help in speed changing

[mohd9011]

hi
Iam building a toy ship that uses 5 ultrasonic sensors to detect any obstacle and the arduino uno use the relay to switch between two motors and rotate the ship and i want to change the speed according to the distance between the ship and the obstacle tried variable resistance but it didn't work so is there is any other way to do that.
thanks
p.s: the ship is 50cm length and 30 width and 30 height and if this way can be controlled by arduino i'll be thankful.

 

[KrisBlueNZ]

Yes: PWM. http://www.google.com/search?q=how+does+pulse+width+modulation+PWM+work

 

[mohd9011]

I read that it's used to control led voltage how can I use it to control the ship voltage putting in mind that the ship's voltage is external one
Thanks

 

[KrisBlueNZ]

You use PWM to control the average voltage to the motor. Wider pulse width = higher average voltage = motor turns faster.

 

[CDRIVE]

Kris, wouldn't average current or even power be a better expression of what PWM does? ..... Or am I being picky?

Chris

 

[Laplace]

With PWM the property being controlled is the average voltage. Of course, this changes the current but the current also changes for other reasons such as the variance in the load. This is not to say that you couldn't design a PWM controller that supplied constant current pulses, and in that case the property being controlled would be the average current. But I can't think of an example where constant current pulses would be more appropriate than constant voltage pulses.

 

[CDRIVE]

I think your misinterpreting my post or perhaps you don't get my point. Come to think of it that may be the same thing.

Chris

 

[Laplace]

Wasn't your point the fact that you were being picky?

 

[CDRIVE]

Ha, that made me laugh but you're right! I did.

Chris