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1 Ac­celerom­e­ter

Ac­celerom­e­ters mea­sure ac­cel­er­a­tion (of­ten called ‘g’) along a sin­gle axis. It is mea­sured in m/s2 (me­tres per sec­ond squared) and the av­er­age ac­cel­er­a­tion caused by grav­ity is 9.81m/ s2. Ac­celerom­e­ters in your IMU will read 0m/s2 in freefall, and 9.81m/s2 when sta­tion­ary on the ground.

2 Gyro

Roll and pitch can be ap­prox­i­mated with ac­celerom­e­ters, but gy­ros are bet­ter as they aren’t af­fected by road bumps. But, small non-zero er­rors in gyro mea­sure­ments mean an­gles cal­cu­lated us­ing gyro data can drift over time. By mix­ing gy­ros and ac­celerom­e­ters, this drift can be min­imised.

3 Pro­cess­ing unit

Con­vert­ing IMU data into chas­sis at­ti­tude is rel­a­tively easy in elec­tronic terms, but the ECU al­ready has other things to worry about, like in­ject­ing fuel and ig­nit­ing it at the right time. It’s not un­usual to off-load some of the pro­cess­ing to other com­po­nents in com­plex sys­tems. With ex­tra pro­cess­ing ca­pac­ity, it’s pos­si­ble to com­bine IMU data with other mea­sure­ments to pro­duce bet­ter over­all in­for­ma­tion on which to act.

4 In­ter­face

It’s hard to check an IMU for fail­ure be­cause data is of­ten out­put on to some­thing called a CAN bus. The only way to tell if there’s a prob­lem is to rely on the dash­board er­ror mes­sages, or to use a CAN bus snif­fer to de­code and in­spect the IMU pack­ets your­self. While this sounds like man­u­fac­tur­ers be­ing dif­fi­cult, it does ac­tu­ally make sense as it’s cheaper, lighter and smaller than more con­ven­tional ana­logue/dig­i­tal meth­ods.

The sys­tem uses a mod­ern elec­tronic ver­sion of a giro

The IMU can be plugged into a com­puter to down­load data

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