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Old 17th July 2012, 03:44 AM   #11
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Quote:
Originally Posted by Nanook View Post
7.5 degree steppers...
Hi,Nanook
My stepper motor kit's type is VEXTA PMD03C+PMM33A2-C11,5 poles,0.72 degree every step,the top speed can be 3000 rpm.I tested it with square wave,it worked smoothly and strong.The only problem is the noise need to be isolated by a sealed metal box.One more motor can improve the operating stability.My next modification is on the base ,not the motor.

I'm using a part of top plate to fix motor,the plate is too thin and light to damp motor vibration.I will rebuilt the base referencing bear's and yours suggestion.
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Old 17th July 2012, 06:00 AM   #12
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Originally Posted by dtut View Post
EB,



A mechanics' stethoscope will help you detect and trace noise. Take the belt off and just run the motor. Spin the platter. Put the belt back on and run the platter with the motor. Do you hear anything any any stage?

Did you clean and polish the platter shaft and bearing walls? Did you check/replace the ball bearing at the bottom of the well? Any wear or dirt can be audible.
Dtut, nice to see your helpful replay again.Stethoscope is an useful tool to trace noise,I'll try it.I run the motor without belt and put stylus on vinylís blank track,the amplified vibration noise is a bit obvious.If running with belt, the noise will be louder and mixing with tracking noise because the motor vibration increased on load.Maybe I select wrong material to build the base,the plywood's density is too small to get enough mass damping vibration.

This TT kit is new and in good storage condition, basically no corrosion,no oxides and no aging on rubber units .I added some lubricating oil in platter shaft and all bearings.The motor run smoothly and silently,and I can feel the vibration while hand holding it.The vibration is higher than stepper motor.The placed platter can keep running for more than 2 minutes if turned by hand.


The pulley sharp was ignored,I will re-machine it,thank you for this key point. I am very happy to discuss TT and LTT DIY with you,I will show some playing video if the noisy is completely removed.

-----eagle bear
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Old 17th July 2012, 07:13 AM   #13
miklos is offline miklos  Canada
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"7.5 degree steppers are essentially 48 pole AC synchronous motors when driven by a PWM signal or a sine/cosine wave pair. See: Altmann DIY Turntable for some details.Using the small low power steppers is superior to using an industrial (square flanged) stepper. Need more power? Add a motor or two..."

Interesting, thanks. I will try this, but what is the advantage to use a micro stepper over a traditional sync motor running on 50/60Hz? Or a DC servo motor salvaged from an old cassette player.
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Old 17th July 2012, 12:27 PM   #14
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eaglebear, sand is a way to add mass to an object, like filling the bottom of a can or box... the sand I was talking about is a base or platform that the entire setup sits on top of. A big tray filled with sand, on top of which you place a flat surface, and on top of that goes your turntable... Now, you can separate the motor from the turntable itself by making it sit on a separate smaller platform on top of the sand. This gives excellent isolation.

For example, the smaller platform for the motor could be a 1" thick piece of steel, say 6" or so diameter (for mass and stability) or just wood, but with a heavy box or can that is even sand filled that holds the motor.

Hope this description is clear enough?

Seems to me that Nanook said that square wave driven steppers are not such a good idea - drive with sinewaves, to eliminate the noise issue... that's what he said.

The simpler sinewave two phase drive system can be built with less trouble, and Altman suggests using a computer with a sound editing program to produce sinewaves of some exact frequency and exact phase shift. You output that line level signal to some little audio amplifier to driver the stepper motor with power... a bit of a kludge, but you could just dump that file to a silly cheapo MP3 player and use a cheap little commercial class D amp and have it all running perfectly in a tiny space and at low cost...

I think I know how to do this even more simply but I have to do some research and look for a particular chip that is intended for other duties that I seem to recall existing. One would still need a stable sinewave source at the right frequency...

Hmmm... glad I read this thread!

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Old 17th July 2012, 01:08 PM   #15
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The requirements for such motor beside the steady speed are the noiseless , vibration less operation. Both can be had in a simple 120 or 220V synchronous motor. Problem arises only if the AC line frequency is not stable, which is not the case in Europe or here in N.America.
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Old 17th July 2012, 03:26 PM   #16
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True, but they tend to have less torque, or so I am let to believe - although I suppose one can find synchronous motors in larger sizes, the typical small clock motor size are a bit anemic, yes?

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Old 17th July 2012, 04:46 PM   #17
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Yes. Only good for clocks.
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Old 18th July 2012, 04:08 AM   #18
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bear,thank you for your detail description,I got it!
miklos,normally the stepper motor's torque is far largger than ac motor in same size,and driving frequency is higher,so the sympathetic viberation frequency is higher also and need lower mass base for damping.Another advantage is the control precision.Dc servo motor is not blushless,the operating life and EMC have to be concidered.
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Old 19th July 2012, 01:16 AM   #19
Nanook is offline Nanook  Canada
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Default advantage of a 7.5 degree stepper...

Quote:
Originally Posted by miklos View Post
Interesting, thanks. I will try this, but what is the advantage to use a micro stepper over a traditional sync motor running on 50/60Hz? Or a DC servo motor salvaged from an old cassette player.
... is I think the available at very low prices. I paid $2 ea. for a half dozen...

... and are easy to control. Just use items recommended for 50 or 60 Hz operation and you're set (the signal frequency can be varied for use as a speed control). The benefit is that the speed can be tightly controlled and varied so that if there is a mismatch between the platter and the pulley/motor, there is an adjustment that can be made. I would also recommend the use of a laser tachometer to verify the accuracy of the speed. The closest I get to a 33 1/3 RPM reading on my Oracle is to within .01 RPM (33.34 RPM, which I can live with), so accuracy is +/-.005 RPM or about .015%. Try measuring that accuracy with anything else except a frequency counter and a test record. I'd also suggest testing the speed while playing a record if using a laser tach.

EB: "True, but they tend to have less torque, or so I am let to believe - although I suppose one can find synchronous motors in larger sizes, the typical small clock motor size are a bit anemic, yes? "

The ones I found were used in a photocopier (IIRC), not a clock.
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Old 19th July 2012, 02:42 AM   #20
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What job did the synchronous motor do in the photocopier - and what size and vintage photocopier?

Thinking about seeking some...

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