View Full Version : 1st & 2nd flight power differences
10-14-2005, 01:04 AM
My Formosa has a Hi-Max 2015-5400, 9x6 prop, 2-cell 1500mAh LiPos and E-flite 20amp ESC. I've got two of the battery packs which have been flown about 60 times each. I get 11-13 minute flights mostly at full throttle which agrees with what the motor calculator says I should expect.
I've had about 10 flights on each battery with the brushless setup and I've noticed some things:
1. After flying the prop is not free turning whereas it is before the first flight. It stays in this condition for several hours after a flying session.
2. The second flight is less peppy than the first. I've tried doing the 1st flight with the #1 and the #2 battery. Doesn't make a difference -- the 2nd flight is less peppy regardless of which battery is being used. (At first I thought one of the batteries was getting weaker.)
I'm wondering why the prop is not free turning after a flight and if that could be impacting the performance of the second flight?
And why would the prop stay non-free turning for several hours after a flying session?
PS: The E-flight ESC has a programmable prop brake function (ON or OFF) but I can't get the ESC programming sequence to engage so I'm using the default (the default is undocumented by E-flite).
10-17-2005, 01:42 PM
I've seen a similar issue with an AXi motor. In that case, it was heat related. The bearings would get hot and stiffen up to the point where the power loss was noticeable. Extended periods of full throttle were also present in that case, because of the pilot's flying style.
Unfortunately, "continuous" doesn't always mean continuous with respect to this electrical stuff. It usually means "continuous under ideal laboratory conditions with active cooling."
10-17-2005, 04:58 PM
Thanks for the reply Matt. I'd be surprised if it was motor overheating. I'm using only 2-cell LiPos and with my setup, the motor calculator says I'm drawing something like 7.9 amps which is why I get such long flights on 1500mAh batteries. The other thing is that the prop stiffness lingers for several hours after flying. As an experiment I'm going to remove the cowel next time out and see if there is any difference. I suppose I could also pull a gear and see if it's the motor that is stiff or if it's the gears themselves.
In my original post I brought up the prop brake. Is it possible the prop brake is getting engaged and staying engaged? Since I can't get the ESC to enter the programming sequence I can't tell if the ESC has it ON or OFF. I also can't imagine it staying on for hours after a flight.
10-17-2005, 06:45 PM
The prop brake shouldn't make any difference when the battery is disconnected.
It also sounds to me that the tolerances in your motor may be a little too tight so when it warms up the bearings get stiff.
I run an EP283012-970KV outrunner on my Formosa with 1300 mAh lipos, a 1047 prop which also draws around 8 amps static at WOT. After about a half hour of flying the motor's warm but not hot and even on dead stick landings the prop's still freewheeling.
10-17-2005, 07:53 PM
I agree with the heat issue. It might be inteh gears, or the bearings if the motor never gets warm. Try lubing the bearings, or just check teh temp by hand of the individual items. If there is any binding (during or after flight) then the amps would be a little higher, thus making a little more heat and longer time to dissapate it.
You didn't mention what kind of GB your using. Is it metal to plastic gears? How is the play?
10-17-2005, 08:38 PM
Definitely check gear lash. Gears being too tight will cause excessive current draw, which in turn will generate excessive heat...
The easy way to tell if the brake is on or off is to run the motor, then abruptly pull the throttle to stop. If it coasts, it's off. If the spur gear gets shredded (!) because the prop stops abruptly, it's on.
As I recall, my brake was on when I last used my Eflite 20A ESC, and I hadn't changed the settings from default.
10-17-2005, 09:00 PM
Re-reading, it sounds like the problem stays after the battery is disconnected? That would not be the ESC's brake. You can simiulate the brake function by hooking up two poles of the motor to power. This will lock the motor in a position. Is this the same feeling?
10-17-2005, 10:42 PM
I just did an interesting experiment with curious results. I didn't fly. I just verified that the prop spun freely and then I turned on the xmitter with throttle at 1/2 and connected the battery. With this ESC that powers up things but does not arm the motor. The prop spun freely. Then I moved the throttle to off which armed the motor. Without running the motor at all the prop was now NOT turning freely. Since the motor and gears did not move at all I don't think this can be about heat or gear lash!
Turning the prop feels kind of lumpy -- that is, the friction is not even all the way around. I pulled the prop and gears. The motor shaft does not turn as freely as I think it should. So whatever the problem is it's in the motor. Oh, Joy!
In answer to some of the other questions, this is the aluminum gear box that came with the motor. The gears have a metal center with set screws. The gears themselves look like they are some kind of hard plastic.
Yes, the prop is still not free turning for several hours after disconnecting the battery.
When I abruptly move the throttle to OFF the prop stops spinning quickly. It does not coast. However, it is not totally locked because, during landings with the throttle off the prop keeps spinning a bit until the plane velocity is low (like just before touching down). This does not sound like a hard brake function to me.
