Bad Turnigy Motor or Bad E-Max ESC??? - RC Groups
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Sep 10, 2009, 09:04 PM
Philippians 4:13

Bad Turnigy Motor or Bad E-Max ESC???

Hey guys,
I recently put a turnigy 35-42 motor and 40 amp E-Max esc in my Multiplex Gemini. AWESOME performance but on about the 9th or 10th flight I noticed a funny grinding sound when going from dead stick to any amount of throttle when pulling out of a dive. Then after I landed tonight, I gave some throttle to taxi her in and I got nothing but motor shaking back and forth and nasty sounds from the motor...
is this the motor or esc???
I have never used either before.
I haven't had any problems with my other turnigy motors but they are a little smaller (shouldn't matter) I have never used this brand of esc.
Thanks for any input.
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Sep 10, 2009, 10:03 PM
Philippians 4:13
help please!
Sep 10, 2009, 10:10 PM
Reduce the drama...
rick.benjamin's Avatar
I think you overloaded your 40 Anp ESC
Sep 10, 2009, 10:13 PM
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rick.benjamin's Avatar
The SK35-42 has two models.
1250 KV rated at 630 watts and 3-4 lipos
1000 KV rated at 605 watts and 3-4 lipos
Sep 10, 2009, 10:17 PM
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rick.benjamin's Avatar
Worst case: 1250 KV model:
630 watts divided by 12 volts (3S) = 52.5 Amps
630 watts divided by 16 volts (4S) = 39 Amps
Which is why I think the 40 Amp ESC is suspect.
Without a wattmeter we have no clue what the motor-prop are actually drawing.
Sep 10, 2009, 10:21 PM
Reduce the drama...
rick.benjamin's Avatar
I'll tell you a secret, don't tell, ok?
Sep 10, 2009, 10:24 PM
Philippians 4:13
ok, what is your secret.
by the way, I just bought what everyone told me to buy for the Gemini on that thread. I wondered about the 40 amp esc not being enough but it never even gets warm to the touch and neither does the motor...
Sep 10, 2009, 10:27 PM
Philippians 4:13
this is the one that I have
Sep 10, 2009, 10:27 PM
Reduce the drama...
rick.benjamin's Avatar
I de-rate my ESC by 120%.
That means for a 40 amp ESC
I don't plan to put more than 33 amps on it.
40 amps divided by 1.2 (120%) = 33.3 amps

Lets say you are feeding your SK35-42 (1250kv) with 4S at 39 amps.
39 amps times 1.2 (120%) = 46.8 amps

I would choose an ESC rated above 46.8 amps.

IMHO, of course!
Sep 10, 2009, 10:30 PM
Philippians 4:13
I agree with that... but wouldn't the esc at least get warm if it was too small for the motor
Did you see the link to the motor that I have. It is not the SK series. I haven't even really looked at those yet.
Sep 10, 2009, 10:34 PM
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rick.benjamin's Avatar
Ok, your motor is between the two I looked at.
All these calculations are a SWAG (scientific wild-axx guess)
until you get a wattmeter and discover what's really happening.

Unfortunately, we can't trust the figures provided by the vendors or manufacturers.
The tests done by Dr Kiwi and Everyday Flyer suggest the performance figures are inflated
Sep 10, 2009, 10:36 PM
Philippians 4:13
why can't I find the sk35-42 on the hobbycity site?
Sep 10, 2009, 10:37 PM
Hey Ya'll!! Watch THIS!!
Michael Paxton's Avatar
It could also be a simple timing/syncing problem.
I've had some ESCs that will do that if the prop spins at a different speed than the esc expects. ESC screeches and you have to drop throttle until it resyncs with the motor. Try changing the timing on the speed control.
Sep 10, 2009, 10:42 PM
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rick.benjamin's Avatar
Here's the figures as posted:
Model: TR35-42C
Input Voltage : 7.4V~14.8V (2~4S Li-po)
Kv : 1100 rpm/V within 10%
Current capacity : 45A/30s
Dimensions : 35mm X 42mm / 1.38in X 1.65in
Shaft diameter : 4mm / 0.16in
Weight : 132g
Number of poles/magnets : 14
Recommended model weight : 1000~2300g / 35~81oz
Power equivalent : .30 to .35 IC glow engine
Suggested prop size: 11x8

I bolded the parts that are signifigent
You are using a 40 amp ESC and the motor factoid says 45 amp at 12 volts (assuming that 30s is a typo and writer meant "3S")
The part I haven't discussed yet is the prop.
We are clueless as to how much load your prop sucks from the battery through the ESC.
And we can't trust what the factoids say till we have some test equipment to verify or disprove them.
Sep 10, 2009, 10:46 PM
Reduce the drama...
rick.benjamin's Avatar
45 amps means the motor shouldn't exceed 45 amps.
Excesses may burn-out motor windings. That may have happened.
Give that motor a sniff, may smell burned.
The ESC maybe smelly.

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