I got a Razer Hydra this weekend and I am pondering its use in a VR backtop style rig. I have a couple questions it seems this board could help with:

1. How does the Hydra actually work? Is the orb detecting the "heads" or vice versa? Basically, is it possible to disable/remove the orb on the Hydra plugged into the backtop, and have the heads react to the orb from a second, stationary Hydra?
2. If I can't separate the heads from the orb, I imagine I will need a separate head tracker. Will the Hydra interfere with that?

Hopefully these questions make some kind of sense! Thanks.

The 'orb' broadcasts the magnetic signal. The handpieces pick up that signal. Not sure what you are trying achieve with '1' but I dont think it will work.

You could mount the orb in the backpack, then you'd have the ability to track to objects like head and hand. You'd however then need some other sensing system to detect your location/orientation.

If you only want to do stand up VR but not walking around, then you can use the Hydra as is, its range is good enough to support someone standing and turning 360 degrees (just not moving around).

I imagine it would be possible to reverse-engineering the connection between the wand and the base, that way you can make then totally wireless. Now, I am not a hardware guy, so I wouldn't know where to start with this. But its probably possible. Even if you don't make it wireless, maybe you could at least extend the wire to make it more mobile (this seems pretty straight-forward).

Mounting the base on your back sounds nice, but I don't think it will work. I just did a quick test with moving the base around in one hand (with the wand in the other). At first it looked OK, but then it signal dropped out for 5-10 seconds at a time. This may be a fail-safe, or some sort of re-calibration that is automatically done in the software. Since I am using the SDK directly, I'd have to assume this is something going on in the background, likely in the driver, though maybe in the hardware itself.

Maybe the best idea I've heard is mounting the base on the ceiling and maybe extending the cables. Still will not be full-freedom, but may be good enough for light sessions. Also, you can try to locate one of the developer prototypes that were in fact wireless, but I doubt anyone would give one of those up.

You dont even have to ceiling mount it, with it on a desk in front of you, range is fine for stand up.

I know the original dev kit had wireless trackers, and I can't imagine it would be that difficult to extend the base unit (probably could do it using a wireless USB thing, but latency would probably suffer). That said, I dont see any way to increase the actual sensors range.

Interesting what you said about it moving CR, not sure why that would be, might give it some tests with my setup. I can't see any real reason for it to need to do a recalibration or have a fail safe etc...

Thanks for the responses.

To clarify, I am hoping for stand up VR with turning 360 degrees, like cybereality's backtop VR movie. To accomplish this, I believe I need the base to be stationary, while I spin around in front of it (within 6 feet). Wires make this difficult, so that's how I arrived at wondering whether the wands in my hands (wires running to laptop in the backpack) could instead pick up their position relative to a second Hydra's stationary base, similar to how a Wii remote can use anything as a "sensor bar".

Hopefully that's a little clearer!

You can do this with a stationary based mounted at around hip level in front of you. However, the twisting wires IS a problem. I found I could only turn around a couple of times before I had to turn in the other direction to 'unwind'. There are a couple of ways this could be mitigated

- by running the cables to a hook above the user, you could attain quite a few more revolutions before needing to unwind

- you could probably develop some sort of sliding contact system similar to telephone cable detanglers that would let you twist to your hearts content if you had cables mounted above you

Ideally however, wireless will be the way, and I hope that the next gen of the Hydra will have wireless handsets, which would solve the problem best.

I dont think you can use a second hub as an additional 'sensor bar', simply due to both how the technology works, and the fact that you'd need to 'hand off' between bases, passing the correct current handset coordinates etc.

Cyber, is it possible the connections of the wires were shaking a bit? On my Hydra they are quite loose. I can't believe they put an accelerometer or gyro in the base unit, seems like a waste of money; and without that, there's no way for them to detect base unit movement vs controller movement is there?

@Chriky: I don't think the cable was loose. It seems pretty tight on the connection. But it could have been something like that. Even so, using on a backtop setup may have similar problems.

It is possible that what is happening here is the algorithms they use rely on the Earth's magnetic field remaining static relative to the modulated magnetic field generated by the base station. If the magnetometers in the wand detect a significant change in the difference between the static and generated magnetic fields (in this case caused by rotating the base station), it presumably goes into a recalibration mode.

Then we would just need to solve the problem of the HMD being wired!

Cyber, I just tested with my Hydra and I don't get the dropped connection when I wave the base around. I've had a ridiculous/amazing idea for a large area VR system.

Basically its a pair of Razer Hydra trousers. You put the base on the small of your back, then one controller on each foot, with the buttons arranged somehow such that they press when you put your foot down. By checking for the button presses you should be able to tell which foot is the standing foot and if you keep that stationary you can tell where the other foot is moving to. By switching which foot you keep stationary and which foot you move relative you should be able to walk around an area in absolute terms.

Hmm.. maybe it was a loose cable or something stupid.

@Chriky: That's an interesting idea as long as the Hydra can operate mobile like that. Sort of a local reference skeletal tracker and used as a pedometer. It doesn't seem like you would need foot buttons though. The motion of the two feet relative to each other and the Hydra should be distinct enough to determine heuristically which was was moving and which was standing.

Sounds promising.

The buttons might not be needed, but would give an absolute certain signal when the foot was on the floor. MIght help if the ground is not flat.

I just tried moving the base around briefly and it seemed okay. So if the Hydra is attached to the player, we can get 6DOF for each wand relative to the player, but we can get absolute orientation from the Rift's Hillcrest tracker.

Oh man, I can picture it now: HMD on my face, Hydra wand strapped to my head, glowing orb coming out of my chest Iron Man style, swinging around wildly pointing the other wand at imaginary objects. My wife is going to love this!

Do we know for a fact the Rift is USB powered only?

I made a really quick and hacky test to see if this would work, and I am pretty sure it would. I have not done any of the code for actually updating the global positions, but this video shows that all the info you need is there...



The first half shows the program output and the second half is me actually walking around a bit, with the screen in shot. I didn't bother getting the orientations out of the Hydra, just the positions. I taped a little piece of wood to the analogue stick so that it would move when the foot was down. Red means the foot is planted, green means it is up. Obviously to be totally mobile you would have to mount the laptop on your back as well.

The video is taking ages to process on Youtube so I've attached it as a file as well

Very nice. An accurate pedometer would be very useful in a free-walk scenario.

That looks promising actually. Nice job.

That's pretty cool actually. I think for accurate tracking of free walk, attaching a pressure sensor to each foot to determine when it is actually down would be required for accurate tracking.

That is very cool. Combined with a wireless usb hub and we are going places http://www.iogear.com/product/GUWH104KIT/