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What are acceptable resistance&continuity values for an ESC?
#1
I don't know quite how to pose this question, please bear with me (and please do enlighten me if you can!). It's crazy how these posts can become a wall of text, I've tried to keep things as clear as I can.

A quad of mine appears to have an unusually low resistance across the XT60 connector, lower than it used to be. Even though I've been flying quite a lot with it lately without issue, I'm now wondering whether a) a motor screw short to motor coils about 25 packs ago and b) a mysterious one-time dropout 10-15 packs ago (see video below) might be related to this observation and whether I should count my blessings and replace some parts.

Reading across the XT60 connector with my multimeter in resistance mode I get +/- 220hm and in diode/continuity mode I get a value of .120 (whatever that means.. what unit is that??). I'm used to my quads measuring anywhere from .460 to 1.500 (I just checked a few) whenever I check for continuity. I've never questioned these values since it's far from 0 (aka continuity beeps) and all the quads fly great. On this quad however, I was surprised to see my smoke stopper light up yesterday when I wanted to change some vcam settings and didn't want to remove my props. Surprising too, since I've been flying this guy quite regularly in the past weeks! I'm also positive that when I first built the quad a few months ago, I used a smoke stopper then and didn't have the bulb light up. So, something has changed. I started disconnecting parts and measuring each time. Started with vtx, rx, cam, low-esr capacitor etc but eventually found that two of my ESCs are the main contributors, particularly the front two.

Here's the measurements over the (desoldered) lipo leads of the ESCs (continuity mode / resistance mode):
motors 1 and 3 (back-right and back-left): 1.350 / 4.3kohm
motors 2 and 4 (front-right and front-left): 0.215 / 220ohm

My questions:
  • Since my smoke stopper didn't always light up on this quad, I'm assuming that my ESCs deteriorated over time. What circumstances contribute to the deterioration*?
  • is it plausible that the deteriorated state of the ESCs were the cause of the sudden dropout I had a few weeks ago (see video)?
  • more in general: can we expect ESCs to have measurable continuity/resistance over the lipo leads? What's normal?
*) More and more possible causality is coming to mind now. About 2 months ago I noticed that I had a short between my motor coils and the frame via a motor screw. One motor got particularly hot (but didn't smoke) and around my PDB a few screws got really hot too, probably due to current flow through them?. The motors in question were motor #1 and #3. Curiously exactly the motors *not* connected to the culprit esc's in this post. After checking that there weren't any more shorts to the motors I've had no more heat buildup near the PDB. I always wondered if the short had affected any parts of my quad. Maybe the observation of this post is it? Maybe something entirely different. 

Here's DVR footage of the dropout I experienced a few weeks ago. Dropout happens at 30s mark but I posted the whole flight so you can see how it flies, image quality in relation to throttle etc.. Notable is how the image suddenly blacks out for an instant an then comes back. By the time the quad hit the ground I could hear the fc and esc's re-initialising.


Partslist (fyi)
  • frame: Realacc X5S
  • motors: Emax rs2205s 2600kv
  • props: Racekraft 5051x2
  • escs: Racerstar MS35a
  • pdb: Matek (generic)
  • fc: Omnibus F4 V2
  • vcam: Runcam Mini
  • vtx: Eachine tx526
  • rx: Flysky X6B

#2
One thing did jump out at me - about your smoke stopper not lighting up. That is the desired outcome when testing. It might light up when you raise the throttle high enough, but *hopefully*, that's about it.
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#3
(10-Aug-2017, 02:15 AM)sloscotty Wrote: One thing did jump out at me - about your smoke stopper not lighting up.  That is the desired outcome when testing.  It might light up when you raise the throttle high enough, but *hopefully*, that's about it.

Correct. Smoke stopper should not light up but it will when arming and raising the throttle. In the last state of my quad (haven't used it since) I could plug in a lipo and fly, but turned out that when using the smoke stopper, it would light up right away (I'd say 75% brightness). That's when I started investigating.
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