Muro Box N40-About the Motor

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We have been trying to solve the noise of the motor. Based on our current understanding of noise, most of the motor noise heard by from the Muro Box N20 is actually the sound of gears, not the sound of the motor itself. In addition, we use a brushless motor, that is, the motor has no brushes, and the rotor only contacts the bearing, so the noise is much lower than that of the brushed motor. However, compared with the traditional music box, the speed of our motor is quite fast, about 3000 rpm, so the friction sound between the gears is the main source of noise, and it is also the problem we are solving now.

The key to solving this problem is to polish the gears. However, because the gears are not flat, this polishing step is very difficult. At present, there is no automatic polishing method. We all use human hands to polish them one by one. Our worker can only manually polish 30 gears per day and it is very time-consuming but the result works well. We have strictly controlled the noise level of the gears of the recently shipped Muro Box N20. Although it is not completely silent, it has become imperceptible when playing melodies.

In addition, many people are concerned about the problem of multi-motor incoordination. Compared with the traditional dual-caliber music box, the traditional music box may have two independent springs and two independent speed stops. It is very difficult to adjust the consistent speed. But our music box motor is controlled by a microprocessor, and every 10 msec simultaneously checks the speed of the two motors for any deviation and makes corrections. That is, the motor incoordination will not be a problem for us.

But in the videos we tested before, it was a fact that the melody was often fast and slow. The main problem at the beginning was the lack of motor torque, so sometimes the sound of the comb would be slow after plucking the comb. Later, we began to use software to solve the problem and detect the motor speed to compensate, but the compensation algorithm was immature at the beginning and then overcompensated, that is, the motor often rushes and stops suddenly, making the sudden speed and slow speed more serious.

The printed circuit board (PCB) we are shipping now is the third version in our mass production. We’ve added about six times of the original torque to the motor, and the software algorithm has been tweaked for months. If the tempo of the songs in our new new demo videos below are still unstable in the future, please be sure to let us know, we will never stop making the music box more perfect.

Video 1: Muro Box N40 Prototype 1 (Demo Song: Saint-Saens/ The Swan)
Video 2: Muro Box N40 Prototype 1 (Demo Song: 何日君再來/When Are You Returning Again)

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