Lowest Emissions Electric Motor - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: July 22, 2024, 11:13:53 pm
content: Hi,I don't know much about the various types of electric motors so just wondering if someone could give me some pointers...A client asked me to design a simple stirrer (just a motor with a shaft) rotating with adjustable speeds between 50 RPM and 200 RPM. The load is just a tiny steel shaft mixing 500ml of liquids. It can take quite a bit o get up to speed too, that is not a problem.Efficiency and power dissipation are also not a problem, so linear drive can also be used (I assume that would be less nosy than a PWM drive).But they need it to be very low emissions (electric, magnetic and electromagnetic) because they have all sorts of sensors around the container which are extremely sensitive to all those emissions.What type of (low-power) electric motor has the lowest electric, magnetic and electromagnetic emission?Or, if when decreasing one, another increase (for example by decreasing the magnetic field the electric field increases) then which solution is easier to shield? I think perhaps higher voltage lower current because the electric and electromagnetic fields are easier to shield than the magnetic ones, perhaps?Any clarifications and pointers are welcome.Thank you

author: uer166
author_rank: Super Contributor
timestamp: July 22, 2024, 11:26:29 pm
content: The lowest noise might be something that can run directly off of mains such as a shaded pole induction motor (or any kind of mains induction motor). Unfortunately this is not compatible with the variable speed requirement, any chance you can vary speed mechanically via belt or gearbox? If not, then some kind of brushless motor driven by a linear power-amplifier instead of PWM as mentioned. A good start would be quantifying the acceptable amount of magnetic/electric field leakage..

author: langwadt
author_rank: Super Contributor
timestamp: July 22, 2024, 11:27:02 pm
content: who not a hydraulic or pneumatic motor? could be made of plastic for zero emmisions

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 22, 2024, 11:33:58 pm
content: First question I would ask is what the sensitivities are. Is the concern strong magnetic fields which might saturate or over bias a sensor. Are there frequencies that must be avoided and are there any that can be allowed?Depending on those answers you might look at a homopolar motor, which has no varying emissions in steady state operation. The magnetic fields can be fairly well contained in the motor. Going the other direction, a motor with very high pole count could drive the emissions up and out of the operating band of the sensors.If the problem is extreme, look into a hydraulic motor or an air motor. By making the piping/hoses long enough you can get all the pumps and controllers isolated. You could use fiber optics to couple a shaft position sensor to the remote location for speed control.

author: coppercone2
author_rank: Super Contributor
timestamp: July 22, 2024, 11:34:09 pm
content: run it on a pulley from a distancethe lowest emissions would be hand powered from a pully, perhaps with a wet rope

author: moffy
author_rank: Super Contributor
timestamp: July 22, 2024, 11:47:58 pm
content: Just use a brushed DC motor and feed it with a variable DC supply, speed control, for suppression put a capacitor across the brushes.

author: David Hess
author_rank: Super Contributor
timestamp: July 23, 2024, 01:14:26 am
content: A DC brushless motor will be electrically quieter than a brushed DC motor because of the lack of brushes and commutator. Speed can be varied by changing the voltage.

author: moffy
author_rank: Super Contributor
timestamp: July 23, 2024, 01:25:47 am
content: Quote from: David Hess on July 23, 2024, 01:14:26 amNot sure you can generalise that, probably specifics dependant. Where I worked we got a 'dunny cart' for the australian army through its stringent emissions testing, it had a brushed DC motor for the pump, we just had to fit a capacitor across the brushes. The BLDC motor has a drive built in which could be noisy, and good commutation doesn't have to spark especially at low voltages.

author: robzy
author_rank: Regular Contributor
timestamp: July 23, 2024, 04:54:00 am
content: Quote from: ricko_uk on July 22, 2024, 11:13:53 pmThe type which is placed far away from the sensors and uses linkage to transfer the stirring force.A hydraulic or pneumatic solution might be the cheapest and easiest way to go.Also you need more specific requirements than "very low emissions". Exactly how low do you need?

