editor's blog
Subscribe Now

Gravity Leaking

I recently had a wide-ranging discussion with Kevin Shaw, CTO of Sensor Platforms. It originated out of this nagging thing I had going on in my head about what can be done exclusively with accelerometers. Early thoughts on the topic stimulated my whimsical figure skating article, but my curiosity hadn’t been satisfied.

The gist of my thinking was that, while, in general, you need an accelerometer and a gyroscope to establish both direction and orientation, if you were in a fixed frame like an automobile, then your direction established your heading, so knowing your direction meant knowing your heading. And you can get direction from an accelerometer. You could even get altitude change by detecting vertical acceleration.

Turns out it’s not quite that simple. Let’s say you’re out in a flat surface (like Nebraska) with an accelerometer that’s perfectly flat – that is to say, coplanar with your flat surface. If it’s a 2-axis accelerometer, then it won’t notice gravity, which would be orthogonal to the two sensed axes. If (as is more likely) you had a 3-axis sensor, then the Z element would detect gravity, and you would subtract that out.

So in both cases, you would calibrate to zero vertical acceleration. And as you drove around on the flatlands, you could figure out where you were. But at some point, you’re going to encounter a hill. Or heck, even an overpass. Now you’ll move vertically. And that’s where it gets tricky.

If you had your sensor mounted in a flexible way that guaranteed it would always remain flat (that is, with gravity being perfectly down), no matter where the car goes, then things would still work. But most of us don’t have that: as we go up a hill, our car tilts, as does any sensor in the car. Gravity is no longer in the Z direction. And we’re only subtracting out gravity in the Z direction. So now gravity is going to show up in some other direction. Not full gravity, perhaps, but a component of it.

The sensor can’t tell whether that appearance of gravity represents gravity in a tilted sensor or acceleration in a flat sensor. And gravity is a large acceleration compared to what our cars can do, so just the mere tilting of the car will suddenly result in a large “leakage” of gravity into the other directions, misleading the accelerometer. That leakage will also reduce what the accelerometer sees in the Z direction, making it think you’re levitating.

This is all the stuff of thought experiments, since we do have and use gyroscopes to eliminate the ambiguity. But I found it an interesting insight into how some of these calculations work as well as a minute aspect of what the sensor fusion guys have to deal with.

Leave a Reply

featured blogs
Apr 13, 2021
If a picture is worth a thousand words, a video tells you the entire story. Cadence's subsystem SoC silicon for PCI Express (PCIe) 5.0 demo video shows you how we put together the latest... [[ Click on the title to access the full blog on the Cadence Community site. ]]...
Apr 12, 2021
The Semiconductor Ecosystem- It is the definition of '€œHigh Tech'€, but it isn'€™t just about… The post Calibre and the Semiconductor Ecosystem appeared first on Design with Calibre....
Apr 8, 2021
We all know the widespread havoc that Covid-19 wreaked in 2020. While the electronics industry in general, and connectors in particular, took an initial hit, the industry rebounded in the second half of 2020 and is rolling into 2021. Travel came to an almost stand-still in 20...
Apr 7, 2021
We explore how EDA tools enable hyper-convergent IC designs, supporting the PPA and yield targets required by advanced 3DICs and SoCs used in AI and HPC. The post Why Hyper-Convergent Chip Designs Call for a New Approach to Circuit Simulation appeared first on From Silicon T...

featured video

The Verification World We Know is About to be Revolutionized

Sponsored by Cadence Design Systems

Designs and software are growing in complexity. With verification, you need the right tool at the right time. Cadence® Palladium® Z2 emulation and Protium™ X2 prototyping dynamic duo address challenges of advanced applications from mobile to consumer and hyperscale computing. With a seamlessly integrated flow, unified debug, common interfaces, and testbench content across the systems, the dynamic duo offers rapid design migration and testing from emulation to prototyping. See them in action.

Click here for more information

featured paper

Understanding Functional Safety FIT Base Failure Rate Estimates per IEC 62380 and SN 29500

Sponsored by Texas Instruments

Functional safety standards such as IEC 61508 and ISO 26262 require semiconductor device manufacturers to address both systematic and random hardware failures. Base failure rates (BFR) quantify the intrinsic reliability of the semiconductor component while operating under normal environmental conditions. Download our white paper which focuses on two widely accepted techniques to estimate the BFR for semiconductor components; estimates per IEC Technical Report 62380 and SN 29500 respectively.

Click here to download the whitepaper

featured chalk talk

Minitek Microspace

Sponsored by Mouser Electronics and Amphenol ICC

With the incredible pace of automotive innovation these days, it’s important to choose the right connectors for the job. With everything from high-speed data to lighting, connectors have a huge impact on reliability, cost, and design. In this episode of Chalk Talk, Amelia Dalton chats with Glenn Heath from Amphenol ICC about the Minitek MicroSpace line of automotive- and industrial-grade connectors.

Click here for more information about Amphenol FCI Minitek MicroSpace™ Connector System