how to start and stop a toy car?
Hi,
Another 'optical sensor' idea would be use optical encoders on the wheels, and a microcontroller to know exactly what position each wheel is in. Whether its an absolute encoder, or an incremental, doesn't really matter. Incremental just measures the speed and direction of each wheel. You could use the sesors/micro to control the speed of each wheel, and make it turn 90 degrees, fairly accurately.
Other than that, you would need a stationary reference (something that isn't on the toy car) like rick suggested. I suppose an extreme solution would be a hall sensor, to use the earths magnetic field as a reference. You can get these sensors sensitive enough to a degree, and with a bit of intelligence, you it to turn your car.
Although, that is only really for a toy that can be placed anywhere. You mentioned 'junction' so I assume this toy is placed on a 'track' or 'road', in which case, a stationary reference wouldn't be difficult to implement.
Is the car a '2 wheel' drive? That is, to turn, could you simply have the two motors going in different directions so it can turn on the spot. Or does it have a steering mechanism similar to real cars? (turns in an arc)? The former would make life easier, since it stops, turns on the spot, then gets going again. The latter requires the car to start turning at a point before the corner.
I'm always full of idea's, most useless, but ya never know.
Regards,
BuriedCode.