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The Trackbot Gets a Price Cut, Who Wants a Powerful Spy Robot?

Posted: 15 Jan 2013 08:55 AM PST

Inspectorbot Trackbot

Inspectorbot Trackbot

The Trackbot by Inspectorbots is a powerful surveillance robot capable of navigating very rough terrain riddled with debris. Its small size makes it particularly suitable for crawling into small tunnels, pipes, and generally inaccessible places for humans. Thanks to its camera and headlights, the human operator can see what the robot sees. The video below demonstrates the robots’ capabilities.

If you already wanted this robot, then you are in for a treat; its price was recently cut by 1000$! Thanks to manufacturing improvements, the robot, which previously would set you back 6990$, can now be bought for 5990$. What tasks would you have this robot do? Leave a comment with your suggestions.

How Do I Choose a Battery?

Posted: 15 Jan 2013 08:33 AM PST

Given the wide range of actuators and electronics which go into a robot, choosing the right battery may not be an easy task. This article guides you through the thought processes involved in choosing one or more batteries for your robot.

Even if you are just starting in robotics, you may have already realized that the components you want to use don’t all operate at the same voltage. If you look at a production robot, you start to wonder “how is everything working off just one battery?”. There are two approaches taken, and we’ll help you determine which is best for you.

Multiple Batteries

Advantages

  • Requires less design time
  • Can be more efficient

Disadvantages

  • Various parts of the robot will stop working at different times
  • Multiple batteries to recharge

How do you know if you need multiple batteries? Check the nominal voltage of each of the products you selected:

  • Electronics (microcontroller,  motor controller power etc) usually operate at 9V-12V. Some operate at low as 3.3V and 5V.
  • Actuators (DC gear motors, stepper motors, servos etc) usually operate at 6V to 12V. A few operate as low as 3V
  • Sensors usually operate 5V

Based on the ranges above, it’s easy to see how, wen selecting optimal components for your project, that the voltage range may differ for each type of component. Fortunately most microcontrollers has a built-in voltage regulator which provides 5V to the I/O pins, so you don’t need a dedicated 5V battery. Should you choose a normal microcontroller, it’s likely that the voltage range is 9V  to 12V. Operating a normal hobby servo motor (rated at 4.8V to 6V) from a 9V to 12V battery would quickly burn it. What to do? The easiest option would be to use a smaller 12V battery for the microcontroller, and a larger 6V battery for the servos.

One Battery

Advantages

  • One battery to charge
  • Lighter weight

Disadvantages

  • (May) require voltage regulator
  • A bit more complex to understand and wire

Continuing the example above, where we chose a 12V microcontroller and 4.8V to 6V hobby servos, we have the option of using one (larger) 6V battery pack and a step-up voltage regulator. A voltage regulator does exactly as the name implies; it regulates the voltage. In our case we would need one which can accept 6V input and step it up to 12V.

Choosing a lower motor voltage does not automatically mean the list of motors available to you will be low power. However, a high voltage motor (36V, 48V, 60V) tends to be reserved for large DC motors. The second approach is to first select the ideal motor and design your robot’s electronics system around the indicated nominal voltage. Both approaches have their advantages and disadvantages and it is up to you to choose which you prefer.

Voltage dividers allow you to power electromechanical devices at different voltages. Voltage dividers are purely electrical devices with no programming involved. If you do not want to use voltage dividers, most electronics operate at 5 to 9V, so choosing either 6 or 9V as your robot’s supply voltage is the best choice (never assume an electronic device operates at 6 or 9V: you always need to read the supply voltage specifications for each electronic component). The other option is to use two different power supplies: one for the motors and another (smaller one) for the electronics.

Should you wish to operate your robot at 9V, you can often still choose a 12V motor, though you must keep in mind the rpm will be less that that listed (estimated as a fraction of the nominal value) and the motor efficiency will be slightly reduced.

