Shock

A PROJECT REPORT ON REGENERATIVE SUSPENSION SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENT OF AWARD OF THE DIPLOMA IN MECHANICAL ENGINEERING 2010-2013

SUBMITTED BY: LALIT MUDGAL (10020170543) AJAY KUMAR

(10020170557)

AKASH

(10020170559)

ASHISH GUPTA

(10020170560)

VINAY CHHILLAR (10020170562)

SUBMITTED TO STATE BOARD OF TECHNICAL EDUCATION, PANCHAKULA UNDER THE GUIDANCE OF MR.ARJUN NANI LECT. IN MECHANICAL ENGINEERING P.D.M POLYTECHNIC, SARAI AURANGABAD (BAHADURGARH)

ACKNOWLDGEMENT It affords us great pleasure our gratitude towards our esteemed & guide Mr. Arjun Nani Lect. of Mechanical Engineering P.D.M. Polytechnic (B.Garh) for giving us the opportunity to work On this project & helping us through-out with his guidance & Suggestions. Our special thanks to Mr. Iftikhar

alam

(H.O.D.

of

Mechanical

Engineerung.

P.D.M.

POLYTECHNIC (B.Garh) for his patronage & Blssings.

LALIT MUDGAL (10020170543) AJAY KUMAR

(10020170557)

AKASH

(10020170559)

ASHISH GUPTA

(10020170560)

VINAY CHHILLAR (10020170562)

DEPARMENT OF MECHANICAL ENGINEERING P.D.M. POLYTECHNIC, SARAI AURANGABAD (BAHADURGARH)

PREFACE This project report is completely guide to the “WIND MILL” According to the need of our syllabus prescribed by State Board of Technical Education Haryana for the Project work. The matter has been discussed piecewise. Every topic has been Explained in simple way, so that everyone understands this easily Great has been taken To frame all topics.So that No. position regarding to this has been left out. Although every can has been taken while preparing this report but the possibilities of finding and error can’t be ruled out. Suggestion for future improvement will be thankfully acknowledged and Implemented.

DEPARMENT OF MECHANICAL ENGINEERING P.D.M. POLYTECHNIC, SARAI AURANGABAD (BAHADURGARH)

CERTIFICATE This is to certify that this project entitle ‘REGENERATIVE SUSPENSION’ combined work of the following students. LALIT MUDGAL (10020170543) AJAY KUMAR

(10020170557)

AKASH

(10020170559)

ASHISH GUPTA

(10020170560)

VINAY CHHILLAR (10020170562)

It is submitted in partial fulfillment for the award of the DIPLOMA IN MECHANICAL ENGINEERING, STATE BOARD OF TECHNICAL EDUCATION, PANCHKULA. Is a record of the student on work carried and completed by them under my guidance and supervision.

MR.ARJUN NANI Lect. IN MECHANICAL ENGINEERING P.D.M Polytechnic (B.Garh) Signature:

MR.IFTIKHAR ALAM H.O.D (Mech. Deptt.) P.D.M. Polytechnic (B.Garh) Signature:

SH. M.M SHARMA Principal P.D.M. Polytechnic (B.Garh) Signature:

ABSTRACT:The project here is all about a Put Coin and Draw Power System, which In this project we have planned to develop a Put Coin and Draw Power System. In most low-acceleration designs, the force is produced by a moving linear electromagnetic field acting on conductors in the field. Any conductor, be it a loop, a coil or simply a piece of plate metal, that is placed in this field will have eddy currents

induced

in

it

thus

creating

an

opposing

electromagnetic field. The two opposing fields will repel each other, thus forcing the conductor away from the stator and carrying it along in the direction of the moving magnetic field.

Intelli Drive illustration The above illustrates that linear motors are rotary motors with the rotor rolled flat to become a magnet track. Then what was a rotary stator becomes the forcer coil assembly in the linear motor. Typically, the magnet track remains stationary, because the magnet track is greater is size and mass to the forcer assembly. However, in short-stroke applications, their positions could be reversed.

Fully active suspensions use electronic monitoring of vehicle conditions, coupled with the means to impact vehicle suspension and behavior in real time to directly control the motion of the car. Thus, if one uses, for instance, frameless, permanent magnet, three phase, brush-less servo motors in place of traditional shocks, then the system must include extremely complex servo control algorithms and superquick sending and receiving of signals throughout the vehicle, so that the linear motors react instantaneously to driving conditions that change constantly.

