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Old Jan 16, 2012, 02:38 PM
Fournier RF4D N1771 Awesome!
jb92563's Avatar
Riverside, CA
Joined Nov 2004
270 Posts
Quote:
Originally Posted by Erknie View Post
1-2 meters indoors is what people report for the BMP085
If you look in the MultiWii GUI you can often see that the altitude changes when the MultiWii sits still on the table. If you need accuracy at low hovers below about 5meters, you don't use a barometer, you use a sonar.
That is always a question, but the accuracy of +- 1m equals a 2 meter range.

I doubt its even that good in practice, probably more like 2-5 meters due to temps, local pressure gradients due to the props etc.

Sonar modules can be accurate to 1-2 inches but only range reliably under 12' unless you optimize the setup considerably.

So Baro is good above tree top level where a 5' difference is not such a big problem and Sonar is good under 12'.

Some of the expensive autonomous systems that land on their own use sonar for fine altitude control in the height critical landing stage.

Maybe one day someone will figure out how to adapt laser range finders for arduino interfacing.

Ray
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Old Jan 16, 2012, 02:46 PM
Mmmmmmm!
WiseDuck's Avatar
Kingdom of Sweden, Dalarna County, Sater
Joined Oct 2011
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I would personally be alright with the height hold if it all it did was bounce up and down a bit. Could be useful in emergencies or if you need to take off your Fatshark goggles and have a look around.

Anyone know how to tune it?
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Old Jan 16, 2012, 02:54 PM
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The Netherlands, FR, Wymbritseradiel
Joined Oct 2005
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Quote:
Originally Posted by leadfeather View Post
What should the typical resolution of the barometer be? +/- how many feet or meters?
On my table it gives -121,6 to -121,8 if I move the quad up 20 cm...it goes to -121,4 and if i put it on the ground it gives -122,4 (table is 80 cm high)

Can someone with a bluetooth record the messurements in baroflight?
and record the quad movement as wel?

Does somebody use the baro that works? I would like to see there PID settings?
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Old Jan 16, 2012, 03:10 PM
Mmmmmmm!
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Kingdom of Sweden, Dalarna County, Sater
Joined Oct 2011
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I'll experiment a bit tomorrow, see what happens with crazy high P values in the ALT field. As far as I know I is ignored. D does... Yeah, don't know. There are no good guides out there for the baro.
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Old Jan 16, 2012, 03:39 PM
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United States, AL, Huntsville
Joined Dec 2007
102 Posts
After reflashing and configuring, my ESC's just beep won't start.

When I received the Red Board from GoodLuckBuy, I made a quick test on my DYI quad X and thought ESC's were starting with too high an RPM.

I recalibrated all four ESC's individually for a throttle range of 1000 to 2000.

I changed minthrottle from 1150 to 1100 and afterward the ESCs just beeped and do not start.

I went back to the original #define MINTHROTTLE 1150, reflashed the board and the ESCs still just beep and do not start

HELP? what do I try next?

Olympian (newbie)
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Old Jan 16, 2012, 03:44 PM
g0t rabb1t?
ABLomas's Avatar
Lietuva, Vilnius
Joined Jul 2011
1,543 Posts
Quote:
Originally Posted by Olympian View Post
When I received the Red Board from GoodLuckBuy, I made a quick test on my DYI quad X and thought ESC's were starting with too high an RPM.

I recalibrated all four ESC's individually for a throttle range of 1000 to 2000.

I changed minthrottle from 1150 to 1100 and afterward the ESCs just beeped and do not start.

I went back to the original #define MINTHROTTLE 1150, reflashed the board and the ESCs still just beep and do not start
Recalibrate ESC again?
They expect 1000, but get 1050 as "zero throttle".
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Old Jan 16, 2012, 04:08 PM
Hooked on FPV
Joined Jan 2012
86 Posts
Hey guys, I'm new to this forum and have been reading your posts about this Crius Multiwii board. I am wanting to build a quadcopter myself but can't decide what controller board to purchase. So far I'm between the Eagle N6 (just because it seems like an easy plug and play board and has MEMS gyros), and this Crius Multiwii. What would you guys suggest?

Also, in return for some help I would like to add some input that may be helpful to you guys regarding this Multiwii board.

I noticed that you are having a lot of trouble getting the barometer to work even remotely well. I read WiseDuck's description of how the barro was acting(starting out ok but then getting more and more unstable until it slams into the ground) and it hit me that the g's from the copter movement were effecting the barro performance. SO I looked up the barro used on the Multiwii chip and I found some very interesting info that I think will be helpful. I found the following info on this site:

http://mbed.org/users/tkreyche/noteb...essure-sensor/

"Most pressure sensors are g-sensitive. If you are using one using in a high-g environment, such as model rocketry, fast model airplane or UAV, the sensor element should be mounted 90 deg to the g-axis, or use two in opposing orientations and average them."

So it seems to me that if you were to mount the barro vertically(may have to unsolder it from the board) and build a little enclosure around it to protect it from the prop wash and wind that you would have a pretty stable barro.
Or I wonder what would happen if you mounted the barro upside down onto the board somehow if that would cause less up and down movement as it wouldn't be constantly compensating for a super high and super low barro reading? The reverse g's would counteract the atmospheric reading and the autocorrection would not be so erratic.
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Old Jan 16, 2012, 04:21 PM
Fournier RF4D N1771 Awesome!
jb92563's Avatar
Riverside, CA
Joined Nov 2004
270 Posts
Quote:
Originally Posted by ariekraakjr View Post
On my table it gives -121,6 to -121,8 if I move the quad up 20 cm...it goes to -121,4 and if i put it on the ground it gives -122,4 (table is 80 cm high)

Can someone with a bluetooth record the messurements in baroflight?
and record the quad movement as wel?