Tips / Tricks

Standard battery voltages are:

  • 1.2V: one rechargeable NiMh AA or AAA battery (unless you want a really small robot, one cell does not do much)
  • 1.5V: one Alkaline AA or AAA battery(disadvantage of not being rechargeable and can’t do much on its own)
  • 2.4v: two rechargeable AA or AAA batteries; still can’t do much on their own, even for small robots
  • 3V: two alkaline AA or AAA batteries; most microcontrollers cannot operate at this voltage, let alone most actuators.
  • 3.6V: three rechargeable NiMh AA or AAA batteries; this is usually the minimum voltage to run certain microcontrollers
  • 3.7V: one LiPo battery; this is close enough to 3.6V and is the minimum to run certain microcontrollers
  • 4.5V: three alkaline AA or AAA batteries… why even consider non-rechargeable in robotics?
  • 4.8V: four AA or AAA together provide the minimum voltage to operate a standard hobby servo motor. These can be either as individual cells or as a single rechargeable battery pack.
  • 6V: four AA or AAA alkaline batteries, five rechargeable NiMh cells or one 6V rechargeable lead acid pack; this is the maximum (and ideal) voltage most hobby servos can handle. Use these if your servos need a bit more power.
  • 7.2V: six AA or AAA rechargeable NiMh batteries is perfect for 7.2V DC gear motors. These are usually in a battery pack rather than as individual cells and you will need a more specific NiMh battery pack charger.
  • 7.4V: two LiPo cells can often power a microcontroller and works great for 7.2V DC gear motors. Unfortunately it’s too high for most hobby servo motors.
  • 7.5V: five alkaline AA or AAA: almost never used because it’s simply too many single-use batteries.
  • 8.4V: 7x NiMh AA batteries (hard to find chargers for 7xAAA NiMh batteries). This is also not used much because it means charging 7 batteries at the same time.
  • 9V: 6x Alkaline batteries, one 9V (NiMh or Alkaline) battery or one 9V lead acid batteru: please avoid using 6x alkaline for the sake of the environment. A 9V single cell rectangular battery is often used to power the microcontroller in dual battery configurations. 9V lead acid batteries are a bit harder to find and although they are quite heavy, are fairly inexpensive and high capacity.
  • 9.6V: 7x NiMh cells, usually in a battery pack configuration. This is good for motors which operate at 9V, and also for microcontrollers (most can operate above 9V).
  • 11.1V: three LiPo batteries produces almost 12V and is much lighter than 10x 1.2V cells or a 12V lead acid battery pack. You need a specific LiPo charger capable of charging 3 cell LiPo packs.
  • 12V: 10x 1.2V cells (always configured as one NiMh battery pack) or one 12V rechargeable lead acid battery pack. 12V is ideal for a variety of DC gear motors and most microcontrollers.
  • Anything above 12V is usually reserved for very large robots. If you have a 14.4V LiPo or 18V NiMh pack from a cordless drill, keep in mind that finding motors which operate at these voltages is not easy.

Robots using servo motors (legged robots or robotic arms) tend to operate at 4.8V (4x AA NiMh cells) or 6V (5x NiMh AA cells). You can use a fairly inexpensive voltage regulator to power the microcontroller, increasing the voltage from 6V to 9V.

Small to medium mobile robots often use a 6V, 9V or 12V NiMh battery pack, the choice of which depends on the nominal voltage of the drive motors. If the robot includes one or more servo motors (for a pan/tilt for example), the microcontroller can usually provide enough current from a 5V digital pin. If your microcontroller operates at 9V and you want to use 6V motors, you might consider a two battery solution.

Medium sized mobile robots tend to use one 12V battery; lead acid or single NiMh battery pack (or an 11.1V LiPo battery if weight is an issue).  Large robots use 12V or 24V from one or more lead acid battery packs.

Chemistry

NiMh: This is by far the most common type of battery used in mobile robots. NiMh batteries are rechargeable and their value (price / capacity / weight) is hard to beat. There is almost no memory effect, meaning every charge should bring the battery up to full capacity.

