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Electric Stunt => Gettin all AMP'ed up! => Topic started by: phil c on June 21, 2019, 07:41:34 PM
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This came to mind reviewing the last couple posts about cooling the motor and another mentioning cooling the battery. I've often thought that anything over 2S, maybe 3S is just inviting the cells in the middle to overheat.
Has anybody tried opening up the battery pack and adding some spacers, say 3/32 balsa, between the cells to allow at least some air circulation around the inner cells? It might even be useful to duct the cooling air into one side of the battery and force it through the gaps between cells to an exit. Hot air from both the motor and the battery could be ducted out the back, at least of the cowl, for a bit of thrust.
Look at full size planes. The cooling air is best brought in from the high pressure in front of the motor into a plenum that allows it to slow down so it can flow between cooling fins.
The Rare Bear and the Cessna 172 are good examples. On the Bear high pressure air(400mph+) enters the cowl through a gap around the spinner into a large chamber in front of the cylinders. Similar on the 172, but the chamber is on top. On both planes the air slows, expands, cools, and then flows through the cooling fins fairly evenly and at a much high Reynolds number.
Cheers I might actually build another electric plane this year.
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Actually, there is a simple solution- but for ukie, it's impractical as we usually don't have the space and can't take the weight penalty. In R/C pattern, many aircraft require 10S and 8S. Using 10S as an example, two 5S packs are separated by two 1/4"X 1/4" light balsa sticks and strap- taped together to allow for cooling; yielding 10S. The bad side: the connector(MPI makes a great one) and wiring contribute weight. Besides the cooling benefits, if one cell goes bad, it's a lot cheaper to replace one 5S than an entire 10S.
I have a classic R/C KAOs that I use two 3S 6000mAh packs to yield 6S. The weight penalty wasn't a concern- it was the cost factor in the event one cell dumped.
I imagine that someone with the room and unconcerned about weight could apply that to say, two 2S 2800mAh packs to make a 4S 2800.
You got a problem, though, if you use 5S ...
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As I can remember, my very first electric used two batteries each one 2S, because that's what I had on hand.
Connected in series, that gave me a 4S system. Only problem was charging via the balancing plug. Had to charge them separately, taking so long that I couldn't try it at the flying field.
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As I can remember, my very first electric used two batteries each one 2S, because that's what I had on hand.
Connected in series, that gave me a 4S system. Only problem was charging via the balancing plug. Had to charge them separately, taking so long that I couldn't try it at the flying field.
Thanks Frank and Floyd. Did't think of the 2S solution because I am a perfectionist of sorts and always want an "elegant" solution.
As far as charging, Floyd, just buy a second charger, or upgrade to a fancier charger that can handle more configurations.
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I soon went on to bigger and better e-stunters. I now fly mostly 60" wingspan types with a 4S or 5S battery pack. Charging problem solved.
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There are some issues with that theory. If you move from 5S 2000mAh to a 10S setup you need a 10S 1000mAh and you can look wherever you want to let me know if you find it. Th second problem associated with that is when you break a battery in to individual or double cells the overall weight of the battery goes up, for example when you connect 2 batteries 3S2800 connected together to make a single 6S2800 are always heavier than a single 6S2800 battery. I actualy looked in to making my own batteries and also to options to drop the storage capacity and connect two battery, the result was that if I wanted to try two 3S2200 they where heavier than the 6S2800 so I dropped the idea in the end because it was not practical.
To be practical the battery gets hot because is small and there is a high demand placed on it during flight. The #1 culprit is a small motor. So if the battery is hot you most likely also have a hot ESC and a hot motor too.
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I don't fly the event or plan to fly the event.
But I can see a way for electric whizzbangs to gain advantage if they have the technical skeels.
Make a system with two or three batteries and a timer or heat sensor that switches from one battery to another as they get hot.
So you could go for one minute at a time per battery pack, then switch to another while the first battery cools.
Or better yet, a heat sensor that switches to a cool battery as one gets hot.
Compared to the schemes guys have used to gain advantage with piston engines this shouldn't be an overwhelming challenge.
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I don't fly the event or plan to fly the event.
But I can see a way for electric whizzbangs to gain advantage if they have the technical skeels.
Make a system with two or three batteries and a timer or heat sensor that switches from one battery to another as they get hot.
So you could go for one minute at a time per battery pack, then switch to another while the first battery cools.
Or better yet, a heat sensor that switches to a cool battery as one gets hot.
Compared to the schemes guys have used to gain advantage with piston engines this shouldn't be an overwhelming challenge.
Or simply set up a system that runs within a safe power range and the battery doesn't get hot. y1
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Make a system with two or three batteries and a timer or heat sensor that switches from one battery to another as they get hot.
So you could go for one minute at a time per battery pack, then switch to another while the first battery cools.
Or better yet, a heat sensor that switches to a cool battery as one gets hot.
Actually this will work just opposite. Loses (that is what heats) are I^2 * R
If you connect those batteries permanently paralel (or simply twice the capacity), then the net resistance will be half of that before, so it will heat only half of that, and radiate twice as long.
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Or simply set up a system that runs within a safe power range and the battery doesn't get hot. y1
But the essence of ALL motor sports is to press BEYOND the acceptable limits.
The winners and champions are those who don't mind smoking a few motors, engines and batteries to win.
The "safe range" is for sport flyers and beginners.
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But the essence of ALL motor sports is to press BEYOND the acceptable limits.
The winners and champions are those who don't mind smoking a few motors, engines and batteries to win.
The "safe range" is for sport flyers and beginners.
That's nuts. If you want to go beyond acceptable limits in the electric stunt world. let me know. I enjoy watching a good fire works show. #^ The only event that I know of where it is necessary to push the limits is a speed event. Back in 1994 I set a world electric RC boat record. At the end of the run motor was all used up. Batteries were toast. BUT I got my name in the record books. #^ #^
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But the essence of ALL motor sports is to press BEYOND the acceptable limits.
The winners and champions are those who don't mind smoking a few motors, engines and batteries to win.
The "safe range" is for sport flyers and beginners.
Nonsense. Utter nonsense for control line stunt.
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But the essence of ALL motor sports is to press BEYOND the acceptable limits.
The winners and champions are those who don't mind smoking a few motors, engines and batteries to win.
The "safe range" is for sport flyers and beginners.
I have yet to see anybody smoke a motor and win.
Ken
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I don't fly the event or plan to fly the event.
IMPRACTICAL, to say the least !
But I can see a way for electric whizzbangs to gain advantage if they have the technical skeels.
Make a system with two or three batteries and a timer or heat sensor that switches from one battery to another as they get hot.
So you could go for one minute at a time per battery pack, then switch to another while the first battery cools.
Or better yet, a heat sensor that switches to a cool battery as one gets hot.
Compared to the schemes guys have used to gain advantage with piston engines this shouldn't be an overwhelming challenge.
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Make a system with two or three batteries and a timer or heat sensor that switches from one battery to another as they get hot.
So you could go for one minute at a time per battery pack, then switch to another while the first battery cools.
Or better yet, a heat sensor that switches to a cool battery as one gets hot.
An interesting, but theoretically flawed solution to a nonexistent problem. Paul Walker had a boss who came up with stuff like this.
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Nonsense. Utter nonsense for control line stunt.
Crist, do you always sugar coat your comments?😊
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I was making a fluid dynamics battery cooling argument recently and was told I didn't know anything. Such is life.
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Paul Walker..no nono..Howard Rush had a boss...no no no, a mentor who came up with stuff like this.
Howard seems to be having memory issues!