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Unread 27-01-2012, 14:12
Unsung FIRST Hero
Al Skierkiewicz Al Skierkiewicz is offline
Broadcast Eng/Chief Robot Inspector
AKA: Big Al WFFA 2005
FRC #0111 (WildStang)
Team Role: Engineer
 
Join Date: Jun 2001
Rookie Year: 1996
Location: Wheeling, IL
Posts: 10,798
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Re: Banebots RS-775 Case Short

No,
I disagree with a statement of myth. At the time that faults were first noted on FRC robots, the IFI control system was being used. It does not have a conductive case. However, robots with any electrical faults to the frame could under certain conditions cause current to flow between robots.

The polarity of the voltage present on the case of a failed motor can change depending on where in the motor the failure occurs. If the fault occurs with internal wiring/brush assy and the case of the motor is tied to the negative lead of the battery (or near that potential) when operated in one direction. Then a motor reversal in this case is likely to put the case at near the positive lead of the battery. If the motor winding alone is the source of the fault, then the polarity on the case will change with rotation and will vary with duty cycle supplied to the motor. There are other variables as well depending on the nature of the fault, such as in a motor where the commutator is bridged by solder splash or two windings are shorted together.

For those just reading the thread and those actively participating, please remember that motor failure is a common occurrence in motors other than the Banebots 775. Mishandling, improper mechanical design and stray metallic debris all contribute to these failures every year. While a failed motor in and of itself may not keep you from competing, other wiring errors will add to the fault and affect your ability to play. Consider for instance, a failed motor on a robot with an insulated Crio but a camera that has not been mounted with the same care. The camera and wiring, and the PD power supply will be affected.
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Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.

Last edited by Al Skierkiewicz : 27-01-2012 at 21:45.