Project: Avenger Rim drive with BLDC motors & Class AB Amp

Project: Avenger Rim drive with BLDC motors & Class AB Amp

Postby vienna acoustics » Thu Apr 30, 2020 10:44 am

Being extremely happy with the performance of my Avenger Reference with the Kuzma 4P and Phoenix Engineering Roadrunner and Eagle (which i was very lucky to find in the market as NOS) I took the initative to call Bill Carlin and discuss with him my idea for a RIM Drive with BLDC low noise/high Torque frequency controlled motors.

I could have opted for the SOTA motor and Condor, since the torque is more than enough for my Avenger, but I would miss the RIM drive sound which I really enjoy.
Bill was very kind not only to accept the challenge but take it further, by counter proposing, that he would design and build two amplifiers, to drive the BLDC rim drive, a Class A and a Class D, amplifier for me to try and see which I would like most. Both would be fed through my ultra low noise linear KECES P8 power supply. The pulleys would also need to be re-designed to fit the 4mm motors' shafts and eventually a set made of Aluminum and another made of Delrin were fabricated.

A VPI RIM drive was purchased from Music Direct and was delivered to Bill for the modification.
After many weeks of work, yesterday evening Bill advised that everything was ready and shipped.
In due course I will write more details about the realisation of this project and as soon as I will receive the shipment I will revert with my sound experience and the eventual comparison between the Hurst Rim Drive and the BLDC Rim Drive driven by a Class A and a Class D amplifier.

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Last edited by vienna acoustics on Thu May 14, 2020 2:21 am, edited 6 times in total.
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Re: New project: RIM drive with BLDC motors and Class A amp

Postby Brf » Thu Apr 30, 2020 10:48 am

Very nice! Looking forward to your thoughts, although I have a very good idea of the outcome! Keep us posted.
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Re: New project: RIM drive with BLDC motors and Class A amp

Postby Dorian » Thu Apr 30, 2020 4:20 pm

Great project Vienna, looking forward to hearing the results!
VPI Prime & Outer Ring| SoundSmith MIMC Star | Herron VTPH-2A | Primaluna DiaLogue Premium HP Integrated | KEF Reference 1 | SOTA Condor & Roadrunner | Audio Sensibility Cables | Symposium Ultra | AQ Niagara 1000 | Stillpoints LPI | Focal Clear
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Re: New project: RIM drive with BLDC motors and Class A amp

Postby vienna acoustics » Fri May 01, 2020 1:31 am

Bill Carlin a genius in electronics, had long ago identified the importance of the turntable motor and the precise stable speed. He has invested to this direction endless personal time and resources. His achievements are a result of his sharp mind, his electrical, electronics and mechanical skills as well as of his sophisticated engineering way of thinking.

This project reflects the importance of a precise and accurate turntable drive. The platter, plinth and bearing are important too, but the motor is more important due to the fact that it’s the only active element. As such it has the most demanding job.

For the specific project, Anaheim automation motors were decided to be used for the BLDC RIM drive. These motors are known for their smooth operation, low vibration and noise as well as for their high torque.

The dilemma was between BLWR172S-24V-2000 and BLWS231S-24-2000.
The BLWR was chosen as it features twice as many poles so it runs slower at the same frequency as the BLWS.

At the photo below the BLWR motor is at the left and the hurst at the right

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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sat May 02, 2020 9:24 am

The class AB amplifier and the controller were built first.
It was seen that excessive heat was generated thus a larger enclosure and an external heat-sink should be incorporated.
The chip amp that Bill is using is ~90% efficient vs <40% for the class AB therefore it is consuming much less power and run cooler. That doesn't sound like that much difference (2.25x) but the class AB amp will dissipate 6x the power as the class D (as heat).

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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sat May 02, 2020 11:31 pm

With the heat problem of the Class AB amplifier solved, the class D amplifier was then fabricated. As expected the later is running much cooler.

The VPI Rim drive had to be modified to accommodate the new BLDC motors. Bill took a shot at the plunge cuts in his woodworking/machine shop; one of his concerns was if he took it to a machine shop, they would most likely use a milling machine which means clamping and possibly damaging the outside of the enclosure. Bill has a small bench top milling machine, but nothing that would do 45mm. He made a template in CorelDraw and was able to determine that a 1 3/4" hole saw would clear the inside wall of the bottom void so he was able to make the necessary cuts on his drill press. He had coated the outside of the motor assembly with masking tape to prevent chips or spirals coming off the drill from scoring are marring the surface and to prevent scratches while handling the heavy enclosure. He also kept the amount of cutting oil to a minimum, just enough to keep the bit from chattering while it made the cut.

The holes are fairly clean, but not as smooth as a milling machine could make, although they are inside and will never be seen. That it was the difficult part completed. Bill fabricated then, the new top plates for mounting the motors. Finally he made autocad drawings and the new pulleys were fabricated too from aluminum. This process was a demanding as Bill wanted a snug dry fit.

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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sat May 02, 2020 11:38 pm

The RIM’s enclosure completed modification:

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The new, 3 phase brushless (BLDC) BLWR172S-24V-2000 motors with the new mounting plates completed:

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Off topic:
At that time Bill completed his Nixie tube display for turntables’ tachometer as an alternative to the LCD, a project that he has generously shared to the DIYaudio community. It’s DIY project for non-commercial use. I think that Nixie is a beauty

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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sun May 03, 2020 9:24 am

The new motors’ shafts are longer and of different size thus new pulleys should be fabricated.
This project would only make sense if the pulleys would be precisely made too.
I had read in the past that besides the precise fabrication, the pulley mass is critical too.
The higher the mass (weight) the smoother the pulley will run. Moment of inertia J = 1/2 mass radius square. The higher the moment of inertia the higher the rotational energy W = 1/2 moment of inertia (2 pi frequency) square. The rotational energy squares with pulley radius (at a given mass) and with motor frequency.
Therefore a not too heavy metal would make a better pulley, this is the reason we went for aluminum pulleys.

Bill made the CAD 3D drawings which were sent to me by email and Solid Edge in Greece fabricated them with CNC

During this process I tried some different metals with my existing Hurst rim drive and saw that every different material will sound differently. The most stable and relaxed sound was experienced with aluminum.

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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby edw » Sun May 03, 2020 2:29 pm

Outstanding. While I don't have a rim drive, I am seriously considering the BLDC motor for the std Prime motor pod to lessen the noise measured from it.
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby powermatic » Tue May 05, 2020 3:36 pm

Wow, fantastic project. Really looking forward to watching this play out. Curious, is your newly machined pulley the same o.d. and groove size as the HR-X pulley, but with a .25" shaft through-hole?
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