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May 17, 2019, 10:07 PM
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What is the recommended battery with good flight time

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May 20, 2019, 07:13 PM
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Quote:
Originally Posted by irtiash
What is the recommended battery with good flight time

Sent from my CLT-L09 using Tapatalk
I'm not quite sure what "recommended" means here, as that kind of depends on what you want to do with it, and what changes you make to the system. I swapped to a smaller motor, and yanked the lead weights out of the nose, and this let me stuff a 4S 2Ah Lipo in it and get perfect balance with no dead weight. I've never flown it long enough to come close to draining the battery, in fact I usually get multiple flights on a single charge, but I don't do long distance flights. I think I could get a 4S LiIon pack in it for a few more grams, and that could potentially get another 50% endurance, but I never want to fly that long. I think the smaller motor and prop let you take out one of the two lead weights without changing CG (much). I will say that on 4S the BEC in the stock ESC can be a bit of a problem if it's windy or you fly hard. I had a brown-out that put me into trees.
May 21, 2019, 10:43 AM
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GeoffS's Avatar

Another CG question/observation...


After some repairs to the tail of my Dart I've been carefully checking the CG.
Before the crash(es) and repair(s) my impression was that the Dart flew best with the CG a bit aft of the wing marks.

Yesterday I flew with a couple of different CG positions and measured the balance carefully back at the shop (probably to +/-1mm).

The best flying configuration had the CG 9mm behind the center of the wing marks.
FWIW, this is a pretty heavy Dart (~400g with the repairs, nose-weights, and battery).

I saw some mentions of aft-CG in this thread, but I don't remember seeing a definitive recommendation for the CG position.

I didn't measure it, but I calculate the CG was about 1-2mm forward when my Dart was flying really poorly.

Does anyone know the balance-point and weight of an empty Dart?
I'd like to create a weight-and-balance spreadsheet but all I have is the data from my "Franken Dart".

An aside: I created a lead-weight holder that fits into the camera cavity at the front of the plane and lets you quickly install/remove up to 49g of lead: https://www.thingiverse.com/thing:3644861
Last edited by GeoffS; May 21, 2019 at 10:52 AM.
May 21, 2019, 02:43 PM
Registered User
Quote:
Originally Posted by GeoffS
After some repairs to the tail of my Dart I've been carefully checking the CG.
Before the crash(es) and repair(s) my impression was that the Dart flew best with the CG a bit aft of the wing marks.

Yesterday I flew with a couple of different CG positions and measured the balance carefully back at the shop (probably to +/-1mm).

The best flying configuration had the CG 9mm behind the center of the wing marks.
FWIW, this is a pretty heavy Dart (~400g with the repairs, nose-weights, and battery).

I saw some mentions of aft-CG in this thread, but I don't remember seeing a definitive recommendation for the CG position.

I didn't measure it, but I calculate the CG was about 1-2mm forward when my Dart was flying really poorly.

Does anyone know the balance-point and weight of an empty Dart?
I'd like to create a weight-and-balance spreadsheet but all I have is the data from my "Franken Dart".

An aside: I created a lead-weight holder that fits into the camera cavity at the front of the plane and lets you quickly install/remove up to 49g of lead: https://www.thingiverse.com/thing:3644861
I think dry weight was posted many pages back. I think ~400g is actually pretty light for the Dart, in particular with FPV gear. I think mine is about 395ish grams, and I have a lighter motor/prop and the lead removed. With the lead out, to get it to balance, I have a Runcam Split jammed in the nose (PCB right behind the camera, sunk into the foam), and a 150g battery jammed all the way forward. I use the stock stab board with all original wires removed, just the lead going to an R-XSR, and I use a TrampHV running off of raw battery, with the SMA lead removed and a UFL side-feed AXII antenna plugged straight in, and no TNR board. I even replaced the wiring between the motor and ESC with lighter wire, and swapped to a Deans mini connector. I guess the lead was slightly further forward than my battery, so if I left the lead in and used a smaller battery I might be about to shave another 10 or 15 grams off. Anything else, and I either have to lighten the tail more, or I guess, try a more aft CG. I'm surprised it does ago with CG 9mm behind their marks. That's a pretty huge change. No nasty behavior?
May 22, 2019, 10:04 AM
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GeoffS's Avatar
Quote:
Originally Posted by jones007
I think dry weight was posted many pages back. I think ~400g is actually pretty light for the Dart, in particular with FPV gear...
Thanks for the info. I thought I read (somewhere...) that 400g was high'ish and 450g was heavy. It looks like weight shouldn't be an issue.

