How to Make a Robot Walk

7/28/2019 How to Make a Robot Walk

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How to make a Robot WalkThis information has been adapted from an excellent site byA Miller.

IntroductionThis section describes how to make a walking robot. The simplest robots are called BEAM ROBOTS. Andthe simplest walkers are called BEAM WALKERS. They consist of just enough circuitry and mechanics tocarry out the intended function, and in this case it is the operation of walking.The simplest circuit to get a robot to carry out the walking function has been designed and patented byone of the earliest developers of Robots, Mark W. Tilden. He gave the name MicroCore to the type ofcircuit that drives these basic designs.The concept of the MicroCore is pretty clever. Using just a handful of components, you can build thecontrol circuitry for a walking robot that senses its environment and adjusts its gait accordingly. The cleverpart is the circuit is so simple!

A MicroCore consists of a capacitor, a gate, and a resistor. This is called a 'neuron.' Each neuron has aninput and an output. The components are connected so that the capacitor and resistor form a delaycircuit. If we make the input HIGH, the output take a short time to react. Mouse-over the animation belowto see how the Neuron circuit works.

The gate is actually an inverter and it also has the ability to strengthen the pulse. If we connect the outputof one neuron to the input of another and take the output of the second to the input of the first we have acomplete loop and we have created a BiCore.

A circuit can consist of as many gates (inverters) as you want, hooked-up nose to tail. Every 'neuron' of aMicroCore consists of a capacitor, a gate, and a resistor. A circuit containing a number of 'neurons' willproduce amazing things. This is what this discussion is all about.If you have a BiCore controlling two wheels, and want the robot to turn right, you have to make the motoron the left run for longer - simply change the resistance for that neuron. If you incorporate 2 photodiodesinto the MicroCore, you can make a robot always zigzag its way towards light! This is really impressiveand demonstrates how simple "complex behaviour" really is. In this discussion we are going to explainthe operation of the . . .

MicroCore

The MicroCore circuit can be likened to a nervous circuit in that it gives life and realism to a roboticshape. The MicroCore circuit is a basic circuit used in the majority of BEAM Biomorphic walkers.

To get an idea of the basics of this topic, the following paper was prepared by Mark Tilden:
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Biomorphic Robotics andNervous Net Research:

A New Machine Control Paradigm

Mark W. Tilden,

Biophysics Division,Los Alamos National Labs

Submitted for publication to the EANN '95 Conference Proceedings "Special Trackon Robotics."Nervous Net (Nv) technology is a non-linear analog control system that solves real timecontrol problems normally quite difficult to handle with digital methods. Nervous nets are toNeural nets the same way peripheral spinal systems are to the brain. This work hasconcentrated on the development of Nv based robot mechanisms with electronicapproximations of biologic autonomic and somatic systems. It has been demonstrated thatthese systems, when fed back onto themselves rather than through a computer-basedpattern generator, can successfully mimic many of the attributes normally attributed tolower biological organisms. Using Nv nets, highly successful legged robot mechanisms

have been demonstrated which can negotiate terrains of inordinate difficulty for wheeled ortracked machines. That non-linear systems can provide this degree of control is not sosurprising as the part counts for successful Nv designs.

A fully adept insect-walker, for example, can be fully controlled and operated with as littleas 12 standard transistor elements.Since the start of research in the winter of 1994, development of this technology hasadvanced to solving currently difficult sensory and cognitive problems. It is hoped in thecoming years Nv systems may do for robot vision (amongst other disciplines) what hasbeen done for autonomous robot vehicles, namely the reduction of currently complexsystems down to an inexpensive but robust minimum. Further efforts are also being madeto apply this control strategy to the expanding nano-technology field. At the nanometerscale Nv's may prove more feasible than nano-computers for control of self-assemblingmicro structures. For now, however, Nv research concentrates on problems of scale

