Data Sheet

Sensor Documentation Modern Robotics, Inc.

Version 1.4.3 20

Integrated Z Value:

The integrated gyro Z value returns the current value obtained by integrating the Z axis

rate value, adjusted by the Z axis offset continuously. This integrated value can be reset

to 0 by issuing command 0x52.

This value can also be used as a signed heading value where CCW is in the positive

direction and CW is in the negative direction.

Z Axis Scaling Coefficient:

The integrated Z value is subject to scaling based on the Z axis scaling coefficient. This

value defaults to 0x0100 which has a binary “decimal point” between bits 7 and 8. Thus

the 0x0100 represents a value of 1.0. This value may be adjusted to ensure that a

reading of 360° corresponds to one exact revolution of the sensor.

The Z axis scaling coefficient must be calculated by dividing the angle the sensor is

physically rotated by the heading value that is returned from the sensor. The “Angle

Rotated” is the number of degrees the Gyro physically rotated (360°). The “Heading

Value” is the value returned by the sensor by the Heading Data registers. Once the value

is entered in the Z Axis Scaling Coefficient register, a command of 0x4E (Null Operation)

must be made to the command register to save the value to the EEPROM.

Step 1: Collecting Values

With the Gyro sitting completely still, type a value of 0x4E (Null gyro offset and reset Z

axis integrator) into the Command Register (0x03) to Null the gyro. Then rotate the Gyro

360° exactly in a counter clockwise direction and write down the heading value that is

returned.

Angle Rotated = 360° - Always rotate 360° when scaling the Z Axis

Heading Value = Returned Value 0x06 (lsb)/0x07 (msb)

Heading Value 0x07/0x06 (msb/lsb) = 0x0163 = 355°

Step 2: Calculate the Scaling Coefficient

Scale Coefficient = Angle Rotated/Heading Value

Scale Coefficient = 360/355 = 1.01

The value obtained in this step is the scaling coefficient. When this scaling coefficient is

multiplied by the heading value, the result is a scaled heading.