What is a gyroscope, and why do I want one on my robot?
The simple answer: It may drastically help you in controlling your robot's steering. The gyro (which hooks between your radio receiver and your speed controller) picks up the rotation of your robot around it's center axis as it drives around, and has the ability to tell if you're actually telling it to rotate via your joystick controller or not. If not, the gyro can automatically communicate to your robot's speed controllers to compensate for the drift or rotation, putting it back on course. All of this happens virtually instantaneously, so that all you need to worry about is driving the bot.

GWS PG-03 Micro Gyro

Finally, a gyro small enough for even the tiniest robots- even Antweights! This little device is only 7 grams!

Simply plug this device into your steering output of your (non-mixed) receiver's steering output (usually channel 2), and then plug your speed controller or mixer input into the slot on the side of this gyro. Mount the PG-03 securely inside your robot, as close to center as you can, and you instantly have better steering control!

Dimensions: 26 x 27 x 11.3 mm
Power Input: 4.8V - 6.0V
Current Draw: 10mA
Weight: 7 grams (with case)
Gain adjustment on unit
Compatible with Futaba, JR, Hitec, Airtronics, Sanwa, Multiplex, GWS.

Head Lock RCE-500X Gyro

This tiny gyro can do either standard rate or head-lock mode. It has optional dual remote or single on-gyro gain control. It also has built-in drift cancelling and temperature compensation technology. See the owner's manual PDF file below for full information.

Dimensions: 23.5 x 21 x15mm
Power Input: 4.2V - 7.0V
Current Draw: 33mA
Weight: 12 grams (with case)
Gain adjustment on unit
Compatible with Futaba, JR, and most other popular radio systems.

GWS PC-3 Gyro Switch

The GWS PC03 In-Flight Gyro Switch allows your gyro to be turned on or off with your transmitter.

This item also works as a bypass or RC switch for any R/C item. Simply activate it to apply or remove signal for just about anything hooked to a receiver (Speed controller, servo, etc)

Dimensions: 27 x 12.5 x 7 mm
Power Input: 4.8V - 6.0V
Current Draw: 2.5 - 7.0 mA
Weight: 6 grams

JR G410T Gyro

Great for beginners and intermediate robot builders

Since most beginners lack the programming experience to fully utilize a tail lock gyro with remote gain and tail lock activation, the G410T uses a pot and switch on the gyro unit itself that lets the robot builder manually adjust gain and switch between tail lock and standard modes. This precision can be used to great effect in the hands of a skilled intermediate or advanced builders as well.

Despite its extremely affordable price, the G410T is not a stripped down gyro. For starters, it's extremely compact because both the gyro sensor and amp are encased in one unit. The high-speed angular velocity sensor will pick up low-velocity rotation just as easily as it recognizes higher velocity drift. A sophisticated, free-floating vibration isolator and reflective silvercase protect the sensor against damaging vibrations and temperature fluctuations.

Specifications
Weight: .80 oz
Gain: Single, Manual
Size: 0.95 x 1.18 x 1.19"