Wheeled Robot Motion Primitives: Is throttling forward and crab motion considered as one?

I am simulating a wheeled robot of six-wheels and can be independently steered, like MER-Opportunity. The wheeled robot can perform throttling forward,

||---|| <--wheel orientation
||   ||
||---||


crab-motion,

//---// <--wheel orientation when heading is 45
//   //
//---//


and turning on the spot.

//---\\ <--wheel orientation
||   ||
\\---//


My question is: Is it correct to say that I have 2 motion primitives? Throttling forward is basically crab-motion with heading zero.

• hmm, I suppose it depends if orientation is important... – Digital Lightcraft Oct 15 '14 at 9:00
• Well, orientation is important. – ikel Oct 16 '14 at 9:50