The Comets are coming

Been side-tracked lately with helping FRC Team 3357 - The Comets, get off the ground.

We have a YouTube site with videos of our progress, check it out -

http://www.youtube.com/user/cometsrobotics

Team website is coming soon!

I intend to get back to the ABC's in the future.

The ABC's of FIRST - The letter H

H is for holonomic.

According to Wikipedia, a holonomic robot has as many degrees of freedom as there are total degrees of freedom. In a nut-shell, this means the driver of the robot can direct the machine in any of the 360 degrees in it's operating plane. This does not mean that the robot rotate (or yaw) first. A holonomic robot will be able to directly move in any vector without changing it's original orientation.

There are several ways a robot can be holonomic, however there always seems to be one configuration that I personally always think of when thinking holonomic. This configuration requires that the robot have 4 omni wheels, one positioned in each corner of the robot, but at a 45 degree angle to it's "standard position". By this I mean that the leading edges of the front wheels point toward the center of the robot frame at a 45 degree angle, and the trailing edges of the back wheels point towards the center of the robot frame at a 45 degree angle.

To control this configuration, a computer program is used to calculate the rotation value of each wheel based on the input from the driver. The computer must dynamically control each wheel continuously based on the input from the driver.

This is a complex system, resulting in a great range of mobility. On the down side, there is a significant (in my mind) loss of overall power. Depending on your application, you must weigh these variables when determining the best drive system.

I expect to see many different versions of holonomic robots in this years FIRST Robotics Competition, Breakaway. Check back as I plan to write about more specific types of holonomic drive systems in the near future.

The ABC's of FIRST - The letter G

G is for gyro.

A gyro, short for gyroscope, is an angular rate sensor. It senses rotation in a specific axis, primarily yaw.

The ADW22307 from Analog Devices has a sensitivity of up to ±250°/s and will probably be the device most used during this year's FIRST Robotics Competition.

I see teams using the gyro to maintain an angular deviation from their starting position, then correcting before traversing a bump during teleop. Just keep in mind the sensitivity of the device you are using. I know you can make a robot turn faster than 250°/s.

In the past, gyros were used extensively in autonomous mode to determine how far the machine had turned.

The ABC's of FIRST - The letter F

F is for fuse.

A fuse is a device that protects the electrical components of the robot in case a component begins drawing too much current. In the classic term, a fuse is an inline device that melts and disintegrates when too much current is passed through it. This breaks the flow of electricity, thus protecting the circuit.

Today, fuses on a FIRST Robotics Competition robot are "circuit breakers" that can be reset if the current threshold is exceeded. Each kit of parts contains various sizes of fuses that are used in specific areas of the robot's circuit. Fuses are inserted into the power distribution panel, which is the main hub for routing power through the robot.

It is very import to use the proper gauge wire on the different circuits on the robot. Refer to the documentation for more information.

The ABC's of FIRST - The letter E

E is for energy.

The only stored energy that a robot may start with in a FIRST Robotics Competition, is in the 12V battery. From that point there are a few methods of converting the battery's energy into other types of stored / potential energy.

Each team has a compressor that is allowed to be built into the robot. This compressor can compress air to 120 pounds per square inch and that air can be used to drive pneumatics to push components in any desired manner.

The robot may also store energy by deforming a specific component, most likely a spring or rubber band type material like surgical tubing. Energy can be built up to release in a quick burst in this configuration.

I expect to see teams building one of these devices this year to kick the ball down the field. Leave a comment if you think one is better than the other, and please share your reasoning.

The ABC's of FIRST - The letter D

D is for deadband

Deadbands come into play in a lot of different components that a FIRST robot may use. The Wikipedia link for deadband explains a lot.

Briefly, a deadband is an occurrence of no output when a specific input was applied. A deadband is sometimes built into a system by design, and sometimes it happens because of wear on parts.

A good example of an intentional deadband is in the thermostat of your house. The thermostat monitors the temperature of your house and is set to heat or cool at a certain threshold. Lets say that you set the thermostat for 68 degrees. The furnace may turn on when the house reaches 66 degrees and may turn off when it hits 70. This is fine for most people and prevents the furnace from running briefly when the temperature dips slightly below 68 and stops it immediately when it hits 68. This situation would be called an oscillation.

A mechanical deadband happens when a worn gear has a little bit of slop or play. As the input gear starts moving, the output gear does not move until the slop has been taken up. That portion of inactivity is the deadband in the gears.

Joysticks have a deadband region that requires the physical movement of the joystick to bypass a certain threshold before the actual output of the device changes.

Sensors may also have a deadband, where it may not read any change until a certain threshold is passed. This, like the thermostat, is by design, to prevent oscillation.

Keep this in mind while building and debugging your robot.

The ABC's of FIRST - The letter C

C is for cRIO

The cRIO is an acronym for Compact RIO (Reconfigurable I/O). This device serves as the computer on current FRC robots. The details of the cRIO are as follows:

400 MHz, 32 bit PowerPC processor

2 Million Gate FPGA (Field Programmable Gate Array)

Various Digital and Analog inputs

The cRIO is rugged. It is capable of taking a 50 g shock and will operate modularly from -40° F to 158° F.

The computer can be programmed in several different languages. C++ and Java are classic text based languages that can be used, and LabVIEW from National Instruments is also available.

Past experience has shown that the plug-in modules in the cRIO will dislodge themselves under extreme conditions. With the 2010 FRC game warning about machines tipping over, take my advice and strap the I/O modules down securely when attaching the cRIO to the robot chassis. If a module slips out during competition, bad things will happen.