NiCd: These batteries are slowly disappearing because of their memory effect: if you don’t discharge the battery properly and then recharge it to full capacity, you lose part of the capacity each time.

Alkaline: These are the least expensive batteries in the short term, and provide a higher voltage than NiMh, but are not great for the environment, and you constantly need to buy replacements.

Lead Acid: Still the cheapest option for high capacity, lead acid is usually reserved for medium sized robots because of their incredibly high weight.

LiPo: These are fast becoming the most popular type of battery because of their light weight, high discharge rates and relatively good capacity, except the voltages increase in increments of 3.7V, so you need to plan to use LiPo before selecting your electronics and actuators.

Nominal Voltage

A motor’s nominal voltage is the voltage at which the motor provides the best power output to efficiency ratio (rather than highest efficiency or highest power output). Operating a motor at the nominal voltage also helps to guarantee a long useful life.

Capacity

A battery’s capacity determines roughly how long a battery will last at a specific voltage given a specific discharge rate. For example, if you choose a 12V, 2Ah (2000mAh) battery pack (regardless of chemistry), the battery should be able to run a 12V motor consuming 2A continuously for 1 hour. Alternatively, it can run a 12V motor consuming 1A for 2 hours, or a 12V motor consuming 0.5A for 4 hours. The rule of thumb is to divide the capacity (assuming you are running an actuator at the same voltage) by the actuator’s current under normal load to get the time the motor will last.

Example 1

2x Drive Motors: 6V nominal, 1A each under normal load

1x 6V NiMh Battery Pack, 2200mAh (equivalent to 2.2Ah)

Note that the battery was chosen based on the motor’s nominal voltage.Should you instead operate 6V motors from a 7.2V battery, the calculations become more difficult (use the total watt-hours divided by the total watts per hour to get an idea).

Therefore the 6V battery pack will last:

2.2Ah battery / (2 motors x 1A per motor) = 1.1 hours

Example 2

18 servos used for a hexapod robot which operate at 6V nominal and consume 250mA under normal load*

1x 6V NiMh battery pack at 5Ah.

First, we will assume that all motors are under load at all times (i.e. worst case scenario) and therefore all 18 will be consuming a total of 4.5A

5Ah battery / 4.5A = 1.1 hours

Note again that the battery was chosen based on the motor’s nominal voltage.

Discharge Rate

The continuous discharge rate of a battery is very important because if you choose a battery that cannot discharge at the required current, the robot will either not work properly or not work at all.

Example 1

You selected four 12V motors for your 4WD outdoor mobile robot. Each motor consumes 1A under normal load, and more in the case of a slope. You decide to choose a 12V, 2Ah NiMh battery pack, not caring about the continuous discharge rate. You discover that your robot stops when it encounters even the slightest obstacle or incline. Why? In this case operating all four motors consumes ~4A while an NiMh pack can only discharge at about 1.2 times the capcity (1.2 x 2Ah = 2.4A). The current draw from the motors is therefore higher than the battery can provide.

Example 2

You selected two 7.2V DC gear motors which consume 1.5A each under normal load, and up to 2A each under stressful situations. This means that the battery needs to be able to provide at least 3A normally and up to 4A safely. If you choose an NiMh pack it would need to be 4A / 1.2C = 3.3Ah. The alternative would be to choose a LiPo pack because they can often discharge at 5C or higher, meaning you would be able to get away with a 4A / 5C = 0.8Ah pack. Granted the capacity is low, and you may opt for a higher capacity pack.

Burst Discharge Rate

 

2008 Robot Hall of Fame

Posted: 15 Jan 2013 08:31 AM PST

The Robot Hall of Fame honors the highest accomplishments of robots in science and science fiction. Their first group of robots inducted into the Hall of Fame in November 2003 represents the best of imagined and real robots. The Hall of Fame celebrates landmark scientific achievements as well as applauding the creative impact of fictional robots. In spring 2009 The Robot Hall of Fame will have a permanent home at the Carnegie Science Center as part of their new roboworld robotics exhibit.

