Razer Hydra and IMU magnetometer interference?

[MSat]

Ok, so I just ordered the Hydra, and then it got me wondering - could the Hydra's base station possibly cause interference for a magnetometer on an IMU, such as the one in the Rift? Anyone ever try operating their IMU in conjunction with their Hydra?

[cybereality]

I've used the Hydra with the Vuzix 6TC tracker with no problem. I could test with the Hillcrest later tonight.

However I do get interference from my ASUS 3D monitor. For some reason when the monitor is on, the Hydra tracking bugs out.

[MSat]

Good to hear.

I actually found this just a little while ago from their site:

"The Razer Hydra uses a magnetic field which is 20 times weaker than the Earth’s natural magnetic field, allowing it to operate without adversely affecting objects in its surrounding, such as credit cards, hard disk drives and speakers."

So I guess the transmitter coil in the base is far too weak to cause significant interference, not to mention saturate the magnetometer in the IMU, which makes me a happy camper. I'm thinking the interference you've experienced is due to the monitor's power supply. How close together did you have the monitor and the Hydra?

[cybereality]

OK, I tested with the Hillcrest tracker and I saw no problems. I think its fine.

The monitor and the Hydra base were about 1 foot apart. Interestingly enough just now it seemed OK with the Hydra SDK example program. Not sure what the exact issue is, but I know other people with the same monitor had the same problem. Works fine with my Zalman, so its not all monitors.

[brantlew]

The Hillcrest has no magnetometer so it would not be affected. I suspect that the Hydra could distort the tracking on a calibrated sensor. I don't have any hard data to back me up, but my experience with 9DOF IMU's is that they are incredibly sensitive to magnetic variation.

[cybereality]

Yeah, you are right. Guess the Hillcrest doesn't have a magnetometer (though they have a new version coming out soon that does).

The Vuzix does, and I recall it being fine playing with the Hydra. Though, thinking back, I may have disabled the magnetometer because it was causing anomalies (not from the Hydra, just in general).

So maybe it would be good for someone with a real 9DOF IMU to run some more tests.

[brantlew]

9DOF trackers work great when you calibrate them at the position you will be playing. Even Vuzix has a little utility for calibrating their tracker. I think you could calibrate an IMU against a powered Hydra and it would work fine as long as you didn't move the device. But I don't know how it would work if you just brought in a Hydra and added an unaccounted field to your environment without calibration.

[MSat]

Filtering out magnetic interference does seem like a tricky subject, though with the hydra's magnetic field being substantially weaker than the Earth's magnetic field I would think that it wouldn't cause any major issues. Though it would be nice to test. Once I get my hydra, I'll try it out against a compass app on my phone.

[alekki]

Compass app on my phone acts funny around my Hydra. Really close to the base station the compass may be more than 90 degrees off, but the interference is very noticeable even about a meter away where my chair is, also when holding the phone at the height where my head would normally be. Moving the phone only a few centimeters can turn the compass up to 20 degrees. I'd make a video but the only camera I have is in my phone.

Edit: Actually there seems to be lots of interference even without the Hydra. Part of the interference could be caused by other electronics or something else. Or maybe the magnetometer on my phone is poorly calibrated. If the problem is the former, it's actually more concerning since I really don't want my computer, headphones or anything else to cause problems with the Rift tracking. I'll let you know if I can isolate the cause of the interference.

[MSat]

Compass app on my phone acts funny around my Hydra. Really close to the base station the compass may be more than 90 degrees off, but the interference is very noticeable even about a meter away where my chair is, also when holding the phone at the height where my head would normally be. Moving the phone only a few centimeters can turn the compass up to 20 degrees. I'd make a video but the only camera I have is in my phone.

Edit: Actually there seems to be lots of interference even without the Hydra. Part of the interference could be caused by other electronics or something else. Or maybe the magnetometer on my phone is poorly calibrated. If the problem is the former, it's actually more concerning since I really don't want my computer, headphones or anything else to cause problems with the Rift tracking. I'll let you know if I can isolate the cause of the interference.

What kind of phone, and what compass app are you using? A poorly designed compass app that just reads raw magnetometer data would have problems. If the app has a calibration function, try running it in the area you're trying to use it.

[alekki]

Compass app on my phone acts funny around my Hydra. Really close to the base station the compass may be more than 90 degrees off, but the interference is very noticeable even about a meter away where my chair is, also when holding the phone at the height where my head would normally be. Moving the phone only a few centimeters can turn the compass up to 20 degrees. I'd make a video but the only camera I have is in my phone.

Edit: Actually there seems to be lots of interference even without the Hydra. Part of the interference could be caused by other electronics or something else. Or maybe the magnetometer on my phone is poorly calibrated. If the problem is the former, it's actually more concerning since I really don't want my computer, headphones or anything else to cause problems with the Rift tracking. I'll let you know if I can isolate the cause of the interference.

What kind of phone, and what compass app are you using? A poorly designed compass app that just reads raw magnetometer data would have problems. If the app has a calibration function, try running it in the area you're trying to use it.

Samsung Galaxy Note. I just tried some random compass app from the Android Market. You're probably right about the poorly designed apps, the performance doesn't seem to be consistent from one app to another.

[rupy]

Why can't the rift use the same tech as the hydra for positioning? And would it need 3 magnetometers, one for each axis?