Into the vibe

Tuesday, 28 February 2017 07:15

Queste to the perfect motor

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A vibraphone differs quite a lot from a marimba. It's not only the bars which are of a different material, but one big part is the feature that gave the instrument its name: the vibrato.

When I started building vibraphone, vibists told me they don't use the vibrato because of the heavy effect to the sound. But there are more things to consider regarding this effect:

  • easy control
  • noise
  • stability
  • consistency
  • control stop position of the fans

Ofcourse I started the same way as how other brands tackle this matter: copy what others have done. So my first ever vibe had a simple AC motor with a belt, to which I could alter speed. Was nice, but it required a pretty big motor with big speed control, and actually it didn't do what I wanted it to do.

So, having been IT-engineer, I was looking into better ways to control, and into smaller motors. I found the solution in using a stepper motor. These motors are easily controlled, are relatively inexpensive, and thru software you can make them do whatever you want, including stopping at a fixed position.
You would think the search for the holy grail was ended: well, forget it.
By itself these steppermotors are quiet. But when they touch anything else the problems begin.
As the rotating of these motorshafts is accomplished by applying pulses to the motor, making the axles rotate in steps (mostly 200 steps per rotation), you got the effect that with every turn of the shaft, 200 times the motor made a small shiver. With the rotation speed needed to get a musical vibrato, it resulted in having made a new sound-source aside the regular bars. 
I had to hang in the stepper motor in springs and rubber grommets. Not a really nice solution.

So I decided to not use these stepper motors anymore, and go up a next level in motors: brushless servo motors. Wow, these were fantastic. Again thru software I could make them do all the things I wanted them to do, and more. 
With that motor system I could finally add a feature I, as a jazz organ player, always wanted to add: the slow to fast effect you get with the leslie systems. It worked perfect, and with adding a touchpanel, all control was thru software, as well as all features.
This gave me a lot of freedom manufacturing, AND on the plus side, I didn't had the excessive noise I had with the stepper motors.
The motor was with its lenght of just 7cm, and diameter of 35mm small enough to embedd into the small endblock, and I could also embedd all controls in the other endblock. It was something that was not been done before by other manufacturers yet.

But, having an extreme silent motor, the noise issue moved over to another part of the system. 
Inevitable with having fans stopping in a fixed positions, means the fans have to be synchronised. This is done by toothed timing belt(s). Pretty easy thing you would say ;-)
Nope, not on a vibraphone
The vibraphone has its pulsator shafts in an angle (94 and 86 degrees to the endblock). This means the teeth on the timing belt do not grab the pulleys' teeth perfectly, but in a slight angle. Ergo, with each tooth grabbing in, you get a bit of noise, which is amplified by the construction of the whole instrument. Although being a relative silent system, it still was not as quiet as I wanted it to be.

So my search went on.

 About 3 years ago I finally found the perfect motor for my vibraphones. The base still is a servo motor, and on every aspect software controlled.

But I left the idea of having the fans to rotate. With the motor I started using, I was able to have the fans swivle, and have them swivle between different angles.
By adjusting the swivelling angle, I am able to adjust depth of the vibrato, so there was no more "heavy" vibrato effect.

But don't think it was just a matter of getting the right motor and put it in. Making it perfect was still a huge queste, with the biggest task "getting rid of the timing belt".
Between the pulsator shaft and the motor, I had to think of something to convert the motors' movement into driving the fans. Looking back, in total this queste took over a year, engineering 14 different drive systems. Realize that for each drive system I had to reprogram our CNC machines to make the parts. So all was an enormous job.

And if you think it is just the motor having a small computer filled with software: forget it. I had to find a way to easily control the motor systems' speed and depth, and ofcourse make it start and stop, and put in suggestions from customers, like making the start-stop buttons' led blinking in sync with the fans swivelling. 
Apart from the motors' computer, we added a board filled with software to the controlpanel. You won't believe all that is happening when you press the start button to make the fans move. Even more is happening when you change the depth or speed.

Think of that next time you press the start button.

Stay tuned.

Read 1583 times Last modified on Wednesday, 10 January 2018 12:00