author: Andy Chee
author_rank: Super Contributor
timestamp: July 23, 2024, 06:32:11 am
content: Quote from: ricko_uk on July 22, 2024, 11:13:53 pmCan you tell us what those sensors are?How about just using DSP to get rid of any noise?

author: David Hess
author_rank: Super Contributor
timestamp: July 23, 2024, 06:21:34 pm
content: Quote from: moffy on July 23, 2024, 01:25:47 amLow power brushless DC motors can use electronic commutation without PWM drive to control speed. Speed is controlled by the back EMF just like with a brushed DC motor. The circuit can be incredibly simple, as shown below with a temperature controlled fan. Modern devices either use one hall effect sensor or sense through the motor windings.

author: Siwastaja
author_rank: Super Contributor
timestamp: July 23, 2024, 07:07:08 pm
content: Quote from: ricko_uk on July 22, 2024, 11:13:53 pmWhat kind of sensor? This sounds like a classic X-Y problem, with assumed problem which very likely does not exist at all. If the sensors are available in the market, and the motor+driver is available in the market, they must comply to both EM emissions and immunity requirements, and will work fine. This is required by law; sensor manufacturer has tested that sensors operate within specifications under radiated and conducted emissions, and motor manufacturer has tested that the motor does not exceed these emission limits. ... in theory, of course.Add to mix some specialty prototypes, Ebay crap etc., and then it might matter. Still, I would not stress about it too much in advance, chances are very high there is no problem with any motor type.Avoid low quality brushed motors. High quality brushed from decent manufacturers are OK; brushless types with short motor wiring are quite safe.

author: moffy
author_rank: Super Contributor
timestamp: July 23, 2024, 10:28:40 pm
content: Quote from: David Hess on July 23, 2024, 06:21:34 pmThanks David, I am moderately familiar with the BLDC topology and you present the operation so concisely. I was just pointing out that the drive electronics perhaps better described as the switching/commutation electronics is a source of noise. A good commutator (round and seasoned), with bedded in brushes, especially at low voltages doesn't have to be noisy, but it would have to be a quality DC motor.

author: coppice
author_rank: Super Contributor
timestamp: July 23, 2024, 11:30:17 pm
content: Nobody seems to have mentioned ultrasonic motors. They have essentially nothing magnetic going on, which is why they get used for things like powering the bed in an MRI machine, although the piezo devices may produce an electric field which can be shielded. They are not great for high speed rotation, but you are only looking for 200RPM.

author: BrianHG
author_rank: Super Contributor
timestamp: July 23, 2024, 11:56:06 pm
content: For DC Brushed motors, not only do you need to place a cap directly across the motor terminals, but you also need to solder a cap on each motor terminal directly to the motor chassis. No wire lead lengths allowed. This is the trick really old, like 1975, RC cars used to use to stop motor commutator noise from affecting the radio receiver which at the time were ~25mhz am radios, sensitive to any noise at all in the system. The caps directly to the motor chassis turned the motor casing itself into a Faraday cage.The cap values would typically be 0.1uf or 0.01uf, ceramic.

author: BrianHG
author_rank: Super Contributor
timestamp: July 24, 2024, 12:05:23 am
content: See here:https://www.eevblog.com/forum/projects/brushed-motor-emi-reduction-with-x2y-caps/

author: Haenk
author_rank: Super Contributor
timestamp: July 24, 2024, 01:08:53 pm
content: Maybe hack something together for a test - use a low noise PC fan motor (brushless) and a metal can to contain the power supply and a PWM controller. So that's a less than 20 bucks setup to check if this is "good enough".A used electrical drill head from a dentist might be a good choice as well, some of them also go down to low 3-digit rpm (brushless motor, too).

