Sim Racing servo ffb systems : OSW & Bodnar

Discussion in 'General Discussion' started by Adrianstealth, Jun 1, 2015.

  1. Spinelli

    Spinelli Banned

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    Thanks again. Well peak torques should only happen once in a while during very heavily loaded corners, and the straights will hardly be outputting torque besides some bumps and road imperfections, furthermore, many cars (if running 1:1 torque up until your wheel's max-set 28Nm) won't be outputting 28Nm except for possibly some curbs here and there, for example, a road car, the Clio racer, etc. It would concern me most on an oval though. The average torque output could very well exceed the small MiGes 10 Nm. If this knocks a few years of the motors lifetime then it won't concern me if the lifetime is still atleast 8 years, however, if the motor's performance suffers due to heat-fade (regardless of age of motor, it could even happen when new) then that would be unacceptable to most simracers I'm guessing - I'd be pissed!

    Is torque directly related to rpm? For example, a small MiGe + IONI Pro may be capable of 28 Nm @ 200 rpm which also means it's capable of 42 Nm @ 50 rpm or something (just an example)?
     
  2. Adrianstealth

    Adrianstealth Registered

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    You'll not suffer heat fade on these servos spiniili, the system will correct under error control,
    The worse that will happen due to heat that the servo gets so hot that it shuts down to self protect but performance will not degrade prior & I doubt you'll manage a thermal cutout for sim-racing -I never have & never will as my servo dosnt even get hot

    Any of these google tests that state otherwise -the servo was just being amped up & not controlled as part of a full servo system
    Best ignore google blubber

    Heat fade does happen on standard systems of course ( non full servo everything except senso bodnar OSW EK )


    "Is torque directly related to rpm? For example, a small MiGe + IONI Pro may be capable of 28 Nm @ 200 rpm which also means it's capable of 42 Nm @ 50 rpm or something (just an example)?".
    - With the deepest respect For sim-racing .....who cares this garbage has taken over this thread
    No offence of course
     
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  3. DrR1pper

    DrR1pper Registered

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    Are you saying sim-pie allows the ioni pro to go up to 30A output?

    That 21Nm number is only possible with 19A pos but I thought the ioni pro could only go up to 18A pos?
     
  4. Adrianstealth

    Adrianstealth Registered

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    Hiya dr. -yes but an add-on is needed. ( being developed now -but sounds imminent & inexpensive )

    As I understand it the custom board ( SIM-ple ) also allows for multiple power supplies ( could be x2 max ) so another will needed to be added also ( not sure at this moment if this will be a part of the "power stage" add on

    Ether way, with this "bolt on" option , large Mige will be utilised up to it max stated power rating Nm
    There'd be alot of power here, I'll give it a try

    Ps I'm just relaying info directly from Ollie ( via emails ) his custom stuff so far seems to be getting good community feedback
     
  5. Spinelli

    Spinelli Banned

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    Ok Adrian, so basically it's always either full performance or no performance (power off) with nothing in between (heat-fade induced reduction of performance). Correct? If so that would be a relief.

    Does the power add-on cause any sort of latency? Instead of just going through the IONI Pro, there'll sort of be 2 "stages" to it?

    Oh and no offense taken, I'm just trying get an understanding of things. I thought torque was nothing without rpm that's why I ask about it.

    To basically sum-up all my concerns/questions, I'm trying to figure out exactly what I'll be loosing (if anything) in the 0-300 rpm range and 0-27 Nm range with a small MiGe + IONI Pro relative to a big MiGe + Argon.
     
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  6. Adrianstealth

    Adrianstealth Registered

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    Hiya spinelli

    No heat fade at all on these systems , thermal cutout if to hot ( but doubt you'll ever cause that )

    Re.latency -I hope not lol, I'm sure Ollie will have to explain things better when he releases it ,
    I doubt it will cause latency as this would be sudden death to olies custom reputation ( we don't like latency Lol )
    It could be just simple power control circuit that run power directly along with existing power ( simple etc )

    Do what I'm doing (decided to again ), order one system but get both small & large Mige
    ( you'll easily sell if you don't want one of them )
    & interchange between the two, I'm pretty sure it's a simply switch between the two, I'm double checking this to be safe though
    ( the holding bracket & the cables/plugs into servo-motor are same )
    The Mige's really don't cost much by themselves

    I'm not expecting much difference though ( in feel for sim racing ), curiosity will be the motivation on running the LG Mige to full power with the add-on, who knows though I may have some surprises

