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Thread: High Accuracy Degree Wheel

  1. #11
    reddirtrider Guest

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    Quote Originally Posted by posplayr View Post
    I found a very accurate method of reading the degree wheel by not using "the point" on a wire which is subject to the errors as I explained.

    Pos
    I'm not disagreeing with your method. To each his own. You once again missed what I was saying. I'll drop it.

  2. #12
    posplayr's Avatar
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    Default Missed something

    You once again missed what I was saying.
    Despite the tangents , puns and misdirections your only point seems to be that you use a piece of wire to degree your cams. That is quiet obvious from your first post and is hardly any surprise as I'm sure 99% of people do it that way.

    As I stated:
    The biggest issue with getting accuracy with your degree wheel is the piece of wire pointer.
    99% of the people degreeing cams apparently have no consideration of the accuracy issues of reading the wheel or are happy with just good enough and as such are happy using a piece of wire. U seem to be in the same camp if I got "the point".

    So other than to say "I could careless about accuracy in reading a degree wheel", I don't get your point. Is there anything else you are trying to say?

    Getting back on point, racers like Rapid Ray are at least sensitive to the accuracy issues of small degree wheels and have taken to using large over sized degree wheel to improve accuracy. The described method exceeds typical 18" degree wheel accuracy using an 8" degree wheel. It might also make a paper degree wheel acceptable but that is subject to too many variables to be conclusive.

    Is there anything else I missed?


    P.S. as to your safety concerns, I did use a safety razor
    Last edited by posplayr; 04-09-2009 at 11:07 AM.
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  3. #13
    reddirtrider Guest

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    Quote Originally Posted by posplayr View Post

    Is there anything else I missed?
    Yes, you've narrowed your focus down to the accuracy at which you can read the wheel and assume that it cannot be done with a pointer (which most tuners use BTW).

    There's a whole lineup of tolerance issues that go into degreeing a cam. For instance, how accurately can you stop the crank? 0.1 of a degree? If not, then your accduracy cannot be within 0.1 of a degree. How about the tolerances associated with the camshaft itself? Do you know what the manufacturing tolerances are?

    Here's the point you missed and it's not tangental, a pun, or a misdirection. You don't need a fine line in order degree a cam. I can use a pointer that covers an entire degree on the wheel and still get the accuracy needed by centering the marker on degree wheel on that fat pointer. It's very similar to shooting at 500 yards. The bullseye is much smaller in diameter than the front blade.

    Hey, it's a nice idea and I'm glad you like it. Bottom line is, It's my opinion it's not going to work any better than a pointer.

  4. #14
    posplayr's Avatar
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    Default reddirtrider

    I can see that this discussion with you is pointless; this is the point I'm finally grasping.

    Just so you know, I have a MSECE with primary focus on Control and Estimation and close to 30 years of systems engineering under my belt. I've worked in the areas of ultra high accuracy inertial navigation, fire control and flight guidance and controls. That means I have a thorough understanding of measurement accuracy, positional accuracy, estimation uncertainly and certainly standard deviations.

    I don't mean this to boast simply to offer that information in leu of a specific answer to your suggestion I missed something about overall engine timing accuracy. Your quotes are incorrect and the proposition is laughable.

    Since you are not willing to read the essential elements of the prior posts, it is hardly worth my time to elaborate considering you don't read or understand what is already written.

    Good Day.

    Pos

    P.S. my Next Tricks and Traps post will be entitled "High Accuracy Engine Stops"; can U guess how that will turn out?
    Last edited by posplayr; 04-09-2009 at 01:09 PM.
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  5. #15
    reddirtrider Guest

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    When all else fails post credentials.

    I won't bother with mine, since they are irrelevant to the discussion. If you refuse to take into consideration other sources of error in this system, then as you say, this discussion is pointless.

  6. #16
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    Default reddirtrider

    When all else fails post credentials.
    Now you are calling me a liar.

    Your tactfulness goes hand in hand with your lack of understanding (to put it mildly).
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  7. #17
    reddirtrider Guest

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    Quote Originally Posted by posplayr View Post
    Now you are calling me a liar.

    Your tactfulness goes hand in hand ignorance.
    I called you a liar? Not at all. What I said was that credentails are irrelevant to this discussion. I could unzip and post mine too, but they simply do not matter.

    Stick to the facts of the discussion and stop taking this personally. It's not.

  8. #18
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    Default Red

    That means I have a thorough understanding of measurement accuracy, positional accuracy, estimation uncertainly and certainly standard deviations.
    The purpose of me elaborating on my background was to provide you with a context to understand the above statement. Unfortunately that context is meaningless and you apparently can't distinguish between these quantities and the relationship of these elements to the numbers I posted.

    Let me be more clear for you.

    1.) measurement accuracy

    Even with a 9" degree wheel, this safety razor welded to a clutch cover bolt allowed for +/- 0.1 degree (+/- 1 sigma) accuracy readings.
    2.) positional accuracy

    It is hard to adjust the valve timing to less than 0.5 degree increments
    3.) estimation uncertainly

    measurement could be off by as much a 1 degree and cause you to chase your tail as you keep rotating the cams looking for open/close 0.050".

    4.) standard deviations.

    (+/- 1 sigma) accuracy


    You made this statement

    For instance, how accurately can you stop the crank? 0.1 of a degree? If not, then your accuracy cannot be within 0.1 of a degree.
    The accuracy of the crank stop (either in piston stroke, or angular accuracy) has nothing to do with the ability to accurately sub divide the degree wheel hash marks.

