How to make a Robot Walk
This information has been adapted
from an excellent site by A
This section describes how to make a walking robot. The simplest robots are
called BEAM ROBOTS. And the simplest walkers are called BEAM WALKERS. They
consist of just enough circuitry and mechanics to carry 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 by one of the earliest developers of Robots, Mark W.
Tilden. He gave the name MicroCore to the type of circuit that drives these
The concept of the MicroCore is pretty clever. Using just a handful of
components, you can build the control circuitry for a walking robot that
senses its environment and adjusts its gait accordingly. The clever part is the circuit is so
A MicroCore consists of a capacitor, a gate, and
a resistor. This is called a 'neuron.' Each neuron has an input and an
output. The components are connected so that the capacitor and resistor form
a delay circuit. If we make the input HIGH, the output take a short time to
react. Mouse-over the animation below to see how the Neuron circuit
The gate is actually an inverter and it also has the ability to
strengthen the pulse. If we connect the output of one neuron to the input of
another and take the output of the second to the input of the first we have
a complete 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 a MicroCore consists of a capacitor, a gate, and
a resistor. A circuit containing a number of 'neurons' will produce 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 motor on the left run for longer -
simply change the resistance for that neuron. If you incorporate 2 photodiodes
into the MicroCore, you can make a robot always zigzag its way towards
light! This is really impressive and demonstrates how simple
"complex behaviour" really is.
In this discussion we are going to explain the operation of the . . .
MicroCore circuit can be likened to a
nervous circuit in that it gives life and realism
to a robotic shape. 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
Biomorphic Robotics and
A New Machine Control Paradigm
Mark W. Tilden,
Submitted for publication to the EANN '95 Conference
Proceedings "Special Track on Robotics."
Los Alamos National Labs
Nervous Net (Nv) technology is a non-linear analog
control system that solves real time control problems normally quite difficult
to handle with digital methods. Nervous nets are to Neural nets the same way
peripheral spinal systems are to the brain. This work has concentrated on the
development of Nv based robot mechanisms with electronic approximations of
biologic autonomic and somatic systems. It has been demonstrated that these
systems, when fed back onto themselves rather than through a computer-based
pattern generator, can successfully mimic many of the attributes normally
attributed to lower biological organisms. Using Nv nets, highly successful
legged robot mechanisms have been demonstrated which can negotiate terrains of
inordinate difficulty for wheeled or tracked machines. That non-linear systems
can provide this degree of control is not so surprising as the part counts for
successful Nv designs.
A fully adept
insect-walker, for example, can be fully controlled and operated with as little
as 12 standard transistor elements.
Since the start of research in the winter of 1994,
development of this technology has advanced to solving currently difficult
sensory and cognitive problems. It is hoped in the coming years Nv systems may
do for robot vision (amongst other disciplines) what has been done for
autonomous robot vehicles, namely the reduction of currently complex systems
down to an inexpensive but robust minimum. Further efforts are also being made
to apply this control strategy to the expanding nano-technology field. At the
nanometer scale Nv's may prove more feasible than nano-computers for control of
self-assembling micro 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 been applied to autonomous
robots because of the difficulty conventional control systems have solving the
seemingly simple task of negotiating undefined complex environments.
or so "biomorphic" robots (from the terms BIOlogy and MORPHology,
the Latin for "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
procedural condition (i.e. they do not follow the rules of an internal program
that mimics the external world, but the world itself).
Nv control architectures
focus on adaptive survival rather than the performance of specific tasks. Once
survivability is under control, goals can be superimposed and the machine used
as a platform to carry sensors and conventional electronic intelligence. It is
believed that these machines, although now in an early stage of development,
can within a few years be brought to the point that they can serve as
inexpensive, robust, and versatile carriers for a variety of instruments.