invariance, proving by example (or exhaustion) this control system can work at all scales,types, and styles of robotic application.The Nv control method could be adapted to most types of machine control, but it has beenapplied to autonomous robots because of the difficulty conventional control systems havesolving the seemingly simple task of negotiating undefined complex environments.The 80 or so "biomorphic" robots (from the terms BIOlogy and MORPHology, and the Latinfor "living" and "form") built so far are not "workers" in the traditional sense, but "survivors,"in that they fight to solve the immediate problems of existence rather than proceduralcondition (i.e. they do not follow the rules of an internal program that mimics the externalworld, but the world itself).Nv control architectures focus on adaptive survival rather than the performance of specifictasks. Once survivability is under control, goals can be superimposed and the machineused as a platform to carry sensors and conventional electronic intelligence. It is believedthat these machines, although now in an early stage of development, can within a fewyears be brought to the point that they can serve as inexpensive, robust, and versatilecarriers for a variety of instruments.

A vast number of applications would then be possible, including the location and possibleclearing of land mines from civilian areas, security, maintenance, medical and prostheticapplications (a cost-effective "walking wheelchair" for example), and even cars with on-board "survival" instincts to save themselves and their passengers, from damagingaccidents. Though the Nv based legged devices built so far cannot go everywhere, theycan certainly go places not currently accessible to wheeled or tracked vehicles of similarscale. It seems that for handling undefined environments, biomorphic designs are a very


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efficient and cost-effective approach.Initially it was thought these devices avoided the problems of an internal worldrepresentation by using a reactive or behaviour-based technique. Recent work has shownhowever that Nv biomorphs instead take a chaotic map of their surroundings onto theirprocess control hierarchy (that is, they dynamically and efficiently adapt to the fractalcomplexity of their surroundings). This is due to the analog-electronic nature of the devices,

the adaptive hardware of their structure, and the topological orientation of theirinterconnections.The defining characteristic of this adaptation is continuously updated by the immediatefractal complexity of the environment. These devices are "soft" designs, in that theenvironmental dimension must be absorbed, modified, and acted on for the devices tomake successful headway through a complex world. These devices do not use "feedback"in the standard sense, but rather "implex", as the driving forces are augmented byperceived load rather than by a separate regulating path. The result is highly compliant,animal-like machine motions that "negotiate" rather than "bully" their way throughenvironments, resulting in minimal damage to both world and robot.We talk about these devices in the general sense because the precepts of their existenceand subsequent design are based upon environmental macros, such as fluidity, turgidity,gravity, scale, materials strength, and many other factors. The power of biomorphic designsis that this information is used as the defining principles to shape appropriate survivor(s) fora particular environment. The machines that emerge are vastly different from anyconventional robotic forms. We suspect, at least from the experimental evidence, that thistechnique embodies a new type of non-linear control paradigm, and at least an entirely newengineering discipline for the matching of competent machines to complex environments.Here, once the problems of existence are ratified, the devices can do unsupervised, longterm work without human intervention (some devices have been in continuous operation forover 5 years).The potential for this control paradigm is vast, but it is far from linear, and requiresintegrated design attempts to pull a competent ability from the Nv nets. To this end, the useof this technology to "evolve" machines from a lesser to a higher operational state hasresulted in not only a wide spectrum of devices, but even completely different "species" ofcreatures, all evolved from a primal "genotype;" the single "cell" creature known as Turbot1.0.

A further advantage is the speed at which this evolution has occurred, indicating that real-world Lamarckian evolution may match the success of many computer models yet seen.The diversity of this technique offers potential solutions to two main research fields, macroand micro robotics, and experimental work has been done to produce adept prototypes forboth.The conclusions are that there may be some universal chaos-bounded concepts that bindsurvivor oriented designs, allowing for the creation and optimization of devices that can dowork in any environment, under many situations, using chemically inert, and therebyrelatively safe, control techniques (the idea of seeding a wheat field with pest-fightingsilicon biomorphs to produce high yield, insecticide-free foodstuffs is an attractiveexample).Considering that biomorphs may last long enough to replace most forms of long-termdamaging chemicals (i.e. pesticides, bleaches, medicines) the potential for the field really

opens up. Deployed artificial chemicals perform a task in their immediate area ofconcentration, and then disperse into the environment where, after a time, they cannot beabsorbed adequately. Biomorph machines, made from biodegradable silicon and traceelements, can be made gregarious so they do not of their own volition disperse, and can beabsolutely controlled by conventional methods. Whether at micro or macro scales, thesedesigns are not just capable, but competent. Furthermore, as they are self "programming"and non-reproductive, their behaviour is both contained and predictable.Nv biomorphs are something new with a demonstrable potential.Future work will concentrate on how this technology could fill in the cracks between science


