Sparkfun MPU9250 Products

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Chrisau
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Joined: Tue Aug 15, 2017 3:37 am

Sparkfun MPU9250 Products

Post by Chrisau » Tue Aug 15, 2017 3:42 am

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.

Chrisau
Posts: 3
Joined: Tue Aug 15, 2017 3:37 am

Re: Sparkfun MPU9250 Products

Post by Chrisau » Tue Aug 15, 2017 5:23 am

Sorry image link wasn't right.

Image

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Ross Robotics
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Re: Sparkfun MPU9250 Products

Post by Ross Robotics » Tue Aug 15, 2017 9:36 pm

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.
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Chrisau
Posts: 3
Joined: Tue Aug 15, 2017 3:37 am

Re: Sparkfun MPU9250 Products

Post by Chrisau » Wed Aug 16, 2017 6:25 pm

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

paulrbarnard
Posts: 6
Joined: Tue Aug 22, 2017 2:01 am

Re: Sparkfun MPU9250 Products

Post by paulrbarnard » Wed Aug 23, 2017 8:38 am

The 9250 will help as it has a magnetometer which can be used to identify the gravitational component.

pbreed
Posts: 1
Joined: Sat Sep 09, 2017 4:40 am

Re: Sparkfun MPU9250 Products

Post by pbreed » Sat Sep 09, 2017 4:57 am

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

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