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volsung
Site Admin
Joined: 26 Nov 2006
Posts: 24
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Crass
Joined: 01 Dec 2006
Posts: 2
Location: Oregon
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 Posted: Fri Dec 01, 2006 1:12 am Post subject: |
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Maybe this is a pointless question, but its one I've thought about for some time. How many points of precision are in the accelerometers in the wii-mote? Ok so I am a flight sim fanatic and I've gone through my fair share of joysticks. When you calibrate a joystick in the regular M$ (ok.. ok.. im not a big linux person) through the control panel, you can show the "raw data" and as you move the stick from side to side and up and down it will show the cooridinates. In older joysticks the range of movement, or points of precision, were usually 128° positive and 128° negative, and newer sticks are usually 1028°+/-. I was wondering if there were similar values associated with the wii-mote because I am interested in using the wii mote as an actuall joystick for a flight simulator type app.
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fashnek
Joined: 28 Nov 2006
Posts: 3
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| Posted: Fri Dec 01, 2006 6:19 pm Post subject: |
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| Crass wrote: | | I was wondering if there were similar values associated with the wii-mote because I am interested in using the wii mote as an actuall joystick for a flight simulator type app. |
Well, keep in mind that a joystick records static values (i.e. how far from center). The accelerometers measure forces, and because acceleration is a double-derivative of position, it takes a bit of work to devise position from the values that come from the Wiimote sensors. I would expect it to be many times more work still to derive (and differentiate) both rotation and movement.
The accelerometers do have a finite number of readings, which I believe is -128 to 127 (this is a guess based on the payload size -- someone who's written software can better tell me) .. I believe the typical value of gravity according to the sensors is between 26 and 29, so that means that with a maximum value of around 128, the sensors read up to about 4.5G.
Can someone with more hands-on experience (no Bluetooth yet for me) confirm this?
Because rotation is calculated based on changes in perceived acceleration, I believe the degree of specificity depends on the smallest and largest possible acceleration values. For example, let's say the sensors measured (0, 0, -G) and then measured something like (0, 0, -G+1). If the remote is at rest, that slight difference corresponds to some change in angle.
This stuff is even more complex than I thought. I'm not sure exactly what the smallest possible angular change is, but I'm sure it depends on the calculations made to determine orientation.
But there are whole other monsters in calculation when just using accelerometers on three axes. I mean, the same reading changes could represent movement or rotation, so it can be tricky.
And now that I think about it, I think it may actually have variably-spaced positions. It may be that as the remote gets closer to fully on its sides, top, bottom, front, or back (as it moves away from intermediate tilt toward full tilt), it gets harder to be accurate (or the measurable angles get farther apart). |
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RandomInsano
Joined: 27 Nov 2006
Posts: 10
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| Posted: Fri Dec 01, 2006 8:56 pm Post subject: |
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| I don't know if I'd bank on it's accuracy. While I played Wii Sport's baseball game over at a friend's house (don't own a Wii myself), the bat was somewhat jumpy when I held up the WiiMote. For flight simulator use, someone would need to smooth out those jumps. |
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Sketchy Fletchy
Joined: 05 Dec 2006
Posts: 1
Location: Wollongong, Australia
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| Posted: Tue Dec 05, 2006 10:34 am Post subject: |
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No worries there, sharp jumps can be filtered pretty well.
I'm a member of the SAE racing team at my university - we build small open wheeler race vehicles. So far, we've used a Gameboy advance (and an SP, for extra bright screen action!) as the driver display on the steering wheel. It's great - built in variable data bus, good processing capacity, easily programmed using a flash cart, and a large, bright display. Oh, and pretty cheap too.
The mind boggles when I think about what the team could do with some of this equipment. Currently, we rely on $450 accelerometers for all our data readings which are great, but very expensive, and once they're on the car, they don't come off. A wiimote and Bluetoth relay in the car would be great for some in car analysis of driver movements, varibal accelerration testing at various positions on the car (like shock and accelerations on the wheel uprights for suspension analysis) and for determining car properties like the moment of inertia.
I look forward to screwing around with this thing on my laptop!  |
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alecool
Joined: 11 Dec 2006
Posts: 18
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| Posted: Mon Dec 11, 2006 4:35 pm Post subject: |
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after some tests, i found out that the precision in angle measures is between 2 and 3 degrees. May be it could be imroved with a better program, I don't know.
I made this script, which show the pitch -the alpha angle) and the roll (the theta angle):
| Code: | var.x0= -2
var.y0= 1
var.z0=-2
var.zh= 23
var.xh=-25
var.alpha= arccos((wiimote.RawForceZ-var.z0)/var.zh)-90
var.theta= arccos((wiimote.RawForceX-var.x0)/var.xh)-90
debug = wiimote.RawForceX+"|"+wiimote.RawForceY+"|"+wiimote.RawForceZ+ "alpha:" + var.alpha + " theta"+var.theta |
I also notice that there is a jump from 73 to 90 degrees, as if there was no reading in this interval...
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French wiimote-on-PC user, so excuse my poor language  |
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homielowe
Joined: 30 Nov 2006
Posts: 2
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| Posted: Wed Dec 13, 2006 12:12 am Post subject: |
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imperial 
9.8 m/s not 26-29 ft p/s |
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