Gazebo Youbot Arm Slowly Drifting

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Hi,

I am running a simulation with a (supposed to be) fixed to the ground youBot arm. I notice that at the first spawn, it doesn't move at all, but then I will send a command to the arm. It normally executes perfectly fine, but then the arm is supposed to hold that position indefinitely until I tell it to do something different. However, I notice that the entire arm drifts slowly (yet significantly enough to see it happening) and will rotate very slowly or do some other weird stuff. Is there a way to fix the robot to the gazebo "floor" so that this doesn't happen? I cannot ascertain as to whether the joints themselves are drifting too, but at the very least I would like the youBot arm to stay put on the ground.

Thank you,

-Adrian