    Measurement accuracy using the degree wheel does have certain error sources, mostly flatness of the degree wheel, run out error in the mount and primarily the error in the ability to sub divide the 0.070" hash marks of an 8" wheel degree wheel. While I did not quantify the first two, I did quantify the largest.

    OK Some numbers.

    for a 8" degree there is 0.070" separation between 1 degree hash marks

    If you have your pointer 0.5" off of the wheel and read the wheel from 3 foot away then

    6 inches of lateral movement in your eyeball is 0.083" (1.2 degrees) error

    If you have your pointer 0.5" off of the wheel and read the wheel from 2 foot away then

    6 inches of lateral movement in your eyeball is 0.125" (1.8 degrees) error

    So how well are you relocating your eyeball measurement to measurement?
    If you have not figured it out by now, measurement accuracy with respect to a degree wheel is a relative accuracy or repeatability of successive measurements which result in a numeric reading. It is the variance in that numeric value that is being reduced. It is not absolute accuracy with respect to TDC. While TDC can be determined more accurately using an improved measurement repeatability that is not the subject. So your statement is relating lack of 0.1 degree accuracy on TDC causing an inability to read the degree wheel is not only incorrect it is 180 degrees out in terms of dependency.

    It is the repeatability of the degree wheel measurement which largely impacts the ability to find TDC not the other way around. TDC accuracy goes beyond this but we would have to delve into the accuracy of the piston stop, the estimation error in successive measurements and how well the final adjustment of the degree wheel was validated.

    No where did I suggest that positional accuracy of 0.1 degree was being sought. In fact the position measurement was suggested to have a total uncertainty band of +/-2 sigma = 0.4 degrees with a suggested position accuracy of 0.5 degree increments. As you must know the measurement uncertainty should be less than the desired positional accuracy by at least a factor of 2. Theoretically it doesn't have to be (e.g. Delta Sigma Modulations), but the only way to get around positional uncertainty is to insure it is random and one must make many successive measurements to rely on the Central Limit Theorm (I can be vague as well).

    As I stated before, you have mis quoted me and have abused the standard terminology. In addition and you have quite INCORRECTLY stated that there is a diminishing return of the proposed method due to uncertainty of TDC. This is patently FALSE. The opposite is true ; the proposed method makes finding TDC easier.

    Given that cams specifications are provided in whole degrees, it is entirely appropriate objective to degree a cam within +/- 0.5 degree (+/-2 sigma). With the calculations above for 0.083" (1.2 degrees) , 0.125" (1.8 degrees) it is entirely possible that using a wire pointer this can not be reliably achieved. I would further submit that since you use a wire pointer you have no idea how accurate you which is probably no better than +/- 1 or 2 degrees (2 sigma) is fine. It won't stop the bike from running

    Ultimately the only use I can derive from your garbled use of terminology is that you don't think that 1-2 degrees of positional error matters. Depending on your purpose it might not. In point of fact measurement accuracy matters most in the repeatability of measurements which allows the cam timing to be established earlier due to the improved repeatability.

    I think I have wasted enough time explaining this. I have just about lost my patience and will have little left to post on the high accuracy engine stop.

    Pos
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  9. #19
    reddirtrider Guest

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    Quote Originally Posted by posplayr View Post
    Ultimately the only use I can derive from your garbled use of terminology is that you don't think that 1-2 degrees of positional error matters.
    I'll leave out everything but this.

    That's what you derive from my comments? For someone who likes to claim I'm not taking the time to understand (or possibly can't) what you're saying, that's quite an eye opener.

    My point, and it's quite simple - until you take in all of the sources of error and quantify them, what you've given us is nothing but fluff.

    I do find it telling that you must resort to insulting me to attempt to prove your point. That's something I never did in any of your threads, including the one on 'sneak paths' for the R/R. You were way off base in that thread and I let it slide. Apparently you like to post and have everyone bow down. I'll keep that in mind.

  10. #20
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    Default Red

    My point, and it's quite simple - until you take in all of the sources of error and quantify them, what you've given us is nothing but fluff.
    This is patently false statement. Anybody that has had any experience at performing an error analysis knows that the first step in an error analysis is to a.) identify the relationships between parameters and performance and b.) Identify the dominate error sources and uncertainties involved.

    NOONE with any experience would attempt to quantify all error sources ( I assume when you say quantify you mean quantitative that means to apply a number to the parameter ).

    Some errors sources are inconsequential and are not "quantified" or are not easily quantified. For example I did not attempt to quantify the change in angle associated with the gravitational pull of the moon on the piston as I went through successive TDC measurements. Why??? because it does not matter. How do I know this? Call it engineering judgment. Could I calculate it ? Sure I could. Is it going to be accurate? Maybe maybe not. But what ever it is it will be so small as to be inconsequential.

    Nobody quantifies all error sources, so maybe you mean that there is a significant error source I have missed? Don't say TDC .

    I do find it telling that you must resort to insulting me to attempt to prove your point. That's something I never did in any of your threads,
    I do not need to denigrate you to make a technical point, I can make a more than adequate technical argument.

    Apparently you like to post and have everyone bow down. I'll keep that in mind.
    You may choose to bow or not, you may choose to participate in a technical conversation or not, but if you try and push uneducated statements like the above statement I will respond.

    Since you have said you are an engineer, I guess I have less tolerance for inaccuracy in your statements. Even further it is insulting me for someone that has supposedly been educated in such to reject albeit informal, a disciplined engineering analysis as fluff when you don't seem to understand the first principles of the process.

    I'm still challenging you to make a technical statement that has any validity in conflict with my statements. If you think that is denigrating then as then say "...stay out of the kitchen".

    oh yea the sneak paths don't have much bearing on deck height, so I did not quantify that either.
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