I need some advice - I modified a Parallax Elev-8 quadcopter by fabricating a boom from alunimum U-channel stock to hang a Tarot 2 axis gimbal/GoPro camera. The aircraft is using an APM 2.6 FCU, with external GPS/compass, telemetry and a small video transmitter. The weight is approximately 4.4 lbs. I'm using the stock motors - KA 1050kv Outrunners with 10x4.7 propellers. My problem is after only about 2 1/2 min the voltage failsafe kicks in and it wants to land. Here is a picture of the voltage log:
You can see where the Failsafe begins - I was able to switch to RTL and the aircraft returned to the launch point.
My question is this: Is it normal for voltage to drop immediately like it did on takeoff? Should I lower the voltage failsafe threshold?
Here's a pic of my aircraft:
Replies
Good points - thanks!
Endurance is a function of aircraft weight vs power system (motors/props/battery) capacity. Your power system cannot carry the aircraft.
What battery are you using and what were your flight times like before you modified the aircraft?
I'm going to try lowering the failsafe to 9.9V and put on the 11" carbon props. Meanwhile, I've ordered parts for an upgrade - gonna strap on Tarot 4006 620 kv motors, with Tarot T-series 1255 carbon fiber props, and a 4s lipo - 6000 mAh battery pack. At 100% power, the motors will pull 26.8 A, so I'll mate the motors to Hobbywing Platinum 30A OPTO ESCs. At 50% throttle, each motor will produce 580 G thrust, at 75%, 1094 G - that should be enough to improve performance...
Ya gotta keep looking at weight, and you're going in the wrong direction.
First off, (and I know its too late..) the Tarot 620Kv motors are junk. I have a set that came with a Tarot 680 Pro Hex ARF kit, and they just can't cut the mustard. You will also find out those motors do not have a 'standard' 19mm/16mm mounting bolt pattern. In their not so infinite wisdom, Tarot picked a 27mm Triangle pattern which means these motors will only bolt on to a Tarot motor mount plate. I replaced them with Turnigy Multistar Elite 4006 740Kv swinging 1344 beechwood props.
For batteries I ran 2 5200mAh 10C LiPos in parallel, and with an AUW (All Up Weight) of 3257 grams I was getting consistant 18+ minute hover times with 20% of the battery capacity in reserve.
Another point is, do not take the manufacture's motor data as gospel. The motors are tested on a bench, so the results may, or most likely may not be an accurate representation of what happens in a flight environment. I saw this with the 740s. HK's motor data chart said I should be seeing a grams/watt efficiency of 9.2 when in flight it was more like 8. And, FWIW, I've tested motors similar to yours and they have g/w of around 7 or so..
I'm not sure what you mean by my going in the wrong direction - do you mean that I'm okay with the KA 1050 kv motors given the weight of my aircraft, or simply that I made a bad choice of motors? I do have a Tarot 680 Pro that I built and I used them - I get around 14 min endurance on that craft and it too has a Tarot 2 axis gimbal and a video transmitter.
Regarding my choice of motors - I got the data from a YouTube video where a guy ran a test: See here
They may indeed be "junk" compared to others - I would have preferred to buy Tiger motors but they are twice the cost..
Anyway, since I've already ordered them (along with the Tarot mounts), I'll proceed with my experiment and see what happens. I thank you for your input though!
You are dropping from 12v to 10.5 almost immediately. A good failsafe is 3.5v per cell so that's 10.5v and that appears to be where your failsafe is set. I agree that your props look very small for 3s. My F450 uses 10" 4.5 props when I use 3S batteries.
Was your endurance much better with this battery before adding the camera/gimbal system? My Tarot T2D and 600mW transmitter pull about 500 mA by itself.
Yes, I had better endurance time before the mods - around 13, 14 minutes.
13 - 14 minutes with one 3300 mAh battery ?
Guess not since with a 3S 3300mAh battery, 10" props and 2200 grams AUW you should fly 8 minutes .
15' 30" if the batteries are two , so 6600 mah 3S.
Anyway you should have around 25A for hovering and a efficiency of 7,7 grams per Watt.
With 6600 mAh it means from 4C to 8C of discharge during a normal flight
Check with Mission Planner or dataflash logs how many Ampere your copter is using during flight , they should be around 25A in hovering with 50A peaks.
The voltage drop , if battery voltage after full charge is 13,2 volts , is due to poor battery quality/conditions.
In a word your batteries are dead.
Like I said, I got better endurance time before the mods - prior to installing the aluminum boom, Gimbal, GoPro camera and video transmitter. Looking back though, you're probably right - I think the 13 - 14 minute flight time was from my Tarot hexcopter and I think my Elev-8 was closer to 11 minutes.
At any rate, I'm suspending any further flights until I receive the Tarot 4006 620kv motors, props, mounts and ESCs.
Without seeing the logs, the props look to be way too small for 3s and the motors are demanding more thrust to keep afloat. I'd venture you're at 60-70% throttle to hover. That puts a large strain on the battery which may be bad in itself.
That's a huge voltage drop. Post logs and more info on the brand/model motor and battery.
-
1
-
2
-
3
of 3 Next