10-17-2005, 10:50 PM
That is interesting. Was the motor warm at all after your test? (without it running)? Do you have any capacitors or anything else inline between the motor and ESC? and last, when it doesn't spin freely for the next hour+ is it still hooked to the ESC? There are capacitors in the esc I think. Hmmm...
10-18-2005, 12:27 AM
It didn't occur to me to feel the motor since I hadn't run it at all. I'll do that on the next round of experiments.
There are simple silicone covered 14 gauge wires with gold bullet connectors between the ESC and motor. The 3 wires are less than 6" long.
Yes, I keep the motor connected to the ESC. I could try disconnecting it but that is more work because I have to remove the wing to get to the ESC.
Larry (who's surprised that electic motors can be so mysterious!)
10-18-2005, 01:02 AM
Larry (who's surprised that electic motors can be so mysterious!)
Tell me about it!
When I got my outrunner I wired it to the ESC by the colors (red to red, black to black, yellow to yellow) and it spun backwards. I already knew that by switching any two wires that it would reverse so I switched the yellow and red. Motor ran the right direction but at anything above half throttle it would scream like a bad bearing and stop. Hooked up my ammeter and found it was only drawing 6 amps before it'd stop then 0 amps when it did stop.
Hooked it up to run backwards again and it worked fine drawing only 8 amps at WOT. Scratched my head a bit then switched the black and red leaving the yellow connected to yellow, it ran the right direction and the screaching/stalling problem was gone. Found out that the ONLY way it runs the right direction is black to red, red to black, yellow to yellow but any other combo (other then color matching and running backwards) the problem shows back up.
10-18-2005, 09:30 PM
Well, I would expect the motor to turn hard after the ESC is powered up, especially if the brake is enabled (default). The "cogging" action you feel is normal for a brushless motor as the poles of the extremely strong rare earth magnets pass over the metal poles of the electromagnets. Having one of the phases in the motor energized only makes the cogging action more pronounced.
Also, most ESCs have a large capacitor or two that will hold charge for quite some time, even after the battery is disconnected. I would guess that if you disconnected the motor from the ESC, it would spin freely once again.
Perhaps we're barking up the wrong tree here? Power loss on the second flight still could be heat related, but the "stiff" motor may not be a symptom of the problem.
10-19-2005, 11:55 PM
I have noticed on occaison that the prop wouldn't spin as freely as it usually did...
There doesn't seem to ba a pattern to it, it just does it when it feels like it I guess?
The thing in common, in my case at least, is the E-flite 20A. ESC
I had a Park 400, a Park 370, and an AXi 2808/24 do it...
Matt, I think you have something there? The caps storing/holding curent? I'm no electronics guy, but I know it isn't a motor/mechanical thing.
Before running, my AXi (for example) will "freewheel" when I spin the prop by hand. Sometimes, after running, if I try spinning the prop, even after the batt. is disconnected, it feels like the brake is "dragging" (for want of a better term...
Oh, and if you're having a problem getting into the brake programming mode w/ your e-flite 20A. ESC? Just adjust your Tx. throttle end point or ATV to max. I have to make my throttle high end point 125% on my Flash 5 to be able to change the brake on/off...
10-21-2005, 06:42 PM
Thanks to proptop for the hint about how to get the ESC to enter the programming sequence. I adjusted the throttle range to 125% and it worked. I then disabled the prop brake and now the prop spins freely after running. So the E-flite ESC, at least mine, defaulted to ON. (I sure wish the E-flite documentation said something on this subject. It also does not describe what happens when the low-voltage cut-off engages but it seems to be a soft cut-off where the motor speed is gradually decreased.)
After getting the prop brake off I tried another experiment. I moved the throttle trim up while at full throttle and the motor speeded up! I guess that means that I haven't been getting full motor speed so I changed the throttle setting to 150%. That did it. According to the documentation the ESC is supposed to automatically adjust the throttle to get the full range of motor speed but it seems that it doesn't.
After making these adjustments I wasn't able to fly - Fog at the field. Soon I hope to get back to the original problem of the 2nd flight being less peppy than the first.
10-21-2005, 06:56 PM
WOOHOO! Fixed and with more power to boot. I wish all my fixes were like that. :)
10-25-2005, 11:28 PM
Is the difference between 1st and 2nd flight performance in my head??
I'm beginning to think so. I flew today and it seemed that the 1st flight was not as peppy as the second and I used battery #2 on the first flight. It was the combination of always using battery #2 on the 2nd flight that made me think that maybe it was that battery. Hmmm.... Well, maybe it's all in my head.
I did learn something though. The prop brake is now definitely OFF because the prop free wheels when I go to throttle off. And after landing the motor is cool and the prop is still free wheeling. But as soon as I disconnect the battery the prop is no longer free wheeling. I asked one of our experts at the field and he said it was acting just like it should.
My next change is to go to the lower gear ratio with the 9x6 prop. This will give more power but a shorter flight. The lower gear ratio with the 9x6 prop is HiMax's recommendation for 2-cell LiPo's.
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