Added IMU sensor noise to the model, to avoid STALE messages (#34)

Author: slgrobotics

models/lawnmower/model.sdf

@@ -221,6 +221,60 @@
       <sensor name="imu_sensor" type="imu">
         <always_on>1</always_on>
         <update_rate>250</update_rate>
+        <imu>
+          <angular_velocity>
+            <x>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.0003394</stddev>
+                <dynamic_bias_stddev>3.8785e-05</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>1000</dynamic_bias_correlation_time>
+              </noise>
+            </x>
+            <y>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.0003394</stddev>
+                <dynamic_bias_stddev>3.8785e-05</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>1000</dynamic_bias_correlation_time>
+              </noise>
+            </y>
+            <z>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.0003394</stddev>
+                <dynamic_bias_stddev>3.8785e-05</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>1000</dynamic_bias_correlation_time>
+              </noise>
+            </z>
+          </angular_velocity>
+          <linear_acceleration>
+            <x>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.004</stddev>
+                <dynamic_bias_stddev>0.006</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>300</dynamic_bias_correlation_time>
+              </noise>
+            </x>
+            <y>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.004</stddev>
+                <dynamic_bias_stddev>0.006</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>300</dynamic_bias_correlation_time>
+              </noise>
+            </y>
+            <z>
+              <noise type="gaussian">
+                <mean>0</mean>
+                <stddev>0.004</stddev>
+                <dynamic_bias_stddev>0.006</dynamic_bias_stddev>
+                <dynamic_bias_correlation_time>300</dynamic_bias_correlation_time>
+              </noise>
+            </z>
+          </linear_acceleration>
+        </imu>
       </sensor>
     </link>
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