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morganh2550
20-01-2009, 00:41
we to hook up a resistor to try to measure to current to the motor and when we turned on the robot, it worked for a while then just died and the cRio will not turn on. any ideas!!???:confused: :confused:
Russ Beavis
20-01-2009, 07:40
How were trying to measure motor current? If you were simply placing a resistor in series with the motor leads and then doing a differential voltage input to the Analog Breakout, I can't think of any way that a failure within that circuit would break the cRIO or its 9201 analog input module. I could believe that you've fried the Analog Breakout adapter module but you shouldn't be able to take down the cRIO with a resistor.

What size resistor did you use? Keep in mind that motor currents can exceed 100A for short periods. Let's just imagine that you used a 50 milliOhm current sense resistor - there would be 5V across that resistor (100 * 0.05) and 500W being dissipated for a short period of time. In other words, all resistances in the path from the battery to the motor need to be in the single digit milliOhm range to keep from frying.

More details please...

Russ
morganh2550
20-01-2009, 23:45
we used a 0.1 ohm resister?
Russ Beavis
20-01-2009, 23:57
Have you been following the setup procedure outlined in http://www.usfirst.org/community/frc/content.aspx?id=10934?

I'm curious to know whether you had been successfully using the system before attempting the current measurement.

Do you have a set of schematics that you've been using or can you post a picture?

Russ
EricVanWyk
21-01-2009, 00:04
Please measure the voltage that is being given to the cRIO.
morganh2550
23-01-2009, 00:19
we believe the reason for this that we wired the to the resistor backwards we do not know why the bumper did not fry before the cRio.
Vikesrock
23-01-2009, 00:33
we believe the reason for this that we wired the to the resistor backwards we do not know why the bumper did not fry before the cRio.

Resistors do not have a polarity, it is not possible to wire a resistor backwards.
BLAQmx
23-01-2009, 14:55
cRIO and its modules are electrically isolated to prevent this from happening. If the cRIO is damaged it is very unlikely it was caused by running to much current into the AI module.

Have you called NI for support? If you cRIO is damaged we will overnight a new one to your team.
crake
23-01-2009, 20:47
This unit has already been RMA'ed, but we haven't gotten the unit from the field. NI has 100% debug on all returned FRC controllers so we'll snag it once it arrives to take a look and determine root cause.
morganh2550
24-01-2009, 01:26
we got a new cRio :D but we are still confused as to why it died in the first place:confused:
crake
24-01-2009, 09:44
We'll take a close look once we receive it.
joek
24-01-2009, 15:59
when any electronics fry, they produce blue smoke (or so i've been told)
crake
24-01-2009, 21:07
Ever seen an electric pickle?
Alan Anderson
24-01-2009, 21:11
when any electronics fry, they produce blue smoke (or so i've been told)

That's close, but it's backwards.

Electronics work because they contain magic smoke. If the smoke escapes, they stop working.