# How to use iPhone to evaluate an IMU chip?

I have a quadcopter like the below (source of the image)

and I have an IMU (inertial measurement unit) having acc sensors in X-Y-Z and gyro sensors in X-Y-Z. Now I am trying to find an iPhone app by which I can check the values such as rotation and accelerations in each dimensions over X-Y-Z coordinates. I need to export the data in order to design a proper smoothing algorithm probably with Kalman filter or incremental filter. I noticed that the IMU needs to be calibrated because levels do not start with zero for non-moving object. For this kind of things, independent measurements with iPhone could help to adjust things.

So how can you use iPhone to evaluate an IMU chip? Which apps? Other considerations?

• Do you have a link to the IMU chip? – Andy aka May 26 '13 at 20:03
• @Andyaka I have many of them from different vendors. The question here is to find a way to validate the results from the chips. I am not sure yet which chip to choose, I am trying to find a quality chip that is able to detect small changes in rotation and acc about the size of hand-rotation and hand-acc. For this I am trying to measure some raw data with iPhone: it has all kind of sensors so it should be possible. – hhh May 26 '13 at 21:40
• You are intending to attach the "sensor" to an iphone and fly it like the video? Is the internal sensor not good enough (bearing in mind I have no idea what the internal sensor is)? – Andy aka May 26 '13 at 21:44
• @Andyaka now you misunderstand. The IMU chip is an essential part for the stable flight with quadcopter. Without real-world testing (to which I need independent IMU-data-logger, here iPhone) and smoothing (Kalman/incremental/etc filter), the flight is very unstable. In order to judge different IMU chips in the quadcopter, I need an IMU in the iPhone/data-logger. The internal chip is irrelevant for this question: I am trying to find a tool/techniques/methods, now with iPhone, by which I can analyze/export the data for data-analysis. Yes, iPhone is attached to the quadcopter like the photo. – hhh May 26 '13 at 21:53
• Why are you trying to use an iPhone for a simple data logging exercise? It seems like it would be an expensive one too when your quadcopter falls out of the sky and smashes your iPhone. A small embedded computer such as a Gumstix would be a better option. – Amoch May 26 '13 at 22:30

## 2 Answers

What are the specifications on the iPhone accelerometer? If this were something I was working on, I would start with a static 3d test to validate the imu output when it was fixed In multiple known positions. The iPhone uses a fairly cheap part, you could probably figure out what the part number is by doing some sleuthing, and then you could figure out if the iPhone is better or worse then the imu's you are looking at

(Updates 5/27/13) From this teardown http://www.ifixit.com/Teardown/iPhone+4+Teardown/3130/2 Apple seems to use a ST Micro proprietary part. This part ST L3G4200D (http://www.st.com/web/catalog/sense_power/FM89/SC1288/PF250373) is mentioned as a potentially commercially available part.

The Iphone isn't intended as an IMU, and so if I were trading off performance vs cost when designing it, I'd go for the lowest performance, cheapest part that would work.

In your case, I'd build a fixture that I could mount an IMU in, and fix it in multiple orientations so I could determine how accurate and repeatable the IMU reading were in a known, accurate position as you're taking data. Make it so that you could put in arbitrary positions and you can evaluate coupling between directions.

I like having measurement techniques that are accurate enough to truly evaluate differences between systems. If you're using a iPhone as your reference, then you'll probably have trouble figuring out the difference between multiple sensors.

• Where did you find the information for "The iPhone uses a fairly cheap part"? Which part? SKU? – hhh May 27 '13 at 12:18
• From this teardown ifixit.com/Teardown/iPhone+4+Teardown/3130/2 Apple seems to use a ST Micro proprietary part. This part ST L3G4200D (st.com/web/catalog/sense_power/FM89/SC1288/PF250373) is mentioned as a potentially commercially available part. The Iphone isn't intended as an IMU, and so if I were trading off performance vs cost when designing it, I'd go for the lowest performance, cheapest part that would work. – rfdave May 27 '13 at 13:24

The manufacturers such as Apple do not seem to publish the details about the IMU chip. The word "teardown" returns ambiguous material over internet about specificications of different devices but hard to judge the material. I could not find the specifications -- anyway iPhone has all kind of sensors so you can get all kind of data. The below hase some apps listed, some of them are free.

Sensors

✔ 3D Accelerometer: X, Y, Z acceleration

✔ 3D Magnetometer and Compass

✔ Integrated Accelerometer and Gyro data

✔ Location and GPS: longitude, altitude, speed

✔ Proximity Sensor

✔ Misc: mic level, capacitive touch, battery, light-sensor


Apps