Electric throttle valve control and direct fuel injection have been in some cars since the 1990s. Now we are beginning to seeing the advent of more sophisticated electronic control.

The electronic monitoring includes the use of linear encoders that encode postions and convert the information into signals sent througout the network

A hydraulic circuit controls a doubling acting cylinder of a vehicle suspension to provide load leveling and shock absorption functions. A set of solenoid valves control the application of pressurized hydraulic fluid from a supply line to the cylinder and from the cylinder to a tank return line to raise and lower the vehicle for load leveling. The chambers of the cylinder are interconnected by a parallel arrangement of a check valve, orifice and a relief valve. Another parallel arrangement of a check valve, orifice and a relief valve couples the cylinder to an accumulator. These parallel arranged components enable the doubling acting cylinder to function as a passive shock absorber. A lock-out valve is provided in the preferred embodiment a to defeat the shock absorber operation and provide a very stiff suspension.

FIELD OF THE INVENTION The present invention relates to suspension systems for off-road equipment, such as agricultural tractors, and more particularly to such suspension systems that provide hydraulic load leveling. BACKGROUND OF THE INVENTION

Off-road equipment, such as construction and agricultural vehicles, can carry widely varying loads. When a relatively heavy load is applied to the equipment, the vehicle body is forced downward with respect to the axles supporting the wheels on which the vehicle rides. This results in compression of the suspension which can adversely affect the maneuverability of the vehicle. On the other hand, if the suspension is configured for very heavy loads, the vehicle may have an undesirable ride under light load conditions. As a result, many vehicles have automatic load leveling systems which employ one or more hydraulic cylinders between the axle and the frame of the vehicle to ensure that the frame is maintained at the proper height above the axle. When a heavy load is applied to the frame, the drop of the frame is sensed and additional hydraulic fluid is applied to the cylinder to raise the frame the desired distance from the axle. Thereafter, when the load is removed from the vehicle the frame will rise significantly above the axle. When this occurs hydraulic fluid is applied to the opposing chamber of the cylinder to lower the frame with respect to the axle. This type of automatic hydraulic load leveling system ensures that the frame and axle will be at the desired separation regardless of the size of the load applied to the vehicle.

One of the drawbacks of this load leveling system is that the opposite chambers of the double acting cylinder have separate pressure control circuits and require high pump pressure to move the cylinder in both directions. Thus the consumption of fluid from the pump for load leveling may adversely affect the availability of fluid pressure for other functions powered by the tractor. In order to compensate for that power consumption, the pump capacity would have to be increased thus raising the cost of the hydraulic system. Although the piston within the load leveling hydraulic cylinders moves under heavy loads, the piston does not move in response to the relatively small forces due to driving the vehicle over rough terrain. Therefore, the cylinders provide a very stiff the suspension system with negligible shock absorption. This results in a very rough ride, which can be uncomfortably for the operator. SUMMARY OF THE INVENTION The present system provides a hydraulic load leveling system that has a passive mode that provides shock absorption.

A hydraulic circuit controls a suspension of a vehicle having a cylinder and piston for load leveling functionality. The hydraulic circuit has a first node and a second node that is connected to a piston chamber of the cylinder. A first control valve has an inlet, for connection to a supply line for pressurized hydraulic fluid in the vehicle, and has a outlet which is coupled to the first node. A control valve assembly connects the first node to a tank return line of the vehicle. In the preferred embodiment, the control valve assembly comprises a second control valve connected to operate a pilot valve. The second control valve has an inlet for connection to the pump supply line and has an outlet. The pilot operated valve has a control port connected to the outlet of the second control valve, a first port coupled to the first node, and a second port for connection to the tank return line. This group of components provides the load leveling function where the control valves are electrically operated to raise and lower the vehicle. The shock absorption is implemented by an accumulator coupled to the first node and two valve subcircuits. The first subcircuit includes a first check valve coupling the first node

