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Spockie-Tech
Site Admin
Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia
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eeouch.. that looks a bit toasty..
Pity you cant determine the sequence of events when its all inside the shell.. It would be interesting to know if it was a wiring fault (as in exposed or spin-damaged wires touching something), or whether it was a MosFet explosion that started the chain reaction.
MosFets (also know as Magical Smoke and Flame Emitting Transistors) tend to fail in short-circuited mode - fusing into a highly conductive lump, which then of course immediately overloads takes out the other Mosfets on the same side of the H-Bridge, which then gives your batteries a nice short circuit to dump hundreds of amps through and electronic chain-reaction melt down quickly follows..
The "Splat" effect on the bottom of the pully looks vaguely reminiscent of 'sploded Mosfet, but it *could* be melted plastic from the wires being flung out from "centrifugal force". odd how it only seems to be on one side of the pulley though.
The exact flavour-sequence of smoke emitted from the bot would probably tell an experienced smoke-makers nose whether it was mosfet followed by melting plastic wires, or the other way around
A little tip for testing purposes is to make a removeable link with a high-current fuse(car stero gear) in place of the wire.. that way if anything goes wrong during testing, the fuse pops, and you know that something has used a heap of juice.
Once all the testing is over and you're heading to the arena for actual combat (where you would usually prefer the bot to give its every last it can amp rather than dying from a fuse blowing) then you replace the fusible link with an unfusible solid wire link.
Can save you some $$ from mistakes when youre just practising/tuning/testing.
Anyway, Nice Smoke job, looking at that, I'm surprised the alloy heatsink didnt melt ! _________________ Great minds discuss ideas. Average minds discuss events. Small minds discuss people
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Thu Jul 08, 2010 11:49 pm |
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