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The similarities between 4 & 3 wheeled options

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The similarities between 4 & 3 wheeled options

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Although there aren't that many similarities between the two options but there is one. When the motors are on the front two wheels the back wheels or wheel is normally a free turning wheel.

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The difference between 4 & 3 wheeled options

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The difference between 4 & 3 wheeled options

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There are many differences between a 4 wheeled vehicle and a 3 wheeled vehicle. The obvious one being the number of wheels but another thing being the way the wheels work. For a 4-wheeled car there is always two motors. Two of the wheels always have motors and in some cases all of the wheels have motors. For a 3-wheeled car the amount of motors can alternate. Either one motor for the front wheel or two motors when the front wheels are two.

https://www.shutterstock.com/video/clip-23492947-stock-footage-versus-fight-backgrounds-vs-on-fire.html

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This is like the opposite of normal cars steering mechanisms. So the last two wheels are free rotating wheels which follow the direction of the front wheels. The front wheels have the motors and they take care of the steering, so its basically front wheel steering like we are going to have but the back wheels move in the direction of the car. However it would be very hard to parallel park since the car doesn't go backwards as easily. You mainly just go forwards.

https://en.wikibooks.org/wiki/Robotics/Types_of_Robots/Wheeled#4-wheeled_vehicles

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2-by-2 powered wheels for tank-like movement

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2-by-2 powered wheels for tank-like movement

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This robot uses two pairs of powered wheels, right wheels and left wheels. All the wheels have separate motors. The hard thing about this design is making all the wheels turn with the same speed. If one is faster than the other the slower one will slip and the robot wont drive straight.  However it would be hard to parallel park using this steering mechanism because it would take a little more extensive programming skill. And would be more difficult than using front wheel steering.

https://en.wikibooks.org/wiki/Robotics/Types_of_Robots/Wheeled

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Omni wheels are wheels composed of smaller wheels which makes it able to drive in any direction pretty much instantaneously. This would be simple to parallel park since you could just line the car with the spot and then just drive sideways. However the disadvantage of these wheels is that they have poor efficiency since not all the wheels rotate in the same direction so that causes loss of friction.

https://www.youtube.com/watch?v=9GQ0lPGDC1w

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With the 3 wheel vehicles its still a front wheel steering however the third wheel isn't powered and is just a free rotating wheel to keep the car balanced and stable. Because these cars don't go backwards too easily I think it would be a hassle for parallel parking however it is possible.

http://www.instructables.com/id/How-to-make-a-three-wheels-vehicle-robot-chassis/