Have you ever tried measuring vibration on a spinning bicycle wheel or a flying drone’s propeller using traditional accelerometers? If you have, you know the nightmare: heavy data acquisition systems, cables wrapping around spinning hubs, altered aerodynamics, and the constant risk of wires tangling or snapping.
Recently, HBK team set out to prove that these physical limitations are a thing of the past. Taking advantage of the streets around our headquarters in Virum, Denmark, we launched a practical test campaign using the new HBK Molecu wireless accelerometers.
The goal? To show that we can easily capture raw, sample-synchronous vibration data from locations that were previously completely inaccessible.
A high-performance sport bicycle featuring a titanium frame and carbon components has both highly rigid structures and rapidly rotating elements (the pedals and wheels), serving as the perfect testbed.
To mount the compact Molecu sensors (measuring just under 2 cm on each side and weighing just 22 g), we used a brilliantly simple approach:
In total, seven sensors were mounted across critical points of the bike, including the handlebar, seat post, frame downtube, pedal, and – most importantly – directly onto the rotating wheel hubs and rims.
Each test run lasted exactly 35 seconds. The rider pedalled up to speed, rolled over a street kerb, made a sweeping turn, hit the kerb a second time, and finally braked to a smooth stop.
To make things interesting and see if the sensors could detect subtle physical changes, we ran the exact same test route under two different conditions:
Back in the lab, we imported the datasets into BK Connect® for post-processing. The results clearly demonstrated the damping effect of the lower tyre pressure:
Even better, because of gravity’s cyclic effect on the rotating sensor, the low-frequency component of the raw signal naturally tracked the wheel’s rotation speed. This means the accelerometer doubled as its own tachometer – no extra tacho probes required!
To take the campaign a step further, the HBK team linked the sensor data to a simplified geometric model of the bicycle frame. Using BK Connect®, the team performed:
This quick test campaign proved exactly what the team hoped: the HBK Molecu wireless accelerometer delivers high-fidelity, sample-synchronous data comparable to traditional wired setups, but with a fraction of the installation time and zero cabling constraints.
By successfully measuring a spinning bicycle wheel on the roads of Virum, we have opened the door to a massive range of new testing possibilities. From rotating helicopter blades and drone propellers in mid-air, to wind turbines and complex industrial machinery – the future of vibration testing is officially cable-free.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, MicroStrain and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
