maxon motor sets more records

Sound Leisure is one of the – er – biggest noises in high quality digital and retro jukeboxes. (For the benefit of readers born after around 1970, the original juke box is an intriguing mechanical device designed to play vinyl records, the user putting money into a slot and then selecting the music track of their choice…..). When Sound Leisure Development Engineer Dave Darby received notice about the forthcoming obsolescence of the AC turntable drive motor used in one of their jukebox models, the business made a ‘last time buy’ to secure stock for forthcoming production and then contacted maxon to discuss a longer term, permanent replacement. 

After looking at the existing motor and its installation, Sound Leisure, together with maxon engineers, agreed on using a maxon brushless EC 45mm flat motor to replace the soon-to-be-obsolete item. The EC45 brushless DC motor is part of wider family of flat motors supplied by maxon and useful when space is at a premium because it delivers good performance and an extensive speed range. For speed and proof of concept, a standard motor was provided for Sound Leisure to test, before fine-tuning to include any necessary modifications. The motor was assembled into a turntable testbed and although the initial testing proved positive with the standard maxon motor it became clear that a longer shaft was preferable.

So maxon engineers created the EC 45 flat motor with a longer shaft. However, Dave Darby and maxon’s Andrew Gibson then recognised an issue caused by a relatively high radial load on the jukebox turntable drive and decided to look at an alternative motor instead. As the EC 45 flat had been working well, it was decided to stick with the multipole motor technology and select the brushless maxon EC-i 30 mm motor for the application instead. The brushless EC-i is one of a  series of such motors which deliver high torque using the same electrical characteristics, but which offered a lower distance between the bearing and  the length of the shaft, overcoming the previous radial loading issue.

maxon created the modified part and samples were built into the testbed and placed on long-term test. The motor performed faultlessly over months of continuous operation and in the meantime, Sound Leisure fine-tuned the drive board and designed the production turntable to integrate the new motor. The first full development turntable system was built and connected to the speakers ready for integration into the jukebox casing.

The owner of Sound Leisure, Alan Black, had worked as a sound engineer for many years and noticed with his trained ears that he could hear variations in the sound. After investigation, this turned out to be the block commutation being used to drive the motor from the motor controller, and the sound he could hear was the torque ripple of the motor poles. The team at Sound Leisure began to explore fixes and one option was using a sinusoidal commutation from a controller (maxon  offers block or sinusoidal controllers) to reduce the torque ripple and make the transition from pole to pole smoother. However, electronically, this would be more complicated than block commutation and would mean further development time. Another option was to revert to a brushed DC motor, and the maxon DC-max 26 mm motor was selected. DC-max motors are part of the DCX range of brushed products from maxon which can be specified and modified online and ready for delivery within 11 working days. Extensive testing – and the ears of Alan Black – confirmed that all was now good, that the torque ripple had gone and that the sound was perfect. 

Although the motor had clearly provided the required sonic performance, Sound Leisure were concerned about the wear on the motor brushes because their jukeboxes are designed to last a lifetime. To assure the desired longevity, it was suggested that a customised DC-max motor be designed that incorporated precious metal brushes, and testing revealed that the motor still performed perfectly, even after many months of continuous use, and would be the ideal solution to replace the obsolete AC motor.