A vast number of applications would then be possible, including the location and
possible clearing of land mines from civilian areas, security, maintenance,
medical and prosthetic applications (a cost-effective
"walking wheelchair" for example), and even cars with on-board "survival"
instincts to save themselves and their passengers, from damaging accidents. Though the
Nv based legged devices built so far cannot go everywhere, they can certainly
go places not currently accessible to wheeled or tracked vehicles of similar
scale. It seems that for handling undefined environments, biomorphic designs
are a very efficient and cost-effective approach.
Initially it was thought these devices avoided the
problems of an internal world representation by using a reactive or behaviour-based
technique. Recent work has shown however that Nv
biomorphs instead take a chaotic map of their surroundings onto their process
control hierarchy (that is, they dynamically and efficiently adapt to the
fractal complexity 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 their interconnections.
The defining characteristic of this adaptation is continuously updated by the
immediate fractal complexity of the environment. These devices are "soft"
designs, in that the environmental dimension must be absorbed, modified, and
acted on for the devices to make 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 by perceived load rather than by a separate regulating path. The
result is highly compliant, animal-like machine motions that
"negotiate" rather than "bully" their way through
environments, resulting in minimal damage to both world and robot.
We talk about these devices in the general sense
because the precepts of their existence and subsequent design are based upon
environmental macros, such as fluidity, turgidity, gravity, scale, materials
strength, and many other factors. The power of biomorphic designs is that this
information is used as the defining principles to shape appropriate survivor(s)
for a particular environment. The machines that emerge are vastly different
from any conventional robotic forms. We suspect, at least from the experimental
evidence, that this technique embodies a new type of non-linear control
paradigm, and at least an entirely new engineering discipline for the matching
of competent machines to complex environments. Here,
once the problems of existence are ratified, the devices can do unsupervised,
long term work without human intervention (some devices have been in continuous
operation for over 5 years).
The potential for this control paradigm is vast,
but it is far from linear, and requires integrated design attempts to pull a
competent ability from the Nv nets. To this end,
the use of this technology to "evolve" machines from a lesser to a
higher operational state has resulted in not only
a wide spectrum of devices, but even completely different "species"
of creatures, all evolved from a primal "genotype;" the single
"cell" creature known as Turbot 1.0.
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, macro and
micro robotics, and experimental work has been done to produce adept prototypes
The conclusions are that there may be some universal chaos-bounded
concepts that bind survivor oriented designs, allowing for the creation and
optimization of devices that can do work in any environment, under many
situations, using chemically inert, and thereby relatively safe, control
techniques (the idea of seeding a wheat field with pest-fighting silicon
biomorphs to produce high yield, insecticide-free foodstuffs is an attractive
Considering that biomorphs may last long enough to
replace most forms of long-term damaging chemicals (i.e. pesticides, bleaches,
medicines) the potential for the field really opens up. Deployed artificial
chemicals perform a task in their immediate area of concentration, and then
disperse into the environment where, after a time, they cannot be absorbed
adequately. Biomorph machines, made from biodegradable silicon and trace
elements, can be made gregarious so they do not of their own volition
disperse, and can be absolutely controlled by conventional methods. Whether at micro or
macro scales, these designs 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 fiction and reality by finding out
what is feasible now, and how to logically proceed to marketable, capable
machines. In the coming years, it is hoped to be possible to demonstrate real
machines to assess feasibility for macro and nano robotic applications.
Expansions of the fields of robo-biology, robo-morphology, and artificial ecologies
will be studied 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 valid work tool.
The basic circuit for a MicroCore consists of a capacitor, a gate, and
a resistor. The arrangement of the components 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:
The capacitor charges and the
circuit changes state a short time later. The capacitor and
resistor form an arrangement called a DELAY CIRCUIT. The LED has been
added to the output of the gate so we can see how and when the circuit
We are interested in the operation of the output AFTER the input has
changed. The circuit is just like a spinal 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 sense than the LEDs.
Two Neuron circuits will work when connected head-to-tail and with the
output of the second connected to the input of the first:
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. The change from one state to the other is almost instantaneous and
only one LED is illuminated at a time. We have slowed down the animation to
show the gates in action and the two LEDs appear to be off for an instant. 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 Nv circuit to the input of the first, we get
a circulating pattern. The circuit will always start-up and each alternate LED
will be illuminated.
