70077005 Robotics Report 2
Mlungisi Mankani
September 2022
Components of Robots
Power Sources
Though perhaps other power sources can be used, the main sources of electrical
power for robots are batteries and photovoltaic cells. These can be used separately or together (for practical applications, most solar-powered robots will
need a battery backup).
Batteries are an essential component of the majority of robot designs. Many
types of batteries can be used. Batteries can be grouped by whether or not they
are rechargeable. Batteries that are not rechargeable usually deliver more power
for their size, and are thus desirable for certain applications. Various types of
alkaline and lithium batteries can be used. Alkaline batteries are much cheaper
and sufficient for most uses, but lithium batteries offer better performance and
a longer shelf.
Common rechargeable batteries include lead acid, nickel-cadmium (NiCd) and
the newer nickel-hydride (Ni-MH). NiCd & Ni-MH batteries come in common
size sizes such as AA, but deliver a smaller voltage than alkaline batteries (1.2V
instead of 1.5V). They also can be found in battery packs with specialized power
connectors. These are commonly called race packs and are used in the more
expensive RC race cars. They will last for some time if used properly. Ni-MH
batteries are currently more expensive than NiCd, but are less affected by memory effect.
Lead acid batteries are relatively cheap and carry quite a lot of power, although
they are quite heavy can be damaged when they are discharged below a certain
voltage. These batteries are commonly used as back up power supply in alarm
systems and UPS.
An extremely common problem in robots is ”the micro controller resets when
I turn the motor on”. When the motor turns on, it briefly pulls tghe battery
voltage low enough to reset the micro controller. The simplest solution is to run
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the micro controller on a separate set of batteries.
History of the Battery
The first evidence of batteries comes from discoveries in Sumerian ruins dating
around 250 B.C.E. Archaeological digs in Baghdad, Iraq. But the man most
credited for the creation of the battery was named Alessandro Volta, who created
his battery in the year 1800 C.E. called the voltaic pile. The voltaic pile was
constructed from discs of zinc and copper with pieces of cardboard soaked in
salt water between the metal discs. The unit of electric force, the volt, was
named to honor Alessandro Volta.
How a Battery Works
Most batteries have two terminals on the exterior, one end is positive end marked
”+” and the other end is negative marked ”-”. Once a load, any electronic device, a flashlight, a clock, etc., is connected to the battery the circuit being completed, electrons begin flowing from the negative end to positive end, producing
a current. Electrons will keep flowing as fast as possible until the chemical reaction on the interior of the battery lasts. Inside the battery there is a chemical
reaction going producing the electrons to flow, the speed of production depends
on the battery’s internal resistance.
Electrons travel from negative to positive end fueling the chemical reaction,
if the battery isn’t connected then there is no chemical reaction taking place.
That is why a battery (except Lithium batteries) can sit on the shelves for a
year and there will still be most of the capacity to use. Once the battery is
connected from positive to negative pole, the reaction starts, that explains the
reason why people have gotten a burn when a 9-volt battery in their pocket
touches a coin or something else metallic to connect the two ends, shorting the
battery making electrons flow without any resistance, making it very, very hot.
Main Concerns Choosing a Battery
- Geometry of the batteries. The shape of the batteries can be an important
characteristic according to the form of the robots.
- Durability. Primary (disposable) or secondary (rechargeable).
- Capacity. the capacity of the battery pack in milliamperes-hour is important. It determines how long the robot will run until a new charge is
needed.
- Initial cost. This is an important parameter, but a higher initial cost can
be offset by a longer expected life.
- Environmental factors. Used batteries have to be disposed of and some of
them contain toxic materials.