Quote:
Originally Posted by jones007
I'm surprised it does ago with CG 9mm behind their marks. That's a pretty huge change. No nasty behavior?
None. I was very surprised too.
I expected it that test-flight would be a quick launch/fight-to-circle-back/land but it seems to fly great (in fact it felt/looked pretty unstable with the CG at or 1mm ahead of the marks).
At -9mm it flies very stably in the 3-axis mode too, so it wouldn't appear that the FC is compensating for the unbalance.
When I switch from 6-axis to 3-axis in level flight the Dart just keeps going along. I can do aileron rolls without any issue.

I'll do some more CG tests and shift the location forward in small increments.
May 22, 2019, 11:30 AM
From the bowels of MI
Where exactly does your stock stabilizer sit? I'm wondering if mine is off it's optimal position.
May 22, 2019, 01:25 PM
Registered User
Quote:
Originally Posted by GeoffS
Thanks for the info. I thought I read (somewhere...) that 400g was high'ish and 450g was heavy. It looks like weight shouldn't be an issue.



None. I was very surprised too.
I expected it that test-flight would be a quick launch/fight-to-circle-back/land but it seems to fly great (in fact it felt/looked pretty unstable with the CG at or 1mm ahead of the marks).
At -9mm it flies very stably in the 3-axis mode too, so it wouldn't appear that the FC is compensating for the unbalance.
When I switch from 6-axis to 3-axis in level flight the Dart just keeps going along. I can do aileron rolls without any issue.

I'll do some more CG tests and shift the location forward in small increments.
I suspect with stock electronics, lead still installed, minimal battery that will allow for CG (the CG they suggest), and no FPV gear you would be around 380ish grams. A camera, VTX and antenna add from about 5 to 15 grams depending on equipment used - more if you actually use an SMA antenna. Add another 10 or so if it's a Runcam Split. Save around 10 grams if you switch to a lighter motor/prop combo. Getting rid of the lead lets you get away with a larger battery without increases overall weight by too much (40g of lead turned into maybe 45g of additional battery). If we allow for CG at -9mm or more, you could ditch the lead and use a smaller battery for balance, and maybe get AUW weight below 375 with FPV gear. The downside of super light, of course, is that lighter wing-loading makes it more sensitive to turbulence.

For an FPV build, I think weights from 400 to 425 are on reasonable, and will likely fly well. Above 425 or so, launches probably start to require slightly more skill. I haven't flown a super heavy Dart, but I would guess above 450 you need a good arm and quite high throttle for launch. Interestingly though - I think many of the folks that tried flying at weights above 450g mostly complained that it landed like a rocket. You're observations that with CG at -9mm is still stable would suggest that the crazy landing speeds were because they were running out of elevator to compensate for a nose-heavy aircraft. Perhaps 450g is fine if CG is right. If it's nose heavy and over-weight, then you will need a ton of elevator to get it to slow down, and too much elevator can lead to loss of aileron sensitivity and other flight quality issues. Heavy is potentially good if you frequently fly in a lot of wind.

