ros control effort controllers explained?

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In my case i cant use effort_controllers/JointGroupVelocityController due to dont exist you need to separate each wheel and use like the example

left_front_wheel_controller:
    type: "effort_controllers/JointVelocityController"
    joint: left_front_wheel_joint
    pid: {p: 1.0, i: 0, d: 0.1}

Hello @PeterBlackerThe3rd, @PG_GrntDare,
I know it is a late question but I have a problem relative to the same point you spook about. I have an articulated truck which has front and rear part connected by a joint to change the articulation angle between them. The truck is weighting multiple tonnes. I created two controllers (effort_controllers/joint_velocity_controller) to control the movement of the truck. First one is to move the truck linearly by rotating the wheel axle. The second is to change the articulation angle between the two parts. I have three problems with that:
1- changing the articulation angle between the parts is done too heavily and slow (as it could be ignored).
2- The truck move linearly when applying a velocity to the wheel axle and its movement depends somehow on the PID parameter values but unfortunately I do not know what is the best value could be used in my case (heavy models).
3- Even though I have controllers to control the joints which means the joint have not to move freely, but they do.
My suspicions about the reasons: 1- The effort limit in the joint description in the urdf/xacro should be adjusted to deal with the heavy weights.
2- The controlled joints move freely because of the weight of the truck. I have tried many times to find the reasons based on my suspicions but I do not know if I do it in the right way. I will appreciate your help and thanks in advance.