Why not use tracks….

An electric motor with two wheels, one mounted vertically and one horizontally. Place it inside a ball just big enough to encapsulate the motor and wheels so that the inside of the ball is always in contact with both wheels.

Two tracks on either side of a center wheel. The center wheel can be engaged to be in an extracted position, or down, to lift and roll and reposition the toy. Then, extracted again to let the tracks roll the toy forward. Ta da….

edit… not a wheel, but a roller ball… much more dynamic.

To Mretropy, That’s a great idea, but I’m aiming to make a toy look more like a robot, so I can’t make it shape like a ball.

To Cazzie, Sorry I have a really hard time picturing what you are describing(part of reason being im ESL). Could you elaborate please? When the ball is engaged, the tracks rolls the ball and drives the toy forward right? But I don’t get “extracted position or down, to lift and roll and reposition the toy”

Wheels don’t take as much time to change direction as you think. Most servos have pretty quick transit time; literally the blink of an eye.

I am against tracks in general due to their complexity, but there are wheeled vehicles like skid loaders that use similar methods (brake/reverse the inside wheels) to turn quicker and sharper than conventional wheeled steering mechanisms allow.

If you are up for some serious craftwork, you can do something like an old rollerball mouse, only using motors to turn the ball instead of using the ball to turn sensors. However, rough terrain might be a hindrance to such a drive system.

But it’s possible that the best solution would be Mecanum wheels
I can’t really describe them, but a picture is worth a thousand words and the video on that page might be exactly what you are looking for.

@jerv Is right. They use this new wheel technology in a lot of places right now including the toy industry. and it is a great way to make a high mobility, low weight vehicles as the “wheel” setups only weigh a bit more than a traditional tire rim combo.

They are a little trickier to drive than a normal R/C car, and some setups require the use of “mixers:“http://www.fingertechrobotics.com/proddetail.php?prod=TR-V-tail in order to translate between the control signals they need and a control scheme that makes sense to a human being. Then again, if you can get the hang of a 3-channel R/C helicopter like the one I have you should be able to control a rig with Mecanum wheels pretty easily.

Also, I would spend the extra $20 to get the Competition grade with the aluminum mounts. You never know when a little extra strength may come in handy ;)