Calculate required torque for differential drive robot

[DannyMoretz]

Hello everyone,
So I am working on a differential drive vehicle... max weight 6kg and using two stepper motors centred on a circular shaped flat body. I want to try and work out if these stepper motors have enough torque to drive the thing. I am a second year engineering student, but I haven't really done any similar calculations before. I also don't understand the spec sheet for the stepper motor... in regards to torque... it says things like:
In-traction torque: >34.3mNm (120HZ)
Self-positioning torque: >34.3mNm
Friction torque: 600-1200 gf.cm
Pull in torque: 300 gf.cm

So once calculated, which one of the above values should I be concerned about.

Thanks guys

 

[gtoguy97]

!The most important value to consider when determining the torque of the stepper motors is the In-traction torque. This is the torque that is required to move the vehicle. The self-positioning torque is not necessary as it is not directly related to movement. The friction torque and pull in torque are also important to consider, as they represent the maximum amount of resistance that the motor can handle before stalling.