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fiction and reality by finding out what is feasible now, and how to logically proceed tomarketable, capable machines. In the coming years, it is hoped to be possible todemonstrate real machines to assess feasibility for macro and nano robotic applications.Expansions of the fields of robo-biology, robo-morphology, and artificial ecologies will bestudied and published, along with extensions of this field from self-repairing processors,new computational paradigms, and even nano-robotic surgeons-in-a-capsule. Biomorphics

is new, but it is slowly gaining the maturity and acceptance necessary to become a validwork tool.

The basic circuit for a MicroCore consists of a capacitor, a gate, and a resistor. The arrangement of thecomponents is shown in the circuit below. This is called a NEURON.

Mouseover the NEURON circuit below to see how it works. The secret to the operation is this: Thecapacitorcharges and the circuit changes state a short time later. The capacitor and resistor form anarrangement called a DELAY CIRCUIT. The LED has been added to the output of the gate so we cansee how and when the circuit operates.

We are interested in the operation of the output AFTER the input has changed. The circuit is just like aspinal cord without anything attached. It is called an Nv circuit. You can't drive motors yet but until you

understand the basic states of the MicroCore circuit, the operation of motors will make even less sensethan the LEDs.Two Neuron circuits will work when connected head-to-tail and with the output of the second connectedto the input of the first:


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The operation of the circuit is shown in this animation:

You will notice the capacitor charges via the 1M resistor as the input of the gate is a very high impedance.When the output of a gate goes low, the capacitor is discharged via a diode on the input line of the gate.

This diode is a Schottky diode and is designed to prevent the input of the gate going below 0v. Thechange from one state to the other is almost instantaneous and only one LED is illuminated at a time. Wehave slowed down the animation to show the gates in action and the two LEDs appear to be off for aninstant. This does not actually occur.If we extend this circuit to the 6 inverters of a hex Schmitt Trigger IC, and take the output of the last Nvcircuit to the input of the first, we get a circulating pattern. The circuit will always start-up and eachalternate LED will be illuminated.


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When the circuit is connected to a Robot, the following effect will be produced:

This is known as the Saturated State. This means all Nv's are firing at Max rate. There is a Maximum of3 Processes. A process is defined as one LED/Nv ON at any one time. Note: there are never twoilluminated LEDs side-by-side at the same time. This is the Fermei exclusion feature of the MicroCore andan attribute shared by biological Nv nets.Saturation is the natural Power-on state. It is the crazy-go-nuts state for a Nv Net - like a bug that has hadtoo much coffee. Saturation will occur when the MicroCore encounters a disruption in main power orwhen too much data is received from sensors or Nu/Nv nets. Fortunately it's easy to get a more stableuseful state.

Adding a Process Neutralization Circuit (PNC). Wire up a switch to short out the input bias resistor likethis.....

Closing the switch destroys any re-circulating pulses. Hold it long enough and all processes aredestroyed. This is called the Null State, Off State. This is a Nv net at rest.

Two Process State. By holding the switch closed for approx 2 seconds you should be able toachieve this....

If all values are even, and no glitches or noise is received from the motor, the processes should fall 180degrees out of phase with each other. This is seen when they appear to be running side by side with eachother. Two processes are like Parkinson's disease. The Nv's are trying to act against each other and ifthey fall into this mode, you have "lock up." This state can be useful in some cases but in the case of asimple walker it's not much use.

Single Process State. By Holding down the PNC switch for another 3 seconds or so you should getthis. This is the stable One Process State that is the basis of most of the Nv walkers.


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Adding a Process Initialise Circuit (PIN). By wiring up another switch from an input to Vcc (+ve)you can introduce processes to the MicroCore. By using the PNC and PIN switches you should be able to

cycle through all the MicroCore's usable states.

