Controlling DC motors with km/h

Hello! I am kind'a new to the arduino world...
My project includes 2 12v dc motors that I need to send them values in km/h... how can I do that?
thanks for the help!

Hi,
First of all do some maths! how big are your wheels, what kind of RPM do you hope to get from your motors...

You've told us nothing, how can we help!! Tell us more if you want an hand.....

What motors? Are they driving wheels? Or tracks? Or propellers? Or ducted fans? Or?

With direct driven wheels you can get a reasonable approximation to speed by controlling the PWM used to drive the motors but you'll need to calibrate it and it will be affected by things like the surface and the load. So it's not easy to get much real accuracy.

Steve

Tutorials on how to select motors, wheels, calculate robot velocity etc are at the Society of Robots page.

Hi!
The motors aren’t used to drive the robot... they are used for launching mechanism so they are not connected to surface and there are not load on them...
The radius of the wheels is 10 cm.

Robots and launching mechanisms obey the same physical laws.

Is your launching mechanism for balls? Like a practice server for tennis balls or soccer balls?

Yes, the mechanism is for balls.