turntable motors...

Status
Not open for further replies.
Jump to Latest
#21
I have been working on building my Turn Table for a while now, I have the material for the platter which will be 3 inch acrylic capped with .250 aluminum plate to shield the pickup from the linear drive. I plan on embedding rare earth magnets in the underside of the platter and placing a multiphase coil wound on a hoop in the base.

Think of it like a monorail that goes in circles, the platter will spin with no physical connection to the motor. I should be able to control the speed of the platter by varying the frequency of the linear drive while the amplitude will remain stable to provide platter suspension.

My biggest concern is whether I will be able to sufficiently dampen the bobbing action of the platter without resorting to runners under the platter.

Any thoughts?

Anthony
 
#23
Hello Alain, I do not have any practical measurements at this time. The linear motor I built a while ago as AC powered from a 3 phase source. The linear motor for my Turn table design would be DC Powered as fixed magnets would be utilized. The current should not be any more than a few amps at 48VDC or there abouts. A centre shaft would still be required for stability as I believe a fully suspended platter would be very difficult to achieve.

I already tried a conpressed air powered drive and the big drawback in both motors is starting torque due to platter wieght. The air powered drive is noisy and the linear motor needs to be shielded. I have built similar units in the past as stirrers for lab use, this is where I got my inspiration from.

Anthony
 
#24
Anthony,

Thanks for these details, I am interested in building a TT and I am looking to
all interesting details, plus a Schroder arm !

Don't you think the magnetic field of the motor could create problems with a Moving coil cartridge ???

PS:
On the other side, I have received the last cables for the preamplifier {with the Apox cards} and I hope to power up on saturday.

Regards.

Alain.
 
#26
Sounds like you're making a giant version of a VCR take-up motor 🙂

I have always wondered with acrylic platters though, that material is super sensitive to heat. Now, 3" would be somewhat immune to warpage, but expansion can be nasty on a hot summer day 😕
 
#34
Papst motors?

I've got experience with their fans, these last forever(dual ball bearing) and have a really good reputation.

Papst fans also have a bad reputation of crreating a lot of vibrations, not good for a turntable if the motors are the same as the fan ones.

They are pretty silent, but the object they're attached to absorbs all the vibrations and this makes them really noisy.

I've got two versions of the well known 8312 fan, the 8312 and the 8312/12HL. The 12HL : twice the speed, cfm, power and ... noise :bawling: These are 120cfm(!) gyroscopes that, as long as I know, can only be found at my local shop. People looking for the 8312 fans generally hate me : I can buy them for 4$CAD instead of 16$USD 😀
 
#35
I know this is probably nuts, but I have to ask anyway. I have a one horse variable speed switch reluctance motor that runs fairly quietly. Now I know that I will need to isolate it. But assuming I can takle the noise issue....

I was thinking that if I ran it at around 7000 rpm. (10000 max opperating) that there would be enough stability to overcome the cogging issues. I will need an idler I'm sure to be able to drop the rpm's enough. Any reason not to try?

DaveM
 
#36
The turntable will still turn even if there's a TV on it 😀 (A 2HP can run a golf cart)

It's quiet, but are there a lot of vibrations coming from it?

You can try, I'd tell you to start by just making the platter to try the motor, and then work with the audio parts. So that if something flies to the other end of the room, it will not destroy the tonearm.

But at that RPM, be sure your flywheel is not too fragile, what else, it will turn in a flying flywheel. Some CDs break@ 5000rpm.

My 40$ grinder is even more dangerous; it runs @ 11000rpm

Question for the forum:
If you were going to buy a motor just for this task, what type would you choose? DC brushed, DC brushless, triphase, asynch. triphase, single phase, stepped?
 
#37
Fortunately the motor is capable of running at anywhere from 120-10000 rpm. I was simply thinking that the faster the motor spins the more stable it would be. Instead of having a small relatively weak motor using the momentum of the platter to maintain speed I was thinking that it would be possible to use a high power motor spinning fast to create stability. I am guessing that it won't work, but I am still thinking of how to make it work.

I have a mill and lathe so anything will be made of aluminum or brass. Stability will not be an issue as everything can be bolted down in a serious industrial fashion.

About the vibrations, I was thinking of using rubber isolators and spikes on a seperat rack located next to the turntable. Then have the motor turn an idler pulley on a seperate mount then use the idler to drive the platter. I'm sure that would help with vibrations, but would it elimenate it? Hmmmm..

DaveM
 
#40
I've also heard that old (not the ones used lately) motors from hard drives and some floppy drives are good to use. I can't personally vouch for that, but sounds reasonable.

Personally I've been thinking about using a motor from an old SCSI drive used in a Sparc20 or scavenging a VCR motor.
 
Status
Not open for further replies.
Top Bottom