A voltmeter is not he best tool for measuring the PWM output (measured from Black to White/Yellow), but you can get an idea of what the voltage would be using the meter in DC mode. A typical servo signal at neutral will be 1.5 ms at 5V and 18.5ms at 0V, giving an average voltage of 0.375V. Max reverse is typically 1ms (0.25V avg), and max forward is typically 2ms (0.5V avg), so you need a good meter to read this.
If your robot is disabled, you will probably get 0V on the signal.
If you can get your hands on an Oscilloscope, it's a great signal to watch, and is a good learning opportunity about test equipment.
I think you do need to get your Driver station E-Stop hooked up as mentioned above. This seems like the most likely barrier to your tests working. One person should be assigned to hold it in their hands at all times during robot testing, in case something bad happens. I assume you're not looking to put any holes in the walls or the people on your team
