# Revision history [back]

### Fail to start effort_controllers/JointVelocityController (ros_controllers)

Hi.

I managed to make the effort_controllers/JointPositionController successfully works, but some of my joints need to be controlled using the velocity.

When using this type, I get the following error message:

gzserver: /home/arnaud/Documents/catkin_ws/src/ros_control/hardware_interface/include/hardware_interface/joint_state_interface.h:71: double hardware_interface::JointStateHandle::getVelocity() const: Assertion vel_' failed.
Aborted (core dumped)
`

Any idea of how to fix this? It looks like a run-time error.