According to Randy the know issue of altitude loss after a high speed run is at its heart a frame issue.This seems to me a very worthwhile discussion to have.Once the majority of us understand this, we will be less likely to muck up other threads.Take it away Randy...
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I just created a thingiverse account. They tell me that I have to wait 24 hours to publish anything. I didn't realize that at first. The link should work tomorrow. I'll check it. If it still isn't good, I'll reply with another.
Not in this round of testing. As I've mentioned, I haven't been terribly scientific in my experiments. I did test with just an open tube, mounted in a similar location, in previous experiments. The result was a negligible improvement, if any, over the internal barometer.
Chris Hardwick > Richard KennedyJanuary 24, 2016 at 7:25pm
Hi Richard,
Thanks.
I'm willing to try, though I suspect I would have the same issue as in previous experiments, wherein the inlet was still inside the airframe's pressure envelope and didn't accomplish anything. That's the reason for the tall mast. I also have the propeller flow-fields to contend with. There is a low-pressure gradient above each prop that changes with RPM. There isn't much room to work with on this airframe.
I'll see if I can get in a flight with a shorter mast this week, but it may have to wait until the weekend.
Cheers!
Darius Jack > Chris HardwickJanuary 24, 2016 at 6:32pm
@Chris,
you can easily correct and control altitude via a simple AltHold energy consumption test. Power meter can give you highly reliable energy consumption vs. altitude (air pressure) at AltHold chart, you can use to support EKF.
If energy consumed by motors and hardware to stay in AltHold mode at altitude 10m is E10, so if energy consumption starts to grow suddenly you can can expect error in bar, GPS, IMU altitude calculations.
Alt control via power consumption exactly resembles manual mode control with joystick.
Saving power consumed data to logfile may give better insight into Drone Fly-away Syndrome, since if energy consumption is steady, all you can expect from your drone is a horizontal drift in Stabilize mode.
Thank you for the suggestion, though I'm not entirely sure that I follow. Are you saying that I may be experiencing voltage droop to the IMU due to motor current surges? If that's the case, I'm pretty sure that my power supply regulation is good. If I had such a problem I would be seeing other issues as well.
I am aware that I can tweak EKF_ALT_NOISE to gain a small amount of immunity to small altitude changes, but this isn't a good option for me as I am currently fighting vibration issues as well.
Maybe I just don't understand what you mean.
Darius Jack > Chris HardwickJanuary 24, 2016 at 8:03pm
@Chris
calibrated power meter can be used to control altitude alike barometer.
For the set altitude in AltHold mode, energy consumed can be constant
- if you notice energy drop, you can expect drone altitude to drop
- for altitude to rise more energy is consumed
so I would suggest implementation of power meter into Pixhawk
as a sensor of special importance to control uncontrolled fly-aways
and have power meter values saved to log file for post mortem analysis.
For what it is worth.... Knowing hover throttle level and frame angle + duration + initial acceleration it should be possible to estimate current speed rather accurately. Combinig the speed + experimantal baro degradation data it should be possible to calculate offset for a given frame angle and speed...
I don't believe true air speed is the issue here. It is change in speed, or more specificly change in acceleration relating to the begining of a maneuver and at the end of a maneuver. Basically,a high pressure bubble compensator.
A parameter that would allow a throttle correction factor relitive to the acceleration/ deceleration rate of the aircraft might do it.
If only acceleration was the case, we would se the copter change altitude right away (upon acceleration) but we usially see it after a certain speed is reached. As illustration, compare the pressure on your arm.if you stick it out of a moving car at 20mph and at 80mph.... Big difference. Not quite the same, bur similar thing is happening with our copters. Also, this offset is not linear and will vary greatly with speed and frame angle at which this speed is sustained. Another experimental point: naza will drop a little altitude when abraptly removing pitch angle and letting it drift. But the drop is negligible compard to AC... a mere. 10-20cm ... I do believe they rely a lot on IMU data for level flight instead of baro. The key there is good vibration filter, so when the change is abrupt, vibrations go outside the filter ability and naza drops a bit falling back to baro data.
Replies
I just created a thingiverse account. They tell me that I have to wait 24 hours to publish anything. I didn't realize that at first. The link should work tomorrow. I'll check it. If it still isn't good, I'll reply with another.
Sorry about that.
Hi nicopter,
Not in this round of testing. As I've mentioned, I haven't been terribly scientific in my experiments. I did test with just an open tube, mounted in a similar location, in previous experiments. The result was a negligible improvement, if any, over the internal barometer.
Hi Richard,
Thanks.
I'm willing to try, though I suspect I would have the same issue as in previous experiments, wherein the inlet was still inside the airframe's pressure envelope and didn't accomplish anything. That's the reason for the tall mast. I also have the propeller flow-fields to contend with. There is a low-pressure gradient above each prop that changes with RPM. There isn't much room to work with on this airframe.
I'll see if I can get in a flight with a shorter mast this week, but it may have to wait until the weekend.
Cheers!
@Chris,
you can easily correct and control altitude via a simple AltHold
energy consumption test.
Power meter can give you highly reliable energy consumption vs. altitude (air pressure) at AltHold chart, you can use to support EKF.
If energy consumed by motors and hardware to stay in AltHold mode
at altitude 10m is E10, so if energy consumption starts to grow suddenly you can can expect error in bar, GPS, IMU altitude calculations.
Alt control via power consumption exactly resembles manual mode control with joystick.
Saving power consumed data to logfile may give better insight into Drone Fly-away Syndrome, since if energy consumption is steady, all you can expect from your drone is a horizontal drift in Stabilize mode.
Hi Darius,
Thank you for the suggestion, though I'm not entirely sure that I follow. Are you saying that I may be experiencing voltage droop to the IMU due to motor current surges? If that's the case, I'm pretty sure that my power supply regulation is good. If I had such a problem I would be seeing other issues as well.
I am aware that I can tweak EKF_ALT_NOISE to gain a small amount of immunity to small altitude changes, but this isn't a good option for me as I am currently fighting vibration issues as well.
Maybe I just don't understand what you mean.
@Chris
calibrated power meter can be used to control altitude alike barometer.
For the set altitude in AltHold mode, energy consumed can be constant
- if you notice energy drop, you can expect drone altitude to drop
- for altitude to rise more energy is consumed
so I would suggest implementation of power meter into Pixhawk
as a sensor of special importance to control uncontrolled fly-aways
and have power meter values saved to log file for post mortem analysis.
For what it is worth.... Knowing hover throttle level and frame angle + duration + initial acceleration it should be possible to estimate current speed rather accurately. Combinig the speed + experimantal baro degradation data it should be possible to calculate offset for a given frame angle and speed...
A parameter that would allow a throttle correction factor relitive to the acceleration/ deceleration rate of the aircraft might do it.
If only acceleration was the case, we would se the copter change altitude right away (upon acceleration) but we usially see it after a certain speed is reached. As illustration, compare the pressure on your arm.if you stick it out of a moving car at 20mph and at 80mph.... Big difference. Not quite the same, bur similar thing is happening with our copters. Also, this offset is not linear and will vary greatly with speed and frame angle at which this speed is sustained. Another experimental point: naza will drop a little altitude when abraptly removing pitch angle and letting it drift. But the drop is negligible compard to AC... a mere. 10-20cm ... I do believe they rely a lot on IMU data for level flight instead of baro. The key there is good vibration filter, so when the change is abrupt, vibrations go outside the filter ability and naza drops a bit falling back to baro data.
Just a curiosity, and maybe a useful data point -
Does the PX4 flight stack have this issue?
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