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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For anyone still interested, I received the barometer inlet that I had 3D printed. I don't yet have the rest of the kit to make a permanent installation, but I was able to cobble together a temporary mast for testing.
The result is fantastic. The new inlet and its revised placement almost completely eliminate the aerodynamic effects that I was experiencing. I had two problems. First, there was a steady, shallow descent in horizontal flight, at anything more than the slightest movement. Second was the sudden drop in altitude at the end of a horizontal run as others experience. This mod cures the former and greatly reduces the later.
It looks like there are two factors involved in my case. I think my earlier attempt failed because I didn't get the remote inlet outside of the airframe's pressure envelope. I was essentially using a remote inlet to sample the same pressure as the internal inlet. The other important aspect is using an inlet that is immune to the pressure changes caused by rapid fluid flow, which the Gill inlet does.
The before and after logs show the difference in barometer altitude vs. GPS altitude, during horizontal runs. The middle of the first screen shot shows a long horizontal run. You can see the barometric altitude steadily increase and surge at the end while the GPS altitude drops off rapidly and comes back up and the end.
The second image includes GPS latitude, so that you can see the horizontal displacement. In this image you can see that the barometric altitude tracks GPS altitude much more closely.
I don't think that the tall mast will be a permanent feature on the F450 airframe. It's kinda impractical. I'll probably switch to a flight controller without barometer and GPS dependency and just fly it for fun. I'll save future barometer adventures for my 750 build, in progress now.
It's good to finally contribute something of substance to this discussion! I hope that someone finds my non-scientific fumbling useful.
Awesome work Chris! Thanks for sharing. I'd love to see how that would work if the mast was no higher than the gps.
Chris Hardwick > Richard KennedyJanuary 30, 2016 at 4:12pm
Richard,
There was a break in the weather today, so I was able to get a little air time in.
The goal of today's testing was to determine the impact of shortening the barometer inlet mast to the height of the GPS mast. I have to say that it worked better than I thought it would. I still think performance was a little better with the taller mast. I noticed a sudden and very brief dip upon rapid deceleration; like when I counter with opposite stick. You can see the small dips in the GPS alt, in the screen shot below. Other wise, pretty flat.
Looks good!! Thanks for sharing your results. I might end up doing the same thing in a future quad.
Chris Hardwick > Richard KennedyJanuary 30, 2016 at 6:19pm
I'm been working on an improved version for public consumption as there was some interest in making the inlet available to the community. This version should be less fragile and printable on lower-end FDM machines, but it will still need support material. Where would I publish something like that? I've never used Github or whatever resource is used for APM/PX4/Pixhawk revision control.
Steven Adams > Chris HardwickJanuary 30, 2016 at 9:11pm
Replies
The Pixhawk.
For anyone still interested, I received the barometer inlet that I had 3D printed. I don't yet have the rest of the kit to make a permanent installation, but I was able to cobble together a temporary mast for testing.
The result is fantastic. The new inlet and its revised placement almost completely eliminate the aerodynamic effects that I was experiencing. I had two problems. First, there was a steady, shallow descent in horizontal flight, at anything more than the slightest movement. Second was the sudden drop in altitude at the end of a horizontal run as others experience. This mod cures the former and greatly reduces the later.
It looks like there are two factors involved in my case. I think my earlier attempt failed because I didn't get the remote inlet outside of the airframe's pressure envelope. I was essentially using a remote inlet to sample the same pressure as the internal inlet. The other important aspect is using an inlet that is immune to the pressure changes caused by rapid fluid flow, which the Gill inlet does.
The before and after logs show the difference in barometer altitude vs. GPS altitude, during horizontal runs. The middle of the first screen shot shows a long horizontal run. You can see the barometric altitude steadily increase and surge at the end while the GPS altitude drops off rapidly and comes back up and the end.
The second image includes GPS latitude, so that you can see the horizontal displacement. In this image you can see that the barometric altitude tracks GPS altitude much more closely.
I don't think that the tall mast will be a permanent feature on the F450 airframe. It's kinda impractical. I'll probably switch to a flight controller without barometer and GPS dependency and just fly it for fun. I'll save future barometer adventures for my 750 build, in progress now.
It's good to finally contribute something of substance to this discussion! I hope that someone finds my non-scientific fumbling useful.
Awesome work Chris! Thanks for sharing. I'd love to see how that would work if the mast was no higher than the gps.
Richard,
There was a break in the weather today, so I was able to get a little air time in.
The goal of today's testing was to determine the impact of shortening the barometer inlet mast to the height of the GPS mast. I have to say that it worked better than I thought it would. I still think performance was a little better with the taller mast. I noticed a sudden and very brief dip upon rapid deceleration; like when I counter with opposite stick. You can see the small dips in the GPS alt, in the screen shot below. Other wise, pretty flat.
Looks good!! Thanks for sharing your results. I might end up doing the same thing in a future quad.
I'm been working on an improved version for public consumption as there was some interest in making the inlet available to the community. This version should be less fragile and printable on lower-end FDM machines, but it will still need support material. Where would I publish something like that? I've never used Github or whatever resource is used for APM/PX4/Pixhawk revision control.
publishing them to Thingiverse is my suggestion http://thingiverse.com
Good idea. Thanks.
http://www.thingiverse.com/thing:1309180
could you check the link, or give the name it is posted as please? that link gave an error
Thing 1309180 is live.
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