Discussion New 6-DOF IMU

[voiceafx]

I am designing a small 6-DOF IMU with digital outputs that uses the newest MEMs devices on the market (some of which haven't been released yet) to keep the footprint small and the cost low. I'm hoping to make a bunch of them and sell them at low margins so that DIY'ers like us can afford to tinker without breaking the bank. If they sell well enough, I'll be able to keep the cost on the order of $100 for the full 6-DOF with digital outputs. :-)

If you had the choice, what do you all think the "best" pinout would be?

My current design has two .1" headers mounted on opposite ends of the board, so that prototyping and mounting is easy.

Alternatively, I could add mounting holes, and then put little shrouded headers that you'd plug into; then, you wouldn't have to mount the IMU on a PCB - you could put it anywhere on the airframe.

Another option would be to use low-profile board-to-board connectors, but they wouldn't be easy to use (have really fine pitch).

What do you think would be most useful to you?

[airmcn_3]

Originally Posted by voiceafx

I am designing a small 6-DOF IMU with digital outputs that uses the newest MEMs devices on the market (some of which haven't been released yet) to keep the footprint small and the cost low. I'm hoping to make a bunch of them and sell them at low margins so that DIY'ers like us can afford to tinker without breaking the bank. If they sell well enough, I'll be able to keep the cost on the order of $100 for the full 6-DOF with digital outputs. :-)

If you had the choice, what do you all think the "best" pinout would be?

My current design has two .1" headers mounted on opposite ends of the board, so that prototyping and mounting is easy.

Alternatively, I could add mounting holes, and then put little shrouded headers that you'd plug into; then, you wouldn't have to mount the IMU on a PCB - you could put it anywhere on the airframe.

Another option would be to use low-profile board-to-board connectors, but they wouldn't be easy to use (have really fine pitch).

What do you think would be most useful to you?

Sweet!!

[fly_boy99]

I agree the pin out at the opposite ends of the boards allows for the greatest flexibility in mounting. As for the mounting holes, that's another good idea instead of trying to double sided tape it to some foam.

How would this compare to the IMU unit from sparkfun already?

B

[voiceafx]

Originally Posted by fly_boy99

How would this compare to the IMU unit from sparkfun already?
B

It is smaller, all sensors mount in-the-plane, and it uses an MCU with a 16-bit A/D converter (as opposed to the 12-bit offered by Sparkfun). It is also modular and scalable - a number of "expansion" boards add extra functionality, like GPS, servo outputs, magnetometer data, etc.

[chopsuey]

So is the MCU just reading the sensors and spitting the data out in digital form? Is the MCU going to massage the data at all? I am just curious but I would definitely be interested in one.

[voiceafx]

Originally Posted by chopsuey

So is the MCU just reading the sensors and spitting the data out in digital form? Is the MCU going to massage the data at all? I am just curious but I would definitely be interested in one.

The MCU will include a digital filter with adjustable bandwidth. I am also toying with the idea of including a simple Kalman Filter to provide pitch and roll angle estimates; the user could adjust the covariances to get adjust the performance as needed.

The MCU operates at up to 50 MIPS, so it is easily able to handle the extra processing.

[rbeall]

I don't know if this is on the table but..... there are already models out there that are just what you are describing for about the same price. However what they lack is maybe a little bit of customization you are offering. I don't know if you will really make a buyer out of me in that reguard....most UAV's are all in the range of 2-5G flight which isn't that hard to tune a general filter for that regime. However (which I am not sure you are doing) what current models are lacking is the coupling of external attitude sensors (ie gps,airspeed what have you). A basic 6dof IMU is useless in an airplane for any customer.

I almost bought a $100 freaking sweet imu with embedded kalman what have you but guess what ..... its miss leading.... no centripetal compensation...

Offer that and you will make money

[sergey123]

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

[voiceafx]

Originally Posted by rbeall

I don't know if this is on the table but..... there are already models out there that are just what you are describing for about the same price. However what they lack is maybe a little bit of customization you are offering. I don't know if you will really make a buyer out of me in that reguard....most UAV's are all in the range of 2-5G flight which isn't that hard to tune a general filter for that regime. However (which I am not sure you are doing) what current models are lacking is the coupling of external attitude sensors (ie gps,airspeed what have you). A basic 6dof IMU is useless in an airplane for any customer.

I almost bought a $100 freaking sweet imu with embedded kalman what have you but guess what ..... its miss leading.... no centripetal compensation...

Offer that and you will make money

What is the name of the IMU you almost bought?

[voiceafx]

Originally Posted by sergey123

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

Hah! Maybe someday... when the market for hobbiest autopilots suddenly increases by an order of magnitude. :-) The problem is that the market is small enough that pricing these things really low doesn't increase sales by enough to make it worthwhile.

[chopsuey]

Originally Posted by rbeall

I don't know if this is on the table but..... there are already models out there that are just what you are describing for about the same price. However what they lack is maybe a little bit of customization you are offering. I don't know if you will really make a buyer out of me in that reguard....most UAV's are all in the range of 2-5G flight which isn't that hard to tune a general filter for that regime. However (which I am not sure you are doing) what current models are lacking is the coupling of external attitude sensors (ie gps,airspeed what have you). A basic 6dof IMU is useless in an airplane for any customer.

I almost bought a $100 freaking sweet imu with embedded kalman what have you but guess what ..... its miss leading.... no centripetal compensation...

Offer that and you will make money

I am looking to do the coupling myself so I am just looking for a 6DOF IMU that is inexpensive and easy to interface with. Is there something like this already out there? Have I missed something on Sparkfun's site?

[voiceafx]

Originally Posted by chopsuey

I am looking to do the coupling myself so I am just looking for a 6DOF IMU that is inexpensive and easy to interface with. Is there something like this already out there? Have I missed something on Sparkfun's site?

Hmmm... I've tried to stay up-to-date on the devices that are available right now. I don't know what rbeall was talking about, but if he knows something we don't, I wish he would enlighten us.

[rbeall]

http://www.vectornav.com/?gclid=CLzk...FQa-sgodLVHUdA

[airmcn_3]

Oh this has got to be good

https://www.vectornav.com/products/74-vn-100

"Temperature Compensation

•VN-100 is currently calibrated at room temperature only.
•Units calibrated over full operating range are expected to be available in November 2009."

Room temp only...... That should be good for an airplane...

[voiceafx]

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