The easiest on-board current measuring system is a PCB trace in series with the power to the Victor.
1.5oz copper clad PCB has a resistance of approximately 0.7milliohms per square. 1.5oz copper is the weight of the copper you get from a custom circuit board from AP Circuits (
www.apc.com).
To measure the current, you measure the voltage drop across the copper trace. TI sells the INA169 through digikey. This chip is designed to provide a ground referenced voltage (0-x volts) from a voltage across a current sensing resistor. Gain is controlled by a single resistor.
Example:
With a 1" wide by 5" long patch of 1.5 oz copper, the final resistance is 3.5milliohms.
In order to see overcurrent conditions lets set 100A=5v output.
This requires a gain resistor for the INA169 of about 14Kohm.
The little breakers open around 30Amps or when we measure 1v out of the INA169.
For those of you concerned about power/voltage loses, we measured 125mV @ 30A across the copper I described above. This equates to 3watts of power. This is approximately the same loss as 5" of the 10awg wire. If you are really concerned, use 8awg wire instead of 10awg and keep the wire lengths as short as possible. The smaller the wire, the shorter the length.
Our custom circuit box includes two of the current shunts described above on one circuit board. A second circuit board is stacked above the shunts. The second board includes the INA169's, a PIC16F877, a 4 channel digital to analog converter to send analog commands to the robot controller. A connector for the Gyro (We scale and filter the gyro data before sending it to the robot controller) Connectors for the optical sensors, and 8 digital outputs to the digital inputs on the robot controller for digital commands. All of our high speed control code runs in the PIC16F877 (100x faster than robot controller) and commands are passed through the digital and analog inputs.