Two NXT robots throw the ball at same time.
How to write a single program to communicate two robots at the same time.
the robots have to throw the ball at same time.

You could do it by having one of them send a message to the other via a couple of different ways:

• Light sensor, the master turns on the light on the sensor and the other "listens" for it with its own light sensor.
• Bluetooth, the master sends a message to the slave
• RS485, the master sends a message to the slave

The top one is the easiest.

- Xander

Thank you so much ..

Any other way to communicate the robot.
what is RS485.

RS485 is a very fast serial protocol but it's a bit tricky to master. Make it work with the light signals first.

- Xander

light signal is little bit time difference..
better how to send a message in bluetooth

If there's a small difference, you can add a wait at the one that goes earlier. Adjust the time it waits to get them equal.

hi team i solve that program . but i have another problem.
the robot have to select the ball . red or blue ..
if the robot have red color ball . the did not take any further action.
how to find out the ball color.