to the second node and permits fluid to flow through the first check valve only in a direction from the first node to the second node. A first subcircuit orifice is connected in parallel with the first check valve, and a first relief valve preferably is connected in parallel with the first check valve and opening when pressure at the second node is a predefined amount greater than pressure at the first node. The second subcircuit includes a second check valve coupling the second node to a port of the rod chamber wherein fluid can flow through the second check valve only in a direction from the second node to the rod chamber. A second subcircuit orifice is connected in parallel with the second check valve, and preferably a second relief valve is connected in parallel with the second check valve and opening when pressure in the rod chamber is a predefined amount greater than pressure at the piston chamber. The second subcircuit meters the flow of hydraulic fluid between the chambers of the cylinder thereby enabling the cylinder to act as a shock absorber. Because a rod is attached to one side of the piston, one of the cylinder chambers has less volume that the other. The extra fluid required for the larger chamber is sent into and out of the

accumulator as needed in response to operation of the first sub circuit. In most low-acceleration designs, the force is produced by a moving linear electromagnetic field acting on conductors in the field. Any conductor, be it a loop, a coil or simply a piece of plate metal, that is placed in this field will have eddy currents induced in it thus creating an opposing electromagnetic field. The two opposing fields will repel each other, thus forcing the conductor away from the stator and carrying it along in the direction of the moving magnetic field.

IntelliDrive illustration The above illustrates that linear motors are rotary motors with the rotor rolled flat to become a magnet track. Then what was a rotary stator becomes the forcer coil assembly in the linear motor. Typically, the magnet track remains stationary, because the magnet track is greater is size and mass to the forcer assembly. However, in short-stroke applications, their positions could be reversed.

Fully active suspensions use electronic monitoring of vehicle conditions, coupled with the means to impact vehicle suspension and behavior in real time to directly control the motion of the car. Thus, if one uses, for instance, frameless, permanent magnet, three phase, brush-less servo motors in place of traditional shocks, then the system must include extremely complex servo control algorithms and superquick sending and receiving of signals throughout the vehicle, so that the linear motors react instantaneously to driving conditions that change constantly.

Electric throttle valve control and direct fuel injection have been in some cars since the 1990s. Now we are beginning to seeing the advent of more sophisticated electronic control.

The electronic monitoring includes the use of linear encoders that encode postions and convert the information into signals sent througout the network

Shock absorber Nomenclature •

The device's name in common parlance (among the general public and auto mechanics) is shock absorber or simply shock.

•

Technical names include damper and dashpot. (They are a subset of dashpots and thus are sometimes called "dashpots", just as cars are a subset of vehicles and are sometimes called "vehicles".)

•

For a while during the 20th century in the U.S., the Houdaille brand (pronounced WHO-dye) was in some places so well known that the name "Houdaille" served as a genericized trademark for the category of product.[1] This is no longer the case; the brand is gone and so is the genericized usage.

Description

Pneumatic and hydraulic shock absorbers commonly take the form of a cylinder with a sliding piston inside. The cylinder is filled with a fluid (such as hydraulic fluid) or air. This fluid-filled piston/cylinder combination is a dashpot.

Explanation The shock absorber's duty is to absorb or dissipate energy. One design consideration, when designing or choosing a shock absorber, is where that energy will go. In most dashpots, energy is converted to heat inside the viscous fluid. In hydraulic cylinders, the hydraulic fluid will heat up, while in air cylinders, the hot air is usually exhausted to the atmosphere. In other types of dashpots, such as electromagnetic types, the dissipated energy can be stored and used later. In general terms, shock absorbers help cushion vehicles on uneven roads.

Applications Shock absorbers are an important part of automobile and motorcycle suspensions, aircraft landing gear, and the supports for many industrial machines. Large shock absorbers have also been used in structural engineering to reduce the susceptibility of structures to earthquake damage and resonance. A transverse mounted shock absorber, called a yaw damper, helps keep railcars from swaying excessively from side to side and are important in passenger railroads, commuter rail and rapid

transit systems because they prevent railcars from damaging station platforms. The success of passive damping technologies in suppressing vibration amplitudes could be ascertained with the fact that it has a market size of around $ 4.5 billion.

