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Old Dec 13, 2012, 12:39 PM
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I donít want to deviate from the discussion of Polarii for the discussion of my esc again with a long post, however since it is in my Polaris I will run it by you all. I had a question/theory I thought that you professionals might be able to help me with. From my previous posts, many have thought that my symptoms sounded like an overheated esc. The esc I have is the turnigy trust 45a with sbec . It has a fairly large factory heat sink on top the esc with a white paste between the circuit board and the heat sink all wrapped up with heat shrink. I sprayed corrosion x into the esc from both ends to saturate it and then let it drain. I heard corrosion x is really good at working its way in-between small places using capillary action and it is a really good insulator from electrical conduction. The esc worked perfectly for the first 3-4 flights( two days), and then started being a little slow to boot up after plugging in the battery, but only sometimes, but still would work fine after booting up. Then after the 7-8th flight, I started having problems with motor cutting off after a minute or two of flight and then doing weird stuff when testing on the ground and then finally smoked. The capacitors on the end of the esc look a little puffed up. My Polaris has spoon scoops, intake and exhaust for cooling.

My Hypothesis: Over a period of a few days, the heavy dose of corrosion x worked its way between the thermal paste and the heat sink with capillary action, severing the heat conductance of the esc to the heat sink. Then the esc had reduced cooling capacity and started overheating and causing small problems and got worse with time and with more use. The esc eventually overheated and shorted out.

Does this sound feasible? I just hate to plug in a new esc without having a good idea of what might have happened to the old one for fear of throwing another $17.00 plus shipping away.
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Old Dec 13, 2012, 02:55 PM
TonyS
United States, AR
Joined May 2010
593 Posts
Quote:
Originally Posted by flybyjohn View Post

My Hypothesis: Over a period of a few days, the heavy dose of corrosion x worked its way between the thermal paste and the heat sink with capillary action, severing the heat conductance of the esc to the heat sink. Then the esc had reduced cooling capacity and started overheating and causing small problems and got worse with time and with more use. The esc eventually overheated and shorted out.
My four cents worth (had to allow for inflation)...... I have been using Corrosion X on ESCs (spraying heavily and allowing to drain) for nearly four years without any noticeable negative effect on ESCs, receivers or connectors. I do not think Corrosion X was any factor in your problem...unless it wasn't applied sufficiently to protect the ESC.

By chance did you extend the wiring from the battery to the ESC? That could create the problem you experienced.

Otherwise, it could be just a bad ESC; a bad motor overloading the ESC, or servo(s) drawing excessive current and overheating the BEC portion of the ESC and causing a melt down.

TonyS
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Old Dec 13, 2012, 06:09 PM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
16,115 Posts
Quote:
Originally Posted by flybyjohn View Post
I donít want to deviate from the discussion of Polarii for the discussion of my esc again with a long post, however since it is in my Polaris I will run it by you all. I had a question/theory I thought that you professionals might be able to help me with. From my previous posts, many have thought that my symptoms sounded like an overheated esc. The esc I have is the turnigy trust 45a with sbec . It has a fairly large factory heat sink on top the esc with a white paste between the circuit board and the heat sink all wrapped up with heat shrink. I sprayed corrosion x into the esc from both ends to saturate it and then let it drain. I heard corrosion x is really good at working its way in-between small places using capillary action and it is a really good insulator from electrical conduction. The esc worked perfectly for the first 3-4 flights( two days), and then started being a little slow to boot up after plugging in the battery, but only sometimes, but still would work fine after booting up. Then after the 7-8th flight, I started having problems with motor cutting off after a minute or two of flight and then doing weird stuff when testing on the ground and then finally smoked. The capacitors on the end of the esc look a little puffed up. My Polaris has spoon scoops, intake and exhaust for cooling.

My Hypothesis: Over a period of a few days, the heavy dose of corrosion x worked its way between the thermal paste and the heat sink with capillary action, severing the heat conductance of the esc to the heat sink. Then the esc had reduced cooling capacity and started overheating and causing small problems and got worse with time and with more use. The esc eventually overheated and shorted out.

