Stepper Motor vs Cassette-Type Motors – Which Is Quieter for Low-Speed Rotation? - Page 1
Forum section: electronics / beginners

author: engineheat
author_rank: Frequent Contributor
timestamp: July 02, 2025, 04:47:44 am
content: Hi everyone,I’m working on a small device that needs low-speed rotation (30 rpm), and absolute silence is a top priority. There’s no need for high torque or precise positioning — I just need a smooth, reversible motor that’s very quiet.I’ve tried several DC motors (e.g., Tamiya, generic 3–6V brushed types), but they tend to be too fast and noisy, even at reduced voltage. Gearmotors helped with speed, but the gearbox noise became unacceptable.After testing a Polulu stepper motor with a TMC2100 driver in stealthChop mode, I was pleasantly surprised by how quiet and smooth it runs at low speed — better than anything else I’ve tried so far. It was literally completely silent.🔍 My question:Would a motor like those used in cassette players (coreless DC motors?) potentially be as quiet than a stepper with TMC2100?My needs:Extremely quiet (completely silent)Very low-speed rotation (30-50 RPM)ReversibleMinimal complexity preferredLow torque is okayThe reason I ask is because I don't need precision movement and the stepper motor is not very power efficient. It also requires a specialized driver to achieve the quietness.I thought about tape players and remember they rotated at the speed I want and were pretty quiet. So I'd like to understand what kind of motors they are, any special driver chips needed or is it easier to DIY the controller, and if they are truly as quiet as I remember.Thanks

author: RoGeorge
author_rank: Super Contributor
timestamp: July 02, 2025, 05:12:37 am
content: Cassette players motors were not low RPM. The typical mechanic for a cassette player used to have only one brushed DC motor of a few thousands RPM (e.g. 2400 RPM, this can be easily heard in a quiet room), and the RPM was reduced with a rubber belt passed over wheels of very different diameters.Another aspect, the cassette DC brushed motors were made to always turn in the same direction (usually CCW), not sure how reliable they'll work in reverse. The forward/rewind change of the tape direction was done mechanically.Sure, there were some high-end models of cassette players with a direct-drive capstan motor, but I don't think those motors can still be sourced nowadays. The normal cassette players used to have only one brushed DC motor, and one or more rubber belts.My guess is the quietest low RPM motor would be a stepper, driven with a driver that can produce sinusoidal currents.

author: amyk
author_rank: Super Contributor
timestamp: July 02, 2025, 05:24:23 am
content: No, cassette decks do not use coreless motors. To elaborate on the comment above, they're usually 3-pole brushed motors with an "oversquare" armature that makes them very stable in speed.A stepper motor can be run like a multiphase AC motor withmanypoles.30RPM may be achievable with a 60Hz AC synchronous clock motor run at 30Hz (with the appropriate lowering of voltage), although rotation direction is fixed.

author: Berni
author_rank: Super Contributor
timestamp: July 02, 2025, 05:53:36 am
content: Stepper with a fancy super fine microstep driver chip is likely the way to go.They don't really make DC motors for speeds that low because that means very strong magnets and a huge number of turns and/or poles. The brushes also make some noise, tho id say the motors in cassette drives are very quiet unless you are going to be putting your ear up to it in a quiet room. To get the low RPM you can do the same thing that cassette decks do to get the low RPM they need. They all have a belt drive. Belts are silent and can provides a pretty high gearing ratio if a lot of torque is not needed.You can likely steal a lot of the parts from the deck that donated the motor.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 02, 2025, 09:42:03 am
content: There is a motor that could meet your needs exactly: an ultrasonic motor. They are silent, they are extremely smooth (no "cogging"), they are relatively slow revving (30rpm is right in their happy place), and they generate a lot of torque (which I know you don't need). The early ones had a limited life, but I believe that has been addressed now.https://toshiba.semicon-storage.com/eu/semiconductor/knowledge/e-learning/village/ultrasonic-motor.html

author: SteveThackery
author_rank: Super Contributor
timestamp: July 02, 2025, 09:45:46 am
content: Quote from: Berni on July 02, 2025, 05:53:36 amThat's interesting. I've never managed to get a stepper motor anywhere close to silent, although if the stepping frequency is ultrasonic that could be a great solution.

author: spostma
author_rank: Regular Contributor
timestamp: July 02, 2025, 09:48:31 am
content: Have you thought of an Automotive Gauge Stepper Motor?Something likehttps://www.adafruit.com/product/2424I think that fits your bill perfectly!

author: SteveThackery
author_rank: Super Contributor
timestamp: July 02, 2025, 10:35:59 am
content: Quote from: spostma on July 02, 2025, 09:48:31 amDoesn't seem to do continuous rotation.

author: BrianHG
author_rank: Super Contributor
timestamp: July 03, 2025, 08:19:33 am
content: Floppy drive motors?They are sinusoidal stepped, slow, silent.I've seen the fake-HD 3.5inch drives run at 150rmp by lowering the 500khz crystal to a lower frequency.Also, similar but much more powerful direct drive capstan motor divers exist for old fashioned VCRs with multidirection and a wide variable speed. Like from stepping, 1/2 playback speed all the way to 25x speed.