Rear shock absorber and spring of a BMW R75/5 motorcycle Vehicle suspension

In a vehicle, it reduces the effect of traveling over rough ground, leading to improved ride quality, and increase in comfort due to substantially reduced amplitude of disturbances. Without shock absorbers, the vehicle would have a bouncing ride, as energy is stored in the spring and then released to the vehicle, possibly exceeding the allowed range of suspension movement. Control of excessive suspension movement without shock absorption requires stiffer (higher rate) springs, which would in turn give a harsh ride. Shock absorbers allow the use of soft (lower rate) springs while controlling the rate of suspension movement in response to bumps. They also, along with hysteresis in the tire itself, damp the motion of the unsprung weight up and down on the springiness of the tire. Since the tire is not as soft as the springs, effective wheel bounce damping may require stiffer shocks than would be ideal for the vehicle motion alone.

Spring-based shock absorbers commonly use coil springs or leaf springs, though torsion bars can be used in torsional shocks as well. Ideal springs alone, however, are not shock absorbers as springs only store and do not dissipate or absorb energy. Vehicles typically employ both springs or torsion bars as well as hydraulic shock absorbers. In this combination, "shock absorber" is reserved specifically for the hydraulic piston that absorbs and dissipates vibration. Structures

Applied to a structure such as a building or bridge it may be part of a seismic retrofit or as part of new, earthquake resistant construction. In this application it allows yet restrains motion and absorbs resonant energy, which can cause excessive motion and eventual structural failure. Electrical Generation

Modern hybrid cars may eventually be able to generate useful energy from the displacement of the fluid in a shock absorber

Types of shock absorbers There are several commonly-used approaches to shock absorption: •

Hysteresis of structural material, for example the compression of rubber disks, stretching of rubber bands and cords, bending of steel springs, or twisting of torsion bars. Hysteresis is the tendency for

otherwise elastic materials to rebound with less force than was required to deform them. Simple vehicles with no separate shock absorbers are damped, to some extent, by the hysteresis of their springs and frames. •

Dry friction as used in wheel brakes, by using disks (classically made of leather) at the pivot of a lever, with friction forced by springs. Used in early automobiles such as the Ford Model T, up through some British cars of the 1940s. Although now considered obsolete, an advantage of this system is its mechanical simplicity; the degree of damping can be easily adjusted by tightening or loosening the screw clamping the disks, and it can be easily rebuilt with simple hand tools. A disadvantage is that the damping force tends not to increase with the speed of the vertical motion.

•

Solid state, tapered chain shock absorbers, using one or more tapered, axial alignment(s) of granular spheres, typically made of metals such as nitinol, in a casing

•

Fluid friction, for example the flow of fluid through a narrow orifice (hydraulics), constitute the vast majority of automotive shock absorbers. An advantage of this type is that using special internal valving the absorber may be made relatively soft to compression (allowing a soft response to a bump) and relatively stiff to extension, controlling "rebound", which is the vehicle response to energy

stored in the springs; similarly, a series of valves controlled by springs can change the degree of stiffness according to the velocity of the impact or rebound. Specialized shock absorbers for racing purposes may allow the front end of a dragster to rise with minimal resistance under acceleration, then strongly resist letting it settle, thereby maintaining a desirable rearward weight distribution for enhanced traction. Some shock absorbers allow tuning of the ride via control of the valve by a manual adjustment provided at the shock absorber. In more expensive vehicles the valves may be remotely adjustable, offering the driver control of the ride at will while the vehicle is operated. The ultimate control is provided by dynamic valve control via computer in response to sensors, giving both a smooth ride and a firm suspension when needed. Many shock absorbers contain compressed nitrogen, to reduce the tendency for the oil to foam under heavy use. Foaming temporarily reduces the damping ability of the unit. In very heavy duty units used for racing and/or off-road use, there may even be a secondary cylinder connected to the shock absorber to act as a reservoir for the oil and pressurized gas. Another variation is the Magneto rheological damper which changes its fluid characteristics through an electromagnet. •

Compression of a gas, for example pneumatic shock absorbers, which can act like springs as the air pressure is building to resist the

force on it. Once the air pressure reaches the necessary maximum, air dashpots will act like hydraulic dashpots. In aircraft landing gear air dashpots may be combined with hydraulic damping to reduce bounce. Such struts are called oleo struts (combining oil and air) [3]. •

Magnetic effects. Eddy current dampers are dashpots that are constructed out of a large magnet inside of a non-magnetic, electrically conductive tube.

