Current reading of motor controllers

[mickztlin]

I am currently working on a project my team were i want to have a box that has a power conector to a battery and a connector out to a motor. Im planning to let the build team use it, but I was wondering if there was a way to record amp draw so we could troubleshoot prototypes. Any suggestions?

[David Brinza]

You can use a current/voltage sensing breakout circuit to monitor power draw using analog inputs in your robot control system.

Here's a PCB capable of measuring up to 180 Amps (more than CIM stall current): AttoPilot Voltage and Current Sense Breakout - 180A (https://www.sparkfun.com/products/10644)

The current measurement is made across a very low resistance shunt (0.25 milliOhm). Voltage measurement uses a 16KOhm voltage divider.

Per 2013 Robot Rules (R54), this breakout circuit should be competition legal:

"Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the ROBOT’S electrical system is acceptable, if the effect on the ROBOT outputs is inconsequential."

[mickztlin]

Thanks a lot, looking for something like this!

[Jon Stratis]

You can also get something like this: http://www.radioshack.com/product/index.jsp?productId=4439164

Simply clamp it around the wire to measure the current through the wire. It works equally well for motor current as it does for entire robot current!

[Michael Hill]

If you use Jaguars, I believe you should be able to read current draw if run in a CAN configuration.

[mickztlin]

We will be using a jag but were planning to use a micro controller and we dont plan to use can. (Arduino does not suport)

[gpetilli]

If you use Jaguars, I believe you should be able to read current draw if run in a CAN configuration.

We have been very successful using the bcd-comm software on a laptop to drive all the motors connected to Jaguars using a single RS232 connector on a laptop. It reports motor voltage and current for debug and if there is an encoder connected to the Jaguar, it also reports RPM. All good diagnostics for initial robot bringup, even if you use PWM instead of CAN on the production robot. No additional hardware or software to buy. We also have used cRIO code to read dynamic currents and diagnose brown-outs at regionals.

I know lots of teams don't like Jaguars, and there are lots of valid reasons not to, but it does provide some very nice features. I am disappointed that the CAN version of the Talon does not appear to be available for 2014. We are looking forward for a more robust CAN based speed controller in 2015.

[gpetilli]

We will be using a jag but were planning to use a micro controller and we dont plan to use can. (Arduino does not suport)

I assume you realize you can not control a motor from an Arduino on a competition robot. All motor controls have to come directly from the cRIO. Inputs to the cRIO are fair game, but outputs are not. This is a necessary safety feature so the field can shut down a rouge robot.

Even if you don't use CAN for drive software, you could use it for diagnostics using bcd-comm on a PC or Mac via a USB-RS232 adapter.

[mickztlin]

I assume you realize you can not control a motor from an Arduino on a competition robot. All motor controls have to come directly from the cRIO. Inputs to the cRIO are fair game, but outputs are not. This is a necessary safety feature so the field can shut down a rouge robot.

Even if you don't use CAN for drive software, you could use it for diagnostics using bcd-comm on a PC or Mac via a USB-RS232 adapter.

It is not ment to be on the robot, it is mearly for prototyping