Does this sound feasible? I just hate to plug in a new esc without having a good idea of what might have happened to the old one for fear of throwing another $17.00 plus shipping away.
It's really simple. You had a faulty ESC. What do you expect for $17? CorrosionX has nothing to do with it. The abnormal overheating was just a symptom of internal failure. If you read other forums about ESC failure, you'll see it's one of the most common problems in electric flying and that some types work more reliably than others.

Replace the ESC and move on.

I don't know anything about the particular ESC you used but can say that we've had good luck with the ESCs from Model Aero (I like the 40A regular and the SBEC Maytech 40A), and the Turnigy Plush 40A (which also has switching BEC). Stay away from the SuperBrain and the SS series.
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Old Dec 13, 2012, 06:52 PM
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United States, OR, Portland
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Just finally got a chance to maiden Cobralaris today, was a very short flight. On the plus side this new motor is WAY more powerful than the one I used on the last one, the thing took off like a bat out of hell on the grass. I think I may be able to do unlimited vertical. As soon as it took off though with slight up elevator input, it did a hard nose dive which I countered with more elevator, but then it started nose diving again so I cut the throttle and aborted the take off as it smacked and bounced off the gravel road to the runway and into the grass, leaving something in its wake. The something turned out to be the bottom plastic folder material ripping off on the gravel. Got a nice gouge in the foam underneath I will have to fill with something.

When I got to the Polaris I noticed the elevator control horn had detached from the elevator. I was stupid to think foam safe CA would be enough to secure it. Every other control horn I epoxied but I thought CA was enough on the elevator. I'm glad I didn't try to fly out of the porpoising only to find out I had no elevator at altitude.

Hopefully I can try again tomorrow fickle weather permitting.
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Old Dec 13, 2012, 07:28 PM
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United States, CA, Chino
Joined Oct 2007
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Elevators are over rated, I always take the stairs.
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Old Dec 13, 2012, 07:48 PM
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Singapore, Singapore
Joined Jun 2012
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I always use CA for my control horns... too impatient to mix up epoxy and put it in. They've never fallen off on me, even the ply ones. Can I ask what kind of control horn it was? The ply one that gets slotted in? Did the foam tear when it came off?

Nowadays I usually use the plastic ones that are meant to be slotted through foam and then capped at the other end with another plastic piece. This is done with no screws. The slot gets a drop of CA, the horn is pushed through, and capped at the end. I hit it with kicker. Then I cut off any excess plastic. It won't come off without destroying the foam too. The horns are similar in concept to this: https://www.hobbyking.com/hobbyking/...9_10sets_.html

An alternative is to use control horns like this: https://www.hobbyking.com/hobbyking/...mm_10pcs_.html. I don't use the flat part or the screws; I cut a slot in the foam and push the entire horn through to the end. The foam is crushed a bit in the process. The base plate now becomes a back plate. Everything is secured with a drop or two of CA. This is how the assassin EPP wing has its control surfaces done. A picture is worth a thousand words, see http://www.rcgroups.com/forums/showp...66&postcount=8.
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Old Dec 13, 2012, 08:05 PM
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Scott, looks real nice..looks like you had a little wind?
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Old Dec 13, 2012, 08:54 PM
UMs & parkflyers... for now.
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United States, VA, Herndon
Joined Apr 2012
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I cooked my first cheap ESC... totaling Polaris Mk 1... it was my first electric scratchbuild and before I learned about the effects of the added inductance incurred by lengthening the battery-ESC wires.
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Old Dec 13, 2012, 11:08 PM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
16,115 Posts
Quote:
Originally Posted by seeingeyegod View Post
this new motor is WAY more powerful than the one I used on the last one, the thing took off like a bat out of hell on the grass. I think I may be able to do unlimited vertical.

I noticed the elevator control horn had detached from the elevator. I was stupid to think foam safe CA would be enough to secure it. Every other control horn I epoxied but I thought CA was enough on the elevator.

Hopefully I can try again tomorrow fickle weather permitting.
It should go vertical with ease.