 

2008 Inductees

Robot Hall of Fame

 

LEGO MINDSTORMS:

This building set combined programming bricks with electric motors, sensors and structural parts to create robots and other interactive systems.

 

This building set combined programming bricks with electric motors, sensors and structural parts to create robots and other interactive systems.

 

RAIBERT HOPPER:

Experiments with this one-legged device in the early 1980's showed how a machine such as Data might someday walk with the agility of a human.

 

NavLab 5:

This robot was one of a series of autonomous vehicles (based around a Chevrolet Lumina)developed at Carnegie Mellon.

 

Lt. CMDR DATA:

Portrayed by actor Brent Spiner during the 1987-1994 run of "Star Trek: The Next Generation," Data was the chief operations officer of the U.S.S Enterprise and possessed both super strength and an encyclopedic memory.

 

2006 Inductees

Robot Hall of Fame

 

AIBO:

In Japanese, AIBO means "companion." In English, AIBO is an acronym for "Artificial Intelligence BOt". In any language, the Sony AIBO represents the most sophisticated product ever offered in the consumer robot marketplace.

 

SCARA:

The first SCARA robot was created as a revolutionary prototype in 1978, in the laboratory of Professor Hiroshi Makino, at Yamanashi University in Japan. The 4-axis SCARA was designed as no other robot arm at the time. Its simplicity was brilliant … with less motion it could do more, with high speed and precision.

 

DAVID:

The character of David, in Steven Spielberg's movie Artificial Intelligence:AI (2001) challenges all of our preconceptions about robots. David is an android that looks like the world's most adorable ten-year old boy, with advanced artificial intelligence and the unique potential for an emotional relationship with a human being.

 

MARIA:

The robot MARIA stands apart as one of the only female robotic images of early science fiction. She appears in Metropolis, a science fiction film produced in Germany in 1927. The entire film is dominated by technology, with a mixture of images from the 1920s and futuristic devices.

 

GORT:

The robot Gort is one of the most memorable pop culture images from the Cold War era. Introduced in the 1951 movie classic The Day the Earth Stood Still, Gort comes to Earth as the killer robot bodyguard of the mysterious spaceman, Klaatu, who is on a mission of peace.

 

2004 Inductees

Robot Hall of Fame

 

ASIMO:

ASIMO was introduced to the world October 31st, 2000.

This engaging humanoid robot is the result of fifteen years of research and endeavor by Honda Motor Co., Ltd., a company dedicated to expanding and enhancing human mobility.

 

SHAKEY:

Shakey began in 1966 at the Stanford Research Institute (now SRI International). Over years of research, this ungainly “bot” developed into a milestone application of artificial intelligence and robotics.

 

ASTRO BOY:

ASTRO BOY, originally named Tetsuwan Atom, was created in 1951 by Japanese cartoonist and animator Osamu Tezuka, only six years after the end of World War Two.

 

ROBBY THE ROBOT:

Robby, the Robot made his first appearance in the 1956 MGM movie, Forbidden Planet. Robby is the film’s most memorable character and responsible for the cult status the movie enjoys.

 

C-3PO:

Of all the mythic STAR WARS movie characters, the one most like us is ironically a robot …C-3PO.

 

2003 Inductees

Robot Hall of Fame

HAL:

The HAL 9000 Computer is a non-human and central character in the film by Stanley Kubrick and Arthur C. Clarke – 2001: A Space Odyssey.

 

MARS PATHFINDER SOJOURNER ROVER:

The Mars Pathfinder Sojourner was the first rover to explore the surface of Mars. For the first time, a thinking robot equipped with sophisticated laser eyes and automated programming reacted to unplanned events on the surface of another planet.

 

R2D2:

R2-D2 is the favorite robot of generations of Star Wars fans.

