[DonRotolo]

Current can be measured in many ways. PWM value only relates to voltage, not current. One way to measure current is to detect the magnetic field surrounding a current-carrying wire. Another way is to measure the voltage drop across a very low-value resistor (specially built to handle the current). Do some research on that.

As to figuring out trial and error, drive the robot in high gear and see at what motor current it starts to lose pushing power. That's where you shift to low. Then drive in low and see where you're coming close to top speed - that's where you shift to high.

For example. Again, this is not wild cutting-edge technology, there's a lot on the web if you take a look.

Don