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

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

Postby vienna acoustics » Tue May 05, 2020 10:40 pm

The BLDC rim drive along with the new controller and AB class and Class D amplifiers were delivered yesterday.
However I had to stay at the office until late so I didn’t have the time to install them.

Bill has advised that the voids around the motors are filled with lead shot. He has also advised that the motor voids are sealed off, so there should be no way for any of the lead shot to escape. The voids are filled to the top with lead and do not make any noise if shaken.

I am thinking that it would be a good idea to measure the vibration/noise levels of the BLDC vs Hurst rim drive first before the first auditioning of the BLDC rim drive.
!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby Mr_Putty » Wed May 06, 2020 5:39 pm

[quote="vienna acoustics"]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.

Interesting. To me this implies that a round metal disc could be applied to the top or bottom of a plastic motor pulley to get similar results (at 33rpm). I have tried adding an O-ring to the 45 rpm groove of a Prime two-speed pulley while using 33rpm belts in their grooves. There was an audible difference, but I have since abandoned the O-ring. I think the O-ring had too much flex or had its own vibration problem. Any suggestions for the dimensions to try if a disc were made of Al or stainless or another material?
Good luck with your project,
JTA
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Wed May 06, 2020 11:16 pm

Mr_Putty wrote:
vienna acoustics wrote: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.

Interesting. To me this implies that a round metal disc could be applied to the top or bottom of a plastic motor pulley to get similar results (at 33rpm). I have tried adding an O-ring to the 45 rpm groove of a Prime two-speed pulley while using 33rpm belts in their grooves. There was an audible difference, but I have since abandoned the O-ring. I think the O-ring had too much flex or had its own vibration problem. Any suggestions for the dimensions to try if a disc were made of Al or stainless or another material?
Good luck with your project,
JTA



Hi Mr. Putty

The disc diameter depends on your platter size and your motor rpm

The formula to calculate the pulley (or disc) diameter in mm is :

[Pulley diameter+ belt thickness] (in mm )=[platter rpm (45 or 33.333333333...) x (platter diameter+Belt thickness) ]/ motor rpm

But the disc should be precisely fabricated, of enough thickness (mass is critical) and must be balanced. The precisely bored center hole should also have a snag dry fit to avoid rotating unbalance or eccentricity issues thus unstable speed and noise.
!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby Mr_Putty » Thu May 07, 2020 12:29 pm

Thanks VA,
I need to put this on my list of projects to do!
JTA
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Thu May 07, 2020 12:45 pm

Being very busy with the business these days, I didn’t have the time to test the new BLDC drive however I managed to measure the noise and vibration levels side by side with the hurst rim drive....

The measured BLDC rim drive’s noise and vibration are tremendously lower compared to the Hurst Rim Drive.

More details and measurements photos will follow during the coming weekend.
!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Fri May 08, 2020 1:45 pm

The vibration measurements results. It seems that Hurst measured vibrations are double compared to BLDC. In addition there are resonances present at the Hurst rim drive:

HURST Motors RIM Drive :

354E9FBE-A375-4E57-A492-A55C14BE0EDD.jpeg
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The BLDC motors Rim Drive:

ADA90E00-F286-42F8-B6DE-47C38E897D32.jpeg
ADA90E00-F286-42F8-B6DE-47C38E897D32.jpeg (711.96 KiB) Viewed 733 times


the new BLDC rim drive :

2B629328-0400-4F66-B102-5B00071593C0.jpeg
2B629328-0400-4F66-B102-5B00071593C0.jpeg (2.5 MiB) Viewed 733 times


FCCECDA3-5215-4568-B611-7E4F6A524212.jpeg
FCCECDA3-5215-4568-B611-7E4F6A524212.jpeg (2.01 MiB) Viewed 733 times
!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sat May 09, 2020 6:04 am

The BLDC rim drive underwent the Si3N4 and sapphire glass upgrade, some mass was also added and the rim drive is now weighting 11.8 kilos (26 lbs). After some hours of running the vibration measurements are slightly improved and some harmonics which were measured before (48Hz and 0.78 Hz ) disappeared.

2034D485-7821-4A26-A923-43A9E30DCBCE.jpeg
2034D485-7821-4A26-A923-43A9E30DCBCE.jpeg (787.77 KiB) Viewed 682 times


this evening i will have the first critical listening
!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby Brf » Sat May 09, 2020 7:24 am

Nicely done and thanks for documenting your journey. Looking forward to your listening impressions.
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby vienna acoustics » Sat May 09, 2020 10:10 am

Thank you Brent.

When the BLDC Drive is started is absolutely silent.
I am convinced that the BLDC rim drive is a milestone for my system, Bill Carlin has really succeeded to elevate my turntable into new unprecedented performance levels. Acoustically this modification has a made a real, huge and clear difference, as expected, from the earlier vibration measurements.
I am not speaking about a mere improvement but for an enormously magnificent sonic upgrade and a completely new experience.
My Avenger has now the absolute torque, fuller sound, the blackest background, dynamics, details and realism. The music is enriched with more octaves and I feel that a thick veil is lifted.

Despite their difficulties, I am a big fan of rim drives and their sound; and I do believe that this BLDC Drive is very special.

35B1C2A9-0FC9-494B-80EB-B4C0B0A4B18F.jpeg
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!
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Re: New project: RIM drive with BLDC motors & Class ABamp

Postby tony22 » Sat May 09, 2020 2:51 pm

Vienna, congratulations on what sounds like a great improvement. Did you do the bearing, sapphire, and increased mass work on the rim drive yourself, or did Bill do it as part of the total effort?
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