If the horn detaches from the control surface without taking a good chunk of foam with it, it wasn't adequately glued. I've had no problem with ply horns glued in with epoxy and microballoons. The microballoons add body to the epoxy while holding down the weight and preventing the yellow look epoxy alone develops in the sun.

All the best with your "re-maiden."
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Old Dec 14, 2012, 12:20 AM
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United States, OR, Portland
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Yeah it didn't hardly take off any foam at all. Came off with a paper thin layer of surface stuck to it. Just a normal dubro or great planes plastic medium sized control horn. It seemed on there with foam safe CA, but I didn't really try and wiggle it too much for fear it would break off. Guess I should have wiggled.

Thanks for the best wishes, hope I get a chance tomorrow. All my other control horns are also just the regular plastic kind that you normally attach with screws through wood onto the square backplate, I just epoxied/mb'd them flat onto the depron. All others seem very secure. I think I may stick some tooth pick pieces through the holes of the elevator horn into the depron with the epoxy.
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Old Dec 14, 2012, 06:05 AM
59 years of RC flying
Daedalus66's Avatar
Canada, ON, Ottawa
Joined Feb 2006
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Originally Posted by seeingeyegod View Post
Just a normal dubro or great planes plastic medium sized control horn. It seemed on there with foam safe CA, but I didn't really try and wiggle it too much for fear it would break off. Guess I should have wiggled.

I just epoxied/mb'd them flat onto the depron. All others seem very secure. I think I may stick some tooth pick pieces through the holes of the elevator horn into the depron with the epoxy.
No wonder it came off. Yes, at a minimum, stick round toothpicks through the holes and use epoxy. But even then it will probably be less strong than the standard plywood horns glued into a slot in the Depron. If you want to use plastic horns, you should probably use the retainer plates as well.

As for being afraid it would break off, that's the point! (As an instructor, I always check a student's model by pulling on the control surfaces. In a couple of cases, the elevator came off in my hand and I was accused of "breaking" the model. I had to explain to the owner that he should be thanking me!)

Happy flying
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Old Dec 14, 2012, 07:38 AM
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Joined Oct 2010
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The new esc is installed and initial static runup all seem good. On this one I did go ahead and cut the shrink tubing off the cooling fins and installed the heatsink through the top of the fuse. I may have added a little weight with the silicon used but hopefully not too much. I will test fly today.

On another note, the 90% is coming along well. Current weight with everything ready to fly minus the packing tape, control surface ply horns and velcro is 12 oz with 1500 mah batt and 12.8 oz with 1800 mah batt. My target finished weight is 16 oz. max. The wing looks a little on the thin side but the flight test will tell us for sure if it is going to be strong enough.
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Old Dec 14, 2012, 09:00 AM
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Northwest Ohio
Joined Jan 2002
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Scott, looks real nice..looks like you had a little wind?
It was 8-10 mph, not too bad.

Scott
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Old Dec 14, 2012, 09:05 AM
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Northwest Ohio
Joined Jan 2002
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Regarding control horns, that is one thing I always check as a pre-flight ritual. Horns have a way of getting knocked loose during transport. I generally use thick CA and find it plenty strong.

Scott

www.modelaero.com
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Old Dec 14, 2012, 05:34 PM
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United States, OR, Portland
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For some reason I just didn't think that the screws and back plates on the plastic control horns wouldn't work in depron. I just went ahead and used them on the elevator and well it isn't going anywhere now without taking a chunk of elevator with it

Re-maiden just happened and was successful! I just have to figure out the CG again, apparently it was too far forward because i had to max out my elevator sub trim and give it almost full up regular trim to get to to stay level at anything other than full bore. Then I remembered I had low rates on the elevator. Switched that off, then gave my 2100 pack a go and that moved the CG back more which helped.

She is much faster than my first Polaris and also more sensitive in all axis. I think I will be leaving everything but elevator on low rates for awhile. The motor is making a weird noise at about 3/4 throttle for some reason, kinda an annoying buzz, not sure what it is, and my color scheme in less than ideal lighting is tough for orientation. I may add some red stripes on the bottom wings.
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