Morricab,
Many thanks for fueling my points - this particular motor suffers from the same problems of core motors - the moving field is created by discrete coils that create a moving magnetic field . In such a simple arrangement they must be driven by a special algorithm with correction that compensates for the typical non linearity of such discrete arrangement - these coils have large gaps between them! Go on reading how it works and what they had to do to help solving, surely with relative success, the intrinsic problems.
"Additionally a large rotating mass of 500 grams, achieved by using a nickel-plated steel motor body, works likes a flywheel. This drives the platter of the turntable with a very even force and reduces vibration".
This type of drive is used, for example, in cheap motors for diskette readers. Brinkman probably optimized the controller and created a fancy, geometry, keeping costs low. This motor costs a lot less than a custom cored motor. It also has some more problems that a classical cored geometry, such as those caused by vertical variable drag.
What do you think of marketing literature that goes on saying "The new motor generates more torque and is therefore able to reduce the start-up time to a few seconds, no problem for the new vacuum tube power supply »RöNt II«, which is also able to handle the direct drive motors as well. ".
IMHO DDK explained fairly well why designers are developing such fancy motors for belt turntables in another thread - no one is currently able to supply the good old synchronous motors of yesterday.
BTW, I have reasons to consider that Brinkmann turntables are excellent sounding, but not because of their literature.
There is very little in common between this motor and the extremely well designed coreless motors of the Calliburn or the VPI, made by Thin Gap, except they obey to the same basic laws of electromagnetism!
No, again you miss the point of the difference. The IRON in the stator of a normal motor makes magnetic attraction and repulsion to the permanent magnets in the rotor. THIS is what causes cogging. Remove the iron you remove the magnetic attraction and repulsion from the iron poles. By going coreless you remove this issue...that doesn't mean there are not other, geometry related issues with motors. By sinusoidally commutating you can bridge between coils as long as there is not the iron there mucking things up.
DDK has his opinions and is welcome to them. They are by no means gospel. I don't see why cheap easy to build synchronous motors would be hard to source. The printed motor (pancake motor) that I have cost me over $1K. A synchronous motor with suitable torque costs maybe $50.
Brinkmann's do sound good because of their design. Their literature merely explains the design and they seem to be a pretty modest and factual company from my experience also talking with Helmut Brinkmann.
I never said Brinkmann's motor was the equivalent of what went into the Caliburn, that seems like a strawman you want to setup. You have to ask yourself though why Continuum used such a coreless motor in their no-holds-barred design rather than a good old synchronous motor...same for VPI, why such an extreme motor if it really doesn't matter so much as you clearly seem to imply?
They all do follow the same laws but different implementations of that law will provide stunningly different results. Removing iron from the circuit reduces torque but removes a main barrier to smooth motion at low speed. Sure at 300 or 1000 RPM it matters very little, so for belt drive it would SEEM less important (Continuum thought otherwise as does Brinkmann and I suspect others) but for a drive turn at 33.33 RPM smoothness matters a lot. The jerkiness cannot be eliminated when it is inherent in the electromagnetic circuit...the rotor magnets are attracted and repelled by the iron poles...it is physics and can't be undone by fancy commutation. Just like crossover distortion in an amplifier cannot be corrected by negative feedback...only the right bias to "smooth out" the transition works.
Going slotless removes further motor noise but doesn't necessarily improve torque ripple.
""Another way to avoid cogging is to go with a coreless design. The rotors of coreless motors consist of skew-wound wire with no core. They offer lower inertia and inductance, as well as zero cogging. Of course, as with all things in engineering, there are trade-offs. Cogless designs may offer smoother torque but that comes at the price of lower torque all the way around. For constant-speed and contouring applications, a coreless motor may provide the best results.
For an application moving at constant speed, the frequency of the cogging depends the speed. By choosing the proper drive and designing the control loop to minimize the amount of gain at that frequency, system designers can minimize the effect of cogging."
"Ultimately, it’s a matter of tradeoffs. For many applications, cogging torque has little effect. In the case of a continuous-motion application like scanning or contouring, however, cogging can be a problem. “Manufacturing or inspection, those tend to be some sort of contour moves where you need smooth motion,” says Profeta. “Cogging can affect you, even if you’re doing a positioning application. You have to ask yourself what type of positioning application you’re doing and does this make sense or no.”
These quotes come from motion control online.
It is clear that industry at large prefers cogless motors for applications where high torque is not required but smooth continuous motion is required...like spinning a turntable perhaps?? This is why the Japanese designers went this way 40 years ago and why new designers are returning to this after a "dark ages" of only synchronous belt drive TTs.
IMO, the printed armature motor could be the ultimate TT motor. It has virtually zero torque ripple by design. It is brushed with 150 or so "slots" per rotation so not as silent as a brushless design but as a DD motor at low speed I have found it to be silent.
http://www.printedmotorworks.com/wp...-motor-versus-conventional-electric-motor.jpg
"With no magnetic material present in the disc, undesirable ‘cogging’ is completely eliminated. This produces perfectly smooth low speed operation and continuous torque down to zero RPM. Torque output in the flat armature motor is not limited by saturation and instead directly proportional to current. At the same time, speed is directly proportional to voltage."
Interesting motor from the 1970s Teac TN-400: https://blogs.yahoo.co.jp/hsgwhz/10589863.html Not coreless but a serious attempt to minimize a normal motor with 20 poles and 60 slots! Probably not as smooth as a printed armature motor but maybe needs a less sophisticated controller.
