While current technology has a six-axis inertial measurement unit available as a single unit smaller than a dime, the IMU in Yamaha's new YZF-R1 has three discrete gyroscopes (the three large integrated circuits here). Each IC is just 15 mm long. While current technology has a six-axis inertial measurement unit available as a single unit smaller than a dime, the IMU in Yamaha's new YZF-R1 has three discrete gyroscopes (the three large integrated circuits here). Each IC is just 15 mm long. Photo courtesy Yamaha

Trevitt’s Blog: The Inertial Measurement Unit

Written by  on Friday, 12 December 2014 10:50

Press material for both the all-new 2015 Yamaha YZF-R1 and 2015 Ducati 1299 Panigale models describes the use of an Inertial Measurement Unit (IMU) as part of their electronics packages.

On the Panigales the IMU plays a part in the new cornering ABS and wheelie control, and it also works with the S model's Ohlins Smart EC semi-active suspension. Yamaha says the IMU works with the R1's Slide Control System specifically, and "communicates with the Yamaha Ride Control (YRC) Yamaha's most advanced electronics package ever offered on a production motorcycle."

The units on the Ducati and Yamaha are six-axis IMUs, which indicates they have three gyro sensors and a three-axis accelerometer; with these sensors and some computer power, it's possible to determine the bike's position relative to a reference point as well as its orientation. This technology was originally used on ballistic missiles, aircraft and spacecraft, and recent advances have made a complete IMU small enough to be used in a motorcycle application. The Bosch Sensortec IMU, for example, is a single unit measuring just 3 x 4.5 x 1 mm - you could easily fit a handful of those on your pinky's fingernail.

With an IMU as part of the electronics package, the bike's ECU has a very complete picture of what the motorcycle is doing at any given moment. An accelerometer's output can be integrated (yes, calculus does come in handy) to find velocity and integrated again to find position. A gyroscope measures the rate of rotation in degrees per second, which can be integrated to find orientation. The ECU would then know, for instance, that the motorcycle is at 32 degrees of lean and lean angle is increasing at 10 degrees per second. Or that the attitude of the bike is nose-down at 5 degrees but pitching rearward at 20 degrees per second - a much clearer indication of a wheelie than by comparing wheel speeds.

To date, most rider aids have relied on wheel speeds and perhaps a single accelerometer or lean angle sensor to determine a course of action, but an IMU provides much more concise information as to what's actually happening.

Electronic aids that require accelerometers are typically more difficult to implement on motorcycles than cars because of the fact that motorcycles lean in corners. A sensor sitting flat on the floor of a car will measure three-axis acceleration just fine in most instances, but on a bike encounters trouble as the sensor must lean with the motorcycle.

The lateral acceleration sensor in the AiM EVO4 data acquisition unit we use on Jodi Christie's superbike always reads close to zero because - relative to the motorcycle's frame of reference - there is no lateral acceleration. Likewise, a vertical accelerometer on a car always reads close to 1 G, but on a bike it fluctuates as the bike leans and the "vertical" sensor is subject to cornering forces. This is partly why GPS-based data systems are so useful for motorcycle applications.

Things can get interesting when an IMU is combined with GPS, as Yamaha has done with its Communication Control Unit (an optional extra for the R1 that records data and allows for course mapping) and Ducati has with its Data Analyzer+ GPS data system for the Panigale.

From a consumer standpoint, GPS with an IMU would allow your navigation system to function for a period of time with no GPS signal, such as in an underground parking garage or a tunnel. Accelerometers and gyroscopes have for some time been used in GPS-based data acquisition systems to improve GPS accuracy, and a complete six-axis IMU takes that one step further with very accurate position and acceleration data updated at a rate much higher than GPS alone is capable of.

As elaborate as the electronics packages are on the Panigale and R1, I would suspect that given the capabilities of the IMU/GPS combination, we are just seeing the beginning of what's possible in terms of rider aids and their refinement.

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Last modified on Friday, 12 December 2014 11:00
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