Hi all,

I tried to control bb9 to turn 90 degrees by the following code:

```
import rospy
from geometry_msgs.msg import Twist, Vector3
from math import pi
rospy.init_node('move_square_bb8_service_client')
pub = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
move = Twist()
move.linear.x = 0.0
move.linear.y = 0.0
duration = 10
move.angular.z = pi*2/4/duration
pub.publish(move)
rospy.sleep(duration)
move.angular.z = 0
pub.publish(move)
```

but it turned out that it rotated clearly far more than 90 degrees.

Can someone give a hint what is the problem here?

thank you so much!

Best regards,

Kailin