Home > VBOX Automotive > Modules and accessories > Inertial Measurement Units > IMU/YAW - User Manual > 04 - Mounting the IMU

04 - Mounting the IMU

Option 1: Roof-Mounting (Recommended)

The VBOX IMU roof-mounting option allows for an IMU04 (only) to be placed directly on the vehicle roof, co-located with the GPS antenna. The IMU is securely fastened within the machined enclosure which has a magnetic base to ensure that it stays in place. 

Co-locating the antenna and IMU improves the performance of the Kalman filter. Putting the two together and mounting them on the vehicle's roof, removes the requirement to measure the separation (difference between IMU and antenna automatically accounted for).

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Please contact vbox@racelogic.co.uk for more information, or to order an IMU Roof Mount (RLACS216).

Mounting Suggestions

The IMU roof mount should be mounted on a braced, stable part of the roof, such as the area over the A or B Pillar.

Care should be taken to avoid placing the mount in a half braced position, where the front or rear magnetic support is on a supported part of the roof, and the opposite end is on a flexible location. The potential pivot can induce a pitch rate oscillation that will influence the accuracy of the results.

The IMU roof mount can be placed on a non-flat surface. When placed on a non-flat surface, the 'ANGLE OFFSET' action should be used to compensate the IMU attitude angle channels (Pitch angle, roll angle). This is performed from VBOX Manager.

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Be aware that when mounting the IMU on an angle, that the raw accelerometer and gyro data will be incorrect, as the channels are not pitch compensated. 

Measuring Translation Points

Customer required translation measurements should be made in the same plane as to which the IMU is mounted (i.e. perpendicular to the IMU base, not straight down to the ground).

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Important notes when using ADAS Setup

  1. If using IMU filter with ADAS mode, the GPS antenna and IMU must be co-located (roof mount) or positioned so there is no relative X or Y offset between them. If there is a difference, manual contact points should reference the IMU location, rather than the GPS antenna.
  2. When using IMU Filter the user cannot use 'SET POINTS' functionality to define contact points in single or multi target ADAS modes

Option 2: Using a Mounting Arm

A flexible way to fix the IMU rigidly within the vehicle is by using the Racelogic Mounting Arm. The three-part telescopic handle is fully adjustable to any length between 70 and 150 cm to which another 20 cm can be added by extending a third section using the compression lever.

Both ends are fixed to an 8 cm x 13 cm plate which sits on a joint to accommodate for uneven surfaces. Pressed against the IMU on the floor and the vehicle's ceiling, the mounting prop ensures that the IMU is fixed tightly.

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Please contact vbox@racelogic.co.uk for more information or to order a mounting arm (RLACS212).

Measuring IMU-Antenna Offsets

When using either a fixed mounting point or the mounting arm, you must measure the relative position of the antenna* in relation to the IMU to at least within +/- 5 cm. These distances must then be entered into the VBOX via VBOX Tools > VBOX Setup, VBOX Setup or using VBOX Manager. These measurements are required when using either an IMU04 or an IMU03 unit.

*When using a twin antenna system, these measurements must be taken from the primary antenna (A). 

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Option 3: Fixed Mounting

The IMU should be mounted rigidly to the vehicle mid-way along the wheelbase. Try to position the unit as close as possible to the centre of the vehicle, making sure it is mounted in the direction of travel - as shown in the image below. It is also important to mount the sensor so that it is level with the ground.

For best results, mount the IMU and GPS antenna as close to each other as possible. For example: Bolt the IMU to the seat rails and place the GPS antenna on the roof directly above.

Note that the IMU and antenna should be mounted on the same rigid body, to provide a relative reference.  So for a vehicle such as a truck cabin, both the IMU and antenna should be fitted to the cabin body (if cabin is air-sprung) or to the vehicle chassis.

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Last modified
17:56, 20 Aug 2014

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