author: Berni
author_rank: Super Contributor
timestamp: July 04, 2025, 05:37:13 am
content: Quote from: SteveThackery on July 02, 2025, 09:45:46 amThey are mainly the chips from Trinamic that got popular in modern 3D printers like the TMC2100They offer very fine microsteping by having some advanced smarts in there. They do closed loop current control that is driven by extra interpolation logic that samples from a 1024 step sine table. So as a result the current on the motor phases become a smooth sinewave, so no sharp transitions that make that annoying noise in steppers. They control the phases with so much care that the driver chip can even detect missed steps on the motor purely from looking at the volts and amps on the phase.Tho they are still not completely silet, but on these 3D printers usually the mechanical bits moving are louder than the motor itself. But even that little bit of noise can likely be reduced if you don't need the high torque and so can use a weaker stepper and reduce the phase drive current.EDIT: Oh and btw there are also tiny weak stepper motors designed for moving analog gauges. These things are used in things car speedometers (from the era that cars are controlled by electronics, but don't yet have full digital LCD dashes). These are likely completely silent since they are not designed to make much torque.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 04, 2025, 09:52:38 am
content: The most silent way to drive a stepper motor is to generate two sine waves with a 90 degree phase difference. Something like a wien bridge oscillator for one phase, and a phase shifting network for the other motor winding, and then add two audio amplifiers.If you want to keep things simple, you can experiment with a simple low voltage transformer, and use a single capacitor for the phase shift for the other winding. You'll never get to 90 degree phase shift, but maybe you get far enough. A regular 200 steps/rev motor has 50 pole pairs, so it would run at one revolution per second (60rpm) from a 50Hz mains transformer.And also, don't forget the enclosure. It can either work as a sound box to greatly amplify the remaining motor noise, or dampen it considerably.

author: tooki
author_rank: Super Contributor
timestamp: July 04, 2025, 11:27:23 am
content: Quote from: RoGeorge on July 02, 2025, 05:12:37 amFYI, in some cassette decks, for example in Sony Walkman portables with logic control, a single motor is used to perform all functions in the deck (including all the mode changes) by controlling that one motor in both forward and reverse at various speeds. It’s a very clever mechanism, using a complex cam wheel with clutches that engage directionally at higher speed. For example, if playing in one direction, to change modes it might first pulse the motor in reverse at high speed to release the clutch, then run at medium speed to move the cam wheel to a particular configuration, then pulse again in forward to re-engage the clutch, then return to normal speed to run in the new configuration. The ones I’ve seen with this support forward and reverse playback (autoreverse), stop, fast-forward and rewind with playback (for auto-seeking), and fast-forward and rewind with head retracted (for true fast forward and rewind).I have never seen this approach used in a home deck, but I can’t rule it out. But in portables, for sure.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 04, 2025, 04:25:15 pm
content: Quote from: Doctorandus_P on July 04, 2025, 09:52:38 amCould you explain this further? I don't think that results in a constant torque, because if you sum the amplitudes of a sine wave and a cosine wave you get a sinusoidal wave of the same frequency and 1.414 times the peak amplitude.I bet I'm wrong and what I've described has nothing to do with the torque, because it doesn't take into account the position of the armature with respect to the stator. Does that smooth out the torque? Keen to learn, here!

author: Berni
author_rank: Super Contributor
timestamp: July 05, 2025, 06:33:55 pm
content: Quote from: SteveThackery on July 04, 2025, 04:25:15 pmThe electromagnets in the motor are also 90 degrees out of phase. This makes the math identical to how complex numbers work. If you plot the two sine waves on a X Y graph you will get it tracing out a circle that is always exactly the same size as the amplitude of the two sine waves. This is also what happens to the magnetic field inside the motor, so you get a smoothly rotating field that stays constant in magnitude, the permanent magnet rotor following this field along, making it spin. The same work for 3 phase motors (or any number of phases really), in fact we invented 90 deg 2 phase motors as some of the first AC motors, but later on figured out that 3 phases are more convenient because the phases sum to 0, meaning you can cheat by not needing a neutral wire.However the real world has extra complications that deviate from this ideal scenario. The feromagnetic cores in motors are not fully linear and the rotor being attracted to it causes coging, so the real ideal waveform for precisely constant rotation is not actually a sinewave, but instead almost a sinewave with some slight harmonic distortions in it. The exact distortion is specific to the particular motors internal construction.For this reason the Trinamic TMCxxxx driver chips i mentioned above have a programmable sine lookup table inside where you can optionally fine tune each step to make it better match the distortions of the motor.However simply picking a lower torque stepper motor gives you extra smoothing because the magnet inside will follow the field more gently, also these distortions are tiny and low frequency so they don't actually produce much noise. The reason most stepper motors make such a loud ungodly whine is because they are often driven with no microsteping or only 4 to 16 step microsteping, putting very sharp square wave like signals into it, that sharp edge has a lot of high freqency components that violently shake the whole motor and whatever is attached to. But sine waves don't have sharp corners so that can't happen.

author: SteveThackery
author_rank: Super Contributor
timestamp: July 05, 2025, 09:11:55 pm
content: Thanks, @Berni - that's a great explanation.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 05, 2025, 10:03:22 pm
content: Just saw there is a recent Hackaday article doing exactly this:https://hackaday.com/2025/07/04/2025-one-hertz-challenge-electromechanical-cmos-clock-keeps-in-step-with-mains-frequency/With more detailed info on the project page:https://hackaday.io/project/172231-the-electromechanicalanalogdigitalclock