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Old Aug 11, 2015, 02:26 PM
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Question
Overheat (?) issue for motor/ESC/prop

Folks –

I’m having what I am assuming is an overheating an issue with a motor/ESC that I’m using to power a classic Supra. Would appreciate any guidance/insight. Here is the hardware:

Motor: HET Typhoon EDF 2W-25; 2720KV, 6 pole
Gearbox: 6.7:1 planetary
Prop: 16x10
ESC: Turnigy Plush 80A (with timing set to “Medium” per manual instructions for 6-pole motor)
Battery: 3S 1500mAh LiPo
What happens: I can run the system for about 2-3 consecutive 30-sec runs, then the power (rpm) drops to about 50%. If it let the system sit (cool) for about 30 min, I get full power gain. The ESC has “over-heat protection” that I assume is kicking in after the motor runs a while. The motor gets quite hot (almost too hot to touch) after about a minute of running (although I understand these motors naturally get hot), even when there is considerable airflow around the motor. The ESC is always cool (does the ESC’s “overheat protection” mean overheating of the motor or ESC?). The gearbox looks fine and turns smoothly.

Anyone have any ideas? I suspect one or several of the following:

1) ESC is faulty
2) Motor is overheating and ESC is not faulty and reducing power accordingly
3) If (2), then motor is overheating because of high load of gearbox/prop or incorrect timing
4) If (3), then perhaps this motor (designed for ducted fans) is not appropriate for gearbox/big props
Could be something entirely different.

Thanks in advance,

- R
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Old Aug 11, 2015, 03:09 PM
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You do not state the current draw or the wattage. Both of these would give a lot of meaning to the drive train specifications.

You say 2-3 CONSECUTIVE 30 second motor runs. If this is the true case, then that is why things are getting hot!

Supras wil not normally run more than 20 to 25 seconds to get to 200M, followed by a 10 minute glide to cool down. MOST props unload a little in the air so ground running is not truely reperesentative of flying conditions.

I hope this helps.

Iain
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Old Aug 11, 2015, 03:14 PM
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Have you measured the current? That would be the first thing to try. With the combination you have listed above, eCalc predicts the current draw should only be about 22A, which is far below the capability of the motor and ESC.

The ESC doesn't know the temperature of the motor. It's thermal protection is only for itself.

I would say there is something quite wrong if the motor is generating that much heat. The current draw must be far higher than predicted for some reason (gearbox ratio, bearings, timing (I always use automatic), motor winding out, ?). Test the current draw.

The HET motor should be fine on a gearbox. It is a heavy combination for an e-Supra but it should be capable of tons more power than you need for the 30 second max run that is usually used in e-gliders. Most e-glider motors are only capable of 30 second runs followed by 10 minutes of gliding, not minutes of running or consecutive 30 second runs. But you have another problem as well. Check the current.

Kevin
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Old Aug 11, 2015, 03:22 PM
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I do not know the exact wattage (sorry, I do not have a watt meter) but according to calculation (via eCalc), it should draw 21.5 amps with the 16x10 prop and 34.1 amps with a 18.5x10 prop (I have run both props with the same power loss issue). I figure that equates to 239 watts and 379 watts respectively with a 3S (11.1volt) battery.

I understand the mandatory cool-down period, but I need to let things cool for at least 30 min before I can get 100% power again - that seems like too a long time.

I am especially interested if "over-heat protection" refers to overheating of the motor or ESC. The Turnigy ESC manual does not say.
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Old Aug 11, 2015, 03:26 PM
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OK - KCaldwell answered my questions about ESC overheat protection and mandatory short motor run and cooling period. I will try to borrow a watt meter to check actual wattage - hopefully that will be a smoking gun.

