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Electric Stunt => Gettin all AMP'ed up! => Topic started by: Curare on June 01, 2015, 02:19:18 AM
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In almost as many flights, good thing they're cheapies.
As some of you may remember I electrified my Chipmunk. Everything seemed to be going OK, but now it's flying time and it's cooked two motors in short order. It's got a big intake under the spinner and the area aorund the esc is releived, allowing blow-by air, and behind that, I've put in a set of 'exhaust pipes', oversized carbon tubes to look like engine exhausts. I thought I had adequate cooling to the motor, but it seems I maybe I don't.
Upon the last one fizzing out I checked the temp of the windings and they were around 92˚C (197˚F). This seems to be the point where the enamel coatings on the windings melt and short.
Strangely, the pack was cool to the touch, and the ESC is out in the breeze, and was also virtually 'room temp'.
This is the first front mount I've done in a while and frankly I'm baffled that I cooked two motors, given the great big mouth the chip has!
Maybe some models just dont like being airborne. :(
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Cheap motors don't last.
I been using the Orbit made by Plettenburg and I have flown in 42c temperatures and no "cooking". (Almost 5 years now.)
Sure, the motor runs hot on hot days but they don't fail. (Not like the cheapies.)
I don't even bother using the Tru-Turn turbo spinner anymore as I think they are a bit ugly.
Get an MVVS or Orbit and you won't have problems provided everything matches. (ESC settings & K/v etc.)
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With the cowl opening below the motor, I've had the airflow bypass the motor. The cure was to put in a baffle to force the air up and across the motor. Just make sure there is a path for the air to get out after it crosses the motor. I put holes in the firewall above the motor and vent it into the battery compartment, then out the exhaust holes. Also, some motors just run hot (less efficient). I tried one motor on a profile that ran extreemly hot. Switched motors (different brand) and it finished the flight with the motor just warm to the touch.
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You want air to go through the inside of the motor. Baffle things appropraiately to make that happen.
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Use heat sink, it is very effective way to cool it down (second best after usage larger motor).
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Where do you put a heat sink on an outrunner?
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rotor does not need cooling, it does not heat, so outrunner or not, still on stator, it is fixed, so does not make problems
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I recently had overheat problems. Fortunately, the controller somehow sensed that, and shut the motor down. An examination of the cooling plan showed I had plenty of intake and exit area. What I had failed to notice is I had a fuselage former which blocked the air from getting to the exit opening under the fuselage, behind the wing. So with an X-Acto knife on a stick, I got in there and cut away the former. That fixed it!
The best cooling plan will be negated unless a clear path is maintained in-between opening and exit.
Floyd
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it could be you had overheted also ESC, I do not know how could ESC see overheated motor without a temperature sensor
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rotor does not need cooling, it does not heat, so outrunner or not, still on stator, it is fixed, so does not make problems
Yes, but it seems like an awfully long thermal path from the wires to the stator.
And, he still needs to arrange for airflow!
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for WIRES? coil heats direcly stator (resistive loses) and loses in iron are directly in stator, so why long way? it cools direcly the part which heas most, I have it always hot after landing, its temperature is certainly hiher then temperature of rotor
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I should have made clear that I think the controller was getting hot.
Floyd
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Greg,
You didn't indicate what motor of prop you are using or the normal static amp draw. You might be on the edge of what the particular motor can handle as far as prop load which the higher temp pushed it over. Check the amp draw, my guess for that size ship would be around 24 amp. All mine are front mount, electric plastic spinner no special open nose. They run <110F, you can grab the motor at the end of the flight. 147F you can't touch so something is loading the motor causing it's temp to be that hot. Try reducing the prop diameter 1" and see if the amps drop, if not check for something rubbing inside the cowl. Keep us posted.
Best, DennisT
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I been using the Orbit made by Plettenburg and I have flown in 42c temperatures and no "cooking". (Almost 5 years now.)
I cooked one. I can show you how to arrange ventilation to cook yours if you want.
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Thanks for the input guys, the setup was a direct transfer from a similar sized profile, that's had well over 100 flights without issue, which is why I'm pointing the finger at cooling.
The setup was a turnigy SK3 35-36 1050kw, 4S 3000mah pack, and a 45 amp speed controller. Prop was an 11x5.5.
In hindsight I had the idea a turbo backplate may not be pushing air into the motor, but actually drawing air into the spinner and ejecting it out the prop blade holes, (centrifugal pump basically). I think I may have short circuited the airflow, going directly from nose scoop to prop holes, and bypassing the motor altogether.
In all honesty, I was never really happy with the chip, it has some issues. My partner thinks it's cursed, and has suggested I build a new one and leave the chip is wall art. I'm half inclined to agree!
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Greg,
I think that you over propped that motor. The 11x5.5 takes lots of amp to get a reasonable lap time. I think you should try a 10x6 at around 9600 rpm.
Best, DennisT
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Dennis, yeah, having a look at Ecalc, considering I obviously have cooling issues, it'll be happier on a 10x6 than an 11 x5.5 for the same aircraft speed.
It might be a good test to see just how much of a difference lower RPM, and higher pitch makes to the overall 'crispness' of the model.
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The Kv rating seems too high for a 4S from what I have seen...
875-930 I think would be about right?
Regards,
Chris
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With a Renecle timer governor, it pays to have some extra voltage up your sleeve, so I tend to do most of my calcs based on "3.5 cells. 1000kv works at around 10000rpm.
...and like I say, that exact setup has been working happily in a profile for the last two years.
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...to have some extra voltage up your sleeve...
I like that metaphor.
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I find it pays to have some when people irritate me.
(http://photos1.blogger.com/blogger/3839/1166/1600/EMPEROR3.jpg)