When the circuit is connected to a Robot, the following effect will be
This is known as the Saturated State. This means all Nv's are firing at Max rate. There is a Maximum of 3 Processes.
A process is defined as one LED/Nv ON at any one time. Note: there are never two
illuminated LEDs side-by-side at the same time. This is the Fermei
exclusion feature of the MicroCore and an 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 had too much
coffee. Saturation will occur when the MicroCore encounters a disruption
in main power or when too much data is received from sensors or Nu/Nv nets.
Fortunately it's easy to get a more stable useful state.
Adding a Process Neutralization Circuit (PNC). Wire up a switch to short out
the input bias resistor like this.....
Closing the switch destroys any re-circulating pulses. Hold it long
enough and all processes are destroyed. 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 to achieve this....
If all values are even, and no
glitches or noise is received from the motor, the processes should fall 180 degrees out of phase with each
other. This is seen when they appear to be running side by side with each
other. Two processes are like Parkinson's disease. The Nv's are
trying to act against each other and if they fall into this mode, you have "lock
state can be useful in some cases but in the case of a simple walker it's
not much use.Single Process State.
By Holding down the PNC switch for another 3 seconds or so you should get this.
This is the stable One Process State that is the basis of
most of the Nv walkers.
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
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 motor
four leg walker
although it is not the most flexible design, it is the easiest to build and has proven its reliability and capability in 35
This is probably the biggest consideration in a MicroCore Walker.
The level of success you have with your walker is directly
related to the type of motor used. The MicroCore itself gets an implicit
feedback from the motors, this is what gives it the adaptability.
What to look for in a Motor....
This is REALLY important
both from a power consumption standpoint (more-efficient motors
require a smaller battery or main-storage electrolytic). High efficiency motors
give you a better chance of success. You should
look for a motor with at least a 35% efficiency rating, good
cassette motors 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
grade motors like "Escap" and "MicroMo." Keep your
eyes open when perusing the surplus catalogues, these sometimes go on
sale for as little as $5.
For the most part, smaller is
better but it's not as important as efficiency. As well, you may
consider your own skill level. In the beginning, don't try to work with things that are
really small. Make sure you have extra motors. They come in handy.
You canít build a walker without them. A motor alone doesn't put out enough torque and usually runs
What to look for in a gearbox...
Efficiency/Size/Numbers: For all the same reasons as above.
This is really critical.
You should be able to grasp the output shaft with a pair of
pliers and turn it to have the gears spin the
motor. If you can't make the motor spin, then you have a gear train that
is too inefficient (most likely) or too high a ratio. Worm drives are
also OUT, they only go one way (motor to gear and not gear to motor)
and they tend to choke under high loads.
The ideal is about 30
RPM @ 5V. Higher RPM means you probably won't have enough
torque (and if you do, the robot will jump around so fast it's hard
to figure out what it's doing). A lower RPM means the machine may
be moving too slow to be of use. A high ratio may mean the legs will bend
under the torque.
INTERFACING MOTOR AND
I strongly suggest you find a factory
motor/gearbox combination. If you have to build your own then bear a couple of things in
Direct gear contact:
belt drives, friction drives, flexible shafts etc all have big problems as
far as efficiency and compliance are concerned.
Keep everything clean:
Glue, solder flux and metal fillings are deadly enemies to gearboxes.
Solder 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 and available at any welding supply place. Any nice shinny option is
High Nickel rod used for TIG welding cast iron but it's MUCH more
expensive. Brass tube and wire found at most hobby shops is good too. I suggest a solder with an
organic/water soluble flux, "Hydro
X" by Multicore is my favourite.
BASIC FRAME LAYOUT
The diagram below shows the basic layout. You need to keep the motors and output shafts lined
up front to back and the front motor should be tilted at 30 degrees. This
means the front motor will supply lift and push but we'll discuss that
more later. You should mount the motors far enough apart to fit all your
electronics including batteries (usually about 4").