•

Inertial resistance to acceleration, for example prior to 1966 [4] the Citroën 2CV had shock absorbers that damp wheel bounce with no external moving parts. These consisted of a spring-mounted 3.5 kg (7.75 lb) iron weight inside a vertical cylinder [5] and are similar to, yet much smaller than versions of the tuned mass dampers used on tall buildings

•

Composite hydropneumatic devices which combine in a single device spring action, shock absorption, and often also ride-height control, as in some models of the Citroën automobile.

•

Conventional shock absorbers combined with composite pneumatic springs which allow ride height adjustment or even ride height control, seen in some large trucks and luxury sedans such as certain Lincoln and most Land Rover automobiles. Ride height control is especially desirable in highway vehicles intended for

occasional rough road use, as a means of improving handling and reducing aerodynamic drag by lowering the vehicle when operating on improved high speed roads. •

The effect of a shock absorber at high (sound) frequencies is usually limited by using a compressible gas as the working fluid and/or mounting it with rubber bushings.

L.E.D. (LIGHT EMITTING DIODE) Light emitting diode (LED ) is basically a P-N junction semiconductor diode particularly designed to emit visible light. There are infra-red emitting LEDs which emit invisible light. The LEDs are now available in many colour red, green and yellow,. A normal LED emit at 2.4V and consumes MA of current. The LEDs are made in the form of flat tiny P-N junction enclosed enclosed in a semi-spherical dome made up of clear colured epoxy resin. The dome of a LED acts as a lens and diffuser of light. The diameter of the base is less than a quarter of an inch. The actual diameter varies somewhat with different makes. The common circuit symbols for the LED are shown in fig. 1. It is similar to the conventional rectifier diode symbol with two arrows pointing out. There are two leads- one for anode and the other for cathode. LEDs often have leads of dissimilar length and the shorter one is the cathode. This is not strictly adhered to by all manufacturers. Sometimes the cathode side has a

flat base. If there is doubt, the polarity of the diode should be identified. A simple bench method is to use the ohmmeter incorporating 3-volt cells for ohmmeter function. When connected with the ohmmeter: one way there will be no deflection and when connected the other way round there will be a large deflection of a pointer. When this occurs the anode lead is connected to the negative of test lead and cathode to the positive test lead of the ohmmeter. (ii)

External resistor. Unless an LED is of the

‘constant-current type’ (incorporating an integrated circuit regulator—see Unit 20.4—for use on a 2 to 18 V d.c. or a. c. supply), it must have an external resistor R connected in series to limit the forward current which, typically, may be 10 mA (0.01 A). Taking the voltage drop (Vf) across a conducting LED to be about 107 V, R can be calculated approximately from: (supply voltage – 1.7) V R = ——————————————————

0.01A For example, on a 5 V supply, R = 3.3/0.01 = 330 Ohm.

(i) Action. An LED consists of a junction diode made form the semiconducting compound gallium arsenide phosphide. It emits light when forward biased, the colour depending on the composition and impurity content of the compound. At present red, yellow and green LEDs are available. When a p-n junction diode is forward biased, electrons move across the junction from the n-type side to the p-type side where they recombine with holes near the junction. The same occurs with holes going across the junction from the p-type side. Every recombination results in the release of a certain amount of

energy,

causing,

in

most

semiconductors,

a

temperature rise. In gallium arsenide phosphide some of the energy is emitted as light which gets out of the LED because the junction is formed very close to the surface

of the material. An LED does not light when reverse biased and if the bias is 5 V or more it may be damaged.

(ii)

External resistor. Unless an LED is of the

‘constant-current type’ (incorporating an integrated circuit regulator—see Unit 20.4—for use on a 2 to 18 V d.c. or a. c. supply), it must have an external resistor R connected in series to limit the forward current which, typically, may be 10 mA (0.01 A). Taking the voltage drop (Vf) across a conducting LED to be about 107 V, R can be calculated approximately from: (supply voltage – 1.7) V

R = —————————————————— 0.01A For example, on a 5 V supply, R = 3.3/0.01 = 330 Ohm. (iii) Decimal display. Many electronic calculators, clocks, cash registers and measuring instruments have seven-segment red or green LED displays as numerical indicators (Fig. 9.18(a)). Each segment is an LED and depending on which segments are energized, the display lights up the numbers 0 to 9 as in Fig. 9.18(b). Such displays are usually designed to work on a 5 V supply. Each segment needs a separate current-limiting resistor and all the cathodes (or anodes) are joined together to form a common connection

Generating Electricity with Stepper Motors All sorts of scrapped and secondhand devices can be used to generate your own electricity. Car alternators are an obvious one if you want to charge 12 Volt batteries. Small permanent magnet motors such as radiator fan motors or cassette recorder motors are easy to use as they produce DC power directly without

any

external

circuits

like

rectifiers

or

control

boxes.