    Also I've considered that as I'm being moved around a bit + vibration on my rig & if the bodnar is subtly more smooth & fluid I may not notice or benefit from this ( when compared to Mige's that could be a tad more abrupt Or slightly less defined -if this is the case )

    The bodnar has very high grade alloys/precision engineered etc ( will survive a much bigger machine bash or jam in industry )
    & will perhaps last 16 human lifetimes
    But I'll have to weigh up comparisons when I have other gear to compare too for sim-racing & for me personally
     
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  7. DrR1pper

    DrR1pper Registered

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    Torque and rpm are not inversely proportionately/interchangeably related like that. A motor's torque output is proportional to the strength of its stator coil magnetic field strength and the magnetic field strength is proportionately to the amount of current (i.e. electrical flow rate) you can pass through it's stator coil winding. Each electric motor has a specific ratio of current supplied to torque produced that is determined by the specific design of the motor (e.g. rotor permanent magnet strength, stator coil winding loop count, stator coil winding wire thickness, surface area of stator coil, lamination count, circuit resistance/impedance/inductance/capacitance/reactance, etc). This results in a quantifiable value called the torque coefficient (Nm/A) for each motor that tells us how much torque the motor will output for some amount of current.

    But how do we get X amount of current to flow through the stator coil windings? By supplying some amount of voltage. Recall the equation V=IR which can be rewritten as V/I=R. So for a fixed/constant amount of net resistance in a circuit (R), the amount of current you want is directly proportional to the amount of voltage you apply to said circuit. So if we use an arbitrary circuit example that has a net resistance of say 2 Ohm, the V/I ratio = 2, which means if we want 5A of current to flow we need to apply 10V of electrical potential energy to the circuit. If we want 10A, we need to apply 20V, etc.

    But how does this relate to speed?

    Electric motors produce torque by creating (carefully timed) specific polarity magnetic fields in sections of stator coils that repel the permanent magnet on the rotor facing directly opposite. But for a spinning rotor, the polarity of the permanent magnet on the rotor facing a section of the stator coil will be constantly changing over time, thus the stator coil must also match it's change in magnetic polarity if it is to continue imparting a net torque on the rotor (which will continue to accelerate the motor). What determines the speed limit though at which a motor can sustain X amount of torque? When at some rotation speed, the stator can no longer maintain the same average magnetic field strength that in turn produces the same average force/torque action on the rotor.

    What causes this?

    To answer that, need a little background in inductors. Inductors are just coils of wire (e.g. stator coil winding) that produce (concentrated) magnetic fields by storing/converting electrical energy into a magnetic field. However, inductors cannot/does not convert electrical energy into magnetic energy instantly. It takes a little bit of time which is why inductors will momentarily resist sudden changes in electric current in a circuit. So it takes a little time for an inductor to build up a magnetic field and also to then dissipate it by converting it back into electric current when the supply current to the circuit is stopped. What you can take from this is that over a period of when an inductor builds up, maintains for some amount of time and then dissipates it's magnetic field (i.e. what happens in half the period of an AC cycle), the time it takes to build up and dissipate the magnetic energy in effect reduces the average magnetic field strength of the stator which in turn reduces the average net torque it imparts on the rotor. Thus you want this percentage of time spent building up and dissipating to be as small as possible.

    So how's it relevant to the speed limit of torque for a motor?

    Well, as you know in order for an electric motor to sustain a net torque output on the rotor shaft, sections of its stator coils must continuously alternate in magnetic polarity to match the changing polarity of the magnets on the rotor (to repel them) as the rotor is spinning at some speed. A net torque on the rotor shaft will in turn continue to accelerate the rotor around and increase it's speed over time. However, when the same average magnetic field strength per unit time (=average net torque per unit time) of the stator coil sections can no longer be maintained, the net torque output will actually stop and no more speed increase will occur. The reason for this is that at such speeds, the frequency of the AC input is so high that the time it takes for the stator coils (i.e. inductor) to build up to maximum and to also dissipate all it's magnetic energy takes up a significant proportion of the time duration per half an AC period. I.e. the average magnetic field of the stator coil cannot be maintained because the coils cannot build up and discharge quickly enough to produce sufficient average magnetic field to continue producing the same amount of torque output.

    There is however a way to increase the speed limit before this effect takes significant effect. Voltage. The fact the inductor impedes current flow acts like an increased resistor in the circuit which means for the same current flow you need more voltage to power it. Thus increasing the voltage here will increase the average current flow back up to what it should be to have the desired amount of torque output. So this is why for some amount of current = some amount of torque, more voltage is required to drive it at that higher speeds.

