# What is the technical name when robot wheels are aligned to perform spot turn?

I have a robotic simulator that enables a 6 wheel rover to perform spot turn. To prepare the rover to spot turn, I have to arrange/align the wheels in such a fashion:

<front side>
//    \\
||    ||
\\    //
<rear side>


What is the technical name of it? Circular wheel arrangement? Circular alignment?

• What robot sim do you use? Is it open and free of charge? Where can I get it? – EEd Aug 27 '14 at 14:15
• @JohnWilliams V-REP (coppeliarobotics.com) is free and being used in my institutions for research. I evaluated a number of robotic simulators but none fit the bill for my use. So I created one of my own. – ikel Aug 28 '14 at 8:12

I'm not aware of any technical name for the alignment of the wheels except -- literally -- "steering".

Spot turns in theory are no different than any other turn. You simply align the axis of each wheel with the radial lines coming from a single pivot point. If that point is underneath the vehicle, you will be doing a spot turn (a.k.a. point turn, a.k.a. pivot turn). If the point is not underneath the vehicle, you will be doing a regular arcing turn like you'd do in a car or bicycle or similar.

Even if not all the wheels have adjustable angles, you're still orienting all the wheels to the same point.

• Steering at Zero Instantaneous Centre of Rotation? – ikel Aug 28 '14 at 8:25

Looks like wikipedia calls it Active Four-Wheel Steering. Although, what you're talking about is the left and right side steering opposite of each, whereas Active Four-Wheel Steering in automobile usually refers to the front and rear steering opposite of each other, I still think your case can still be considered Active Four-Wheel Steering the way it is defined there:

In an active four-wheel steering system, all four wheels turn at the same time when the driver steers.

This is similar to crab steering, but with crab steering all the wheels turn in the SAME direction at the same angle so the vehicle can travel in a straight line at an angle.

• Does it also apply when you have 4+ wheels? Say MER-Spirit or NASA's Athlete (athlete.jpl.nasa.gov)? – ikel Aug 28 '14 at 22:24
• Wow, thats quite a vehicle. I think I would call that Active All-Wheel Steering. I don't think there is an offical term for it though. – Airuno2L Sep 2 '14 at 11:45
• Yep. My robot rover has only 6 active wheels, not as many as NASA' Athlete. – ikel Sep 3 '14 at 20:50

Differential drive

Left and right wheels drive clockwise and anticlockwise, at same speed, for robot to rotate with reference to central point between wheels

You may want to let front and back pairs of wheel free spinning (if gear ration small, open electric circuit will do) and only drive the central 2 wheels. Or, you need to model all six wheels, may be some skidding for spot turning.

There is no "term" for this arrangement of wheels, just like there is no term for this arrangement:

 //    //


other than "turning right"