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Silent electric motor to drive turntable.

David Aungier

Sep 4, 2017
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Hi all, I have been trying to rotate a 'turntable' through 90 degrees and back continuously and silently. The turntable weighs about 200lb. I find that the 12v motors (described as silent) that I have tried, make more noise when linked to a gear train or ram. I am wondering if there is a super quiet motor available or possibly a better way of going about it, ie electro magnets? I would be grateful for any advice on this matter, kind regards Onja.
 

Minder

Apr 24, 2015
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You would have to calculate the torque required and then decide if gearing is warranted, one of the quieter means of gearing is using a planetary G.B.
Most DC motors and BLDC are extremely quiet, especially if ran at low RPM with gearing.
Rotating 200lbs is probably going to be difficult to become completely silent.
What is the speed of rotation?
Another method to consider could be a linear actuator driving with a small length of rack with a pinion on the turntable.
M.,
 

Ylli

Jun 19, 2018
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Another method to consider could be a linear actuator driving with a small length of rack with a pinion on the turntable
This is what I was going to suggest, except coupling with a mechanical linkage that does not involve gears.
 

BobK

Jan 5, 2010
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Can you make the turntable itself the motor, by placing alternating pole magnets around it then driving it with a couple coils? I.e. turning it into a stepper. That would be as quiet as the rotating turntable itself.

Bob
 

Bluejets

Oct 5, 2014
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Worm drive gearbox would be relatively quiet with a crank output for the 90 degrees and the motor would continually turn in the one direction.
Worm drive as an added plus are high gear ratio in small space.
Could adapt a small cap run motor from the likes of a small twin tub washing machine where motors are quiet operation.

Sources for low voltage units might be auto windscreen wiper motor which already has a crank output but only suitable for one direction as it has just 1 thrust bearing.
Window winder motor would have dual thrust and would suit reversing.
As M says, all is dependant on speed you require as it is the governing factor in motor size.
 
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David Aungier

Sep 4, 2017
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You would have to calculate the torque required and then decide if gearing is warranted, one of the quieter means of gearing is using a planetary G.B.
Most DC motors and BLDC are extremely quiet, especially if ran at low RPM with gearing.
Rotating 200lbs is probably going to be difficult to become completely silent.
What is the speed of rotation?
Another method to consider could be a linear actuator driving with a small length of rack with a pinion on the turntable.
M.,
Thanks for the replies. I have tried motors with in built step down gearing and actuators but in the end the noise goes up when they are connected to the turntable and further reduction through Timex pulley arrangement. The turntable speed required is very slow -no more than 5RPM but the transmission noise is too great. I'm wondering if there is an electric pump/master cylinder available that would operate a slave cylinder ram in one direction and rely on a strong spring to return. A small bore master cylinder and large bore slave would help to lower the turntable speed and also add mechanical advantage. Hoping that it could also be a quiet method. I am keen to hear any observations for or against .
 

WHONOES

May 20, 2017
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The following link might help to identify ways of reducing gear noise. How much noise is too much. What is the purpose of your device.
It takes surprisingly little power to rotate a mass at a relatively low speed.
 

Minder

Apr 24, 2015
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A bit of an extreme to a 200lb T.T. but as a comparison the old LP record tables were extremely quiet and worked by using a synchronous AC motor and belt drive.
You may achieve this using a timing belt and pulleys for drive and reduction.
DC or BLDC servo motors are extremely quiet.
M.
 

BobK

Jan 5, 2010
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I gave you a possible silent solution.

Bob
 

David Aungier

Sep 4, 2017
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Can you make the turntable itself the motor, by placing alternating pole magnets around it then driving it with a couple coils? I.e. turning it into a stepper. That would be as quiet as the rotating turntable itself.

Bob
Thanks Bob, that is the kind of suggestion I was hoping to hear. I can remember reading about a surface train that was 'suspended' above the rails by magnets and also propelled by 'linear magnets'? I'd wondered if it could be arranged in radial form but as you probably suspect, I am quite clueless on the subject. If you could provide me with a plan or layout of the components required I would be extremely grateful. Onja.
 

David Aungier

Sep 4, 2017
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The following link might help to identify ways of reducing gear noise. How much noise is too much. What is the purpose of your device.
It takes surprisingly little power to rotate a mass at a relatively low speed.
Hi WHONOES, the apparatus will be used in a domestic situation so it would need to be extremely quiet to be acceptable and I am aware that it will not be easy to achieve this. You are right when you say that rotating a mass requires little effort, especially if the bearing surfaces are low friction and the axis is verticle therefor not lifting any weight. I am only looking to rotate 90 degrees inclusive, (45 each way) and about 4 or 6 times a minute. Talking at the moment about achieving the motion with magnets.
 

David Aungier

Sep 4, 2017
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A bit of an extreme to a 200lb T.T. but as a comparison the old LP record tables were extremely quiet and worked by using a synchronous AC motor and belt drive.
You may achieve this using a timing belt and pulleys for drive and reduction.
DC or BLDC servo motors are extremely quiet.
M.
I've tried most types of motors and actuators also mechanical gearing plus Timex pulleys, even suspended the motors in rigid foam so there are no securing bolts to transmit noise but in the end too much noise. Listening now to people with expertise with magnets in case that might be the way to go. Regards Onja.
 

BobK

Jan 5, 2010
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Here is the basic idea, please excuse my lack of drawing skill.

upload_2019-10-12_10-10-35.png

You place neodymium magnet discs around the rim of the turntable, with alternating poles out, N S N S...

You arrange two electromagnets, spaced apart half the spacing of the magnets,.

