some ones been down this path before. and improved some things?
Generally you dont want to reuse a conformal materiallike thermal pads because its been formed once it often wont reform or make contact the same way again.
– https://www.reddit.com/r/buildapc/comments/bo5gin/reusing_thermal_pads/
someone saying don’t reuse a bit less firmly and with a reason.
my Jedbox thermal pads came out without marks, intentions, or any indication of use at the FETS
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Ok,
My plan now is:
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take apart motor and look for any signs of shorts. perhaps learn more tests. because it seems ok.
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replace the 1.7 blown focbox with a 1.6 I have on hand. rolling with the 1.7 on the other side. not blocking on understanding the differences better.
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the replacement 1.6 will go in the existing 1.7 base case. so I don’t have to take all the electronics out. I will reuse the nice thermal pad from the 1.6 which is nice and clean. I will transfer it with tweasers.
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I’ll watch thermals. for variance between the two.
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I’ll order some 8W/mk 2mm thick thermal pads and when they come swap it out.
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observe thermals see if there’s any difference.
after that… if you see any observable differences in temp. maybe try a .75-.8mm copper shim on the heatsink use artic silver or the like to afix it… from my studying, thicker thermal pads are way less efficient at heat transfer… I just made the heat sink come up and match the 1mm thick thermal pads effectively squishing the thin thermal pad properly…
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gonna be harder than easy.
I loctite 680’d my bearings to the shaft to prevent reoccurance of motor shaft wear
now I’m paying that price. 
heat got me some of the way there.
just bitchin’ for the moment. will keep trying.
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bearing stuck on the shaft from the other end of the bell.
for now I’ve installed a replacement motor. till i figure outif I can deal with the bearings.
inspecting the removed motor I don’t really see any signs of short.
also don’t seem to have shot all the pictures I thought I did.
TLDR status: Board is together with focbox 1.6 transplanted and a new motor. still inspecting old motor to see if cause lies within.
Not sure I ruled out the motor. but I didn’t find anything obvious. so I still don’t know why it happened. or if it’ll happen again.
Got an inductance meter. following a suggestion from @kook
I think I figured out how to calibrate it and use it.
then I went to find the docs and… they’re not too much more help.
measuring between any two phase wires they all show about 51µH saved vesc configs said inductance was 11.18µH not sure what to think there.
Wanted to check the resistance of each phase, but it turns out my multimeter doesn’t really go that low. it will display down to 1/10th an Ohm. and it measured each pair of phase wires at 0.2Ω
could do some trickery with a voltage divider
so nothing obviously wrong? or maybe better tests on the motor required? not really sure.
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@Deodand mentioned this in another thread:
In that temp sensor fault example what I observed was that the fault codes were recorded by
metr. as well as still available in vesc_tool because the focbox never fully bounced.
in this incident there were early cutouts and no recorded faults. which started my investigations before the final blown fet.
It’s still possible that the lower fault stop time contributed to this blown fet. it would have to be a contributing factor to something that did throw faults though which I didn’t catch. so jury’s still out on what blew this thing.
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A little bit of a derail here @fessyfoo but regarding this pic
Is that a rubber seal on top? My aps motors don’t have that…
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it seems to be plastic. bearing seat. the bearing stayed on the motor shaft. loctite for sure got on it because of the way I applied it.
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dude… the motor appears pristine… the inductance loops equivalent… it may be spurious… but did you do a continuity to ca/bearings/shaft test… the impedance check says no… but I’d still check…
my k00k approved guess is…
your motor is gUUd
continuity tests from each phase lead to bearings, ring on sensors, backs of stator windings (not sure what that’s called). any part I could prove conducted between my probes itself. showed no continuity to the phase leads.
inductance does seem off though
testing inductance on 3 other identical mortors I get values from 20-27 µH
testing this motor I get 50-52 µH
that’s leading me to suspect that high reading means something. the smaller value is close to double the vesc_tool recorded value which could make more sense than quadruple.
still considering that motor suspect. curiosity wants to find out more but I think I’m at a dead end.
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ooo thank you. i thought it was some type of seal to prevent dust getting to the bearing, nvm me haha 
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The only thing you will notice between FocBox 1.6 and 1.7 is that 1.7 will heat a tiny bit more. It uses mosfets with a bit higher internal resistance.
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I think it’s a combination of not noticing the fault and maybe resuming motor control when the circumstances that caused the initial fault are still present.
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I should add to this thread that this setup is a 10s
Thermal pads […] are one-shot solutions only. You have to replace the pad if you ever remove the heatsink from its mounted position, because the heat of the operating CPU will have caused the thermal pad to conform the top. So, once you move the heatsink there will be new gaps between the surfaces. So never forget: If you dismount the heatsink, replace the thermal pad and remove all debris.
– https://blog.arctic.ac/blog/2015/07/23/thermal-pads-or-thermal-paste/
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went ahead and got this stuff to act as replacement thermal pad inside the focbox 2mm thick 8 w/mk conductivity.
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