So How's it done?
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 18th July 2007, 11:04 AM #1 Brainticket   Account Disabled   Join Date: Jul 2007 So How's it done? Hi Comrades So whats the mathmatic formula for deciding the motor pulley diameter to sub platter diameter for AC 50Hz cycle? Thanks in advance..
 18th July 2007, 12:03 PM #2 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders Hi, it will depend on what slip occurs between the belt and each pulley. But [motor rpm] / [platter rpm] gets you close. Do you realise that mains frequency has a high tolerance around the nominal 50Hz. That in part is due to the enormous flywheel energy in all the generator/motor assemblies that are "locked" together throughout the British Isles. As the power demand goes up so the generators slow down releasing some of that energy rather than only using fuel to meet transient demand. When demand reduces the fuel builds the speed back up to above nominal waiting for the surge (TV tea breaks). Effectively, allowing a wide tolerance reduces the cost of energy supply. __________________ regards Andrew T.
Brainticket
Account Disabled

Join Date: Jul 2007
Quote:
 Originally posted by AndrewT Hi, it will depend on what slip occurs between the belt and each pulley. But [motor rpm] / [platter rpm] gets you close. Do you realise that mains frequency has a high tolerance around the nominal 50Hz. That in part is due to the enormous flywheel energy in all the generator/motor assemblies that are "locked" together throughout the British Isles. As the power demand goes up so the generators slow down releasing some of that energy rather than only using fuel to meet transient demand. When demand reduces the fuel builds the speed back up to above nominal waiting for the surge (TV tea breaks). Effectively, allowing a wide tolerance reduces the cost of energy supply.
Hi Andrew
! I'm sure i can sort everything out from that thanks

Ok in English, i have an extremely well made platter,sub platter & bearing i wish to use but need to work out a pulley to suit my Premotec AC motor.I'm in the UK on a 50Hz cycle..Not intrested in 45rpm only 33.3..All i need are the aid to the mathmatics, then i can take it from there.

 18th July 2007, 01:12 PM #4 AndrewT   R.I.P.   Join Date: Jul 2004 Location: Scottish Borders How many poles are used in the synchronous motor? A two pole motor turns at 1500rpm. Most belt drive motors are much slower, 8pole/12pole/16pole are fairly common. Can you measure or estimate the motor speed? __________________ regards Andrew T.
 18th July 2007, 01:21 PM #5 lcsaszar   diyAudio Member   Join Date: Mar 2004 Location: Budapest, Hungary It depends on the revolution per minute of the motor. For the most frequent 1500 rpm the diameter ratio would be 1:45. In reality a bit larger pulley diameter is needed because of the motor slip. Slip is called the few percent slowdown of the asynchronous motor related to the rotating magnetic field (and not the belt "slipping"). Once I have made a pulley like this by machined to about 5 % larger and then gradually reduced it with sandpaper while rotating (belt removed, diameter adjusted, belt up, speed check,...).
 18th July 2007, 01:30 PM #6 Brainticket   Account Disabled   Join Date: Jul 2007 Its a Premotec 9904 111 31504 50Hz 250rpm. Synchronized Turntable motor..That im wanting to used to turn the platter at 33.3 rpm..
 18th July 2007, 01:45 PM #7 tade   diyAudio Member   Join Date: Feb 2005 Location: Ralieigh nc 33.3/250= factor factor* platter diameter= pulley diameter.
AndrewT
R.I.P.

Join Date: Jul 2004
Location: Scottish Borders
Quote:
 Originally posted by oshifis In reality a bit larger pulley diameter is needed because of the motor slip. Slip is called the few percent slowdown of the asynchronous motor related to the rotating magnetic field (and not the belt "slipping").
synchronous motors do not slip.
Induction motors slip. As the torque imposed on the motor increases the slip increases and the current increases to the point that the motor is turning slowly and current is sufficient to cause overheating. The next stage the motor stalls.

In a synchronous motor the phase lag of the motor increases as the torque increases but the speed stays locked to the incoming frequency. As the torgue varies the motor oscillates up and down the phase lag. Again increasing the torgue too far and the motor drops out of lock and stalls. The belt stretch and platter inertia hide/attenuate the speed variations due to torgue variation.

But the belt does slip as it comes out of contact with both the drive pulley and the driven pulley.
The overall effect is that the drive pulley should be slightly larger than calculated.
But what is the correct calculated diameter?
The drive pulley is not cylindrical, it is barrel shaped to keep the belt central on the pulley. I suspect the narrowest part of the barrel should be close to the calculated diameter. The middle of the barrel will be significantly more than the calculated diameter.
I have no idea what the ratio of diameters for the barrel should be to achieve good belt centreing.

BTW,
250rpm tells you it is a 12pole synchronous motor.
__________________
regards Andrew T.

 18th July 2007, 09:51 PM #9 Brainticket   Account Disabled   Join Date: Jul 2007 Ok right so i'm back to square one & obviously no one knows... DIY Audio forum!!! Seems not. Thanks anyway..
Mark Kelly
diyAudio Member

Join Date: Feb 2006
Location: Willy, VIC
Quote:
 Originally posted by tade 33.3/250= factor factor* platter diameter= pulley diameter.

Quote:
 Originally posted by Brainticket Ok right so i'm back to square one & obviously no one knows... DIY Audio forum!!! Seems not. Thanks anyway..
You don't deserve this but here goes:

The correct answer depends on the type of belt used. If you are using a standard rubber belt the required pulley diameter is given by

Pulley diameter + belt thickness = (platter diameter + belt thickness) * (platter speed / motor speed) * (1 + creep rate)

This refers to the crown of the pulley.

Since creep rate depends on pulley diameter this is a recursive calculation, start with an estimated creep rate of 0.1%. Creep rate is not slip and it cannot be cured, although it can be ignored as most designers do.

If you use any material other than rubber the equation changes and you must use (belt thickness * 2 * Poisson's ratio) where I have belt thickness. Rubber has a Poisson's ratio of 0.5 hence the simplification.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 New To Site? Need Help?

All times are GMT. The time now is 11:46 PM.