Electric Circuit?RC Car question?

Question

I have to build a car, that travels between 5-10 in 45 seconds or less and stops whrever the judges tell it to, we wired an RC car to run in a strait line when you turn it on, w/o the remote, now for our breakign system we need a small second timer that could cut off the electricity to the motor, and stop the car on a dime, does anyone know of a "timer switch" small enoguh for an RC car?

and I'm a student, please use simple techonlogy and explain what you mean please.

Answer 1

A 555 timer is an integrated circuit with uses an RC time constant to determine the time limit. If you don't know what that means then get a kit(see link)

A timer especiallyy a 555 timer is not going to be very precise especiall if you have to change the timer settings in the field during the test. Consider the difference in time the car takes to travel 6 inches. Your timer has to be set more precisely that what ever that 6 inch travel time is. In addition you have to be very precise in starting the timer as the car starts moving.

Consider using a counter instead to count the revolutions of a wheel. This would be very precise and easy to set in the field. You could mount a small magnet on the wheel and use a reed switch (magnetic switch) or a hall effect sensor to detect the wheel rotation. Using a count down counter the power to the motor would be stopped when the counter reaches zero. Just compute how many turns the wheel must make to travel a given distanct and set this count into the down counter.

The magnetic reed switch will be easy to use and wire up. If you want even more precission or can use a magnet for some reason you can try the following.

Another means of counting wheel rotation is to use an optical interrupter. This is a small light source and sensor witch has a small gap between them. Anything passing between, blocks the light and generates a pulse. The old style PC mouse (the one with the rubber ball) has a couple of these in it along with slotted disks which are used to detect how much the mouse is being dragged. So you could either use the slotted disk from a mouse or make your own.

Answer 2

use a 555 timer. you could set it to time out after 45 seconds or whenever it received a remote signal. The output could then trigger a couple SCRs or PNP transistors, causing a charged capacitor to dump reverse polarity on the drive motor for a few seconds.

Answer 3

Cmos 555 timer
Simple integrated circuit.. astable or monostable
just put 555 timer into Google and pick a manufacturer
and d/l the data sheet (pdf)