US Patent 9874061 Tractor traction control for cased hole

Traction for a downhole tractor in a wellbore. A downhole propulsion system can provide a first traction module; a second traction module; and a controller configured to compare a first input parameter representing operation of the first traction module with a second input parameter representing operation of the second traction module. The controller can adjust a first output parameter of the first traction module and/or a second output parameter of the second traction module based on an input representing slip of the first traction module relative to the second traction module.