After we had enough fun with the tank we took it apart and made a bowling machine, just like the ones you use for cricket. The machine uses the same mechanic as the bowling machine in sports but we have also put wheels on the bottom so it could move forwards and backwards.
We have met several challenges while building this robot (making it stable, positioning of the wheels, etc.) but have successfully managed to get it to work, even with an on switch using a white plate with the colour sensor.
Here is a video of the bowling machine moving forwards and backwards, with a frontal support wheel to prevent it tipping.