Now build the circuit and play with it. In this discussion we are going to concentrate on a two motorfour leg walkerwhich although it is not the most flexible design, it is the easiest to build and hasproven its reliability and capability in 35 existing machines.

THE MOTORSThis is probably the biggest consideration in a MicroCore Walker. The level of success you have with yourwalker is directly related to the type of motor used. The MicroCore itself gets an implicit feedback from themotors, this is what gives it the adaptability.

What to look for in a Motor....EFFICIENCY:This is REALLY important both from a power consumption standpoint (more-efficientmotors require a smaller battery or main-storage electrolytic). High efficiency motors give you a betterchance of success. You should look for a motor with at least a 35% efficiency rating, good cassettemotors and pager motors typically fall into this range, Mabuchi hobby motors are way off (typically10%).Much higher efficiencies are possible (up to 88%) but this is usually found in expensive medical grademotors like "Escap" and "MicroMo." Keep your eyes open when perusing the surplus catalogues, thesesometimes go on sale for as little as $5.SIZE:For the most part, smaller is better but it's not as important as efficiency. As well, you may want toconsider your own skill level. In the beginning, don't try to work with things that are really small. Makesure you have extra motors. They come in handy.

THE GEARSYou cant build a walker without them. A motor alone doesn't put out enough torque and usually runs toofast.What to look for in a gearbox...Efficiency/Size/Numbers: For all the same reasons as above.Compliance: This is really critical. You should be able to grasp the output shaft with a pair of pliers andturn it to have the gears spin the motor. If you can't make the motor spin, then you have a gear train thatis too inefficient (most likely) or too high a ratio. Worm drives are also OUT, they only go one way (motorto gear and not gear to motor) and they tend to choke under high loads.Output RPM: The ideal is about 30 RPM @ 5V. Higher RPM means you probably won't have enough


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torque (and if you do, the robot will jump around so fast it's hard to figure out what it's doing). A lowerRPM means the machine may be moving too slow to be of use. A high ratio may mean the legs will bendunder the torque.

INTERFACING MOTOR AND GEARSI strongly suggest you find a factory motor/gearbox combination. If you have to build your own then bear a

couple of things in mind......Direct gear contact:belt drives, friction drives, flexible shafts etc all have big problems as far asefficiency and compliance are concerned.

Keep everything clean:Glue, solder flux and metal fillings are deadly enemies to gearboxes.MATERIALSSolder is our friend, only use materials that can be easily soldered. This will make it easy to build a frame.Welding wire or filler rod is the best. Copper clad carbon steel rod 1/6" to 3/32"diameter is cheap andavailable at any welding supply place. Any nice shinny option is High Nickel rod used for TIG welding castiron but it's MUCH more expensive. Brass tube and wire found at most hobby shops is good too. Isuggest a solder with an organic/water soluble flux, "Hydro X" by Multicore is my favourite.

BASIC FRAME LAYOUTThe diagram below shows the basic layout. You need to keep the motors and output shafts lined up frontto back and the front motor should be tilted at 30 degrees. This means the front motor will supply lift andpush but we'll discuss that more later. You should mount the motors far enough apart to fit all yourelectronics including batteries (usually about 4").

More on . . How to make a Robot WalkThis information has been adapted from an excellent site byA Miller.

ADDING THE LEGS
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Leg shape and configuration will vary greatly between machines. A few things to bear in mind are:Contact point:This is the most important aspect of leg design. The shape of the leg is less important than where ittouches the ground. By placing your robot on a sheet of graph paper as shown above you can getsymmetrical contact points.Width:Try to make the legs at least 2/3 the length of your robot, this of course will depend on the availabletorque. It has also been shown that making the back legs slightly wider than the front helps stability.Connection:Make sure your legs are connected with something structurally sound, krazy glue doesnt cut it. If youcan't solder the legs directly to the output shaft then try and find some sort of locking ring or set- screwthat will fit. Look for brass gears or pulleys that have their own set-screw and then you can solder the legsdirectly to the brass.Angle:By angling the legs slightly forward they will have the ability to "ratchet" over obstacles.Your legs will change shape several times before you are finished so it's best to make a set of "test" legsthat are easily recoupable before you use the good materials. 12 or 14 gauge household copper wiremakes effective re-configurable "Gumby" legs.MAKING IT WALK:We are going to make a minor detour here (you may have noticed we don't have the MicroCoreconnected to anything yet).