The ABC's of FIRST - The letter B

I'm having a difficult time coming up with a good B word relating to FIRST Robotics Competition. I'm thinking that battery & bumper are not too interesting to write about, however both of those items are necessary parts on every FRC robot.

The term that I've chosen for B is not very technical, but it was a new method in 2009 and caused a little confusion as to how it would work in the beginning of the season. The B term is Bag & Tag.

Teams that are not in Michigan must crate up their robot on the last day of the build season. This date is known as ship date and was established so that teams had no way to work on their robot after the build season was over. The crated robots needed to be shipped to the venue of their first competition, thus removing the machine from their possession. This established a level of equality for all teams, no matter if their first competition was in the first week or the fourth week.

Crating and shipping a 120 pound robot is not cheap. In 2009 FIRST established a new and separate version called FIRST in Michigan. This was established to get FRC teams in Michigan more competitions for less money. One of the cost saving measures was to have teams "Bag" their robot instead of shipping them as in the past. Last year all teams competing in the Michigan District events, bagged & tagged their robots and transported them themselves to each event.

Again in 2010, Michigan teams will be bagging and tagging their robots as a cost savings to each team. The tagging process is in place to prevent anyone from actually working on the robot during times that are prohibited. Teams are given several locking tags with unique serial numbers. When the robot is to be locked up, the team will lock the robot in the bag with one of these tags. An individual not associated with the team is responsible for logging the date/time the robot was either locked in the bag along with the serial number on the tag. At certain times, the robot is permitted to be "out of the bag" and at these times, a person not associated with the team will log the tag as it is removed, and then log it again as a new tag is locked on the bag when the work time has expired.

See the FIRST documentation for official details on when the robot can and cannot be worked on after build season.

The ABC's of FIRST - The letter A

As promised, I'm going to attempt to go through the alphabet and write something interesting and probably technical about components that are commonly used in a FIRST Robotics Competition robot. Today is day 1 - thus the letter A.

A is for Accelerometer

An accelerometer is a sensor typically placed on the robot that is connected to the on-board computer system. The accelerometer detects both rates of acceleration and deceleration. This was a helpful device to teams trying to determine optimal acceleration in last years game, Lunacy, where traction was an issue.

According to Wikipedia, the structure of an accelerometer is as follows:

Conceptually, an accelerometer behaves as a damped mass on a spring. When the accelerometer experiences an acceleration, the mass is displaced to the point that the spring is able to accelerate the mass at the same rate as the casing. The displacement is then measured to give the acceleration.

Modern accelerometers are often small micro electro-mechanical systems (MEMS), and are indeed the simplest MEMS devices possible, consisting of little more than a cantilever beam with a proof mass (also known as seismic mass). Damping results from the residual gas sealed in the device. As long as the Q-factor is not too low, damping does not result in a lower sensitivity.

Under the influence of external accelerations the proof mass deflects from its neutral position. This deflection is measured in an analog or digital manner. Most commonly, the capacitance between a set of fixed beams and a set of beams attached to the proof mass is measured. This method is simple, reliable, and inexpensive. Integrating piezoresistors in the springs to detect spring deformation, and thus deflection, is a good alternative, although a few more process steps are needed during the fabrication sequence. For very high sensitivities quantum tunneling is also used; this requires a dedicated process making it very expensive. Optical measurement has been demonstrated on laboratory scale.

Another, far less common, type of MEMS-based accelerometer contains a small heater at the bottom of a very small dome, which heats the air inside the dome to cause it to rise. A thermocouple on the dome determines where the heated air reaches the dome and the deflection off the center is a measure of the acceleration applied to the sensor.

Most micromechanical accelerometers operate in-plane, that is, they are designed to be sensitive only to a direction in the plane of the die. By integrating two devices perpendicularly on a single die a two-axis accelerometer can be made. By adding an additional out-of-plane device three axes can be measured. Such a combination always has a much lower misalignment error than three discrete models combined after packaging.

Micromechanical accelerometers are available in a wide variety of measuring ranges, reaching up to thousands of g's. The designer must make a compromise between sensitivity and the maximum acceleration that can be measured.

In this year's game, Breakaway, the accelerometer might be used as a sensor to determine if the machine has run into a "bump" on the field. The accelerometer would actually be indicating a drastic decrease in acceleration, thus alerting the system to halt movement or change configuration.

Breakaway

Today was kickoff for the 2010 FIRST Robotics Competition season and the new game "Breakaway" was announced. Breakaway looks like an exciting game that will be easily followed by all spectators. The game animation follows -

Our new team met immediately following the broadcast of the game description and we spent almost 4 hours digesting the game rules, the arena and robot requirements. We ALL have a very good understanding of the base rules and regulations. I'm sure as we dig deeper, we'll uncover the more subtle and interesting points of the game. I'm looking forward to this season and our new team taking hold as a permanent fixture in FRC.

FIRST Robotics Competition Kickoff

Tomorrow morning is the kickoff to the 2010 FIRST Robotics Competition. Teams all over the world will learn for the first time how the game/sport/competition will be played. Every team will get their standard kit of parts that they can use to build a machine to compete in this year's competition. From that point every team will have 6 weeks to design, build, program and test a machine and make it ready for competition.

Smart, ambitious high-school kids all over the country, and world, are anxious for tomorrow's game details. Our new team from Forest Hills is ready too. We've got a great team assembled and are looking forward to this year's challenge.

Also, beginning tomorrow, I plan to start blogging my A, B, C's of FIRST. Check back tomorrow to see what I've got in store.

And to all the FIRST FRC teams out there preparing for the new season, good luck to everyone!