Hand launch crash repeatedly,

Hello can I have some help here. it was really frustrating. the plane were crashed for many times repeatedly. it was fine to launch and then became like this. the log recorded multiple times of crash for the same plane and one time success launch before of that crash. can anyone tell me what is happening there.

I am not an expert log analyst. But I see your battery going down when you demand a lot of amps from it. In less than 5 seconds you go from 16.5V to 12.87V when you draw 46.71A.

Do you use Lipo or Liion? Liions aren’t the best for squeezing out a lot of amps.

This record is from crash2.BIN

Thank you for your answers

I am using 21700 battery. It has good power density for long traveling. I guess the thrust should be enough for taking off. as my other airplane are using same battery without problem for taking off.

The success hand launch has the same battery.

Liion batteries have good charge density but poor discharge capacity. You can see how once in FBWA (and the plane on the ground) the battery recovers its voltage because it has enough mAh; Your battery has charging capacity but it does not have the discharge capacity that you are requesting.

Analyze the flight logs of the other plane; the other plane may have less power demand on takeoff.

Try modifying TKOFF_THR_SLEW and that way, perhaps, you will get enough electrical power to overcome takeoff.

Try to make the takeoff as efficient as possible and that the energy demand does not increase too much (for example: TKOFF_LVL_PITCH, TKOFF_THR_MAX, BATT_WATT_MAX)

thanks for spending time on the logs.

Here are what I think. please correct me if I am wrong.

I am using shake-to-wake to hand launch. so I think TKOFF_THR_SLEW does not matter here.

The plane is Vtail minitalon, weights around 1.8kg. The rough estimated thrust is 40amp by 14V with 4g/W, so it should be more than 2kg. so I guess it is enough thrust to launch this plane. I just could not figure out why the plane is decenting right after tossing in the air. it should not be like this with this much thrust.

do you mean to lower the TKOFF_LVL_PITCH and increase the TKOFF_THR_MAX

shake-to-wake has to do with how the auto takeoff mode is activated while TKOFF_THR_SLEW refers to how the engine is revved. One option and the other are not exclusive.


All the data you provide is theoretical but the reality is that your record shows a consumption of 46.71A. In the second graph (it is from one of your ESCs) you can see how as the voltage values fall, the engine revolutions also fall; and if the revolutions fall there is no longer that supposed push.

Yes I am talking about lowering TKOFF_LVL_PITCH and no, I am not talking about increasing TKOFF_THR_MAX but about reducing it. If your battery does not have the capacity to power your motors, do you still want to increase the power?

I recommend that you read the Ardupilot documentation that explains all the aspects very well.

Hi thank you for your answers.

my understanding of TKOFF_THR_SLEW is the time takes that throttle from 0 to max. it is not very important if it is shake-to-wake.

it was the same plane same battery same setup. and it were all fine to hand launch. then crash all the time after that. this is confusing me. I think it is the same on the other bin file of success hand launch that volt and curr drops as much as the crash launch does.

I am lower the TKOFF_LVL_PITCH. and probably use the lipo battery to give another try. I am really not confident to do that again. it takes lot time to repair :sweat_smile:

yes I did read takeoff doc again. i guess I have set it up correctly. tridge also helped some on another post. Take off Hand launch does not flying straight

I had already read your steering problems at takeoff in the other post. When I saw your flight logs I understood.

There are no errors or misconfigurations (I am talking about the steering on takeoff). Your plane does what it has to do. Simply take off and once reached TKOFF_LVL_ALT turn towards the takeoff direction. What happens is that the take-off direction is the one it points to when the AUTO mode is activated. From what I saw in your records, you have the plane on the ground at -90º from the direction in which you launch it, you activate AUTO mode, you take the plane and turn it 90º, you launch it … as soon as the plane reaches TKOFF_LVL_ALT it turns -90º to comply with the take-off direction.

On the ground before takeoff

At launch

Here are the procedure for what I usually do the hand launch.

When everything is ready,arm the plane on the ground.

Turn the plane to the direction that going to be hand launch.Switch to take off mode.

Push the throttle to the maximum. Gently lift the plane up and trying not changing its angle and direction. Shake to wake then toss in the air.

I can see the launch angle on OSD screen, but don’t know how it define, because it changes everytime, even the launch condition are same every time.

Your records say that the takeoff mode is activated with the plane on the ground and at -90º from the takeoff direction.

is it not OK to change the heading after takeoff mode is on? can you tell me what is right sequence?

I see a few things that might be a problem.
In the following graph taken from a middle attempt in your first binary file…it looks like the plane stalled less than a second after the throw. Look at the orange line (CTUN actual pitch). At the second IMU squiggle is the throw… Actual pitch prior to the throw is ~5% up. During the throw, you pitch up sharply to 30%. This is too steep for the 7m/s speed that the yellow line shows for your ground speed (unless you had a big headwind). So the plane noses over and is diving at -76 degrees about 1 second after the throw.

It’s not trying to roll, the problem is all with pitch.

If you threw flatter, it would work better.

The current does drop at the exact moment of the throw, but it seems like too big a drop to attribute to the plane just moving forward (and putting the prop into a moving air situation). I doubt it’s a battery capacity issue, the line is too flat in the two seconds before the throw. If it was battery capacity, the line would tilt down to the right instead of making a big drop.

thank you for spending time on the logs.

I will try threw flatter and change the battery. to see if I can get it right.