Current Measurement

[ChuckDickerson]

Our programming team would like the ability to measure the current drawn by the various motors on our robot. The new Jaguars are supposed to have this ability built in but unfortunately we are not allowed to use that feature this year.

I do not know enough about measuring current to guide them but have searched the various electronics supply house catalogs (Digikey, Mouser, Allied, etc.) for current sensors, etc. and am now convinced I know even less than I thought I knew before. I had been under the impression that we were never allowed to place anything inline between the power distribution and the speed controllers but under careful rereading of rule <R44> I’m not so sure that is the case:

<R44> Custom circuits shall NOT directly alter the power pathways between the battery, Power Distribution Board, speed controllers, relays, motors, or other elements of the robot control system (including the power pathways to other sensors or circuits). Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, because the effect on the ROBOT outputs should be inconsequential.

Could someone please assist me in how we can measure current drawn by the motors while maintaining compliance with the rules? Specific part numbers, links to online references, schematics/circuits that teams have used in the past, etc. would be most helpful. I am NOT an electrical engineer but I am envisioning a sensor that connects between the power distribution board and the speed controller and then to the analog inputs that has a 0-5V output proportional to the current being drawn by the motor. For those that are familiar with them, we have a Medusa Power Analyzer that we use in testing and are looking for similar “real time” functionality on the robot during competition.

Thanks!