Quote:
Originally Posted by Al Skierkiewicz
Don't forget that the voltage polarity on the case will reverse when the motor direction reverses.
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This is actually one of most common myths in FRC, perpetuated in a blue box in the rules each year. The real reason we isolate our frame is to allow the system to survive single-fault wiring failures.
Quote:
Originally Posted by Joe Johnson
Has anyone tried monitoring the voltage on the case live while the robot is in action?
I am thinking that I could have put connect the case to a resistor network. For example, I could put two relatively high resistors in series between the battery and ground and tie the case to the middle of these and monitor this voltage. This monitor voltage (i.e. the case) would sit at roughly 6-8V (1/2 battery) unless a short starts and then it would start going rail to rail 12V - gnd - 12V - gnd - ...
And this is when I would replace that motor.
What do people think of this scheme?
Joe J.
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This is similar to the way the PD's prototype big brother detected chassis faults, except we pushed an active signal instead of using a resistor divider. The control system would be fine with 100 Ohms, but that'll burn three fourths of a watt. I'd bump up your impedances into the 5-20k range. You're signal quality will be unaffected but it can be smaller and safer.
Quote:
Originally Posted by artdutra04
If the 775 is completely electrically isolated (via both the case and output shaft) through plastic mounting plates and either acetal gears or timing belts, will the cRIO ever actually reboot if a motor starts to go bad?
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No. A fully isolated but faulty 775 will not have an adverse impact on any portion of the control system electronics. I do not have any information as to whether or not this fault will have an adverse impact on the motor itself.
Quote:
Originally Posted by jason701802
I thought the chassis of the cRio was tied to 24V.
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To the negative lead
through a fuse and a self-resetting fuse. If bonus current is sent through this path, the two race to see who will blow first. The single-use fuse rarely wins, but can go with repeated abuse.
Quote:
Originally Posted by jason701802
Even if on one robot the chassis is connected to 12v and on the other it is connected to gnd, nothing would happen if these two robots touched each other. Sure, you'd be able to read 24v between the (-) terminal of the first robot and the (+) of the second if you stopped the match and walked out there with a voltmeter, but there is no complete circuit for current to flow through. Both the (+) and (-) of the same battery would have to be connected the different parts of the chassis and/or frame for any current to flow.
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True. This is another myth that used to be in a blue box.