- R
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Old Aug 11, 2015, 04:29 PM
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Ecalc is normally close. If the wattage is okay try swapping the esc. HK stuff is weird sometimes, sometimes it's aces.
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Old Aug 13, 2015, 02:19 AM
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A wattmeter is the best investment you will make in electric flying. For the price it can save a lot of heart ache, time and money.
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Old Aug 13, 2015, 09:58 AM
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OK - here are the watt meter results (using fully-charged 3S LiPo at 12.5 volts for each trial):
Motor only: 2.5 A, 30.5 W - ran hot after 30 sec
Motor & gearbox: 3.4 A, 41.8 W - ran hot
Motor, gearbox & 16x8 prop: 16.2 A 188 W - ran hot
Motor, gearbox &18.5x10 prop: 22.6 A, 250 W -ran hot
Amps and watts are a bit less than eCalc predicts, but are reasonable.

Motor manufacturer (HET) got back to me and recommended the motor not be used with gearbox and large prop.

So, motor seems to be ok but perhaps not appropriate for sailplane application. I still have doubts about the ESC. May try it with a different ESC but it's looking like a new motor is in my future as well, especially if I use a 4S battery (which may be needed to get the somewhat overweight Supra Classic up to 200m in under 30 sec).

Thanks for everyone's help.

- R
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Old Aug 13, 2015, 11:24 AM
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Like I said eCalc is close. That motor shouldn't run hot after 30 seconds of no load. Check the ESC timing settings. A lot of ESCs are set for outrunners as default and not inrunners. Makes a big difference.
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Old Aug 13, 2015, 01:10 PM
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I am quite surprised at the behaviour you have observed.
I have used exactly the same motor fitted to a Kontonic KPG 5;1 box for a number of years with no problems at all.Most of the time the power was around 450-500 Watts.
Also the HET motors,with a variety of gearboxes are very common here in Europe. In fact Vladimirs (the makers of the Maxa) sell a couple of drives incorporating HET motors. See www. f3j.in.ua/motors-for-f5j.html
It may be worth trying a different Esc and/or timing as suggested above.
Perhaps a more minor point,but I did notice that the difference in no load current with and without the gearbox is in the order of 1 Amp. I normally try to keep this value to the Reisenauer recommendation of less than 0.5 Amp. So,you might just check the gearbox fitting to see that the pinion is mounted centrally.
By the way what type of gearbox are you using?

Spencer.
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Old Aug 13, 2015, 01:43 PM
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I did try running the motor with the 16x8 prop at the 3 timing settings that the Turnigy Plush 80A ESC offers:
low: "general inrunner or outrunner motor, 2 pole motors"
medium: "general outrunner motor, 6+poles"
high: "specialized outrunners"
Motor heated up regardless of timing setting. I assume the "medium" setting is the proper one as this motor has 6 poles.

I checked continuity between the three motor wires; near zero ohms for all combinations. It seems like the motor is ok but maybe not.

There are no markings on the gearbox - I assume it's European; see attached photo. Pinion is mounted centrally.

Testing with a different ESC will be the next step.

- R
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Old Aug 13, 2015, 01:59 PM
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You need to check for internal short circuit. You may have mounted with bolts that are too long. Doing so will allow the bolts to bite into the insulation on the wires, causing short circuit.

Test your motor for continuity from each motor lead to the case, and then check resistance for each motor lead pair (a-b, b-c, a-c).

You should have no continuity between leads and case.
You should have very nearly the same resistance from pair to pair, on the leads.
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Old Aug 13, 2015, 02:18 PM
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Mounting bolts that I used to connect the motor/gearbox to the bulkhead screw into the gearbox, not the motor, so I don't think those are a problem. Bolts connecting the gearbox to the motor are the original stock bolts (which I have not touched) - I don't think those are a problem but I will check for shorts between the wires and case anyway.

As I said earlier, resistance between all wire combinations was the same (near zero).

- R
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Old Aug 13, 2015, 02:41 PM
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Ok. Missed that. Do check between each lead the several point on the case.

FWIW, Inside the motor, each of your motor leads all tie into each other. Delta wind motors are sequentially terminated and Wye wind motors are common point terminated.
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Old Aug 16, 2015, 03:35 PM
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Could the problem be mechanical?
Bent shaft?
Faulty or miss aligned bearings?
Something rubbing inside?
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