Hi all,I'm just wondering how can we perform a position hold (within 10-20 cm, just like microdrone MD4-200 did ) with a GPS and IMU because I know that the accuracy of normal GPS is aroung 2m and can not achieve up to few cm level if we dont have DGPS. So I'm thinking of a Kalman fusion between GPS and IMU to give a more accuracy in position ? I'm not so clear about that, it has made me confused for a long timeThat's why I post this entry to get your inputAny idea are appriciated and welcome.I forget to post a link to you guy for easy imagination of GPS position hold.http://microdrones.com/en_mc_videos.phpthen looking for a video name "flight-performance md4-200, part 3", this is what it called "GPS positon hold"
hi Caleb, it's alright for me to understand linear algebra, I'm waiting for your tutorial of KF and fixed gain observer :)
@Tom Yochum : I did develovep Kalman filter before for my quadrocopter project to track bias of gyro and get pretty accuracy tilt (pitch and roll) infomation
@all : I have a silly question regarding accuracy of GPS, please help me make it clear :
if I hold a GPS and then read positon value from GPS , then i walk 30cm then record position value again . .the 2 value is the same or different? I just want to know that with a small difference in position of GPS , will GPS output the same data?
Tom Kent,
Your idea about creating our own DGPS base station sounds great.I have Xbee for 2 ways data down link already . Its easy to send correction data back to the air .You should start an entry for that stuff.
You could use the IMU as a turn coordinator to do what we pilots call a procedural turn when assigned a holding pattern. The IMU would be very useful in providing the aircraft with a coordinated turn. Time, heading and standard rate turns will ensure that your autopilot holds the coordinate. Wow, this sounds like a heading indicator :)
Just out of curosity...you mention that the problem could be solved by using DGPS, why aren't you doing that? I believe that the new uBlox supports outputting the necessary data to roll your own DGPS, you just need one for a known base station and one of the onboard receiver, then a datalink to send the corrections up to the aircraft. Am I missing something?
hi Jordi, thanks for your advise , I found some guys use pressure sensor for altitude hold and combine with accelerometer to use in GPS position hold with great result (while altitude hold mode active)
hi Caleb, regarding fixed-gain obsever you mentioned it sounds nice to me. Have you ever experienced that method in something ?can you share it ?
Well some GPS give the vector velocity (X,Y,Z) ready to use. You can integrate the Accelerometer to obtain the velocity in three axis too (X,Y,Z) compensating your heading and your pitch and roll, you will need to use some matrices over there. Then feed the vector velocity from the GPS and the one you calculated from the accels to the Kalman filter (I'm not so good with Kalman right now, but someday), the output should be the estimated and ultra filtered vector velocity of your system. Now is about control, try to keep always the velocity's zero to maintain the same spot, you can use this for navigation too and fly around. You can add a pressure sensor to have better altitude control too.
And i don't even know if this is the correct way. I'm just telling you what i believe based on my experience in direction cosine matrix, kalman filters, etc. and the way other systems work.
OK, I thought you were trying to use the IMU to increase the accuracy of absolute position. I'm not using an IMU yet so I'm curious how this works too.
For now I'm doing a simple rate of turn calculation with the IR sensors to increase the accuracy of the course bearing between GPS reads. It's a simple internal simulation, but it helps keep the turn angle under more control and it doesn't give me math headaches.
hi Jordi, I did think of Kalman filter but still not so clear how to implement a kalman fusion for gps and IMU to my microcontroller.BTW i know that kind of optical flow using in Helicommand module.
Comments
@Tom Yochum : I did develovep Kalman filter before for my quadrocopter project to track bias of gyro and get pretty accuracy tilt (pitch and roll) infomation
@all : I have a silly question regarding accuracy of GPS, please help me make it clear :
if I hold a GPS and then read positon value from GPS , then i walk 30cm then record position value again . .the 2 value is the same or different? I just want to know that with a small difference in position of GPS , will GPS output the same data?
Your idea about creating our own DGPS base station sounds great.I have Xbee for 2 ways data down link already . Its easy to send correction data back to the air .You should start an entry for that stuff.
hi Caleb, regarding fixed-gain obsever you mentioned it sounds nice to me. Have you ever experienced that method in something ?can you share it ?
And i don't even know if this is the correct way. I'm just telling you what i believe based on my experience in direction cosine matrix, kalman filters, etc. and the way other systems work.
For now I'm doing a simple rate of turn calculation with the IR sensors to increase the accuracy of the course bearing between GPS reads. It's a simple internal simulation, but it helps keep the turn angle under more control and it doesn't give me math headaches.
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