I had nothing better to do...

So i build my Paketlogger (thats a pun for German speaking people ;0)

I attached a Nunchuck as accelometer to an arduino and that one with an SD Card so i could log all the information - and all this was put into a box which was mounted on a small RC car.

Here are a few pics:

And now the results for the x axis acceleration:

Its nothing big, but at least its something that had worked G

Cool!

I think I need to get a hold of some wiimotes to play with. Looks interesting!

Maybe now, you should try repeating some basic sequences like forward 1 second, pause 1 second, backward 1 second, pause 1 second, and trying to compute the output data to be able to get the distance and speed from the acceleration, stuff like that. Maybe this way, you can store some basic acceleration / movement translation rules that would allow you (and me ^^) to do basic "motion capture" using the wiimote

i thought so as well, but after the drydock tests with the nunchuck in my hand or lying on my desktop i had to see that this whole matter is getting somewhat spoiled. I dont know about 'real' nunchucks, as this one is a 12$ imitation from china. It is good for playing, but the overall accel sensor output is extremely noisy. When lying flat on the desk i have quite some noisy ouput. Then again a ssecond problem was that lousy box, the chuck was able to move in it any way it wanted, so i could never get the real G forces as i had some fatigue movement on the chuck itself..

It was just that - a small experiment out of massive boredom ;0)

Has anyone seen/done any comparisons of the cheap Chinese nunchuks to the originals?

I just checked dealextreme.com, and they have the imitations for US$10.40 shipped (just under $10 apiece if you buy 3). Since 3-axis accelerometers on a PCB are $20 and up from places like Sparkfun and NKC (and even from Chinese vendors on ebay), it's tempting to buy some of the game controllers and cannibalize them. But it wouldn't be such a good idea if they're using QC fallout chips to build the cheapies.

Ran

trying to compute the output data to be able to get the distance and speed from the acceleration... do motion capture

You're never going to get good enough samples to re-integrate velocity and absolute position from this kind of accelerometer. These things are extremely noisy and granular, and our sample time is limited by the i2c bus (Wii Nunchuck). Slightly better, get an ADXL330 without a Nunchuck so you're as fast as analogRead() but it still won't be very good.

Ran: That is exactly that Nunchuck. From my point of view it is comparable 1:1 with the original nunchuck when playing… but i guess it has a far different noise level… i cant believe the original ones are as noisy… but i havent tried a real one though.

i cant believe the original ones are as noisy

Oh, I can: try reading the raw values from an analog joystick. It's surprising that anyone can use a flight simulator program without crashing on take-off :)

Have you tried adding some software filtering? I've had good results in some resource-constrained micros with a simple weighted moving average, done by adding the latest value to the previous value and dividing by 2. This gives you a sum of (1/2 reading[n]) + (1/4 reading[n-1]) + (1//8 reading[n-2]) ...

This does well on signals where there's a lot of small-amplitude "jitter", but not much drastic change in the "true" signal between samples.

Have you opened up the nunchuk to see what's inside? I suspect it's mostly empty, with only a small PCB that you could mount to your car a lot more solidly than the whole nunchuk.

Ran

Have you opened up the nunchuk to see what's inside? I suspect it's mostly empty, with only a small PCB

Yup. Check out this thread where someone opened their Nunchuck and found so much room in there they put their Atmel and XBee antenna INSIDE it.

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1215475673

i havent opened it because i lack that screwdriver, but i am more than confident that it is almost empty. just hold it in your hands and think about the weight and balance points...