Which is the best Direct Drive motor? Simucube developers will find out

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#61

@Mika Fanatec gave us a screenshot of the DD2 holding torque stress test. Can we have the same for your servomotors to make comparaison ?


#62

Torque is as stated on the product specification page. There is throttling when there is danger of exceeding safe requirements for motor surface temperature, and should not be able to be reached even when using 100% torque when driving.


#63

It could be useful @Mika to have the same graphic to know exactly how much time the Pro motor for example could reacht 25Nm for stall torque. So we can have a precise vision… Or your motor can’t do this torture ? :stuck_out_tongue_winking_eye:


#64

Mika,

Excuse my lack of knowledge in this area but if I am correct you are saying that it is almost impossible for us to stall the motor during normal use and so if you showed a chart like the one above it would show a straight horizontal line?


#65

Yes, it would be a horizontal line and the throttling definitively would not be visible in the first 10 minutes - but I do not know the specific time on when it would start.


#66

This picture (to my eyes) is about verifying the cooling performance of the product design under stress test. This manufacturer has said that they use outrunner motor inside the product, which means that the coils (stator) are inner parts of the motor (and rotor is outside). Stator is (typically) the part where the coils are and where heat is created inside the servo motor). Outrunner motor design is typically such that it does not have large heatsink or surface by its design that would keep the motor parts cool enough without some active cooling. As I understand it, this mfg. has added also some layers of casing material that affect so that without active cooling it would make the temperature of the motor coils and parts too high so that product life / reliability could be compromised. Therefore verification of the cooling design is actually needed for them (so that the motor can be run on the torque level they use it under all the layers of material).

The psu power drawn in picture is such that 25 Nm is the max power in stall situation, then in the first 3 minutes the torque is lowered linearly to about 20Nm. The previous means that needed electrical power is lowered by ~36%, then again after perhaps after 13 minutes the torque is lowered to 15Nm, which represents about ~36% power requirement from the psu ( or 64% reduction from peak power which may be the overall cooling power of the product design so that the motor does not overheat inside of the product in long use sessions).

Inrunner motors (when the motor is correctly chosen for the task) do not need active cooling in this use case as the motor’s design itself is good enough to keep the temperature of the motor cool enough in this use case, (barely even warms, considering how hot the motor is designed to run). Moreover, advertising stall torque is actually irrelevant in this use case as nobody hangs in the corner for several minutes, (as far as I know) there are no such turns in real race tracks that would require a driver to turn the wheel with let’s say 15Nm of torque for 15 minutes. Quite describing title of the picture to my eyes could be something like “verification of the product’s active cooling performance under stall torque test” which in engineer’s mind also translates to, “how many watts of heat the product’s active cooling design can cool the product under use and with known fan characteristics”.

So, basically as we have had no use for these sort of graphs / tests in our product design process, we have not made such graphs and likely will not make these as these seem more or less irrelevant as we have passive cooling and different objectives in our product design.


#67

So what we’re seeing here is thermal throttling to stay within the TDP of the active cooling solution’s capabilities from sustained running?


#68

Unfortunately in addition to what was said above in a FFB situation the servo motor is never in a Stall characteristic unless you are going in circles with 100% saturated force (which just doesn’t happen) so the stall torque for the most part means nothing… even on an oval track where you could be cornering for a decent length of time road texture and corrections by you as the driver alters the torque so rapidly that the motor is never actually stalled. I have NEVER felt a servo derate while driving on any of the DD wheels I have run, which includes both versions of the DD’s in question just this week back to back. I can tell you though that by their calculated display when actually held in torque on the hardware bump stops they do drop the current to the Servo which reduces the 20Nm to about 18Nm and the 25Nm to about 23Nm. which could be protection from heating as Tommi has mentioned… but it also happens MUCH sooner than the graph above would indicate (it happens within about the first 10-15 seconds). Though like I said this de-rating has never happened while driving.

So basically the Graph is marketing trying to bring up questions about competitors that either aren’t asked (which could be appropriate) or not really relevant (which is what this one is) to promote.


