Platter and bearing sources besides Teres and Scheu?

meby · « **on:** 28 Mar 2005, 05:13 pm »

I am contemplating building a new turntable and looking for a source for platter and bearing that is cheaper than Teres but good quality. I am having a hard time to get Chris Feickert of Scheu to respond to questions, so I am hesitant to purchase from Germany with such poor response.
Any Ideas?
Mike

beat · « **Reply #1 on:** 10 Apr 2005, 03:25 pm »

Hey Mike,
Whatcha going to use for a motor? That is the one I am having trouble with. I'm getting to the end of this platter/bearing prototype I have been working on so I'll keep you posted. Are you interested in a 2, 3, or 4 inch platter? I've been focusing on the 3 for myself but anything is possible. Currently, I am just waiting on some lubricant/damping samples.
thanks, beat

meby · « **Reply #2 on:** 10 Apr 2005, 06:27 pm »

I was thinking the Teres because of the speed control, but for $500 I was think of buying a Milling machine and building the case myself and just getting the board from somewhere. I was thinking 3" platter as 4'' might be too much damping. I am also researching a mini-lathe and building the bearing myself for the experience and for fun.

dr_minky · « **Reply #3 on:** 18 Apr 2005, 08:09 am »

Hey, I have been having a hard time getting chris to respond to my questions too! I've shot him 3 emails over the last month about buying a new motor from him and nada in return! Maybe there's something wrong with his email still?

..In the meantime, I'm left with no motor for my tt!

aLL dIgiTaL aNd nO VinYL mAkeS MinKY A DulL duLL BoY!

dr_minky · « **Reply #4 on:** 18 Apr 2005, 08:30 am »

Hey, I have been having a hard time getting chris to respond to my questions too! I've shot him 3 emails over the last month about buying a new motor from him and nada in return! Maybe there's something wrong with his email still?

..In the meantime, I'm left with no motor for my tt!

aLL dIgiTaL aNd nO VinYL mAkeS MinKY A DulL duLL BoY!

AKSA · « **Reply #5 on:** 18 Apr 2005, 11:22 am »

What would be wrong with using a stepper motor? With 400 steps to the rev, and careful software instructions to ramp each pulse, it should be possible to get a stepper to rotate incredibly smoothly........

Cheers,

Hugh

beat · « **Reply #6 on:** 18 Apr 2005, 04:31 pm »

Quote from: AKSA

What would be wrong with using a stepper motor? With 400 steps to the rev, and careful software instructions to ramp each pulse, it should be possible to get a stepper to rotate incredibly smoothly........

Cheers,

Hugh

Hugh,
Please tell us more about these motors! I'm down to give it a shot.
thanks,
beat

meby · « **Reply #7 on:** 18 Apr 2005, 05:00 pm »

Beat,
How is that bearing coming along?

meby · « **Reply #8 on:** 18 Apr 2005, 05:01 pm »

Beat,
How is that bearing coming along?

dr_minky · « **Reply #9 on:** 18 Apr 2005, 11:02 pm »

Quote from: beat

Quote from: AKSA
What would be wrong with using a stepper motor? With 400 steps to the rev, and careful software instructions to ramp each pulse, it should be possible to get a stepper to rotate incredibly smoothly........

Cheers,

Hugh

Hugh,
Please tell us more about these motors! I'm down to give it a shot.
thanks,
beat

yes please, I'm interested to!

beat · « **Reply #10 on:** 19 Apr 2005, 03:26 am »

Quote from: meby

Beat,
How is that bearing coming along?

Hey Meby,
so far so good. I'm just waiting for some machine work to get back to me. It is probably a couple weeks out. I will let you know when they come in and how this batch performs. For the two inch platter you want, are you ok with it being 13" across? That is how I think I will spec this out figuring that the more rotating mass the better. I'm going to experiment with different lubes/dampening liquids for the bearing so I'll keep you posted as my findings progress.

peace, beat

AKSA · « **Reply #11 on:** 19 Apr 2005, 10:28 am »

Steppers are widely used in robotics, even in fuel injection systems in auto engines. They are brushless, can be had with as little as 0.9 degree steps, 400 to the revolution. They have much more torque than DC motors, typically create 10-20 times the detent torque in operation, and because they move in incremental steps - which can be made continuous, giving constant speed rotation indefinitely - they are much smoother than conventional AC or DC motors which have a limited number of poles and thus 'cog' badly.

Let's do the math. If you have a turntable speed of 33 1/3 rpm, and a 15:1 speed reduction on the drive, then your stepper should rotate at 500 rpm exactly. With 0.9 degree steps, this is 200K steps each minute, and if each step delivers a sharp pulse to the drive system, the number of steps per revolution of the platter is very high - namely 6000. The more pulses, then the less is the rotational inertia requirement to iron them out - so it has the potential of being very, very smooth.

The last advantage is speed control. You control a stepper motor by switching current pulses across the coils in quick succession, and this is normally done with a software driven microprocessor, which is often crystal controlled. This gives accuracy of up to 12 ppm, pretty good for a platter, I'd say...... The drive would need to generate a pulse train, switched of course, of 3.33333KHz - chicken feed for a microprocessor which can run at up to 16MHz like the Atmels.

Hope this gives you a few ideas. Google 'Stepper Motors', there are quite a few good sites which discuss their control in detail. Then take a look at http://www.alltronics.com and marvel at how cheap they are!

Cheers,

Hugh

beat · « **Reply #12 on:** 19 Apr 2005, 03:44 pm »

Awesome Hugh,
I have been looking at something like that at the surplus store here. I didn't know how to get it to work though. How would you go about finding one with enough strength to spin a 25lb platter?

thanks again,
beat

AKSA · « **Reply #13 on:** 19 Apr 2005, 09:59 pm »

Beat,

I have to withdraw a little here; I've not been through the production process, so can't comment much further.

Even at 15:1 step down, it's tough to crank up a 25 lb platter, so you need to ramp up the stepper by driving it slowly at first, then bringing it up to speed in a few seconds. It's all doable, though the software would be quite involved. You'd need a stepper with at least 7 oz.in of torque, this would become 6.56 lb/in after gearing, which is not sufficient to bring up a 25 lb platter in less than about five seconds, but a cheap fix might be to use a rubber wheel on the platter with low rubbing force, so it could slip as speed builds up.

You do not need a lot of power to hold speed, and opinion is divided on whether you need a speed feedback loop or not. Corrections can, if done too quickly, cause pitch changes which are audible, so closed loop correction to drops in speed need to be very slowly introduced. This would tend to indicate that an open loop solution is probably best.

Cheers,

Hugh