These diagrams show the principal. In the diagram above,
the constant force spring is wound against its curvature
from the storage spool onto the torque spool. Once fully
wound and released the spring then returns from the
torque spool to the storage spool, thereby producing a
constant force on the torque spool as it unwinds. The
spring has an end stop for over wind protection.
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GEARS
The torque from the spring is transferred via a compound gear train to the dynamo. The compound gearbox
speeds up the speed of rotation from one to one thousand in a three-stage gear system. The gearbox then drives
a dynamo (a small DC motor in reverse) that produces about 100 watts. For sixty winds of the crank handle, the
spring will generate around thirty minutes of airtime.
The spring in the radio is designed to operate for
10,000 windings. This will allow approximately three
hours use each day, for five years. The spring will then
gradually weaken and reduce in efficiency. The radio
will still work, however, its batteries will need to be
charged from an external power source.
The engineers faced new problems with the design of
the Freeplay lantern. The lantern uses an energy
efficient bulb and high quality lens, yet the clockwork
mechanism can still only provide five minutes of light.
Research established that torches are used for
approximately four minutes each time. To ensure that
the torch is capable of shining for longer than five
minutes, it has a facility to transfer the mechanical
energy stored in the spring into a battery store. The
battery store is capable of holding up to two hours
worth of energy. Three windings of the spring will
generate enough energy to power the torch for fifteen
minutes.
Views of the compound gear train and spring
STORING ENERGY
In addition to the spring and gearbox for providing power, the Freeplay 360 radio uses a high performance
amorphous 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 to
sunlight decreases, the radio will automatically compensate by drawing
from the spring to maintain power.
The batteries can also be charged from an external power source via the
jack 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 the
following address:
www.freeplay.com
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GEARS, MECHANISMS AND BEARINGS
Gears are wheels that have a number of teeth evenly spaced
around their perimeter and they are designed to transmit rotary
motion and force. Gears mesh together when their teeth interlock
with each other. A gear transmits force when its teeth lever the
teeth of a connecting gear. When two gears mesh, the larger gear
is called the wheel and the smaller gear is called the pinion. When
a series of gears mesh together they are called a gear train.
The diagram to the right shows a small gear train. If the wheel
turns anticlockwise, the pinion will turn clockwise. Since the gears
are of different size, they will rotate at different speeds. The
difference in their speeds is called the Velocity ratio, and can be
calculated using the following:
VR=
No. of teeth on driven gear
No. of teeth on driver gear
A third gearwheel called the idler can be placed between
the two gears to make them rotate in the same
direction. The idler gear has no influence on the speed
of the other two gears. An example of an idler gear is
shown in the diagram to the left.
To achieve a large velocity ratio a compound gear train
is used. A compound gear train combines two or more
simple gear trains by mounting them on the same shaft.
To calculate the combined velocity ratio, you have to
establish the velocity ratio of each pair:
VR1=
VRT =
VRT =
VRT=
BEARINGS
Bearings are used to reduce friction on rotating shafts and to
give support.
The simplest bearing is a bush bearing. As the shaft rotates in
the bearing, it rubs against the sides. The friction between the
rubbing surfaces is reduced by using materials, which slide
easily against each other.
Bush bearings are frequently made from nylon or brass. The
type of material used for the bearing depends upon the force it
is designed to hold.
Radial bearing
Nylon is generally used for bearings
that are designed to support small
loads. They are inexpensive and
easy to manufacture.
The bearings shown in the diagram
to the left are designed to take both
radial and axial loads.
Axial bearing
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2:1 VR2= 8:1 VR3= 4:1
VR1 x VR2 x VR3
2:1 x 8:1 x 4:1
64:1
QUESTIONS
HISTORY
1. 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 went
into production?
3. Find out what was unique about the production line for the
clockwork radio in South Africa? How many radios do they
produce 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 clockwork
radio and lantern.
GEARS
1. 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 two
larger 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 by
engineers to represent a gear on drawings?
Driver 80 teeth
5. The diagram to the right shows two gears meshing. The driver gear has
80 teeth and the driven gear has 12 teeth.
If the driver gear is rotating at 900rpm, what is the output speed?
A Driver 60 teeth
C 60 teeth
B 12 teeth
D 15 teeth
6. The diagram to the
left shows a
compound gear train.
Calculate the total
velocity ratio.
Driven 12 teeth
7. If the driven gear is
rotating at 500rpm,
what is the speed of
the driver gear?
NEW PRODUCTS
1. 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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