author: Martinn
author_rank: Frequent Contributor
timestamp: July 24, 2024, 04:45:19 pm
content: If you can place a VFD (which generates a lot of noise) away from the test setup, you could use a sine output filter, removing most of the harmonics. These are expensive, but at this power level (few watts?) maybe acceptable. Small induction motor then. Sounds overkill though.More exotic: Use a small BLDC motor and drive it with three sine waveforms. Use three (linear) audio amplifiers to create the phase voltages. Drive the BLDC open loop (for a stirrer this should do) in stepper motor fashion (enough current to have plenty of torque, with slow enough acceleration profile).

author: wilhe_jo
author_rank: Regular Contributor
timestamp: July 24, 2024, 05:10:24 pm
content: Quote from: ricko_uk on July 22, 2024, 11:13:53 pmWell, I'm currently building a linear stepper motor driver to be used in an EMC-Chamber... lowest emission is essential.My first prototype does run, but there'll be some time to go since this is one of my commercial filler-projects that may get eventually sold.If your problem is not time-critical, this could work.I'd stay away from speed drives (VFDs, BLCD-drivers,...).Depending on your mechanical setup, filtering may get a non-trivial task...73

author: Siwastaja
author_rank: Super Contributor
timestamp: July 24, 2024, 06:27:40 pm
content: When I built a film scanner with a linear CCD and 14-bit ADC, I did build a linear stepper motor controller (basically DAC + class AB amplifier stage) for it, "just for safety" against noise. In retrospect, I don't know if an even semi-decently designed normal PWM stepper motor controller would have caused any issue. Probably not. The motor is a huge inductor which limits dI/dt. That leaves capacitive coupling, which attenuates pretty fast.

author: Jeroen3
author_rank: Super Contributor
timestamp: July 24, 2024, 07:13:59 pm
content: I've been dealing with a project with similar constraints (military) of silencing a brushed generator. Impossible job, even the flexcoupling emits emi.Brushes are out, they generate soo much noise. You won't be able to keep this contained. So no DC motors.If static field is a problem, then you can't use brushless dc's motor with magnets. So shaded pole/induction is the only option then.You could use a vfd/motor controller with reactor filter (inductors). If it's very low power you can maybe use a low voltage one through a transformer, as that would completely remove the common mode. Starting torque may be limited.However, this all focusess on the electric options. What about mechanical options?- increase the distance with a long shaft or flex axle (like those dremels have)- mechanical gearing- hydrolics?

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2024, 09:59:06 pm
content: Quote from: Jeroen3 on July 24, 2024, 07:13:59 pmI suspect Tektronix had the opposite conclusion. They originally used shaded pole motors, but had to add extra magnetic shielding in some cases. Later they made their own DC brushless motor which required no external shielding, but I assume they took steps in its design to control leaking magnetic flux.

author: BrianHG
author_rank: Super Contributor
timestamp: July 25, 2024, 03:04:41 am
content: You can use a mechanical wind up motor, with nothing more than a solenoid to enable/disable it.This used to be used in old battery powered radios for the auto-radio station seeking feature. No motor meant no interference in the rf signal level radio station detector.Though, you will need to wind up the thing every once in a while...

author: wilhe_jo
author_rank: Regular Contributor
timestamp: July 25, 2024, 10:13:32 pm
content: Quote from: Siwastaja on July 24, 2024, 06:27:40 pmWell, the common-mode noise introduced is pretty high if you need to ground the motor.Adding filters makes the current control of the drivers I tested pretty unhappy (works in principle, but the motor screams as hell).YMMV, but I go for linear drives inside the EMI chamber73

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 25, 2024, 10:39:04 pm
content: Clockwork?

author: David Hess
author_rank: Super Contributor
timestamp: July 25, 2024, 10:48:59 pm
content: A stepper motor could be driven by an analog quadrature oscillator eliminating switching noise.

author: coppice
author_rank: Super Contributor
timestamp: July 26, 2024, 12:41:25 pm
content: Quote from: mikeselectricstuff on July 25, 2024, 10:39:04 pmIf we are going outside the box, we ought to consider a mouse in a wheel.

