Discussion New 6-DOF IMU

[airmcn_3]

Originally Posted by voiceafx

For what it's worth, the IMU is finally ready: http://www.chrobotics.com. The cost works out to be $125.

Looks good! Nice and compact.

[Krogoth]

Does the 9d in your CHR-9d stand for 9-DOF? I've seen many people make this mistake - adding a magnetometer only performs heading correction, it doesn't give you an additional 3 degrees of freedom so it's still 6-DOF (unless you're living in a 4th spatial dimension I don't know about :P )

To do centripetal correction you need to know something that gyros and accelerometers won't tell you, namely either your forward velocity or turn radius. The latter is extremely difficult to work out, but centripetal force can be found as follows with velocity:

Fc = m.v.w

where m is your mass, v is a velocity vector and w an angular velocity vector. Angular velocity comes from your gyros, and linear velocity comes from a combination of integrated accelerometers and GPS or airspeed velocity.

Originally Posted by sergey123

6dof + airspeed + altitude + gps connection, kalman inside with serial out for 100$
will fly from warehouse fast and in formation :-)

If I wasn't so busy, believe me I would build one. Especially with some of the new amazingly cheap MEMS devices out there, like the single-chip 3-axis ITG-3200 Invensense has just released:

http://www.invensense.com/products/itg_3200.html

Apparently $3 in volume, I'm guessing around $10 from Sparkfun once it comes out? Couple this with a mini 3-axis accelerometer and magnetometer, possibly a Venus GPS (cheapest from Sparkfun and seems to work well), SCP-1000 for altitude and some sort of small differential pressure sensor for airspeed, and you can probably get away with a full 6-DOF INS for around $100-150. Provided, of course, someone can write the firmware for you...

Will.

[sergey123]

Yes, Krogoth you are wright !!!
Multidimensional worlds exist in theoretical physics but in real live we can enjoy only 6dof + time. Misunderstanding coming from multiple state Kalman filters . It could be even 12, 17 or 21 state Kalman ....
The first step I would say will be building "all in one" sensors board itself and provide all data out via serial. Simple Kalman can be inside but good one will require a lots of CPU, so it is better to have it in different board for flexibility...

[zlite]

Originally Posted by voiceafx

For what it's worth, the IMU is finally ready: http://www.chrobotics.com. The cost works out to be $125.

I think people are getting a little confused over terms. Some of the devices discussed in this threads are just IMUs (just sensors plus some hardware filtering). Others are IMU+AHRS (sensors plus processor running Kalman or DCM software filters to output corrected attitude information). Pure IMUs are available from many sources today, and are not very hard to make. An IMU+AHRS is much harder, and tend to be more expensive.

The VectorNAV device is an IMU+AHRS, as is our own ArduIMU. The chrobotics and sparkfun IMUs are just IMUs.

[kbosak]

Originally Posted by sergey123

Yes, Krogoth you are wright !!!
Multidimensional worlds exist in theoretical physics but in real live we can enjoy only 6dof + time. Misunderstanding coming from multiple state Kalman filters . It could be even 12, 17 or 21 state Kalman ....
The first step I would say will be building "all in one" sensors board itself and provide all data out via serial. Simple Kalman can be inside but good one will require a lots of CPU, so it is better to have it in different board for flexibility...

9DOF in elastic body mechanics would be 3D position, 3D rotations and 3 independent axis of compression.

[Krogoth]

So the next addition to 6-DOF IMUs will be a 3-axis load cell, to find out which axis the plane is going to snap in half in first? Could be handy for those pushing the limits in the DIYDrones T3 contest :P