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3 Phase Class D amp for DIY BLDC motor Drive
3 Phase Class D amp for DIY BLDC motor Drive
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Old 22nd November 2017, 12:37 PM   #261
coolmaster is offline coolmaster
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Quote:
Originally Posted by Pyramid View Post
The angle of the grooves shouldn't make any difference in speed, except for how they affect the depth.

You said you followed the same diameter as the previous (VPI factory) pulley? Did the pulley have both 33 and 45 RPM spindles, or was it only 33? If it was 33/45, the spindles are tapered for coarse speed adjustment so the diameter at the top will be undersized and the diameter at the bottom of the 33 spindle will be oversized. If you measured at the top, that would account for your slower speed.
Hi Bill,
Its the original VPI 33/45 stepped pulley that I modeled the new only for only 33rpm with multiple belts if needed.
I agree the diameter would affect the resultant speed. OTH, I read somewhere claiming a different groove angle on a consistent pulley diameter would change the speed incrementally pointing how the stepped VPI pulley works. I don't know if this is true.

Yes, I used the same measurement on the top and replicated that on the new pulley. I didn't realise the possibility of an incremental measurement further down each step. This being a first, I didn't realise the importance of "tapered pulley" but believed it was a different groove angle on each step that gave user option to vary accordingly.
Guess its back to the drawing board and I measure again the 2nd or 3rd step diameter and analyze where I've missed or gone wrong. Lastly I'm retaining the use of the original VPI belt which is about 2mm thickness.
A 2nd test with a loaned speed controller revealed increasing to another 0.33hz to get it correct.

Thank you for your prompt response,
Lee
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Old 22nd November 2017, 04:14 PM   #262
coolmaster is offline coolmaster
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Update:
Further to investigating of causes why its off the mark
1) I brought out to use a more accurate Micrometer screw caliper (which I failed to use) and measured each step on the original pulley. It measures 0.754", 0.755" and 0.756". The new pulley measures 0.7535 thereabout. I had used the top diameter and measured with an ordinary digital Vernier caliper. My Mm caliper revealed more exacting measurements during the comparison. I see the problem now.
2) I stuck a piece of 3M transparent tape around the new pulley to see a possible effect of change, increasing the diameter by 0.004", fitted the pulley and measured the platter RPM, now it checks out at 33.4rpm which is closer to ideal.
3)I reckon its back to the machine shop to have one made at 0.7555" diameter and maintain everything else.
4)This is scary! Am tackling very close tolerances to obtain the right speed. I hope the machine shop can turn one out to my expectation.
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Old 22nd November 2017, 06:04 PM   #263
Pyramid is offline Pyramid  United States
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This is why we use a variable frequency drive (that and the wall power is only accurate when averaged over a long period of time).
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Old 17th December 2017, 07:10 AM   #264
InSides is offline InSides
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I was able to finally get the motors (BLWR) after a lot of going back and forth with AA - ultimately had to have a friend get them from AA and ship them over - I take it AA have a lot of large orders and are not that willing to accommodate individual purchasers that their online system will not accommodate.

@Pyramid, your efforts are much appreciated - both in offering this project and communicating with AA.

That said, back to the business of motors and pulleys - attached here is one of the failed attempts at a pulley (*). It is made of Delrin with a bronze hub, and, even though we have tried numerous times, cannot machine a satisfactory ID of 4mm with the bronze hub - using both (1) multiple precision reamers and (2) grinding rods.

(*) The photo is crap, but it was the best I could do with limited camera options, and the pulley being white.

Thought the issue might be with the motor shaft, but both motors, measured with a precision Mitutoyo micrometer, are well within the spec published by AA.

As a last ditch effort, we machined a pulley from Delrin without the bronze hub, same procedure as tools as earlier, and achieved an interference fit. Further testing at a range of 200 - 2800 rpm revealed a runout of ~0.005mm.

This pulley is a bit different that the ones presented here due to the design of my turntable and experimentation with a minuscule flywheel effect. The diameter of the belt area (working pulley diameter) is 16mm, for a 1:20 drive with my 320mm platter.

After all this, I can understand how machine shops have difficulties providing satisfactory results over a larger run of pulleys without dry fitting against each motor. The SDP-SI pulleys might be a very good option for both BLWR and BLWS motors - but I have been unwilling to pay the shipping premium to test that hypothesis.

On to building the electronics now - so another question to @Pyramid - I have asked earlier about the possibility of stacking the boards for a compact enclosure - apparently that is doable.

