FreeTrack Forum

Hi, im new to this whole free-track thing. I got a cheap webcam looks exactly like Staylos VIMICRO 301 cam. But its called a "ICatch IV". It says on the box it will do 640x480 at 30FPS. I have built a 4 point cap as per the documentation with the recommended OSRAM SFH485P IR LEDS. Theres no IR filter on the camera, so i just added a piece of negative in behind the lens.  I start up FreeTrack and set it to 4 point cap mode and it all seems to work ok.

I have many questions:

1. Whats the advantages of the 4 point, versus the 3 point cap, versus the 3 point clip? I normally play with a headset - and i see the 3 point clip is made for headset wearers. Is the 4 point cap the best setup? If so, what makes it better than the others??

2. The 3 point clip - Is that mounted vertically on one side of the head? As opposed to sitting up on top of the head horizontally?? Anyone got some images of how it sits on a person?

3. With my 4 point cap, i find it next to impossible to turn my virtual head all the way back to look backwards. I tried a 3 point cap, and thats much better and more sensitive. Why is this?

4. With a 4 and 3 point cap, the LED assembly is sitting so far forward (about 15cm or so) of the natural head rotation axis (eg neck). When i rotate my head left and right, i get a certain amount of yawing as part of the movement. If the 4 points where right over top of the spine (eg set back further), then would this eliminate the sympathetic yawing i see when i rotate my head. Eg when i rotate my head, i only want the virtual head to rotate, not yaw as well.

5. The LEDs are giving off LOTS of head, and almost burn when you touch them. Im running a 3volt 2xAA set up all LEDs in parallel with no resistors. What is the forward voltage of the OSRAM SFH485P?? The place i bought them from claim they are 3V. So im running on a 3V battery pack, the calculator says no resisters are needed. Have i got all this right? The heat seems like a sign something is not right.

6. Webcam. FreeTrack says its only getting 15 FPS from the webcam. I followed Stylo's recommended set up. Exposure 1 (low as it can go), gamma 0, 'outdoors' mode USB=6, auto exposure off, auto white correct is off. colour enable is unchecked. Background comp is off too. The cam claims 30FPS, but i cant seem to get it to do that. No, im not running instant messenger in the background either.


SOrry for the huge list of Questions, but before i get too carried away, i would like answers to some of them

1. The 4 point  cap does the same trick as the 3 point cap version. The only difference is that with 3 point cap version, you have less points to intercect with each others. 3 point clip is designed to be attached onto your headphones. Or like I've been planning to make a 3 point clip to be attached onto my eyeglasses

2. Vertically on one side of the head. Google TrackClip and you'll get the idea

3. Have you given the correct measurements of your 4 point unit in FreeTrack?

4. I have the same problem actually so I can't really help you with this. But this really doesn't bother me cause it's natural for me

5. I'm not sure about the forward voltage of those LEDs but I'm pretty sure that they need resistors. If they're really giving off that much heat they won't be lasting that long

6. Can't help you with this one either, sorry

Hello spatula , mdds.


1) First of all :
as already stated in several places in this forum :


- leds are current driven , not voltage driven.
- So you CAN'T directly attach your led setup to a battery pack or power supply, even if voltages seems to correspond.
- Resistors are MANDATORY.

You may fry your leds if you don't respect this !!!!

2)

- The max operating current of the SFH485P is 100mA.
- This max value is lowered to 70ma if you use those leds on wires, rather than printed circuit board.
- Remember this is a max value : you can use them at less current and still have a fully functionnal setup ! We want to make markers, not flashlights.

- Using these "standard" current, the sfh485 as a forward voltage of about 1.5V

- Some websites claim (ie : FARNELL) that the SFH485 has a 3V forward voltage : this is FALSE (3V is the forward voltage when pulse driven at 1A, which is definitely not the case in freetrack setups).

- for info, my setup runs with sfh485p powered at less than 20ma, and works flawlessly.......

So my suggestion would be to calculate your resistors with :
- led forward voltage : 1.5V
- led current : start with 50ma, its a good value.
- your power supply or battery pack voltage

and let the led wizard calculate the appropriate resistors.




hope this helps.

cya.

Cool - yes, i got my LEDs from Farnell and they stated a 3v forward voltage, and when i plug those figures into the calculator it says the resistance will be 0 - so i took this as meaning no resistors...

Will recalc with the figures you provided. Thanks very much.

Also may try the 3 point clip and see how that goes.

Can anyone else help with my other Qs??