    There are also other properties such as the skin effect that affect AC circuit resistance as the frequency increases, all culminating it higher voltage requirement to drive the same current flow as AC frequency also increases.

    Hope that made sense.
     
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  8. wgeuze

    wgeuze Registered

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    That is why they probably don't even want to deal with puny consumers ;)
     
  9. Spinelli

    Spinelli Banned

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    Thanks, DrR1. I appreciate the time and effort you took in the explanation but it's all a little over my head. Adrian said to not worry about rpm (or x amount of torque @ x amount of rpm) for simracing. I'm trying to figure out at what point this is true and at what point it does indeed affect us simracers. If the Accuforce cannot reach the point where any further increased rpm/torque@rpm doesn't make a difference for simracing then I want to make sure that I do indeed reach that point (regarding anything from 0-27 Nm) with Ollie's pre-built small MiGe setup.
     
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  10. DrR1pper

    DrR1pper Registered

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    I have to go for now but have a response to that for you but it'll have to wait.
     
  11. Adrianstealth

    Adrianstealth Registered

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    my thoughts exactly, thankfully this technology is now I n our reach

    spinilli, I think your over thinking this, up to you but do try & see a difference between these hi grade servo systems and all other wheels ( including the AF ) , maybe you should just get yourself on ollies waiting list, flip a coin on which midge if you can't decide as you'll be fine with both ( don't worry about rotational phonological disorder forces ) :D
    (I'd be saying something very different if you were building a hi speed production robot )
     
  12. Spinelli

    Spinelli Banned

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    Ok but now I'm stuck waiting to see if I should wait for Ollie to finish that extra power add-on thingy (lol!) before purchasing. I don't want to be stuck without it wishing I had it...
     
  13. Adrianstealth

    Adrianstealth Registered

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    Lol, remember there's a 2 to 3 month waiting list

    I'll post pics etc of mine when it finally shows up (due early to mid sept)

    (The add-on can be added in at a later stage, not sure when it will be ready but hopefully I'll get it all together if it's released before my main orders are sent )
     
  14. DrR1pper

    DrR1pper Registered

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    I'm 99.99% certain that peak speed for ffb matters to sim racing and if you're willing to bare with my explanation, it'll be absolutely clear to you why:

    First thing first, we must get on the same page with how the physics of interacting with an ffb wheel (or for any other moving/rotating object with mass) actually works because the conventional wisdom that it's just about the torque output of the ffb wheel motor is completely and utterly wrong. Demonstrably wrong. Yes, bold words (pun not intended) but i can and will back them up.

    How the physics of interacting with objects with mass actually works:

    We need to make sure we're on the same page first. As unintuitive as it may or may not seem to you, the amount of torque you "feel" when you interact with an ffb steering wheel is not determined by the amount of torque output from the electric motor at that point in time. To try and make this point as evident as possible, take an ffb wheel which will have rotational inertia because the steering wheel has mass and turn off the electric motor. Even if the rotor shaft was perfectly frictionless, when you try to change the position (by changing the rotation speed) of the steering wheel you will feel some amount of torque. Furthermore, the quicker you try to change the position angle (by changing the rotation speed) of the steering wheel mass, the more torque you will "feel". So how can an ffb wheel with zero friction and powered off (i.e. zero torque output from the motor) cause you to "feel" a torque from the steering wheel? Simple. The steering wheel has inertia because it has mass and that inertia resists changes to it's motion (as per newtons 1st law of motion..."a body at rest or in motion will remain at rest or in motion unless/until an external force acts upon it"). So whether the steering wheel is stationary or moving at some constant velocity, even with zero friction (i.e. no mechanical resistive forces) and zero torque output from the electric motor and zero torque input from a driver (i.e. no hands on the steering wheel), due to the properties of inertia, the steering wheel will remain in its current state of motion (be it zero speed or some amount of speed).

    So where is this torque you "feel" coming from when you interact with the ffb steering wheel? Well, the torque that you "feel" from the steering wheel is the reactionary torque from the steering wheel mass in response to the torque you are applying to the steering wheel when you are trying to change it's motion. (as newton's 3rd law states, "every force will have/produce an equal and opposite reactionary force"). The point is, the amount of torque you perceive (i.e. "feel") as coming from the ffb steering wheel at any moment in time is from the amount of torque you are applying to the steering wheel mass.

