Science Competition Help

[Sapp]

I am trying to help some students with a science competition name MagLev. The goal is to propel a magnetically levitated vehicle down a track using a 9 V power supply, DC motor, and propeller. The finished product looks like an "air boat" out on the bayou. The kids want the DC motor to "pulse" or go from full power to low power repeatedly throughout the run. By controlling the ratio of high to low speed of the fan they can control the time it takes to go down the track,which depending on the competition is 5 to 15 seconds. They first tried to control it with a potentiometer but the vehicle needs full power to move. There problem is that they need to be able to control the timing of the "pulses." Integrated circuits are NOT allowed which is complicating the problem. The kids were wanting to start with a one second on to one second off pulse. Any ideas and circuit diagrams would help.

 

[mursal]

Welcome to the forum Sapp

To get things started, could you use a simple start button (full power) to get it moving, then use a simple circuit to control speed?

 

[davenn]

Hi there Sapp
welcome to the forms

A PWM ( Pulse Width Modulation) control of the motor is what you need
you can do it with with all discrete transistors but that COMPLICATES the job

google circuits for PWM control of a motor
you may find a totally non IC circuit

cheers
Dave

 

[Arouse1973]

If you want pwm. You need a triangle wave oscillator and a comparator with an adustable input using a pot. The pot picks up on a portion of the signal and as you vary the pot the pulse width changes.
Adam

 

[Sapp]

New approach

Possible change of plans. Is there a way to turn on the DC motor and have is "slowly" increase to max RPM? Would an inductor do the trick?