Hi All

So, I managed to break 45 mins flight time today with a 'normal' set up including GOPro & Brushless gimbal.

  • Tarot Iron Man Quad frame (600mm)
  • Turnigy 390KV Motors - 4 off
  • 40Amp Hobby King ESCs - 4 off (Over spec but I had them lying around)
  • 8300mah Battery - 3cell
  • APM2.5+ Board
  • 15 inch Carbon Fibre props.

The Rig was really stable and there was a light wind but I had an issue with the quad dropping and then regaining height. For no apparent reason it would suddenly lose altitude regardless of the amount of throttle I applied, then it would touch ground and recover the hover.

This got more frequent in nature as the flight progresses until the descents became so rapid that I got a bit twitchy about the rig being damaged.

No ESCs were hot, nor the motors, nor the APM, nor the PDB. All seemed fine but somethign WAS happening.

Anyone had this before on longer flights or know of a possible reason for the sudden drops in what I am presuming is Motor Performance



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Are you using a lipo alarm.

Hey Dave

Yes I had a Lipo Alarm on. All Cells were at 3.6+ and the battery went to 23% on the meter. So should have been all good


Do you have the barometer covered with foam.

Yes. The fact that the drop increases in frequency and severity pushes me more towards the whole electrical/mechanical system and away from the APM. But nothing is overheating. Its weird

Off topic, but why does nobody use motor watts? The 390KV is only good if you what the rmp is.

As for the drops, do you have the fc in a case? Wind blowing across the top can cause play with your barometer. Also, it could be temp loss of motor sync if you have simon k flashed esc, low KV motors have some chance of that. The last thing I can think of is loss of gps 3d fix can cause your quad to drop some, but it's usually only a foot or so in my experience.

Here's a quick video of my test quad in 22 mph wind in gust up to 29 mph. It drops a bit vertically, but it's mostly because of gusting wind. Not the greatest video, but it think it shows how good of lock you can get with a gps with a flat antenna.


What was your hover throttle?

I am guessing you're flying at >80% throttle, and "Stab Patch" would start to clip your throttle limit to leave enough room for stabilization.

If you upgraded to 17" props which that frame can take, it might perform better, if the motors can take it.

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