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The CREATE base on the earlier versions of turtlebot has some drawbacks when it comes to hardware (IMU and Battery). If the Ni-Mh battery is old and used over many charging cycles, it will tend to create power fluctuations in your power distribution board. You will need to do a power reset (switch off, unplug cables from turtlebot, remove battery, press and hold power button for a few seconds, connect battery, plug in cables and then turn on).

Moreover, the IMU used is a cheap odometry estimation gyro, which is not reliable for mapping complicated environments (few features, many turns). The calibration process done on a clean power supply can still give you values close to each other, if done multiple times, however, it does not converge to a precise particular value for which the delta yaw (heading error) is close to zero.

In the calibration process, the turtlebot is supposed to rotate 720 degrees first, followed by three 360 degree rotations at varying speeds. It is supposed to point at the wall, or the configuration at which you started the calibration. If this doesn't happen, try changing your odom parameters using rqt_reconfigure.

There is no documented calibration routine, hence it is hard to guess how the gyro_correction factor and the odom_angular_correction factor change the calibration routine.

If you are facing trouble over a long time, you can do the following: 1. Check pin out at the power distribution. Between pins 8 and 14, a steady 5V DC should be present when powered on. 2. Change battery, or get an alternative LiPo power supply (4 cell battery with higher mAh would do) 3. Use a custom IMU 4. Get a kobuki base. It is fairly accurate and factory calibrated.