MicroCore/Leg Interfacing


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This section covers connecting the Nv net to the Muscles - the motors. The following is a Low Currentsolution. High current motors and drives present a whole new set of problems that, trust me, you don'twant to deal with right now. Besides, the MicroCore does its best when driving through a low gain system.

Rethinking the Nv net:By now you should have familiarized yourself with the basic 6 Nv MicroCore circuit. But a few calculations

will show that with two motors and two directions, 4 Nv's would seem appropriate. For basic walkingfunctionally 4 of the 6 available Nv's in a 74C14 chip (40106) are needed in a two motor walker (although6 makes for a whole new set of behaviours), so rebuild the basic circuit to get this....

Have no fear, the other two Nv's will be useful later...

The ALS245 Driver:The 74ALS245 is an Octal bus transceiver designed for data transmission. We are going to use it to driveMotors. If you've chosen your Motor/Gear combination properly, this won't be a problem. If you look up a

TTL data book you'll see the '245 has 8 bi-directional non-inverting amplifiers each capable of driving50mA, a direction pin (Dir) for selecting the direction of the signal through the chip and an enable pin (E).If you tie the Dir pin to +ve and the E pin to -ve, you can essentially think of the chip as 8 active driversgoing from left to right like this graphic.... A data book will show you more but for the purposes of drivingyour legs this'll do......

The ALS version has been found to be the best for current, feedback etc...CMOS such as HCT, HC, C will work but they loose a little in the feedback. They do consume less powerso for solar applications they are the better choice.....If you are building a battery walker use ALS where-ever you can and contrary to what some people willtell you, they are still available.


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Ganging up for CurrentIf you've tested your motors you will probably find they need a little more than 50mA to do anythinguseful. And with a few calculations, you'll see there are 2 drivers available for each Nv, so gang themtogether like this....

The result is four drives capable of 100mA each. Good, but not great.... So if you need more, double youroutput by stacking a few chips like this...

The connectionSo now you have a 4 Nv loop set up and a 4 channel driver set up. The next step is to glue them togetherand add the motors. Like this . . .

Power UpPower on the whole thing, stabilize the loop (use the PIN and PNC buttons to get a "One Process"), andwatch this animation:


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If things aren't right, change the polarity of one of the motors and it should work.

Tuning for a walking Gate...Convergence, or the subtle art of falling over.....

This is where we try and make your pile of wire and batteries walk. This is kind of the counter-intuitive partof the whole thing. Most people are of the misunderstanding that in order for a Robot to remain on its feet

it has to be balanced at all times. This is the train of thought that leads to so many 6 leg walkers; three

legs is a stable platform from which to move your other three. Although this is in some cases successful, it

makes for a robot that doesn't adapt well. Walking should be thought of as controlled falling. Static

Balance is not the key, rather it's Dynamic Imbalance.....

Methods of adjustment...

There are several ways to make your walker stumble around. All of which are in some way related to the

center of gravity of your bug. None is more important than the others nor is it possible to make it walk

without adjusting all of them.

Nv Time value:You'll note that in its raw state the Nv is just an RC time value (but remember it is not

a constant, it adjusts itself according to load). So at a base level you can change the Duration of Rotation

of each of the motors. One Meg Ohm is the default value, it is just a good starting point. You can adjust

the values as high as 20 Meg Ohm or as low as a few k Ohms. By changing the duration of the leg's

movement you change where it stops. If you think of the Walker as a first class lever (there are three

classes of levels and the first class is the see-saw class) and the feet as fulcrums, you'll see that the

position of the leg when it stops is crucial to which direction it tips.

Weight Redistribution:This one is obvious. By moving the components from front to back youchange the Center of gravity. The batteries are a good candidate for this since they are invariably the

heaviest thing on the bug.

Leg Shape:This is the thing most likely to change dramatically. By bending the legs back and forthyou change the fulcrum point and thus the balance. Remember that contact point is more critical than leg

shape.

