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By Chrisau
#195849
Hi,

I would like to know if the Sparkfun MPU9250 products would solve the problem I'm having, as follows.

I've been using an MPU6050 (3 axis gyro, 3 axis accel, with the built in motion filter called DMP) on a car axle to measure axle angle when driving. On a long banked corner (2 degrees) the sensor reads 0 degrees while moving (~40km/hr), but when stopped on the corner it reads correctly (2 degrees). The physical axle angle is the same though in both scenarios.

I believe the lateral force from going through the corner when moving is affecting the sensors interpretation of which way gravity is, and is adjusting the roll angles accordingly. See image;

[img width=500 height=197]http://i.imgur.com/IRLiGRU.png[/img]

Given that the Sparkfun MPU9250 sensors have a built in magnetometer and/or use a Kalman filter, will these fix the above issue?

Time is a critical factor at the moment in my project.

Thanks in advance for your input.
User avatar
By Ross Robotics
#195855
Sounds like the sensor is vibrating and being subject to forces which are out of spec. Even if it does sense that the vehicle is angled, with the vibration it just filterss those out. Once the car settles, the sensor isn't filtering out the "noise" and you are getting a correct reading.

My advice is to search around and make sure that it's automotive compliant. Or at least purchase a sensor that doesn't have a filter and use software to average out the readings.
By Chrisau
#195870
Thanks Ross.

The vibration when driving straight and cornering at the same, yet readings when driving straight at speed are accurate.

Some further research is giving me more insight into what the problem is and how others solve the problem. It seems those using fixed-wing UAVs also experience this. They primarily use a method to calculate the centrifugal acceleration, and then compensate for it.

These solutions come from William Premerlani in the fixed-wing UAV community.

Using GPS;
http://diydrones.com/profiles/blogs/acc ... ht-testing

Using only Accel and Gyro;
http://diydrones.com/forum/topics/centr ... lerometers

This solution coming from a research paper for fixed-wing UAV;
http://users.cecs.anu.edu.au/~Jonghyuk. ... _v1.04.pdf
By pbreed
#196085
For those of you using the MPU9250 break out board,
I've posted a STL file on thingverse that mounts the break outboard in the center of a cube.
This allows you to precisely rotate the MPU for calibration etc....

You can also clap a block or square to your desk and use that to constrain how the cube moves for more calibration options.

The details are somewhat fine it printed well on a form 2, not so sure how it would do in FDM.

https://www.thingiverse.com/thing:2525140