#69

Even then you probably won’t know what servo it really is, You might be able to find out the manufacturer in a round about way by construction techniques to types of parts used, BUT… order enough servos and you can spec things for your own needs which is what I am guessing has happened through the testing… they found out the little differences between a few servos that did what they wanted and set out to spec a motor that did all of these things properly for their needs.


#70

So basically those charts that Fanatec are so keen to show are meaningless and pure marketing hype meant to impress uneducated, non servo motor experts like myself :blush:


#71

I understand the reason why some DD wheel suppliers choose to show torque-charts are shown, they serve a dual-purpose, from my humble point of view.

Be assured though, those tests are not required for DD wheels based on Simucube1/IONI or Simucube2 controllers and related servos design, more so for SC2 with it’s silent, smooth and efficient passive-cooled design concept.

As I have stated quite a while back when these first appeared, Stall-torque is meaningless really in a sim-environment, peak-torque is really what matters, as we never enter extended stall-conditions in racing-sims, where one might exceed the mechanical time-constant of the servos, forcing torque-deration. At least not with in-runner servos with their much higher thermal-mass.

Out-runner servos is a different proposition, the higher torque capacity/weight/size comes with the disadvantage of a significantly reduced area for the stator, which causes big challenges for ripple-control algorithms, as well as the challenge getting the heat out of a servo, very often requiring active cooling. Fan-noise will be dependant on the quality and size of the fan.

So whilst out-runner style-servos are great for lightweight torquey equipment, higher-end precision position-based CNC Automation equipment are all using in-runner style servos due to their superior smoothness wrt significantly reduced ripple-torque due to a large stator-area (by design) and thermal management properties, reduced ripple allows for much greater positional accuracy, vs the out-runner style servos.

Guys, there are very good reasons an industrial drive-controller supplier like Granite Devices went with in-runner servos over other types: quality, reliability, absolute the best in positional accuracy, smoothness and other factors, are only a few key differentiators.

SC2 is in-runner and passive cooled, by far the best current DD wheel on the market, from my initial testing. More later after longer seat-time.

Cheers,
Beano


#72

To me it seems as thermal throttling to stay within safe operating temperature, but without known fan characteristics (fan speed) and overall sound characteristics if those aspects are interesting things to the user. The product seems to have fan control algorithm that has “steps” as the stall torque also decreases in “steps”. In anycase, this picture is needed/useful for the mfg engineering work, not so much to the end-user provided that the product’s torque output does not (in normal conditions) behave as a function of the temperature of the parts inside the product -> thermal throttling in normal conditions. According to Brion the wheelbase should have linear torque output with the exception of the end to end travel bumb stops where torque is little bit lowered after some time which is unlikely to concern the users as a feature.

In our opinion the aspects that matter for the drivers (and what aspects we have used in our product design ) are smoothness, low cogging, low ripple, high torque response rate, and high motor efficiency which enables passive cooling (and lower power consumption) and low noise.


#73

So SC2 is now using in-runner type of motor, then how about small / big mige on SC1 ? I only know they are servo type, are they also in-runner type ?


#74

And about the heat generation in Fanatec DD testing video, I still remember it shown as around 60℃ under stress test, with two motor stick together and twist in opposite direction I believe.


#75

They are in-runners too :wink:


#76

Wrt the stress-test, one doesn’t know the torque applies to those servos under test, it could be 5nm or 2.5nm or 12.5nm…

Unless those are done against a set criteria, it doesn’t prove /disprove anything.


#78

I have recently done some thermal time constant experiments and math on SC2 motors.

Assuming passive cooling in room temperature, SC2 Sport motor can keep full 100% torq for 4,5 minutes and Pro/Ultimate for 6 minutes before torque begins to throttle at all.

Best thing here is that the torque will stay constant before it’s beginning to reduce. This is significant characteristic as it ensures linear and consistent force feedback. In practical racing, there is no such long periods of peak torque, so it is unlikely that torque would start throttling at all.

I hope this helps!


#79

Thanks for this response @Tero:slight_smile: Very powerful and strong motors…


#80

Except for maybe oval racing?


#81

That might be the toughest case for wheel. I have plan to study & test that kind of driving too.