author: max_torque
author_rank: Super Contributor
timestamp: July 28, 2024, 09:23:45 pm
content: Without some actual limits for noise and a definable problem this whole thing is obviously pie in the sky, but clearly the "best" solution if electromagnetic noise is an issue is to quite obviously not use an electric motor!An air motor, or hydraulic motor, or clockwork one (as mike suggested!) or perhaps a hamster running in a wheel all are clearly quieter than ANY electric motor as none of them use electricity! With any practical electric motor, the devil is in the details, and the precise implementation is going to domiate the emissions profile rather than the fundamental architecture.And of course as an electric fields strength decreases with an inverse square of the distance between the emitter and the reciever, again, clearly, by far the best option is to seperate the energy conversion from the energy consumption and transmit that energy non-electrically, ie back to the air motor again etc......

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 28, 2024, 10:17:42 pm
content: Quote from: max_torque on July 28, 2024, 09:23:45 pmOr simply use a mechanical coupling - shaft, chain, belt etc. to increase the distance

author: coppice
author_rank: Super Contributor
timestamp: July 29, 2024, 09:45:32 pm
content: Quote from: mikeselectricstuff on July 28, 2024, 10:17:42 pmA lot of the applications for ultrasonic motors are places people previously had to do just that.

author: coppercone2
author_rank: Super Contributor
timestamp: July 30, 2024, 03:12:20 am
content: How much does a piezo motor cost to replace a belt drive motor?In some cases it seems like the kind of lab equipment that can bleed some QC or analytical place dry for no good reason.If similarly priced its a great achievement though.Lol, it sets off an alarm for me. Like if there is some new lab equipment that makes something spin by some other means but then its like 5000% more expensive.I just know, there is the laboratory interior decorators ministry that will think a 2 foot long belt ruins the decour of the lab bench that's going to be empty. And they will pay 500% extra if you can replace a box shape with a mitered box shape.Oh man I know some people if you put like a swiss rubber belt drive type mechanism in their building they won't ever sleep soundly again. Like one of those belt drive vacuum pumps. The old ones. To them its like you put a dead racoon on the table. They need the throw away "mitered" look box vacuum pump instead, so you can neatly stack them in a dumpster once they get friedthe illusion of high tech. it might make sense in a nuclear submarine, but not your labthe machine that used to get you a reasonable pension plan! currently being replaced to ensure your workplace looks "lab-core"

author: coppice
author_rank: Super Contributor
timestamp: July 30, 2024, 11:36:50 am
content: Quote from: coppercone2 on July 30, 2024, 03:12:20 amThey aren't as cheap as more conventional motors, but they aren't only used in exotic applications, like MRI patient bed drives. For example Lexus uses them for the motors in its seats. They are quiet, need no brake or heavy gearing to maintain their position when the motor isn't running, and the final cost doesn't stop a Lexus being well priced against other cars using conventional motors. I looked into them for a couple of anti-tamper applications, where a conventional magnetically based motors can be susceptible to being stalled by powerful external fields.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 30, 2024, 12:58:41 pm
content: Quote from: coppice on July 30, 2024, 11:36:50 amI believe Lexus's first application for ultrasonic motors was for the steering wheel adjustment on the LS430. It was a really bad idea - they virtually all fail after a few years. Last time I checked, refurbed ones were over £300 each. When I took a failed one apart it was full of shredded black plastic. Presumably there was a plastic disc sandwiched between two metal surfaces, and it just got chewed up. I'm sure the ultrasonic motors will be much better in the later models.

author: coppice
author_rank: Super Contributor
timestamp: July 30, 2024, 02:08:32 pm
content: Quote from: SteveThackery on July 30, 2024, 12:58:41 pmInteresting. Maybe that was a bad design. I assume you mean the adjustment of the steering wheel to the driver's size. Like the seat motors, I wouldn't expect that to be operate often enough to have any kind of wear and tear issues. The ultrasonic motors used for focus and zoom in lenses go back and forth a lot. typically spending most of their time over a small part of their range. They seem to last.