What it should be achieving: The easiest way to get an idea about what the legs should be doingis to step through the motions manually .. This is where the compliance thing comes in. If you cant


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move the legs manually then the motors are not going to provide an appropriate feedback to the

MicroCore

By twisting the front leg CW approx 45 off center and the back leg approx 30 CW you have what well

call start position. The Walker should now be balanced with its front left foot in the air and be just on the

verge of tipping forward onto it.

This is where the dynamic imbalance thing comes in, the bot Literally falls over onto its front foot.

You should be able to tell if it is at the tip point by giving its butt a little tap, it should tip to the front foot

and stay tipped. If it doesnt, try moving the battery forward or back in order to find the balance point (leg

configuration will come later). The next step (literally) may or may not be obvious. By moving the back

legs CCW you will move the fulcrum back, thus making the front tip down and the rear right foot raise off

the ground. Keep rotating it until you have moved it 60 or so. The front two feet and the back left one

should be flat on the ground and the rear right will be just off the ground towards the front of the walker.

The walker has just completed a half a cycle (two Nv processes).

Now, by moving the front leg CCW 90 you will provide lift and drive with the front left foot and raise the

right side of the front into the air just to the tipping point. Now it's time for the rear to produce the drive

forward that tips the walker forward and raises the rear left foot while stepping. This is done by rotating

the rear CW 60.

Finale! One walking cycle and a full loop around the MicroCore.Now go through the process a few more times manually with the power off, and familiarize yourself with

what it should be doing. You may have to move the battery around and change the legs a little. But

remember that Symmetry is VERY important. In order for both sides to be doing the same thing you need

to have the feet contacting the same place with respect to the body (how the leg gets there isnt as

important). The body should also sit flat when all feet are down and the legs are straight out. If the body

leans, then one leg is shorter than the others and your bug will limp.

On the next page we will show how to connect a 4 Nv MicroCore circuit to two motors via a 74HC245

octal buffer chip.

To search more than 40 BEAM sites, clickBEAM ONLINE.

In this section we show how to connect a 4 Nv MicroCore circuit to two motors via a 74HC245 octalbuffer chip.This is not a project with a kit. It is a Feature Article with references to sites on the web. You will need togo to hobby supply shops for the components - especially the hardware items and motors. Try theLINKSpage of BEAM ONLINE for suppliers.The circuit has been taken fromChiu-Yuan Fang's excellent site. On it he has produced a BEAM Robotcalled "Walker" and has a number of photographs to show how it has been put together.The following are thumbnails of some of these shots:
http://www.beam-online.com/http://www.beam-online.com/http://www.beam-online.com/http://www.beam-online.com/General_Links.htmlhttp://www.beam-online.com/General_Links.htmlhttp://www.beam-online.com/General_Links.htmlhttp://www.geocities.com/SouthBeach/6897/beam2.htmlhttp://www.geocities.com/SouthBeach/6897/beam2.htmlhttp://www.geocities.com/SouthBeach/6897/beam2.htmlhttp://www.beam-online.com/General_Links.htmlhttp://www.beam-online.com/


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Front view of Walker Side view of Walker

The electronics, batteries and motors The undersideView 2 more pages of the excellent pictures of Chiu-Yuan Fang's WalkerVersion 2:Page-1 photos andPage-2 photos

The circuit diagram for the Walker is shown below. The diagram has been laid out to show how the signalprogresses though the circuit. It circulates around the four Schmitt trigger gates, while at the same timedriving two motors, in either forward or reverse direction. The circuit turns on with a long delay via thegate between pins 1&2. Two 1M trim-pots provide "straight-line" motion.
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The 74HC245 octal buffer (driver) chip has a 50mA capability per output and two outputs are joined inparallel in the diagram above to get 100mA per line. If you require more current, the following transistorH-Bridge can be used:

The circuit above will provide up to about 500mA drive-current for each motor and this is needed when amotor has to be started under load. As soon as the motor "starts", the current will drop, but it's the abilityof the circuit to provide a high starting-current that prevents a "stalled condition." The LEDs provideindicators to show the operation of the circuit.

How to Make a Robot Walk

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