Counteracting the Lever-Arm effect during Brake Tests

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Range rover brake stop

Counteracting the Lever-Arm effect during Brake Tests

Counteracting the Lever-Arm effect during Brake Tests

It is largely accepted that the most accurate and cost effective way to perform brake distance tests is with the use of a high speed GPS sensor which can measure distances to within a few cm.
During a brake test however, the necessary placement of a GPS antenna high up on the vehicle roof can lead to a certain amount of unwanted variation in GPS speed output. This occurs due to the way that a car pitches forward and backwards as it travels, a feature particularly prevalent during braking. Due to the roof momentarily travelling faster than the rest of the vehicle, the ‘lever-arm’ effect can cause an overshoot in the GPS speed recorded compared with the speed at the wheels.

Brake stop Travel

By using an Inertial Measurement Unit (IMU04) with a VBOX3i, it is now possible to compensate for this overshoot. It works by calculating the pitch and roll angles of the vehicle, and translates the data measured at the antenna point on the car roof to the Centre of Gravity where it is mounted. As a result the speed measurement closely represents the true speed of the vehicle.

Brake stop graph

For more information on how our IMU04 can be used to improve the accuracy of brake and vehicle dynamic tests, click here.
You may have seen the article that was published recently in Vehicle Dynamics International magazine which focusses on using an Inertial Measurement Unit to aid GPS test systems. Click here to read more.