It combines many of the most desirable attributes of synthetic creatures and as well as those of a perfect servant. His little 0.96-meter frame is packed with all sorts of tools that make him a great starship mechanic and computer interface specialist.

 

UNIMATE:

In 1961 the first industrial robot, Unimate, joined the assembly line at a General Motors plant to work with heated die-casting machines.

 

Source: Robot Hall of Fame, viewed April 24, 2008

 

Find out more about and visit the Robot Hall of Fame at the Carnegie Science Center.

Robot Leg Torque Tutorial

Posted: 15 Jan 2013 08:29 AM PST

The Robot Leg Torque Tutorial is intended to compliment the RobotShop Leg Torque Calculator found in the Dynamic Tools section of the RobotShop Learning Center. This tutorial explains how to find the torques acting at each degree of freedom of a 6-legged (hexapod), 3DOF / leg "insect" robotic leg.

Robot Leg Torque Tutorial

Hexapod (6-legged) robots are most commonly configured in either two rows of 3 legs (3+3) or at 60 degrees from each other and equal distance from the center. This tutorial will explain only the 3 + 3 configuration. With some modification, the equations can be adapted to find the torque required at each joint of an n-legged walking robot with “insect-like” leg configuration.

Dynamic stability:

A dynamically stable walking robot must be in motion in order to prevent it from falling over. If the robot were to stop while walking (walking pattern can also be referred to as a "gait"), the center of mass would cause it to fall over.

Static stability:

A  statically stable robot can be stopped at any point during its gait and it will not fall over. In the case of a hexapod, so long as 3 legs are always in contact with the ground and the center of mass is located within the triangle formed by these feet, it will be statically stable. This tutorial considers only this situation, as shown in the image below (N is the "normal force" the ground exerts on each foot):

Robot Leg Torque Tutorial

The links that make up an "insect" leg do not necessarily need to be perpendicular to one another, as shown in the image below:

Robot Leg Torque Tutorial

 

The angles are taken between the horizontal and the link and it is assumed the legs are configured the same on both sides. The following assumptions must also be made in order to simplify the calculations and inputs required:

1) 6 legs, configured as two rows of 3.

2) All the legs are identical

If you are unfamiliar with the concept of torque, you are encouraged to first read through the Robot Arm Torque Tutorial. In order to find the torque acting at each joint, a free body diagram must be drawn. All supporting legs must be considered:

Robot Leg Torque Tutorial

N1,2: normal (reaction) force

L1,2,3: length of the link

W1,2,3: weight of each actuator (W2,3 are assumed to be very close)

W4: Weight acting at the center of mass

T1,2,3,4: Torque acting at each joint (each side is different)

In order to determine the torque T1 acting at the “knee”, we must assume that the rest of the structure is rigid (not moving). Similarly, when finding T2, acting at the “hip” the rest of the structure (including the torque T1) is considered rigid. If you are uncertain as to the direction of the torque, consider applying torque in the opposite sense and notice that the leg would retract. The links are considered to be massless. The torques T3 and T4 will be different than T1 and T2 because the central weight is not being supported equallay among the three legs. In this case, T1>T4 and T2>T3, so we will only calculate T1 and T2 (an actuator is chosen based on the maximum torque required).

The weight W4 acting at the center of the robot when 3 legs are raised is a combination of various parts below:

Robot Leg Torque Tutorial

The weight of the robot is assumed to be evenly distributed on both legs on the right side, so the reaction forces, N2 and N3 are equal. Three legs must support the entire weight of the robot, as well as their own weight:

Robot Leg Torque Tutorial

The value of the normal force N2 can be found by doing a torque balance about N1:

Robot Leg Torque Tutorial

Although long, the equation uses only known variables, and since the combined torque about the left foot is zero, this equation will allow you to solve for N2. This value is inserted into the equation above, to solve for N1. Using conventional notation (counterclockwise is considered positive) we can find the torque about the knee joint:

Robot Leg Torque Tutorial

The above equation considers that there are three legs supporting the robot on the right side. As with the previous equation, the sum of the torque for an object not in motion is zero (in this case the leg is simply supporting the body and not moving). The torque needed at the hip joint can be found as well by doing a torque balance about that point:

Robot Leg Torque Tutorial

Once more, the total torque about the point is zero because it is not moving, allowing you to solve for T2. At this point, there are two different approaches you can take: one decision is to make all 18 motors identical, while the other is to select motors based on the torque required at each joint. There are arguments to both and the decision is yours. The final torque to calculate, exerted at the shoulder, is used to propel the robot forward.