author: coppercone2
author_rank: Super Contributor
timestamp: July 30, 2024, 04:28:48 pm
content: That seems like a reasonable price. The ones on google come up in the 5000 dollar range making it a little obscene for a stirrer

author: BrianHG
author_rank: Super Contributor
timestamp: July 30, 2024, 05:59:27 pm
content: Quote from: mikeselectricstuff on July 25, 2024, 10:39:04 pmRead 2 posts before yours:https://www.eevblog.com/forum/projects/lowest-emissions-electric-motor/msg5583643/#msg5583643Example:Seek to 56:45 to see it working.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 30, 2024, 06:46:50 pm
content: Apparently OP got his answer and we will never hear what was driving his problem.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 30, 2024, 09:24:30 pm
content: Quote from: coppice on July 30, 2024, 02:08:32 pmThe LS430 has a feature whereby switching off the ignition causes the steering wheel to move upwards and inwards, giving the driver more room to get in and out. The steering wheel returns to the driver's preset position when the ignition is switched on. It's a cool feature, but clearly the ultrasonic motors couldn't handle the workload. It was a rare, but serious, design mistake on the part of Toyota.

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2024, 03:12:08 pm
content: Quote from: SteveThackery on July 30, 2024, 09:24:30 pmMaybe I missed it in the previous discussion, but what advantage did Toyota think ultrasonic motors had for that application?Ultrasonic motors would still require some type of position encoder.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 31, 2024, 04:17:15 pm
content: Quote from: David Hess on July 31, 2024, 03:12:08 pmYou didn’t miss anything. Ultrasonic motors generate loads of torque at very low rpm, plus they are self-locking when not powered. The alternative way to get that much low speed torque is with a traditional electric motor and a gearbox. You'd need to incorporate a worm drive as well to make it self-locking. Adding a worm drive and reduction gears increases the overall size of the package. Ultrasonic motors are unbeatable when it comes to their compact size. I believe that Toyota used ultrasonic motors for their compactness and - equally important - their silent running.

author: coppice
author_rank: Super Contributor
timestamp: July 31, 2024, 07:31:51 pm
content: Quote from: SteveThackery on July 31, 2024, 04:17:15 pmI think it was more simplistic "A Lexus LS needs silent motors" thinking, and all the other plus points followed.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 31, 2024, 07:39:59 pm
content: Quote from: coppice on July 31, 2024, 07:31:51 pmYeah, maybe. Probably. It's hard to know, 20+ years later. I'm inclined to agree that silent operation is probably the most important requirement. Having worked on the Lexus, it's clear that the small size was a desirable bonus.

author: coppercone2
author_rank: Super Contributor
timestamp: July 31, 2024, 08:28:46 pm
content: I think not having a gearbox is the most appealing factor.Now we need a ultrasonic motor kitchenaid stirrer. In the back of my mind I am wondering how many loaves of bread it can make before the worm gear strips again

author: Terry Bites
author_rank: Super Contributor
timestamp: August 01, 2024, 11:47:42 am
content: Could you mix using a fine stream of bubbles instead of a stirer? Use an aquarium air Stone and a bottle of argon.Ever touched a portable radio antenna with a metal thingy. Crackle crackle!Pneumatic, hydraulic and clockwork will all create low level RFI as metal parts move against each other.Pneumatic motors can create a lot of static.Put the motor in a shielded grounded box. Ground the final bearing and or motor case and put a grounded slip ring on the shaft.Join the motor to the stirer with a nylon shaft coupler. Fit a nylon bearing where the shaft exits the box.

author: coppice
author_rank: Super Contributor
timestamp: August 01, 2024, 12:03:54 pm
content: Quote from: coppercone2 on July 31, 2024, 08:28:46 pmIn a lot of applications that use ultasonic motors, the enormous torque needed to turn them externally when they are idle is a huge plus. It can eliminate an entire braking scheme.