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Topic: Replacing a turntable AC motor (Read 2227 times) previous topic - next topic

rabati

Mar 28, 2013, 08:38 am Last Edit: Mar 31, 2013, 05:46 pm by rabati Reason: 1
Hello to all.

I have to replace an old broken turntable motor, and there are no spareparts so i would like to adopt a DYI solution.

The original motor is a 2poles asynchronous motor with speed of (i suppose) 1400rpm and powered at 220V, AC, power is around 10W.

I would like to replace it with a DC motor with speed regulated via an arduino  plus some electronics to have a almost perfect speed, maybe with a feedbeck via some sensor.

Do you have a suggesione on the best Dc motor type I have to adopt ? And on the better shield to manage the speed?
Brushless ? Or any other kind of motor.

Thanks to all
RA


jackrae

If you use a "standard" DC motor you will need a speed sense circuit in order to control motor speed accurately.  If you use a brushless motor, which in effect is a 3-phase motor then speed is determined by supply frequency (minus a little bit of slip) so you can easily control speed by setting the drive voltage frequency.  Alternatively you could use a small stepper motor, in which speed is accurately determined by the step rate.

michinyon

A brushless motor should have no slip.   It is a kind of synchronous motor,  not an induction motor.

jackrae

It depends on the type you use.  The following text extracted from wikipedia :  "The motor part of a brushless motor is often a permanent magnet synchronous motor, but can also be a switched reluctance motor, or induction motor."  If the latter two then slip is required.

rabati

First of all thank you for the answers...
But I'm a little bit confused.

I know DC asynchronous motors and I know that speed is related directly to frequency, so I need an inverter to pilot them and this solution is not cheap for 220V motors. (as far as I know)
I know that DC motors are cheap but speed is not stable.

So I didn't understand which is better (price/quality) solution.
Maybe if you have links to shops that sell these motors I can ask directly to them.

Cheers, RA

jackrae

If you intend using  DC motor brushed or brushless then you need to look at low voltage ones (12 or 24 volts say).  So you need a power supply to provide the required DC for powering your arduino and the motor driver.

rabati

Ok, but jumping back to my original question: which is the best motor for my needs?

Best in terms of enough power and on stability of the speed.

RA

jackrae

In my view, a small stepper motor since you can ACCURATELY determine rotational speed from the step rate.  To minimise any notching effect, since the motor moves in steps, the motor needs to drive a toothed belt wrapped around the turntable, or drive the table periphery via a rubber wheel.  Both of these effectively provide a step-down gearing.  The record-table also acts as a flywheel to smooth out any speed  pulses.

rabati

As standard mechanical connections between the motor and the "plate" there is a rubber wheel.

I did not imagine that a stepper motor could be the solution...

I'll give a look to this idea but I see some side-effects of this solutions..

Cheers, RA

jackrae


rabati

I have to admit I'm not en expert on stepper motor but my concerns are that I don't know if I can run a stepper motor as a normal motor.
this means run it for some hours continuously, without have over-heating and mechanical stress.

Regarding speed and slip I can imagine that the huge amount of poles of a stepper motor can be a guarantee of constant speed for the whole 360 degrees.

Thanks, again, RA

jupiterengineering

i collect old akai stuff from the early 70s, turntables, reel to reel and cassette decks for the most part....and have dealt with speed and motor issues...in your case, the simplest way around it is to replace the synchronous motor with another if you can find one, speed in these is dependant on frequency and your mains frequency should never vary...unless of course you want fully adjustable speed, in that case you are best to use  something like a small rc brushless esc to control a three phase brushless motor as previously mentioned...and use arduino to feed a pwm signal to the esc, using a 10 k pot to vary speed...


hope this helps! :)

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