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Lithium-ion Batteries
Advantages:
These batteries are much lighter than non-lithium batteries of same size. Made
of lithium (obviously) and Carbon. The element Lithium is highly reactive
meaning a lot of energy can be stored there. A typical lithium-ion battery can
store 150 watt-hours of electricity in 1 kilogram of battery. A NiMH (Nickelmetal hydride) battery pack can store perhaps 100 watt-hours per kilogram,
although 60 to 70 watt-hours might be more typical. A lead-acid battery can
store only 25 watt-hours per kilogram. Using lead-acid technology, it takes 6
kilogram to store the same amount of energy that a 1 kilogram lithium-ion battery can handle. That is a huge difference!
Disadvantages:
Begin degrading once they are created, lasting only two or three years tops,
used or not. Extremely sensitive to high temperatures, heat degrades battery
even faster. If a lithium battery is completely discharged, it is ruined a new one
will be needed. Because of size and ability to discharge and recharge hundreds
of times it is one of the most expensive rechargeable batteries. And a small
chance they could burst into flames (internal short, separator sheet inside battery keeping the positive and negative ends apart gets punctured).
Alkaline Batteries
The anode, the positive end, is made of zinc powder because the granules have
a high surface area, increasing the rate of reaction and higher electron flows. It
also helps limit the rate of corrosion. Manganese dioxide is used on the cathode,
or the negative side, in powder form as well. And potassium hydroxide is the
electrolyte in an alkaline battery. There is a separator inside the battery to
separate the electrolyte between the positive and negative electrodes.
Actuators
Actuators are like the ”muscles” of robots, which convert energy into movement.
By far the most popular actuators are electric motors.
The vast majority of robots use electric motors, often brushed and brush less
DC motors in portable robots in portable robots or AC motors in industrial
robots. These motors are often preferred in systems with light loads, and
where the predominant form of motion is rotational.
AC (alternating current) motors are rarely used in mobile robots because most
of the robots are powered with direct current (DC) coming from batteries. AC
motors are mainly used in industrial environments where very high torque is
required, or where the motors are connected to the mains/ wall outlet.
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Motor controller
A motor controller is an electronic device that helps microcontroller to control
the motor. Motor controller acts as an intermediate device between a micro
controller, a power supply or batteries, and the motors
Although the micro controller (the robot’s brain) decides the speed and direction of the motors, it can not drive them directly because of its very limited
power (current and voltage) output. The motor controller, on the other hand,
can provide the current at the required voltage but can not decide how the motor should run
Thus, the microcontroller and the motor controller have to work together in
order to make the motors move appropriately. Usually, the microcontroller can
instruct the motor controller on how to power the motors via a standard and
simple communication method such as UART or PWM. Also,some motor controller can be manually controlled by an analogue voltage (usually created with
a potentiometer).
The physical size and weight of a motor controller can significantly, from a
device smaller than the tip of your finger used to control a mini sumo robot to
a large controller weighing several kg. The size of motor controller is usually
related to the maximum current it can provide. Large current means larger size.
Since there are several types of motors, there are also several types of motor
controllers:
Brushed DC Motor
A brushed DC motor is one which uses two brushes to conduct current from
source to amature. There are several variations on the brush DC motor, but
permanent magnet DC motor (PMDC) is used extensively in robotics. Brushed
DC motors are widely used in applications ranging from toys to push-button
adjustable car seats. Brushed DC (DBC) motors are inexpensive, easy to drive,
and are readily available in all sizes and shapes.
The brush DC Motor consists of six different components : the axle, armature/rotor, commutator, stator, magnets and brushes. A brush DC Motor consists of two magnets facing the same direction, that surrounding two coils of wire
that reside in the middle of the Brush DC motor, around a rotor. The coils are
positioned to face the magnets, causing electricity to flow them. This generates
a magnetic field, which ultimately pushes the coils away from the magnets they
are facing, and causes the rotor to turn.
