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What is an IMU and what does it mean for my motorcycle?


The chances are, over the past few years, any high-end or performance-oriented motorcycle you have read about or bought has a little black box hidden away in the bowels of the engineering, which goes by the name of IMU.

But what even is an IMU? The three letters stand for Inertial Measurement Unit and the function of the small box is to tie together all of the other electronic rider aids like traction control, wheelie control and the now mandatory ABS, as well as even more advanced features too.

The advancement of IMU technology has been rapid and the levels of sophistication they manage to implement would have been considered absolutely cutting edge in MotoGP racing just a decade ago. Advances in computing power, reductions in the size of components and costs have all meant this technology is likely to be standard on all but the very cheapest motorcycles in just a few years.

The biggest issue facing the widespread pick-up of IMU and other rider safety aids over the past decade has had nothing to do with the actual technology but more to do with the attitude of many motorcycle riders, who did not trust electronics on motorcycles.

The tide of change has changed when it comes to ABS, with more riders now trusting ABS to help rather than hinder the bike. Indeed, where ABS (that’s anti-lock braking, if we need to explain) was once a super-duper optional extra, it now barely warrants a mention on the spec sheet.

A large part of the suspicion of riders has to do with their (or friends or press) experience with older systems. You can trace traction control and ABS back to the late 1980s and 1990s in various guises but the fact is that while they were fitted to bikes like the BMW K100 range, they were crude and didn’t work very well – certainly not for the more spirited riders.

It’s the same with the early iterations of traction control which, even when they progressed from the likes of that seen on the Honda ST1100 Pan European to bikes from the BMW K1300 range, were still fairly unpleasant to experience, due to the brutal throttle chop these systems implemented.

Now, traction control is so advanced there are track modes available that meter out an allowed amount of rear wheel spin, the engine braking can be adjusted to suit, and combined with cornering ABS, they can allow even experienced riders to go faster with everything left switched on. This, in part, is down to the IMU.

So what does an IMU do and how does it work?

An IMU uses a technology referred to as MicroElectronic Mechanical Systems (MEMS) which are actually mechanical and not purely electrical components despite looking very similar to those microchips found in your laptop or smartphone.

An IMU takes gyroscopes and accelerometers and uses them to accurately measure both acceleration in a linear direction but also changes in orientation. There are five and six-axis IMUs available and in use today.

These five or six-axis descriptions refer to the number to the total number of sensors gathering the information; there are either two or three gyrometers and three sensors working at once.

There are six possible movements that can be detected and measured by the IMU. Three of these are linear, three are rotational.

The linear ones are left and right, up and down and forwards and backwards. Because motorcycles lean over there is also the need to measure the pitching forces when accelerating or braking, as well as the yaw as the bike leans over and makes directional changes.

This information is all part of a broader set of information that is gathered from other sensors including front and rear wheel speed sensors, engine ignition, fuel injection and others. Combined, they build as complete a picture as possible of what the motorcycle is doing. All of this information allows the bike to control wheelies, rear wheel spin, the ABS and wider braking pressure in order to keep the bike working within a set series of parameters.

Global giant Bosch is the world leader when it comes to IMU technology; just as it led the world in the development of ABS, traction control and electronic stability control in motorcycles and cars.

The mechanical element inside the Bosch IMU is essentially a tiny mass that sits on microscopic springs made of silicone inside a vacuum. This tiny mass moves within a comb-like structure that measures that movement by detecting changes to electrical capacitance.

At the heart of this huge and precise information-gathering operation sits the IMU. It gathers all of the information and then uses it to inform the other elements running the bike like the ABS, engine management and even the suspension.

What does the future hold?

The future is already almost here in regard to many new innovations that have come from the car world. Adaptive cruise control is going to be available on bikes from Ducati and KTM later this year and has been officially confirmed.

Next up could well be enhancements of this technology which will involve adding collision mitigation systems where the motorcycle can ‘see’ dangers and pre-emptively act to apply the brakes if, following a warning to the rider, no action is taken.

Moving on, there is lots of work going on with cooperative research between vehicle manufacturers to work out how best to ‘connect’ all of the traffic on the roads so they all know where each other is –  meaning no more cars pulling out on bikes because they didn’t see them. The car’s sensors will know there is a bike coming because the bike’s sensors are broadcasting its location.

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