Bioloid IMU Bus Sensor - Working

[JonHylands]

Hi everyone,

Well, I'm very happy to report that my 6-axis IMU bus sensor is now working, and (pending some more rigorous testing) complete, at least from a software perspective.

I've put up a preliminary version of the "user manual" here:

http://www.bioloid.info/tiki/tiki-index.php?page=6-Axis+Bus+IMU+Documentation

Comments are welcome.

It is running on an ATmega168 board, which you can see here:

http://www.bioloid.info/tiki/tiki-index.php?page=6-Axis+Bus+IMU

I will be adding a page that describes how the circuit is put together.

The source code has been put up in my brother's SVN repository:

http://websvn.hylands.org/listing.php?repname=Projects&path=%2Favr%2Fbioloid-imu%2F&rev=0&sc=0

I will be working on the final PCB design this week, and will be having a batch of custom boards printed soon.

- Jon

[limor]

Great work!
Love the way you nonchalantly make those board images in 3D with such ease.

[pepperm]

Looks fab Jon. How do you make the 3D images please?

Mark

[JonHylands]

I use Rhino3D for all my CAD modeling stuff.

I can build a model like the 6-axis IMU board in less than an hour. The model of MicroRaptor, on the other hand, has probably 100 hours of work in it.

- Jon

[Juha]

Jon, the switching regulators you've found seem very nice. I might have to order few of those I do have one for 5V, but it's so much larger then the ones you use.

[JonHylands]

Juha,

They are from Dimension Engineering. I will not be using them on the final IMU board (the regulators are about the same size as the entire board).

http://www.dimensionengineering.com/DE-SW0XX.htm

I have those devices to provide 5.0 and 3.3 volts for various components on the electronics package (the ATmega128 runs off 5 volts, and the wifi module runs off 3.3 volts).

I will be using LDO regulators on the final IMU board (LM3480 series), since none of the sensors or the microcontroller draw much current, it won't end up wasting a lot of power.

- Jon

[JonHylands]

Well, the initial PCB order is going out tomorrow (Friday) morning. I should have the first few boards by next Wednesday, and I plan on putting the first IMU board together by the end of next week.



Keep in mind the actual size of this board is 29mm x 19mm...

I'm also getting the foot pressure sensor boards printed at the same time. The software for that board is almost identical to the IMU - the only real difference is I will be using 4 A/D ports instead of 6 or 8.

I will keep everyone updated on my progress...

- Jon

[JonHylands]

Well, I have a board, and last night I populated one of the IMU boards, and "baked" it in my friend's oven.



http://robosavvy.com/site/Builders/JonHylands/IMU-PCB-01.jpg

Turns out I made a mistake in the programming header (MISO and MISO are switched), so I had to make a simple programming adapter cable, but with that made I was able to program the onboard ATmega168.

However, things aren't working correctly, so I need to spend some time analyzing the board further, to see if I can figure it out. I suspect I put at least one of the LEDs on backwards.

- Jon

[JonHylands]

So, it turns out there were two problems with the board, and one other software issue:

- the afore-mentioned MISO/MOSI swap
- easy enough to fix with an adapter cable for now - when I get the real board run done (probably next week), I have this fixed already in the PCB file

- the chip ground pad wasn't connected to the rest of the ground system
- I've also fixed this in the PCB file, and for now I've soldered a jumper so my board will work

The final problem was a software/fuse issue - turns out the fuse setting I was using was for the internal 8 MHz oscillator, and I programmed the code for 16 MHz. After I fixed the fuse, everything runs fine with the 16 MHz external resonator, and I can communicate with it as a bus device.

Once I get the standoffs machined for this first version, I will solder on the headers for the two sensor boards, and take some pictures/video/etc, as well as update the info on the wiki. The first versions of this IMU board should be available in a few weeks, if anyone wants one. I haven't worked out what the price will be, but it will be in the $40-50 USD range (not including the two sensor boards, obviously).

- Jon

[JonHylands]

So, here it is:







I'm pretty happy with how it all turned out...

- Jon

[DerekZahn]

That came out great Jon, nice work!

I see that the guy you referred me to with the kalman filter code has released a new version. I glanced at it and it looks a bit cleaner than his old code, which wouldn't compile and had some oddnesses like comments saying that things don't work right and commented-out code that looked reasonable.

I don't know if you're planning on doing a kalman filter as a next step but good luck if you do! I have not yet been motivated to do so as what I have is working adequately for my needs. It helps for me that I'm not normally interested in tilts of more than say 30 degrees.

Now get ready for the Bioloid owners asking: "great, now what do I do with it once I build it?"

[SK]

Nice work, surprisingly compact.
What are your plans with the IMU, will you use it mainly for robot control, or do you plan to try "some inertial navigation" with it also?
Would be interesting to know if such a small IMU gives useable results with an adapted strapdown algorithm. I wouldn´t bet on it, but it would be kinda cool, especially when looking at stuff like self-localization.

[JonHylands]

Thanks...

I'm not planning on using this sensor for localization, mainly because the two-axis gyro isn't temperature compensated, and you really need that to help offset drift.

- Jon