Hi Pyramid.
I assembled two amplifier boards and tested with both BLWR and BLWS motors. BLWS motor is slightly quieter and both motors produce more than enough torque to drive 20kg stainless steel platter.
Currently I am using BLWS motor and it works great. I did not have time to compare it to SG4/PAPST ac drive yet but I can tell that BLWS motor is quieter than PAPST.
One question... I think I followed your set up instructions exactly but the lowest reading that I was able to obtain at TP1 was about 20mV AC on true RMS DMM.
Is 20mV low enough or am I doing something wrong?
Thanks!
I assembled two amplifier boards and tested with both BLWR and BLWS motors. BLWS motor is slightly quieter and both motors produce more than enough torque to drive 20kg stainless steel platter.
Currently I am using BLWS motor and it works great. I did not have time to compare it to SG4/PAPST ac drive yet but I can tell that BLWS motor is quieter than PAPST.
One question... I think I followed your set up instructions exactly but the lowest reading that I was able to obtain at TP1 was about 20mV AC on true RMS DMM.
Is 20mV low enough or am I doing something wrong?
Thanks!
With BLWS motor there is barely detectable cogging so one would easily say there is none.
Stator core is made of stacked silicon steel laminations and there are small gaps between adjacent poles. Therefore, permanent magnet rotor will get 'caught' between two poles but this drag is so low that you can barely feel it. BLWR motor is not as smooth as BLWS but they are both excellent.
PAPST rotor feels a bit smooter than BLWS and I would expect this due to a flywheel effect of the large and heavy PAPST rotor. Besides that, absence of gaps and permanent magnet rotor eliminates coghing all together.
I am familiar with PAPST motors and I did some pretty crazy things with those, such as replacing sintered bronze sleeves with ABEC5 bearings, made a new stainless frame with adjustable thrust plate, etc.
Ball bearings in PAPST motor made it considerably noisier. PAPST shaft is precision ground to 6mm OD and all the bearings I cound find were only only 'slip fit' so I cound not preload them. I did not give up yet but I have to find a way to preload those bearings. Adjustable thrust plate made it possible to control/eliminate axial play.
Stator core is made of stacked silicon steel laminations and there are small gaps between adjacent poles. Therefore, permanent magnet rotor will get 'caught' between two poles but this drag is so low that you can barely feel it. BLWR motor is not as smooth as BLWS but they are both excellent.
PAPST rotor feels a bit smooter than BLWS and I would expect this due to a flywheel effect of the large and heavy PAPST rotor. Besides that, absence of gaps and permanent magnet rotor eliminates coghing all together.
I am familiar with PAPST motors and I did some pretty crazy things with those, such as replacing sintered bronze sleeves with ABEC5 bearings, made a new stainless frame with adjustable thrust plate, etc.
Ball bearings in PAPST motor made it considerably noisier. PAPST shaft is precision ground to 6mm OD and all the bearings I cound find were only only 'slip fit' so I cound not preload them. I did not give up yet but I have to find a way to preload those bearings. Adjustable thrust plate made it possible to control/eliminate axial play.
20mV is typical. What you are reading most likely is 3rd harmonic distortion and noise. If the drive is putting out 4.5VRMS, that's -47dB down. The reading will never hit zero; 20mV is fine.
My PAPST motor is connected as single phase, with two 2.2uF capacitors paralleled, and it runs very smooth. I could possibly get it to run smoother if I optimize capacitor value instead of using off-the-shelf capacitors with +/_ 10% tollerance.
If I hold BLWS motor in my hand I can barely feel that it's running - It feels as smooth as PAPST.
Let's not forget that PAPST heavy and large diameter rotor spins at 1800 rpm. Gyroscopic effect definitely 'stabilizes' it so it feels steady in your hand. In case of a small diameter rotor spinning at 600rpm (BLWS/R rotor) gyroscopic effect is much lower.
The AA motor has a relatively small mass; if you bolt it to a motor housing or even a metal plate that can sink some of the remaining very small vibrations, it will quiet down even further. Even holding it tightly against a butcher block bench top will see an improvement. I filled my motor housing cavity with lead shot and its completely still when spinning.
You are not getting the most from the Papst motor running single phase and capacitor. It runs much smoother on 3 phase, has much more torque, and runs cooler too. An apples to apples comparison with both motors running 3 phase would be helpful.
twystd
I posted this pic in the motor thread already, but I figured since there was a discussion here about motor weight, vibration and damping I would chime in with a little more info.
My motor housing was made from 1/2" wall 4" diameter aluminum pipe with 5/16" aluminum plate to cap the ends. The total height of the housing is just over 4" with a 3.5" tall cavity. I used the smallest diameter lead shot I could easily source (#9) to fill it once it was complete.
The only other items I added to the assembly was the XLR connector and a small plate of aluminum that is bolted across the bottom of my BLWS motor using longer hall sensor mounting screws so as to prevent the lead shot from possibly entering the motor or binding against the bottom of the motor shaft.
I was able to achieve a total weight of the motor assembly that is just under 8 lbs.
My motor housing was made from 1/2" wall 4" diameter aluminum pipe with 5/16" aluminum plate to cap the ends. The total height of the housing is just over 4" with a 3.5" tall cavity. I used the smallest diameter lead shot I could easily source (#9) to fill it once it was complete.
The only other items I added to the assembly was the XLR connector and a small plate of aluminum that is bolted across the bottom of my BLWS motor using longer hall sensor mounting screws so as to prevent the lead shot from possibly entering the motor or binding against the bottom of the motor shaft.
I was able to achieve a total weight of the motor assembly that is just under 8 lbs.
Attachments
Yes, I have several available. They are not OSH Park (green, not purple), but mine built up fine and works.
Regards,
Russell
Pyramid,
My controller / amp / motor combo is working perfectly! Thanks for all of your time put into this project. I can't wait to finish mounting everything into an enclosure. I'm planning on replacing C21 with a Nichicon URS1E102MHD to lower the total height to get it into an enclosure that will fit under my turntable. It's 15 mm tall instead of 30 mm (12.5 mm wide). I will probably also be looking into having one of the round motor housings built as well.
Thanks again!
My controller / amp / motor combo is working perfectly! Thanks for all of your time put into this project. I can't wait to finish mounting everything into an enclosure. I'm planning on replacing C21 with a Nichicon URS1E102MHD to lower the total height to get it into an enclosure that will fit under my turntable. It's 15 mm tall instead of 30 mm (12.5 mm wide). I will probably also be looking into having one of the round motor housings built as well.
Thanks again!