The Brush DC Motor has two terminals; when voltage is applied across the
two terminals, a proportional speed is outputted to the shaft of the Brush DC
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Motor consists of two pieces: the stator which includes the housing, permanent magnets, and brushes, and the rotor, which consist of the output shaft,
windings and commutator. The brush DC motor stator is stationary, while the
rotor rotates with respect to the Brush DC motor stator. The stator generates
a stationary magnetic field that surrounds the rotor. The rotor, also called
the armature, is made up of one or more windings. When these windings are
energized they produce a magnetic field. The magnetic poles of this rotor will
be attracted to the opposite poles generated by the stator , causing the rotor
to turn. As the motor turns, the windings are constantly being energized in
a different sequence so that the magnetic poles generated by the rotor do not
overrun the poles generated in the stator. This switching of the field in the rotor
windings is called commutation.
Unlike other electric motor types (i.e.,brush less DC, AC induction), BDC motors do not require a controller to switch current in the motor windings. Instead,
the commutation of the windings of a BDC motor is done mechanically. A segmented copper sleeve, called a commutator, resides on the axle of a BDC motor.
As the motor turns, carbon brushes slide over the commutator, coming in contact with different segments of the commutator. The segments are attached to
different rotor windings, therefore, a dynamic magnetic field is generated inside
the motor when a voltage is applied across the brushes of the motor. I is important to note that the brushes and commutator are the parts of a BDC motor
that are most prone to wear because they are sliding past each other.
Advantages:
Inexpensive.
Lightweight.
Reasonably Efficient
Sensors
LiDAR Sensors for Robotic Systems
LiDAR (Light Detection and Ranging) technology assists robots to navigate
their surroundings through object perception, identification and collision avoidance. LiDAR sensors provide information in real time about the robot’s surrounding such as walls, doors, people and other objects. LiDAR can assist
robots to carry out a wide range of tasks and to operate autonomously.
It operates on the time of flight concept, which is a very well tested concept in
industry. We know the speed of light through our atmosphere so that means
we can send a pulse of light, bounce it off a target, and measure the amount
of time it takes to come back. By halving the total time and multiplying by
the speed of light, we know the distance to the target. This is the core of how
LiDAR works.
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To capture more data about the surrounding contours, we take pulse of light
and bounce it of a rotating mirror. As the laser rotates around, we get all these
measurements in a flat plane of measurement. This plane of measurement can
be stacked with subsequent planes (like a loaf of sliced bread) to create a threedimensional map, called a point cloud.
LiDAR technology has a number of advantages, including a high degree of accuracy, high resolution, and a long-detecting distance. This makes it beneficial
to use in numerous applications.
First uses of LiDAR
The concept of LiDAR was first discovered in 1930 to estimate the distance
and density of clouds using searchlights, photographic paper, and a telescopic
lens. Building upon that concept, the first prototype for LiDAR technology
came shortly after the invention of the laser in 1961 from Hughes Aircraft Company. The original intention was to use it to track satellites and also measure
clouds and pollution in the air. The technology gained popularity when the
United States’ space program used the technology to map the surface of the
moon during the 1971 Apollo 15 mission.
Since then, it has been used in numerous applications across a number of industries. NASA continues to use LiDAR for topographic mapping of earth and
to study climate change . Geologists use it to create shoreline maps or make
digital elevation models. Archaeologists use it to create high resolution maps
for surveying. It’s even been used in the entertainment industry to create scans
of buildings and cities in 3d for production. You may even have LiDAR in your
pocket. The latest iPhones have a tiny LiDAR sensor for augmented reality
apps.
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Sensorized LiDAR
This type of LiDAR comes in the form of a compact and lightweight laser scanner. These are considered entry-level technology as they are typically used
for simple area monitoring tasks. Sensorized LiDAR products function well
even in high ambient light thanks to the High Definition Distance Measurement
(HDDM) technology from from SICK. This reduces cost and complexity in LiDAR detection.
This type of LiDAR is used in some autonomous vehicle applications, but it
is also increasingly used for basic applications on the factory floor. The LiDAR
sensor creates an invisible plane of detection and can be oriented to detect the
presence of objects that should not be there-perhaps an overfilled bin or a tote
with objects hanging out of it. This is especially useful in a packaging and
production environment.