    So how does the torque output from the electric motor fit into all of this because ofc it has to play a role and ofc it does. It's just not a direct transference to the driver. By this i mean the torque output from the electric motor does not directly transfer to the drivers hands when he/she is gripping the steering wheel. No, a torque output from the motor first causes a change in motion of the steering wheel mass. Then we (i.e. the driver) in turn try to change the steering wheels motion by applying our own torque onto the steering wheel mass.

    So in summary,

    The driver does not directly interact with the torque output of the electric motor. The torque from the electric motor first changes the motion of the steering wheel mass and then the driver applies his/her own torque to the steering wheel to try and change it's motion as desired. And the amount of torque they apply is the amount of torque they will "feel" as if coming from the motor (when in fact is not but simply a reflection of the torque they are applying to the steering wheel mass).

    I know that was long winded but hope you understood it fully because it's a very important distinction to make. With the above intuition you can correctly model how objects with mass will react to forces in the real world.

    Ok, this next bit is just an adjunct to the above if you're interested. But feel free to skip past it if you want:

    [HR][/HR]When an object with mass is in motion (linear or rotational), it has momentum. Momentum is simply the mass x the speed (i.e. the motion) of the mass. Since the mass of the steering wheel is constant, the only other variable that determines it's momentum at some moment in time is the speed of its motion (in this case rotational motion). So if something increases it's motion (speed), it's momentum will also increase. Vice-versa, decrease it's motion and its momentum will also decrease.

    So what does a change in momentum equate to? Well, a change in momentum = applied torque x some length of time. Thus to change its momentum you need to apply a force/torque for some amount of time. And if you want to make the same change in momentum in a shorter amount of time, then you must apply a higher force/torque to it. The less force/torque you apply, the longer it will take to make the same change in momentum.
    [HR][/HR]


    So back on point.

    How/why is peak speed important. Simply put.......MORE ENERGY and MORE MOMENTUM.

    A little thought experiment to help you see what i mean. Imagine a bowling ball dropped from a height. Over time as the bowling ball falls, it's speed (i.e. momentum) will increase because it is being accelerated by gravity (a constant gravitational force). But what is the downwards force of the bowling ball at any moment of time during it's fall? It's the weight of bowling ball (= mass x acceleration = the constant mass of bowling ball x the constant gravitational acceleration rate). But you know that if you laid on the floor and i drop the ball from a height of 10cm above your chest vs 1m above your chest...one may somewhat bruise your chest whilst the other will crush/shatter your rib cage.

    Why is it that despite the bowling ball having the same net force in both scenarios anywhere during their fall (i.e. analogous to the same torque output from two different electric motors), one will cause so much more damage than the other? Because the ball dropped from higher up will have more energy upon impact because it will have accelerated up to a higher speed upon impact. More specifically, it will have more kinetic energy = 1/2 x mass x velocity^2. So for the ball to be stopped just as quickly as when dropped form 1m vs 10cm, the kinetic energy of the ball dropped from 1m will produce a much higher torque for the same duration of time it takes to come to rest as for the ball dropped from a height of 10cm.

    So it's equivalent to a steering wheel that has a higher rotational velocity/momentum potential which in turn will have a higher (rotational) kinetic energy potential which will require a much the larger exchange of torque to/from the driver and steering wheel mass if you want to stop it in the same amount of time as steering wheel mass that has less momentum. I.e. it actually results in a larger perceived torque output from the ffb wheel which translates to a larger impact, more violent/strong ffb experience.

    As you now know, increasing an electric motors voltage threshold will increase its peak speed and the higher it's speed can be the higher the steering wheels rotational kinetic energy can be. Which in turn increases the impact energy when you try to stop the steering wheel from rotating. And it's the higher threshold of kinetic energy and momentum that can be delivered to the steering wheel mass by an electric motor that gives you the perception of greater ffb strength, detail and responsiveness of one ffb wheel vs another, despite the fact that both ffb wheels may have the same peak torque output possible from it's electric motor.


    Conclusions:

    It is my contention that it is not only the difference in peak motor torque output but also the difference in peak motor speed that is why the AF Pro feels weaker than other DD wheels such as the bodnar and OSW. And to prove that the peak speed is relevant, i used this video from mockerracer's review to measure the peak speed of the AF Pro to find out just how quickly it takes for the steering wheel mass to reach peak speed in practice:



    It works out that it takes less than 0.1s to reach its terminal velocity of 2.5hz = 150 RPM. Not far off my prior prediction of 176 RPM based on the known facts of AF Pro's psu peak output of 240W peak and the peak motor torque output of 13Nm peak. (prediction was calculated by 240W/13Nm/2/pi = 2.9hz = 176 RPM).