EDIT: I left the stock stab exactly where it came, but honestly it shouldn't matter where it is as long as the orientation is correct. If it's super far from CG then it will measure a bit of acceleration when you do pitch maneuvers, but I don't think they use accelerometers for much, and certainly not in a loop where this would cause a problem. In acro mode you only use gyros, and for that the sensor can be anywhere you want - as long as the axes are aligned properly.
May 22, 2019, 10:36 PM
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GeoffS's Avatar
This evening I rigged up a two-scale CG measurement system and re-measured the CG that I flew two days ago, along with the CG adding increasing amounts of lead at the nose. I used a jig to hold the lead so I can place it in the same location when I go flying next to compare CG vs. flying quality.

I was happy to see that the two-scale measurement was almost identical to my "balance on two posts" measurement (I double checked the two-posts measurement and got the same result). All came in at about -9mm.

I can adjust the CG from -9mm to about +1.5mm so I should be able to get a pretty good set of flight-data.

I've attached a photo of my CG measurement setup.
May 23, 2019, 02:06 PM
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GeoffS's Avatar
The more I fly this plane the more impressed I am!

I just in from a quick 1-battery flight in gusty winds 15-20+mph.
No problem.

It was nice to have a plane that could easily fly upwind into that breeze (half-throttle or a bit less).
Most of the time I was in 6-axis mode since the area I was flying is pretty small and the wind was really tossing the plane around.

Landings were lots of fun. If I got it just right the ground speed in the flare was zero.

I broke the original prop so I'm flying with a 5x4 3-blade that seems to work really well.
Last edited by GeoffS; May 23, 2019 at 02:27 PM.
May 23, 2019, 08:06 PM
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GeoffS's Avatar

Flying qualities with CG at -9mm


I haven't had a chance to fly with the range of CG locations yet (I forgot my weights at home...), but I did a bunch of stalls and other tests at the -9mm CG location this evening.

All the stalls were with the 6-axis stabilization enabled.
I entered the stall by reducing the throttle slowly and increasing the up-elevator until the throttle was all the way down and the elevator all the way back.
They were all basically non-events. The plane just decelerated and slowly descended in a nose-high attitude with full up-elevator.
During the stall I still had some aileron authority (not a lot, but enough to slip to one side or the other).
Adding some power would recover into a climb. Adding a bit less-power and releasing the elevator would also recover.

I did a number of landings and low-approaches. I didn't have any problems with elevator authority as the plane slowed into the flare.
I could abort a landing at a slow speed just by adding power and climbing away (basically the same behavior that I observed while stalling at altitude).

Switching from 6-axis to 3-axis mode in level flight at medium throttle caused no change in attitude (as before).
I tried aileron-rolls and loops and didn't see any bad behavior exiting the maneuvers (I'm not a great aerobatic pilot).
May 24, 2019, 02:23 PM
Registered User
Quote:
Originally Posted by GeoffS
I haven't had a chance to fly with the range of CG locations yet (I forgot my weights at home...), but I did a bunch of stalls and other tests at the -9mm CG location this evening.

All the stalls were with the 6-axis stabilization enabled.
I entered the stall by reducing the throttle slowly and increasing the up-elevator until the throttle was all the way down and the elevator all the way back.
They were all basically non-events. The plane just decelerated and slowly descended in a nose-high attitude with full up-elevator.
During the stall I still had some aileron authority (not a lot, but enough to slip to one side or the other).
Adding some power would recover into a climb. Adding a bit less-power and releasing the elevator would also recover.

I did a number of landings and low-approaches. I didn't have any problems with elevator authority as the plane slowed into the flare.
I could abort a landing at a slow speed just by adding power and climbing away (basically the same behavior that I observed while stalling at altitude).

Switching from 6-axis to 3-axis mode in level flight at medium throttle caused no change in attitude (as before).
I tried aileron-rolls and loops and didn't see any bad behavior exiting the maneuvers (I'm not a great aerobatic pilot).
Are you flying the stock stabilizer board? If so, when you refer to 6-axis stabilization are you talking about their take-off mode, and I guess that would make 3-axis stabilization their rate control? In the take-off mode, I believe the controller over rides your elevator commands, so will likely prevent real stall, and there they also doctor up the elevon movement to only move them up in an effort to prevent tip stall.