However, I failed to note the height of the C21 capacitor on the MA-3D board. @rsritchey had asked earlier about an alternate capacitor due to similar reasons here:

3 Phase Class D amp for DIY BLDC motor Drive

My specific question is two-part:

1. Is there a replacement you would suggest here that would come out at a lower height (not more than say 15mm?)

2. Alternatively, can one mount C21 off-board at an angle (with longer leads, of course) - could that cause circuit stability issues?

Option #2 is preferable unless it compromises functionality.

Again, much appreciated for an excellent gift to the DIY community.
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File Type: jpg pulley_pom_bronze.jpg (87.9 KB, 219 views)
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Old 17th December 2017, 12:31 PM   #265
Pyramid is offline Pyramid  United States
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Quote:
Originally Posted by InSides View Post
My specific question is two-part:

1. Is there a replacement you would suggest here that would come out at a lower height (not more than say 15mm?)

2. Alternatively, can one mount C21 off-board at an angle (with longer leads, of course) - could that cause circuit stability issues?

Option #2 is preferable unless it compromises functionality.
Option #2 will work. C21 is a reservoir cap; there are 0.1uFd caps on each supply pin of the amplifier chips for stability. You can mount the cap on the back side of the board (observing the proper polarity arrangement) and bend the leads at right angles to mount the part flat.

You could also try a short cap with the same lead spacing mounted on the top side of the PCB. You can reduce the value somewhat (use the same voltage rating though), but I would keep the value as high as possible and definitely don't go below 100uFd.
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Old 17th December 2017, 05:32 PM   #266
force of 1/2 is offline force of 1/2  United States
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Quote:
Originally Posted by InSides View Post
That said, back to the business of motors and pulleys...

...After all this, I can understand how machine shops have difficulties providing satisfactory results over a larger run of pulleys without dry fitting against each motor. The SDP-SI pulleys might be a very good option for both BLWR and BLWS motors - but I have been unwilling to pay the shipping premium to test that hypothesis.
I'm not sure why one would need a brass insert in this application. The torque needed to start and drive a turntable platter isn't high enough to necessitate a grub-screw fixing. I found, personally, that with both tight-grained wood like maple, or Delrin/Acetal an interference fit is more than adequate (one needs only to drill a hole the exact size of the shaft, and the fit is perfect.) And machining for an interference fit is much easier; allowing me to get a passable pulley with only a drill press, table saw, and the motor itself as a lathe to do the final shaping and polishing.

That said, the SDP-SI pulleys with brass or aluminum inserts are quite nice and run true (I ordered a couple). But, unfortunately, their flat-belt pulleys don't have upper or lower belt guides, so the belt just falls right off. If using a round O-ring style belt, their pulleys are great--and a bargain.

I have really been enjoying my set-up with the BLWS motor, and homemade pulley. Pyramid's controller is a real treat!
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Old 17th December 2017, 08:28 PM   #267
InSides is offline InSides
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Quote:
Originally Posted by Pyramid View Post
Option #2 will work. C21 is a reservoir cap; there are 0.1uFd caps on each supply pin of the amplifier chips for stability. You can mount the cap on the back side of the board (observing the proper polarity arrangement) and bend the leads at right angles to mount the part flat.
Much appreciated!
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Old 17th December 2017, 08:31 PM   #268
InSides is offline InSides
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Quote:
Originally Posted by force of 1/2 View Post
I'm not sure why one would need a brass insert in this application.
Based on the SDP-SI pulleys, I thought it would be a good idea. It might have been one, of course - but we haven't yet managed to make it work.

And as you stated - for this application is probably not needed.
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Old 2nd January 2018, 09:21 PM   #269
jobst is offline jobst  New Zealand
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Has anyone else had issues with electrical noise coming from the MA-3D / SG-4 combination? I'm getting a hum that only starts when the MA-3D is plugged in, and gets worse when the motor is actually started.

I don't have an enclosure for the motor control boards (or the motor), nor is any of it grounded. There is good physical separation- all the motor bits sit on one side of the platter, and the tonearm, preamp, and amp on the other. Each side is plugged into different outlets (though not different circuits).

The tonearm is probably quite susceptible to acting like an antenna- it's based on the Altmann design, with no shielding.

Do I need to do something to ground the motor side components? Or would an enclosure for the motor control boards be a better place to start? Or is my time better spent looking at the tonearm wiring first?
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Old 3rd January 2018, 05:19 PM   #270
coolmaster is offline coolmaster
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Originally Posted by jobst View Post
The tonearm is probably quite susceptible to acting like an antenna- it's based on the Altmann design, with no shielding.
Hello,
You must shield to ground any exposed tonearm wires which run along the tonearm wand to the RCA. These wires are sensitive enough even if its through a non metallic wand to pickup external interference or EMI noise. Twist each pair separately and shield them all as much as possible.
Lee
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