    The bodnar and OSW motors have at least twice the amount of voltage and power output. Combine this with their higher torque output too and you end up with their steering wheel masses reaching far higher momentum and kinetic energy levels than the AF Pro in the same 0.1s. The resultant effect is that the bodnar and OSW motors will feel a LOT more responsive and powerful than the AF Pro. Which is what we have consistently heard from people who have compared both.

    So back to peak speed of a specific motor...the higher you can get it's peak speed the stronger and more violent it will feel which translates to feeling more detailed and responsive in ffb. How does one increase the peak speed of the motor? By increasing it's available voltage supply range that it can draw from. Furthermore, if the supply voltage of the AF Pro could be set so that the peak speed of the AF Pro could match the respective bodnar and OSW motors (with their respective psu's) peak speeds, and the bodnar/OSW motors were limited to the same 13Nm peak torque output as the AF Pro, the ffb would feel exactly same. Same level of ffb strength, detail and responsiveness.

    We've been told that the IONI and Argon drives have been software limited to 300RPM and supposedly for safety reasons which i can understand. But make no mistake, two motors with the same (peak) torque output range but one that can only go up to 200 RPM vs the other that can go up to 300RPM, the 300RPM peak speed motor will make the ffb feel considerably stronger, more detailed and more responsive in ffb. Up to 50% more in fact.


    Closing remarks

    Now i know my response is embarrassingly long and you and others will most likely (and understandably) not read it or not read it all but it was the only way to demonstrate exactly why and how the motors peak speed does in fact matter for sim racing. If you follow the logic i've set forth which is based on first principles, i'm absolutely sure you'll agree.
     
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  15. Adrianstealth

    Adrianstealth Registered

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    way to long to read, but I'm sure it sounds good (-:
     
  16. jkn87

    jkn87 Registered

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    Excellent post Dr.
    Very explanatory
     
  17. DrR1pper

    DrR1pper Registered

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    Thanks jkn87. I've since made some corrections and additions to it but am now 100% finished with it.

    edit: sorry, had to make a few more tweaks but for sure finished now. Just added that fact that a higher peak speed will actually result in the perception of more torque output from the ffb wheel in fact. So if the for the same motor, you increased it's peak speed by 50% (e.g. from 200RPM to 300RPM) you would also in effect be increasing the perceived ffb output from the ffb wheel up to 50%. I.e. the torque output will feel up to 50% higher. To some that may sound odd but it's true.
     
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  18. Adrianstealth

    Adrianstealth Registered

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    small mige just added to my order, seems it's totally fine to swap/switch between small & large

    good

    ( £270 for the small mige as an addition )
     
  19. Adrianstealth

    Adrianstealth Registered

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    drriper

    not read your post completely ( looked at bit near vid ) ,
    I've stated differences in specs between servo motors for sim racing , ( mige lenze bodnar EK senso )
    -not the AF

    but differences between the servo systems shouldn't be noticeable for sim racing ( or very very subtle at most ) different manufacturers no doubt will have some different characteristics

    apart from Nm for peak ffb ( but again only subtle once going over 15Nm - ish which is plenty of power )

    I'd love to see you standing by these claims during a blind test ( that's servo vs servo ...forget the AF )
     
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  20. DrR1pper

    DrR1pper Registered

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    I know but whilst answering spins question where i quoted in bold, i wanted to hit two birds with one stone and set the record straight once and for all by demystify what is really driving the performance difference between what some call would call the more mainstream/common ffb wheel motors (such as in the AF Pro and lower torque ffb wheels) vs the superior "industrial grade servo motors/systems". And it has nothing to do with them being "industrial grade" or servo motors, except for that fact that these motors are being driven with more power and are rated to safely go up to such powers without issue, where as the AF Pro motor may not (hence why Berney has only paired them with peak 24V psu's vs the bodnar and OSW's that start at least 48V...twice as high = at least twice the power output potential). However if safety is the issue, take a larger sized but same type motor as in AF Pro and juice it properly and it will sing just as well as the "industrial grade servo motors" when used for sim racing.

    You need to read my prior post. I explain completely how higher peak rotation speed will actually increase the perceived torque output from the ffb wheel, despite the fact that you leave the peak torque output from the electric motor the same. I cannot explain any simpler why this is than what i've already written a few posts back.

    Me too. In fact when you get your OSW wheel you could technically test this yourself but you'd need two different psu's. Both able to output the same peak current but one with less peak voltage than the other. This will limit the speed of the motor by half with the psu that has half the peak voltage supply capacity. That would result in the perception of up to 100% more torque from the ffb wheel.
     
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