Measuring motor current (anyone tried this?)

[reversed_rocker]

i'm not sure if i'm remembering this correctly, but we were playing around with connecting a wire to the negative portion of the main breaker lead and measuring the voltage drop when current draw increases using an analog in on the CRIO. The voltage drop has a linear relationship with the current draw, so if you apply a couple known loads and measure the voltage drop you can get a constant to multiply your voltage drop by to give you your current draw. If you have your controller on then run all 4 CIMS at full power you should be able to calculate how much current they draw. If you work out the kinks this can be a great way to monitor current during robot operation and put some safeguards in the code to stop you from drawing too much.

Our mentor showed up with a hall effect sensor rated up to 180 amps that he said he got for 8 bucks. We were going to put this on our robot to see if we were drawing to much current during the comp, but when the battery voltage drops below 9v it sends back angry readings.