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Lowest electrical noise type of motor for low speed applications

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T3sl4co1l:

--- Quote from: filssavi on May 24, 2020, 04:07:37 pm ---What you are suggesting is a poor man BLDC, then he might just as well use a proper one...
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Exactly.  Stick to the classics -- AC motors (BLDC being just another type) are hard to beat, with good reason. :)



--- Quote ---The problem with BLDCs is that, similarly to steppers they are usually driven By fully energising a phase at a time, that  has its advantages (mainly its cheap) But will generate quite a lot of noise. The least noisy way to drive a machine is with sinusoids (ok it is not that simple I know but let’s not go too much into details) so PMSM (also knows as BLAC) or induction machines

Also the placement for the MCU is completely irrelevant, as the machine drive and machine themselves will spew out much much more EMI
--- End quote ---

Well, once you're driving the phases with a linear amp and sine wave, the MCU noise will be quite relevant!

Also since mechanical constraints or available space is undefined, why not use a bog standard gear head motor or servo, and an insulated shaft of sufficient length? :)

Tim

filssavi:
Pretty much spot on

I did not consider linear driving because is is usually too inefficient (basically is becomes uncoolable really fast, however reading the OP specs more closely it is likely a very small setup (less than 10W) and in that case you are right


I would usually vote against long shafts as they are quite nasty to drive (lots of low frequency resonance modes, transient issues due to inertia and compliance etc) however if the load is basically almost zero and a those low speeds it could work

However I would still use a belt (even without speed reduction) as it is much easier to design, certainly much cheaper and much more forgiving, it also insulates from drive side vibrations which can be usefull

wizard69:

--- Quote from: beanflying on May 24, 2020, 10:28:50 am ---
--- Quote from: Someone on May 24, 2020, 09:52:38 am ---
--- Quote from: beanflying on May 24, 2020, 07:55:06 am ---
--- Quote from: nfmax on May 24, 2020, 07:44:51 am ---If the diameter of the turntable is large enough, you can use a flexible belt drive, as your torque and acceleration requirements are low. A speed reduction of 100:1 should be feasible. This is how they did it in record player turntables back in the day, though the primary concern was mechanical noise rather than electrical. Both shaded pole induction motors and BLDC motors were used.

With a suitably large moment of inertia, would it possible to simply turn the motor off briefly while you make your measurements, and let the turntable 'coast'?

--- End quote ---

He wants a turndown rate from 1-200 RPM which is not feasible with a single reduction.

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When you open up design concepts (and your mind) a little, its not hard at all to meet those speed requirements with direct drive.... coming from experience putting precision motion right on top of low noise electronic sensing.

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When you consider the 'low noise' part of it initially requested it limits the options. If you ignore it then a stepper/gearbox makes a lot of sense but they are a long way from low noise.

So rather than 'open your mind' then offer ZERO how about you make a suggestion?

--- End quote ---

Stepper noise depends upon the driver.    The motor itself isn't electrically noisy.

As for the application here I'm not sure if a stepper fits the need as there is too much missing information.    If not there are a number of Brushless designs on the market that would do the trick but you still have the issue of the driver creating most of the electrical noise.

wizard69:

--- Quote from: ricko_uk on May 24, 2020, 01:44:18 am ---Thank you wizard69 and Someone,
don't know much about motors apart from the basics. All I need to understand/find-out is what type of motor is best suited (brushless DC, stepper, etc).

--- End quote ---
That is where the problem is, it is hard to say for sure from the information available.

--- Quote ---The only requirements are:
- must be electrical
- max voltage available on the board: 12V

--- End quote ---
That right there can be an issue, I really like to see motor supplies separate fro the supplies going to the controls.

--- Quote ---- as low noise as possible in terms of amplitude as well as frequency spectrum (this is as specific as I can get)

--- End quote ---
This really isn't useful.   First of in a stepper or even the brushless solutions a vast amount of electrical noise comes from the driver.   Beyond that you leave open a range of possibilities from below one Hz to many MHz.

Consider this in many applications audible noise is a big factor to be controlled.   A common approach is to implement drivers with very high switching frequencies.   That however can lead to radiated high frequency noise.

--- Quote ---- drive speed 1 RPM to 200 RPM that I can control through a micro
- load/torque next minimal as I only have to rotate a 200 grams plastic disk. It can take few seconds to accelerate, it doesn't matter.

--- End quote ---
Open loop or closed loop.    How tight on the measured RPMs?   I ask these questions because various methods are available and frankly you may have to experiment to find the best fit.   I don't really thing that anybody can say for certain that one solution is the best here.

For example back a few decades ago I worked on machinery that need spindle control to one hundredth of an RPM.    In that case we used an AC driver (3 phase) to an synchronous AC motor.   The drive was rather huge compared to what you can buy today for a 1/3 HP motor.   But was probably the best solution at the time, using a ring counter driving hilariously large switching modules.

Would that be the right choice today?   probably not.   In fact I believe there was an upgrade to a DC drive that had a really good velocity control loop, a couple of decades later.

--- Quote ---That's all that is required. And all I need is to understand what is the type of motor with the lowest electrical noise (again, in terms of amplitude as well as frequency spectrum). Would it be a stepper with some slew rate device (after some Googling still no idea what they are) like NiHaoMike suggested or some other motor types?

Thank you

--- End quote ---
This really can't be answered as there are too many depends that must be addressed.

NiHaoMike:
Are there times when bursts of noise can be tolerated? Perhaps the solution could be as simple as a flywheel with a DC motor pulsed on to keep it turning.

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