I suspect the data is still quite relevant, but I'd be curious to see how it behaves with no stabilization (middle switch position), where you have un-doctored input to the controls.
May 28, 2019, 03:49 PM
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GeoffS's Avatar
Quote:
Originally Posted by jones007
Are you flying the stock stabilizer board? If so, when you refer to 6-axis stabilization are you talking about their take-off mode, and I guess that would make 3-axis stabilization their rate control? In the take-off mode, I believe the controller over rides your elevator commands, so will likely prevent real stall, and there they also doctor up the elevon movement to only move them up in an effort to prevent tip stall.

I suspect the data is still quite relevant, but I'd be curious to see how it behaves with no stabilization (middle switch position), where you have un-doctored input to the controls.
Good points.
I was flying in the "take-off mode" (auto-level).
I'm not sure what the FC does when it can't satisfy the control inputs. For example, when you pull back full on the elevator the FC limits the horizon-angle to 90 degrees (straight up). At low airspeed it can't make that happen. Without the firmware to examine it's impossible to say, but I'd bet it just maxes out the elevator setting and uses the aileron parameter to keep the plane level. I've seen it do what looks like that on a couple of landings. As the plane slows it seems to behave as if the elevators are full-up and it bobbles around side-to-side trying to stay level.

I don't know how the FC could prevent a stall since it doesn't have an airspeed indicator.
I guess it could detect that it can't do the requested attitude and revert to a limited nose-up angle. That seems a bit sophisticated for a hobby-grade FC though.

Lots to investigate. Good thing it's a fun plane to fly!
May 29, 2019, 02:53 PM
Registered User
Quote:
Originally Posted by GeoffS
Good points.
I was flying in the "take-off mode" (auto-level).
I'm not sure what the FC does when it can't satisfy the control inputs. For example, when you pull back full on the elevator the FC limits the horizon-angle to 90 degrees (straight up). At low airspeed it can't make that happen. Without the firmware to examine it's impossible to say, but I'd bet it just maxes out the elevator setting and uses the aileron parameter to keep the plane level. I've seen it do what looks like that on a couple of landings. As the plane slows it seems to behave as if the elevators are full-up and it bobbles around side-to-side trying to stay level.

I don't know how the FC could prevent a stall since it doesn't have an airspeed indicator.
I guess it could detect that it can't do the requested attitude and revert to a limited nose-up angle. That seems a bit sophisticated for a hobby-grade FC though.

Lots to investigate. Good thing it's a fun plane to fly!
You're right - no airspeed sensor, so no stall detection, but you may notice that they mix in elevator with throttle. I think they have a pre-planned elevator schedule based on the throttle setting. I'm guessing this is their version of stall prevention. I'm not sure now if there is an active loop on elevator in take-off mode, or perhaps just a bias based on throttle.
May 29, 2019, 05:23 PM
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GeoffS's Avatar
Quote:
Originally Posted by jones007
You're right - no airspeed sensor, so no stall detection, but you may notice that they mix in elevator with throttle. I think they have a pre-planned elevator schedule based on the throttle setting. I'm guessing this is their version of stall prevention. I'm not sure now if there is an active loop on elevator in take-off mode, or perhaps just a bias based on throttle.
Good point!
You could probably come up with a pretty good estimate of airspeed by combining throttle (even better prop-RPM) and horizon-angle from the gyros.
You would have to assume a number of things (notably weight).
The only case that really needs the extra adjustment is the slow, nose-high case (i.e. landing flare).
They can't have put in too much correction or it wouldn't be possible to flare to land.

I'll have to watch the prop speed carefully next time I do some stall tests.
Jun 03, 2019, 06:35 PM
Registered User
How do you attach vtx to the cover of this wing?
What about gps?


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