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.