Source: Cycling Electric

Researchers at the University of Delft are currently working on a study of electric bike motors’ lifespans, gathering data from a wide-ranging survey of 500 e-bike and speed pedelec owners, where they have found patterns such as failures beginning to cluster between 16,000 and 20,000 riding kilometres.

The research is being led by Sonja van Dam, Assistant Professor of Circular Product Design at Technische Universiteit Delft; she spoke to UK biking media outlet, Cycling Electric, to discuss the study’s progress, and to highlight a potential solution to some of the issues found.

The headline finding so far is that up to 43% of e-bike owners would dispose of the whole bike if the motor failed, even if the fault is something relatively simple such as a failed bearing. Repairs can be costly, especially if falling outside of the warranty period; Sonja cites her own mother’s experience, of a motor failure after 12,000 km of riding and 3.5 years of ownership (and outside the warranty threshold), which led to a “near €1,000 replacement cost.” Such experiences, coupled with a five-week motor replacement timeline, which has been commonly reported during the research process, compare poorly to the expectations of car owners.

Sonja says, “Existing studies have suggested that as many as 24% of people have motor issues during the lifetime of their e-bike and we have tended to find that after around 20,000km, about 13% of current e-bike owners encounter an error.” She continues, “Our data shows that people will replace their entire e-bike 24% of the time if a battery fails, and of course, these are even less repairable. Research from the automotive industry suggests that remanufacturing can happen.”

Extrapolating from the survey sample, Sonja calculates that 360,000 e-bikes are being scrapped each year in Europe (based on the top eight countries by volume sales, which amounts to four million units). Of these, a staggering 80% are calculated by the Delft study to be repairable.

A potential solution

Sonja describes a relatively inexpensive item which manufacturers could incorporate during the production process, which would warn customers about potential breakdowns. A Piezo sensor is a specialist pattern-detection device which can identify anomalous behaviours coming from a motor in motion.

“Piezo sensor technology is used in other sectors, often to measure if bearings are wearing out. In over half the cases we have studied it is the bearings or the gears inside a motor that degrade. Also, electronics are vulnerable to water ingress too, but most are true hardware faults. There are causes we can identify for failures, which can be pieces of bearings breaking when, for example, a bike hits a curb, but perhaps more often it is using too high a torque in too high a gear, which ups the pressure on parts over the course of rides. There are too some cases where nylon gears on the inside wear too quickly.”

She adds a conclusion from Msc. Student Dion Vijverberg, who has been leading on the Piezo sensor research: “Ideally bike makers begin to build a Piezo sensor into the motor so that faults are flagged to the user ahead of a mechanic discovering it too late. This is a relatively affordable and simple thing to implement. Think of it like a light on your dashboard alert on a car.”

The research team also expanded on the topic of water ingress as a key failure reason. The heating and subsequent cooling of motors can lead to small quantities of water building up inside motors, and the effectiveness of seals can degrade with time. Sonja says, “Keeping it airtight when you have moving elements is actually a big design challenge. Our students are looking at how you can avoid that moisture, causing an issue. They are looking at silicone pearls, for example, that you can build that into a motor to absorb minor moisture ingress.”