Keep in mind that a hexapod with three degrees of freedom per leg has a total of 18 degrees of freedom and as such there are configurations possible where less torque will be required when climbing an incline. One example of this is when the rear legs are used to push the robot up the incline, while the front legs pull it up.

In order to find the torque required to move the robot up an incline with each leg positioned identically to the rest, a different perspective must be chosen. If your robot will not encounter steep inclines, or will move in roughly horizontal planes, then it is a good decision to choose the same motor used in either the knee or the shoulder.

The torque calculation required is similar to that of the Drive Motor Selector Tutorial, where the maximum torque will arise when the robot is on an inclined surface. The difference in perspective is such that the "wheel" is placed horizontally rather than vertically. The force of friction acting on the three feet (the other three are raised) is what allows the robot to move up the incline. In the first scenario described here, the robot must simply maintain its position on the incline.

Robot Leg Torque Tutorial

The reaction forces counteract the weight of the robot which would otherwise cause it to slide down the incline. The magnitude of the weight of gravity along the slope can be calculated as:

Robot Leg Torque Tutorial

A torque balance about the left shoulder actuator gives:

Robot Leg Torque Tutorial

In order to move straight, the force on the left side must equal the force on the right side, otherwise the robot would begin to turn.

Robot Leg Torque Tutorial

The torque T2 will be less than T1, so a second equation is not necessary.

The torques above represent the required to keep the robot stationary and does not include the extra torque required for motion. When looking for an actuator, you are encouraged to add 25% to each torque as a safety factor.

Useful Links

Website

Hexapod Robot Development Platforms

Quadruped Robot Development Platforms

Lynxmotion Robotic Leg

Documentaries

Posted: 15 Jan 2013 08:27 AM PST

Documentaries

Bots High

Remember BattleBots? The TV show where two remote controlled robots would enter a weaponized arena and fight it out for 3 minutes or until one stopped moving. The name “Bots High” is a combination of “Robots” and “High School”.

Well, even though the show ended, the competitions have continued. More so, there's a whole high school division where teams of high school students build and compete with the same size robots and rules of BattleBots, and that's what Bots High is about.

Bots High is a documentary that will follow multiple high school teams in South Florida throughout the school year as they design, build, and then compete in the BattleBots National Championship in April 2010. Think Mad Hot Ballroom with robots.

RobotShop is currently a sponsor of the documentary. Here is a video teaser:

Articles

Posted: 15 Jan 2013 08:24 AM PST

Here you will find articles written by RobotShop and external authors. Articles have been placed in the closest relevant category. If you have an article you would like to share, please submit it to the RobotShop Support Center, Subject: Learning Center Article.

General

General articles, which could be placed in multiple categories, are found here. Articles with multiple topics are also placed here.

Domestic Robots

Domestic robot articles relate to robots you would or could find around the house and include vacuum cleaners, pool cleaners, lawn mowers, robotic assistants and more.

Robot Toys

Robot Toys include products that are currently available, may soon be available or are imagined. Robot toys are considered only if they are pre-assembled.

Robot Kits and Development Platforms

Robot Kits and Development Platforms are useful for designing more customized solutions. Articles including product reviews, current uses and more can be found here.

Custom Robotics

Any articles that include discussion about building custom robots, including parts, coding, “how-to”s, design and fabrication and more are found here.

Construction

Electronics

Motors and Actuators

Programming and Software

Projects

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