There is another type of electric motor worth considering - the small stepper motors used in old computer printers. They are quite small and aren't suitable for producing more than a few Watts, but there are good reasons for looking at them. For a start, the lunatic speed at which computer equipment goes obsolete +means there are enormous numbers of them available free. Unlike small DC motors, steppers will generate power at very low rotation rates; typically only about 200 rpm for a good output which is ten or fifteen times slower than the rate for a DC motor. Small scale generators to run things like computer games or flashlights can be made without mechanical complications like gearing. Because of their small size they're obviously not suitable for charging large batteries. Better applications would be pocket sized generators to convert things like Walkmans and MP3 players to wind-up power, saving the waste and pollution of chemical batteries. Another possibility is small wind generators as the low rpm needed means a propeller could be mounted directly on the motor shaft. (Actual gears in a wind generator are generally a disaster - the whining noise is amplified by the blades and spreads over a wide area because of the height). The present generation of printer motors are admittedly not large, and in fact are getting smaller as the old daisywheel and dot matrix printers are replaced by inkjets and smaller lasers. It is definitely worth experimenting with them

though, as it is likely that the next generation of domestic appliances will be heavily computerised, and so full of nice big steppers. Anyone who has acquired experience on the small ones will be able to make these into some really nice generators.

Selecting

Suitable

Motors

Old Dot Matrix computer printers (the larger and older the better) contain at least two steppers. Usually one drives the roller and another moves the print head back and forth. Daisywheel printers will also have one to turn the daisywheel which can be a bit inaccessible but worth the effort. Tiny steppers were also sometimes used to wind the ribbon and in colour printers another minute one moved a striped ribbon up and down. Disc drives tend to be a bit disappointing - often the motors are built into the drive hub and contain some electronics so you can't get easy access to the coil connections. Really old 5.25" floppy drives contain a nice motor used to move the reading head back and forth - it's a lot more useful than the one for turning the disc which was sometimes a DC motor on older ones and tangled into the circuit board on later models. Very old hard drives (on 286 or 386 computers and less than 100M) use a small stepper to move the head array. Modern hard drives use an analogue galvanometer instead; it contains a pair of amazingly strong magnets mind your fingers if you extract them! Physically large motors like the single ones which drive laser printers are obviously more powerful than small ones; anything less than an inch in diameter is probably only suitable for running a few LED's. They're OK for educational purposes or making illuminated things for playing with at chill-outs. (See the page on making Hub Disc Twirly Things)

Steppers come with different resolutions. Virtually all steppers are either 1.8° or 7.5° per step; (200 steps or 48 steps per revolution) the difference can be felt easily if you turn the spindle by hand. The 1.8° ones are obviously better for generating at really low revs, but also 'top out' lower. The coils in steppers have a relatively large inductance, and beyond a certain speed the output frequency gets so high that the impedance of the coils starts to become significant and limits the current. When making a stepper based generator, you need to keep the motor speed to around a couple of hundred revs per minute - something like the

normal

speed

of

a

bicycle

wheel.

Apart from printers, plenty of other things contain steppers. Scanners, shredders, faxes and photocopiers are also worth checking out. Be careful with things like copiers and laser printers not to get toner all over your workshop, especially if it doubles as your living room! Don't vacuum clean toner as the particles are so small they'll go through the bag into the air. Wash it off with water or clean it up with a damp cloth. Really large steppers are found in automated industrial equipment and the large tape drives used with old mainframe computers which you might still find at auctions. The next generation of highly automated washing machines and dishwashers, household robots etc. will contain some nice big steppers, and it won't be too long before they are superseded and start to turn up at the rubbish tips and car boot sales. There's already a nice example of this in New Zealand where Fisher and Paykel have been selling stepper-driven washing machines for some years, and scrapped ones have been made into neat hydro generators by a local company appropriately called Ecoinnovation. The 20cm diameter motor in the Smart Drive washing machine is an example of the nice big motors just around the corner.

