Electric Stunt > Gettin all AMP'ed up!
Electrocuting the Atlantis
Ken Culbertson:
--- Quote from: Crist Rigotti on July 26, 2019, 07:19:07 AM ---How much do you figure will be the final weight? Depending on the weight, I think you have too much battery. I'm flying on a 5S 2450mah battery with a weight of 52 ounces. I'm using @ 75% of the battery.
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I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%. With the right prop a 3300 is almost enough for 2 flights but I wouldn't try it. The 5s is better but if size and weight are an issue a 4s will work just fine. If your ESC keeps the rpm's constant then they will fly nearly the same and your only issues will be heat and battery ware.
The COBRA's seem to fare better with a front mount. I am using both and I have yet to have an issue because of the way it was mounted. They do exert a tremendous amount of torque when changing speeds and they do it quickly. Make sure you have adequate space beside the rear of the motor if you front mount it.
What are you doing for cooling? The pictures don't show any. The esc and motor will heat up a bit and both need good ventilation. The COBRA's need a gap between the fuselage and spinner to vent if you rear mount them. 1/16 is plenty. Air will actually draw through the motor to cool it. Outside of the rotating housing you just need to be able to move the heated air out but you will not get much cooling from airflow on the outside the motor. Also put a hole somewhere in the top, sort of like that little hole we put over an IC. They will stay hot and need a place to vent after the flight. The ESC and battery need the wind so keep the airscoop from the IC and try and put the battery and esc in it's path. If you had a pipe in there and still have the tunnel then you have a great place to put them. On one of my conversions I mounted all of that stuff on the bottom of the IC Cowl and cut some humongous vent holes at the back. Just keep it cool. The bigger the "S" values of the battery, the cooler they run. One more point on heat. An IC can be cooled by restarting it making back to back flights safe. IMHO this is not true with electric. They need to cool down a bit before going up again for a full pattern.
The clips are a rear "through the mount" where the motor uses the rear mount and prop adapter. This one currently has a 2826 on it. The nose views are to illustrate how you can use the pipe tunnel to advantage. I have moved the ESC to mount over the wing so that I can fit a 6s battery. The one in there now is a 5s 3000 Turnegy. I mount them skinny side down to get as much airflow around the battery as possible and give me room for all of those wires and crud. I mount the timer on the side of the fuselage with all of the pins pointing up. Biggest mistakes I made at first were locating the timer where it was difficult to hook up the programmer and putting the safety plug too close to the esc so that the wires wouldn't bend. Finally, when you locate stuff do it with everything connected (except the battery of course). The connectors don't bend and it really sucks when you have finally found the perfect place for the timer only to find out after you mounted it that the ESC cable won't attach or you can't get to the starting switch connector.
Have fun and you are doing the right thing asking. I just blundered into it a couple of years ago and made a whole bunch of really dumb mistakes. Like most IC types, I was focused on the motor, With electric it all starts with the prop. I don't think I will ever fully understand what changes what in electric but there are a whole lot of people here that do, so ASK, they will only occasionally bite your head off or call you an idiot.
Ken
Tim Wescott:
--- Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM ---I agree with Crist - I fly a 2820/12 on a 4s 2800 with 35% remaining and I have flown my 2826 on a 4s 2200 with 18%.
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With a steady-speed timer a pattern consumes an average of 7 watts per ounce of airplane weight (somewhere I have a spreadsheet where I worked that out from all of the then-extant planes on the "list your setup" thread). So you cannot just say "this battery + this motor = works" -- the motor supplies what energy it needs to keep the plane going, and keeps some for itself to keep warm at night. That's why I took Crist's 52 ounce weight and used it to scale up his battery usage.
--- Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM ---The COBRA's seem to fare better with a front mount.
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Thanks for that. The consensus seems to be that the best mount varies by motor brand. I certainly like a front mount better, although it means ripping into the plane more.
--- Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM ---What are you doing for cooling? The pictures don't show any.
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The current project plans say "TBD". I'm aware of the need, and will be doing (and verifying) something. I'm hoping to keep the look of the airplane, so I'm going to try to get enough air flowing through all the right places without messing with the outside envelope.
--- Quote from: Ken Culbertson on July 26, 2019, 12:46:53 PM ---Have fun and you are doing the right thing asking.
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Thanks.
Ken Culbertson:
--- Quote from: TDM on July 26, 2019, 10:45:38 AM ---Perhaps Cobra 3520-14 is a better option for the prop chosen and I assume it looks like it is a 60 size ship.
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Check out the pictures above. The 2826 barely fits that nose. If you want to put in a 3820 you are going to have to rear mount it. The 2820 will easily match the LA46 and the 2826 is a tad stronger. If you can rebuild the nose then I would say go for the 3520. I really don't like the battery that close to the sides but I also don't see any other way. Also while we are in the nose, if that exit ramp at the end of the cowl is all there is then he needs to cut a whole bunch of slots in the back of it. About 4sq" worth. Exit area has to be greater than input area on an electric.
Ken
Sorry, I hadn't seen your last post before posting this. Glad you are keeping cooling in mind. It is really very different than IC. Just a couple of shots of how slots do not distort the look of the plane, especially if they are on the bottom. Some of the guys I fly with have twice that many.
Mike Alimov:
--- Quote from: Tim Wescott on July 26, 2019, 08:20:05 AM ---It's 64 ounces with the 46LA and all the slimer equipment. I'm assuming it'll be the same or slightly more with the electrons.
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Unfortunately, not slightly more, but significantly more. You are probably looking at total up weight of north of 70 oz. That’s with 5S battery and 6” prop (more efficient, less battery consumption). 6S and 5” pitch prop, add another 2-3 oz.
Maybe better to leave the poor Atlantis alone and throw together something purpose built?
Tim Wescott:
Howard's 73 ounce Impact is quite similar in size to the Atlantis, so I suspect I'll be OK if it's not too far north of 70 ounces.
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