PWM communication between dobot magicians


Is there a way for one dobot magician to talk to another dobot magician using PWM? We have been handshaking between them using simple high/low signals through an optocoupler but that just works asa basic trigger. We would like to be able to send more complex information (like a color of a block from the conveyor belt set) between the magicians.

We can see that there is a PWM function and we have had one dobot sending a signal to small servos but we cannot get a second dobot to respond to PWM from dobot #1.

Any thoughts?