IMU ( Inertial Motion Unite) price and distance measurement

"adelmakram" wrote:
1) Why there is a significant variation in prices between different IMU in the market? for example 10DOF price is 30++ $ while LPMS price is 800 Euro?
2) ...

Some units are just the raw sensors, with no processor, no software, no sensor fusion, and very low cost.

Others (such as that expensive one you linked to) are complete units, with BlueTooth wireless interface, and the price includes whatever price they decided their included software could fetch on the open market (depending on their target audience, of course). Things targetted at military or medical applications require much more stringent design and certification, and fetch a much higher price.

You can get even cheaper IMU devices, such as a GY-85, for as little as $16 with free shipping. I2C interface only, and requires a processor (such as an Arduino) to be useful. Or you can just hack a video cable and connect it to the I2C wires and run the sensor fusion software on your host PC:

GY-85 9DOF 9axis degree of freedom IMU sensor ($15.99, free shipping):
http://www.ebay.com/itm/281089415111

Arduino/GY-85 open source head tracker project (for FPV):
http://www.rcgroups.com/forums/showthread.php?t=1677559&page=88

World's Cheapest I2C (I-Squared-C) Adapter:
http://www.instructables.com/id/Worlds-Cheapest-I2C-I-Squared-C-Adapter/?ALLSTEPS

The 25¢ I2C Adapter:
http://www.paintyourdragon.com/?p=43

And more:
viewtopic.php?t=984&p=12330#p10447

"adelmakram" wrote:
1) ...
2) Does IMU measure the distance? if so, what is the origin of frame of reference? do I have to calibrate it each time I use?

IMUs cannot accurately measure absolute position, due to drift problems. You need to add a GPS unit to your sensor fusion algorithm for free walking, or some other reliable position sensor like the Razor Hydra or optical tracking for short range position tracking. However, the IMU can predict position for a short while during absolute position sensor dropouts, or for a longer time with laser gyros and very accurate atomic clocks (such as in military applications).

There is also research showing that IMUs can do a pretty good job of position measurement if they can be regularly recalibrated by mounting on a foot or ankle and forcing estimated velocity to zero whenever the foot is in contact with the ground.

Also, I (and others) have researched head-mounted IMU positition tracking for seated or standing (not walking) gaming use. I have "proof-of-concept" code demonstrating that this is feasable. Although not very accurate from a measurement perspective, it should still be useful for gaming. For that matter, the Razer Hydras are not very accurate at determining absolute position, although they are repeatable to within 1mm precision (i.e. precisely inaccurate).

Nice IMU relative distance and direction measurement with a single foot-mounted IMU:




Tracking like this can be calibrated to a known interior map, using landmarks such as doorways, stairs, and detours around furniture to adjust the estimate to a known position on the map.

IMU's are ideal for joint based body tracking, which ofcourse results in position tracking.

Here is an example video:



Here the website of the product if you are interested:
http://www.noitom.com/products.html

In my opinion this is a pretty good solution for VR, but ofcourse i am a greenhorn on this topic and currently i can't see all the flaws. What i like about this solution is you can easily create different price ranges which ofcourse is dependent on the number of sensors.

For example you can create a beginner version, with only 2 IMUs, one which is alread in the Oculus Rift and one which measure the torso angle. Based on this simple version you can already do the following things:

Usage while seated:
- Full position tracking for head mounted display (you have to stay seated of course).

Usage while standing:
- Limited position tracking for head mounted display, bending movement only

The software of course has to be flexible here, movement calibration is very important. This system does not know how much you use your legs while your bending to one site or if you'r in crouch position etc. but it can calibrate your preferred bending style.

If you want more accurate movement you have to add atleast 4 more sensors.

Advanced version, possible scenarios:

Usage while seated:
- Full position tracking for head mounted display
- Full position tracking for arms (No Hand movement can be detected).

Usage while standing:
- Limited position tracking for head mounted display, beding movement, limited walking movement.

The system is not capable of tracking your foot, so if you stand on your toes the system cannot regocnize it. But if you add more sensors... etc. you get the idea.

For this system you will ofcourse need accurate body data to improve the position tracking. You cannot easily jump into it and play right away, which ofcourse is one major flaw of this system. If you enter your hight you should already be able to do some approximations, but of course if you have the correct lower and upper leg length it will be way more accurate.


Negative Aspects:
- High number of sensors necessary (high costs) for full body tracking.
- Complex calibration system (no plug an play).
- Not completely accurate system even with all sensors http://www.youtube.com/watch?v=solJzP7pbzA

Positive Aspects:
- Low cost variants possible (upgradable system)
- Very fast and relatively accurate system (dependent on usage)
- No drift, you can reset the system as soon as you go back to allowed movement (depending on system variant, beginner, advanced ...)

Hi, I have am inertial measurement unit that I no longer need. It's an x-IMU by x-io technologies (http://www.x-io.co.uk/). Does anyone have any ideas about where to sell such an item. It cost £309.00 new so I'd like to recoup at least some of that money!