In bin-picking and pass-through detection applications, sensorized LiDAR can
also be used. This allows manufacturers to monitor the production of products
and ensure quality control. If an operator reaches into the incorrect bin, the
system will signal the operator. Historically this was oft6en done with multiple
light curtains , but a single LiDAR device is much simpler to install and wire.
Multi-layer LiDAR
Some people call it 3D LiDAR and others refer to it as multi-layer or multi
channel. This type of LiDAR provides not just a single plane like 2D LiDAR,
but three more planes that that provide additional detection. This can be used
to detect objects at long distances.
Additional planes add an extra layer of detection that 2D LiDAR lacks. For
example, if an object isn’t correctly aligned with the plane, another plane may
pick it up instead. This allows more flexibility so that if things aren’t perfectly
aligned or 100% always in the exact same position, a multi-layer sensor can
adapt to it.
Solid-State LiDAR
Still another type of LiDAR is solid state. Instead of a single plane or multiple planes like the previous two, this type of LiDAR provides a camera view
of everything it looks at With this technology, a 3D snapshot is taken of the
surrounding area that goes beyond just an image. It also provides the depth or
distance associated with each ”pixel” of that image.
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This type of LiDAR can be used in many AMR applications, but also works well
in other applications. For example, in bin picking applications, the LiDAR can
provide a 3D image of whatever is in the bin, allowing the robot to know when
and what it should pick up.One final application is in package dimensioning for
pallet loading. In pallet loading it’s common to use a robot’s suction gripper to
collect several cartons and stack them on a pallet. By adding LiDAR to the end
effector, the robot can now determine the position and dimensions of the carton
so that it can adapt its grip dynamically to improve efficiency and reduce errors.
The camera is quick to install, ready for operation immediately, and provides
reliable high-quality 3D data in just one shot.
Controllers
Advanced RISC Machine (ARM)
Advanced RISC Machine (ARM) is a processor architecture based on a 64/32
bit reduced instruction set (RISC) computer.
ARM features include:
• Load/store-based architecture.
• Single-cycle instruction execution.
• Link register.
• Easy decoding and pipelining.
• Power-indexed addressing modes.
• Fixed 32-bit instruction set
History of Arm Processors
ARM machines have a history of living up to the expectations of their developers, right from the very first ARM machine ever developed. It all began in
the 1980s when Acorn Computers Ltd., spurred by the success of their platform
BBC Micro wished to move on from simple CMOS processor to something more
powerful, something that could stand strong against IBM machines launched in
1981. The solutions available in the like the Motorola 68000 were not powerful
enough to handle graphics and GUIs leaving only one option with the company,
make their own processor.
Inspired by the making of 32 bit processors by some undergraduates at Berkeley
and a one man design centre Western Design Centre, Phoenix, Steve Furber and
Sophie Wilson of Acorn Ltd. set out to make their own processors. Sophie developed the instruction set and simulated it on the BBC Basic which convinced
many in the company that it was not just anything half hearted shotaimed in
darkness. With the support and permission of the then CEO Hermann Hauser,
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the ARM project formally took off inn the 1983 with VLSI Technology as their
silicon partner, to produce an ARM processor with latencies as low as that
of the 6502. The first ARM core dubbed as ARM1 was delivered by VLSI
Technology in 1985. This processor used in conjunction with the BBC Micro
helped in the development of the next generation called ARM2. 1987 saw the
release of ARM Archimedes.
Applications in robotics like the ARM Rubik’s Speedcuber are gaining popularity. With the rising popularity of smartphones as their market penetration
increases, the ARM cores are gaining more popularity.Over 1.15 billion ARM
chips have been placed in tablets and smart phones. Dual cores like the LG
Optimus 2X have started using the latest in the line Cortex cores to deliver
more performance in reduced space requirements.
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