Does somebody use the baro that works? I would like to see there PID settings?
Seems like the baro readings are reversed.

The baro readings do wander a fair bit so I wonder if that is just its +- 1m accuracy wanderings.

A thought occured to me about the baro and how to steady the readings.

I fly full size gliders and they have a total energy system that buffers and compensates the pressure readings to a variometer. The buffering is accomplished by what is called a capacity flask and allows air to flow in and out through a tiny orifice, thereby buffering or moderating the pressures seen by the instrument.

Perhaps a similar thing can be done with the baro.

Perhaps glue a nipple on it so you can relocate the pickup out of the prop blast. Perhaps sealing one of the arm tubes and using a tiny hole on the inboard side away from the props will create a small capacity that can buffer the baro better than just having it open to the free airstream and turbulence that invariably causes the baro readings to fluctuate even more rapidly.
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Old Jan 16, 2012, 04:59 PM
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Austin, TX
Joined Jan 2009
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If you look at the MultiWii coding forums, several coders are working to improve the altitude hold function....the sensor puts out very noisy values...the VEL PID lopp currently has bugs, but is being worked on...its the vertical rate of speed from the ZACC sensor...its the inner loop on altitude hold...but you have to have a quiet ZACC output (vibration sensitive) and enable TRUSTED_ACCZ in the code to have the inner loop operational (don't bother yet...its got bugs)

also, there is work ongoing to get better auto-level in the presence of vibrations...

the Arducopter folks apparently have better code for this BARO sensor and seem to have real +/- 1m results being reported....not runwaways like this code seems to do sometimes....give the coders some time (maybe some encouragment on the MultiWii forums toos)...should be improved in the future...I hope
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Old Jan 16, 2012, 05:11 PM
Registered User
Australia, QLD, Brisbane
Joined Nov 2011
949 Posts
Quote:
Originally Posted by jb92563 View Post
Perhaps glue a nipple on it so you can relocate the pickup out of the prop blast. Perhaps sealing one of the arm tubes and using a tiny hole on the inboard side away from the props will create a small capacity that can buffer the baro better than just having it open to the free airstream and turbulence that invariably causes the baro readings to fluctuate even more rapidly.
You certainly need some isolation of the baro, on the multwii forums one person reported he can see noise from a fan running in the other room!

So outside on a windy day, all bets are off!

Personally I would only use the baro for rough altitude hold. Sonar has better accuracy, or incorporate a laser range finder, or just mount your camera on a balloon tied to a few long pieces of string and forget using a multi-copter.
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Old Jan 16, 2012, 08:00 PM
FPV really is fun.
Scotth72's Avatar
Sedona, Az
Joined Sep 2001
938 Posts
My altitude hold works within a meter and a half, in the wind. Two different quads, one a light weight build, another a bit heavier. You have to cover the baro with foam or a cotton ball, and keep it out of the sunlight. Then read this thread:
http://www.multiwii.com/forum/viewto...t=363&start=30
I am using a bma180 accel, and a bmp085 baro. You must use trusted z accel in the code, and have very little vibration.
I ended up using these values for the lighter quad:
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Old Jan 16, 2012, 08:17 PM
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ssatoru's Avatar
Chiba, Japan
Joined Jan 2002
1,044 Posts
Hi Olympian,

I am also a newbie. I stuck with the same issue before. My ESC is TowerPro 'MAG8' 12A. It did not arm when powered on (before 'arm' is set on), kept beeping.

Try to change MINCOMMAND in config.h to 900, then your ESC should arm.

Satoru
Quote:
Originally Posted by Olympian View Post
When I received the Red Board from GoodLuckBuy, I made a quick test on my DYI quad X and thought ESC's were starting with too high an RPM.

I recalibrated all four ESC's individually for a throttle range of 1000 to 2000.

I changed minthrottle from 1150 to 1100 and afterward the ESCs just beeped and do not start.

I went back to the original #define MINTHROTTLE 1150, reflashed the board and the ESCs still just beep and do not start

HELP? what do I try next?

Olympian (newbie)
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Old Jan 16, 2012, 10:31 PM
Registered User
United States, AL, Huntsville
Joined Dec 2007
102 Posts
ESCs wont start...

More info..

ESCs are HobbyKing HK HW30A...
I substituted one with a Turnigy Plush 18A and it starts!

I don't understand why reprogramming the HK HW30A ESCs make them fail to accept the 400 Hz signal rate? They did start as previously programmed.

Unfortunately, I don't enough of the Plush 18A ESCs to populate the Quad.

I will try reprogramming the HK ESCs one more time.

Olympian (newbie)
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Old Jan 16, 2012, 10:39 PM
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United States, AL, Huntsville
Joined Dec 2007
102 Posts
Thanks Ssatoru!

Setting MinCommand to 900 gets them to start!

Olympian
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Old Jan 16, 2012, 11:10 PM
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ssatoru's Avatar
Chiba, Japan
Joined Jan 2002
1,044 Posts
Good to hear it worked! When I got into the same situation, I suspected the same the ESC cannot accept 400Hz input and ordered different ESC sets. Now I have parts to build more quad...

Satoru

Quote:
Originally Posted by Olympian View Post
Thanks Ssatoru!

Setting MinCommand to 900 gets them to start!

Olympian
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