What's

Inside

a

Stepper

Motor

In the early days of DIY renewable energy, it was popular to make small wind generators out of bicycle wheels containing Sturmey Archer Dynohubs. Now almost a museum piece, they were the predecessor of the bottle shaped rim 'dynamo'. (I don't know what was the matter with the people who named these things - they were both ALTERNATORS producing AC; the term dynamo is better used for generators incorporating a synchronised contact breaker turning the output into DC. Maybe it was something to do with marketing) Anyway, the Dynohub was a small multi-pole alternator in the hub of either the front or rear wheel with an internal resistance of 6 Ohms and capable of generating 6 Volts when turned at 60 rpm. The performance wasn't that good - the internal resistance means that if you took a current of half an Amp from it the voltage would have dropped to only 3 Volts. In spite of this, many people made wind generators out of them by sticking blades in the spokes, rectifying the AC with a bridge rectifier and putting them on the roof of their caravan or bus to trickle charge batteries. Stepper motors are also a small multi-pole alternator, but being more modern they have four phases while the old Dynohub had only one. In use, the computer puts a pulse of current into each phase coil in turn, moving the shaft on one step. As with a DC permanent magnet motor, turning the motor's shaft makes it work backwards, causing pulses of current to come out of the windings. However, the current is AC, going plus as a magnet pole approaches a coil and then minus as it goes away again. Usually there are four phases at 90 degree intervals so when one comes down to zero, the next one has reached maximum. This is a benefit as it means the output can be rectified to produce much smoother DC with hardly any gaps, but it means they have a scarily large number of wires coming out. Luckily it's quite easy to figure out which way

around they are using a resistance meter (preferably digital), and getting them the wrong way around won't do any damage. The most common type of stepper has six wires coming out. (There are also five, four and eight wire versions; I'll come to those later - they are easy to understand once you've sussed the six wire one) The six wire stepper is actually two motors on one shaft, so the six wires can immediately be separated into two groups of three. Each group will have some connection to each other, but no connection to any of the other group. In each group, one wire is the common and the other two are the opposite ends of a winding which will give out oppositely phased AC. In terms of resistance, the reading from the common to either end will be half the reading across the two ends. Having found the common on one set, you can use the same process to find the common in the other one. All four windings will

have

almost

exactly

the

same

resistance.

The majority of steppers are six wire, but there are other varieties. Five wire ones are easy; the two commons on the six wire have already been connected together for you which makes things easier. Eight wire ones are just like a six wire but with all the windings separate, and four wire ones are half of an eight wire one (or half a six wire one with the two windings separate). There's more than one way to wire up the stepper to get a DC output. Unlike the dynohub, you can't wire it up to a bulb and run it off AC as it's got four separate phases and connecting any two directly will cause a short and stall it. On the other hand, if you're bursting to generate some power, connecting a small light bulb, say 6V 100 mA from ONE of the live phases to the common and turning the spindle with your fingers should get a result. It's quite a good way to find out if you're going to get a useful amount of power out of it, but you'll only get a quarter of the possible power that way. The simplest way to wire it up is to link the two commons to the minus terminal and then connect

each of the four live phases through a small diode to the plus one as shown. Here's what it looks like. The four lives will each go positive (and then negative) one after the other like the cylinders of a car firing and the diodes collect together all the positive pulses and feed them out. Because of the overlapping phases, the rectified AC never goes down to zero like it would from a normal bridge rectifier. Putting the bulb across the output should give a stronger result than before and a DC voltmeter will show that the output voltage is more or less proportional to the rotation speed. This is normal for a permanent magnet alternator and you will need to use a regulator limit the voltage. Because the stepper is acting as an AC generator, it doesn't matter which way you turn it so designs in which it is turned alternately forward and back by a treadle or foot pedal are possible. If the motor you've got is rated at 5V but you want to generate enough voltage to charge a 12V battery, you can often get away with just spinning it a bit faster. If that doesn't work, you may be better off using this voltage doubler circuit with two bridge rectifiers. I've built a pedal generator which can be switched between the two configurations, and there's less difference between them than you'd expect. The double voltage configuration gives a good voltage at lower speeds but has less current capability as there's twice the winding resistance. The normal four diode setup gives more current when driven faster, but not twice as much as the AC impedance of the windings has an effect due to

the

•

higher

frequency.