To move clockwise:

1. Activate coil A with a N pole. This will pull a S pole magnet it front of it, as shown in the diagram.
2. Deactivate A and Activate B with an S pole. This will pull the N that is too the left of coil be, to it, rotating the the turntable 1/2 a stepl
3. Now you activate A with an S pole. That will pull the N from coil B to A rotating it another half step.
4. Now activate B with an N, and it pulls the next S to be in front of B.
5. And finally, activate A with an N, which puts you back at step 1 and you repeat the sequence.

I will leave it as an exercise to the reader to figure out the sequence to rotate the other direction.

This is exactly how a stepper motor works.

The beauty of a stepper is that you do not need any feedback on position or distance moved because it moves in repeatable discrete steps.

Bob
 

Minder

Apr 24, 2015
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Listening now to people with expertise with magnets in case that might be the way to go. Regards Onja.

If using the 1:1 ratio like that, you may need quite a bit of power to rotate 200lbs and also stop it precisely at the 90° point.
If it has a vertical shaft and bearing below the table, one method to reduce friction is to place a large ball bearing below at the bottom of the shaft to support it, i.e. reduce the pivot point area.
I once did an interesting 300lb T.T. project that used an air bearing, the whole table is lifted with compressed air before rotation.Very friction free.!!
M.
 

BobK

Jan 5, 2010
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Yes, you could use a whole series of coils operated simultaneously to get more power. I just showed one pair to make it simple.

Bob
 

Alec_t

Jul 7, 2015
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Have you considered a microwave oven turntable mechanism with further reduction (if necessary) by belts and pulleys?
 

Minder

Apr 24, 2015
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The only thing I can see might happen with a stepper principle, especially at low RPM, is 'cogging' also seen on (multi-pole) BLDC motors at low RPM when used with no PID feedback.
M.
 

BobK

Jan 5, 2010
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Agree. Getting smooth motion would not be easy, but it is possible. You might need to monitor the back EMF on the non energized coil to determine the optimal switching time.

Bob
 

David Aungier

Sep 4, 2017
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Here is the basic idea, please excuse my lack of drawing skill.

View attachment 46220

You place neodymium magnet discs around the rim of the turntable, with alternating poles out, N S N S...

You arrange two electromagnets, spaced apart half the spacing of the magnets,.

To move clockwise:

1. Activate coil A with a N pole. This will pull a S pole magnet it front of it, as shown in the diagram.
2. Deactivate A and Activate B with an S pole. This will pull the N that is too the left of coil be, to it, rotating the the turntable 1/2 a stepl
3. Now you activate A with an S pole. That will pull the N from coil B to A rotating it another half step.
4. Now activate B with an N, and it pulls the next S to be in front of B.
5. And finally, activate A with an N, which puts you back at step 1 and you repeat the sequence.

I will leave it as an exercise to the reader to figure out the sequence to rotate the other direction.

This is exactly how a stepper motor works.

The beauty of a stepper is that you do not need any feedback on position or distance moved because it moves in repeatable discrete steps.

Bob
Here is the basic idea, please excuse my lack of drawing skill.
Thanks Bob, I have read your 'work' a few times and will continue to do so as I digest and understand the content. I get the principle but need to ask certain questions like : when you activate a coil with a N pole and then activate it with a S pole, is this done by reversing the coil supply wires ? Also, would I be wasting my time trying to run it on 12v. Apologies for the basic questions but if I'm anything I am an engineer and not well versed in electronics.
View attachment 46220

You place neodymium magnet discs around the rim of the turntable, with alternating poles out, N S N S...

You arrange two electromagnets, spaced apart half the spacing of the magnets,.

To move clockwise:

1. Activate coil A with a N pole. This will pull a S pole magnet it front of it, as shown in the diagram.
2. Deactivate A and Activate B with an S pole. This will pull the N that is too the left of coil be, to it, rotating the the turntable 1/2 a stepl
3. Now you activate A with an S pole. That will pull the N from coil B to A rotating it another half step.
4. Now activate B with an N, and it pulls the next S to be in front of B.
5. And finally, activate A with an N, which puts you back at step 1 and you repeat the sequence.

I will leave it as an exercise to the reader to figure out the sequence to rotate the other direction.

This is exactly how a stepper motor works.

The beauty of a stepper is that you do not need any feedback on position or distance moved because it moves in repeatable discrete steps.

Bob
Here is the basic idea, please excuse my lack of drawing skill.

View attachment 46220

You place neodymium magnet discs around the rim of the turntable, with alternating poles out, N S N S...

You arrange two electromagnets, spaced apart half the spacing of the magnets,.

To move clockwise:

1. Activate coil A with a N pole. This will pull a S pole magnet it front of it, as shown in the diagram.
2. Deactivate A and Activate B with an S pole. This will pull the N that is too the left of coil be, to it, rotating the the turntable 1/2 a stepl
3. Now you activate A with an S pole. That will pull the N from coil B to A rotating it another half step.
4. Now activate B with an N, and it pulls the next S to be in front of B.
5. And finally, activate A with an N, which puts you back at step 1 and you repeat the sequence.

I will leave it as an exercise to the reader to figure out the sequence to rotate the other direction.

This is exactly how a stepper motor works.

The beauty of a stepper is that you do not need any feedback on position or distance moved because it moves in repeatable discrete steps.

Bob
 

David Aungier

Sep 4, 2017
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Agree. Getting smooth motion would not be easy, but it is possible. You might need to monitor the back EMF on the non energized coil to determine the optimal switching time.

Bob
I wouldn't mind if the motion wasn't dead smooth as long as it was quiet.
 
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