DIY Turntable Control Calculator - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

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
Reply
 
Thread Tools Search this Thread
Old 24th October 2010, 03:48 PM   #1
diyAudio Member
 
Join Date: Jul 2005
Location: Montréal QC
Default DIY Turntable Control Calculator

Hi Guys,

I just thought I'd knock up a quick calculator for a turntable motor control system. You can go as deep as you want into topologies (From simple LM317-style regulators up to full-blown Buck/Boost/Flyback circuits) and if you need assistance on that, please email me at : liam(at)liammartin.com.

This would be a closed loop (ie. with feedback) system, so it'll try to keep the speed as constant as possible with respect to load.
The overall accuracy will depend primarily on the % of allowed variation around the reference voltage...although most switching regulators are accurate to within a few percent these days.

However, this is simply a calculator for the 'handy-to-know' ratios - contained herein are :

Platter vs Drive wheel RPM
Motor RPM + Drive wheel vs Platter RPM
DC-DC Controller Feedback Resistances based on the above.

http://liammartin.com/Misc/TTCalc/Turntable_Driver_Calc.xls

If you spot a hole in the calculations, please let me know!
I hope this is of help.

Liam
__________________
http://blog.liammartin.com

Last edited by Psychobiker; 24th October 2010 at 03:54 PM.
  Reply With Quote
Old 24th October 2010, 07:31 PM   #2
diyAudio Member
 
Join Date: Feb 2006
Location: Willy, VIC
Your platter speed to pulley speed ratio is wrong.

The correct ratio for rubber belts is (platter diameter + belt thickness) / (pulley diameter + belt thickness).

For non rubber belts the belt thickness term on top and bottom must be multiplied by twice the Poisson's ratio of the material. For rubber and other incommpressible materials the Poisson's ratio is 0.5, hence the short version above.
  Reply With Quote
Old 24th October 2010, 07:34 PM   #3
diyAudio Member
 
Join Date: Jul 2005
Location: Montréal QC
Cheers for that! I will make amends ASAP. It's a couple of MM, if that...so can it be declared negligible?
__________________
http://blog.liammartin.com

Last edited by Psychobiker; 24th October 2010 at 07:44 PM.
  Reply With Quote
Old 24th October 2010, 10:25 PM   #4
diyAudio Member
 
Join Date: Jul 2005
Location: Montréal QC
Updated to reflect Mark Kelly's suggestions, however I will assume a non-compressible material - if you want to go into compressible belt media, so be it - and I will pop it in the calculator if enough people ask for it! Hope it's OK!

L
__________________
http://blog.liammartin.com
  Reply With Quote
Old 30th October 2010, 03:16 AM   #5
diyAudio Member
 
Join Date: Jul 2005
Location: Montréal QC
Something simple to calculate weights required/exerted on the tonearm.
VERY simple, though! No circular torque is taken into account.

L

http://liammartin.com/Misc/TTCalc/Arm_Calculator.xls
__________________
http://blog.liammartin.com
  Reply With Quote
Old 30th October 2010, 09:02 PM   #6
cbdb is online now cbdb  Canada
diyAudio Member
 
Join Date: Oct 2008
Location: Vancouver
Quote:
The correct ratio for rubber belts is (platter diameter + belt thickness) / (pulley diameter + belt thickness).
Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.
  Reply With Quote
Old 30th October 2010, 10:41 PM   #7
diyAudio Member
 
Join Date: Jul 2005
Location: Montréal QC
Quote:
Originally Posted by cbdb View Post
Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.
I thought this too.
__________________
http://blog.liammartin.com
  Reply With Quote
Old 31st October 2010, 02:03 AM   #8
diyAudio Member
 
Jacques Merde's Avatar
 
Join Date: Oct 2009
Quote:
Originally Posted by Psychobiker View Post
I thought this too.
The effective radius of each pulley or platter actually occurs at somewhere near the belt centerline.
__________________
"For every complex problem, there is a solution that is simple, neat, and wrong." -- H.L. Mencken
  Reply With Quote
Old 31st October 2010, 05:10 AM   #9
diyAudio Member
 
Join Date: Mar 2005
Location: MI
Quote:
Originally Posted by cbdb View Post
Maybe I am missing something, but this dosnt make sense to me. Draw a picture with 2 pulleys and a very thick belt. The only thing that matters is the inside surface of the belt (the surface touching the pulleys). The thickness dosnt matter.
You are missing something, Mr. Kelly is dead on with his explanation.
  Reply With Quote
Old 31st October 2010, 08:19 PM   #10
Nanook is offline Nanook  Canada
diyAudio Member
 
Nanook's Avatar
 
Join Date: Feb 2004
Location: Chinook Country.Alberta
Default well, belt drive is not the only drive system out there....

after doing some thinking (which is not always my way...), I've given up on belt drives when designing a drive system, I'm sticking with either idler drive or rim drive. I've looked at various systems and ran my choice and basic design past a mechanical engineer whose opinion I trust.

As Mark Kelly points out, the modulus of elasticity is quite high for rubber (regardless of thickness but at smaller thicknesses the forces required to deform it is smaller) if using a rubber belt at room temperature. This implies that in small enough diameters to allow use in belt drive systems the modulus of elasticity does need to be considered. I think this is one of the reasons why many have reported the benefits of changing belt materials--- belts do vibrate and can introduce "smearing" of the sound. Even some rather expensive tables have benefitted from a change in belt materials or in motor or drive type upgrades (like the Teres Verus upgrade)

Perhaps a different belt material could be used. I have used high strength nylon upholstery thread to very good effect. Difficult to get the correct length and tension required to drive a platter, but stable once done. I assume a good quality silk thread would also provide the same, and perhaps unwaxed dental floss. Something that may be considered is what some have used. 1/4" cassette tape, or 1/2" video tape or mylar (as per the Redpoint and Teres designs) with suitable pulleys.

Take care all...
__________________
stew -"A sane man in an insane world appears insane."
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
DIY turntable using parts from DIY Hi Fi Supply gadfly Analogue Source 6 9th August 2009 04:59 AM
turntable motor & speed control space-cake Analogue Source 0 22nd September 2007 07:51 PM
DIY Turntable Dougie085 Analogue Source 8 2nd July 2007 12:35 PM
turntable diy audiofilofine Analogue Source 6 3rd September 2006 12:38 PM


New To Site? Need Help?

All times are GMT. The time now is 06:44 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2