Check my math Please


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  1. #1
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    Default Check my math Please

    My goal is a pretty accurate small scale machine and now that I have the Lexium drives operating I did the calculations and just wanted to get some feedback.

    First off Lexiums are quite amazing and I see some new ones on eBay for really short money...just make sure you know the interface and can communicate with them and they do have to be Lexiums (not just Mdrive) if you want to be able to enable Step/Dir inputs. Clearly put if you don't have a Lexium specifically for S/D then you will have to configure it...but you can...super fast and quiet and appear, if my math below is on, to be very accurate as well...highly recommend them over a standard stepper if you can find on eBay.

    Also don't make the silly mistake I did and miscount the Pin/Output configuration...Pin 1 is Reference NOT Input 1...so when you count over Step 3 is Pin 4.....sounds easy but had a me stumped for a bit...technical dyslexia...

    Anyway Lexiums do not suffer from High Micro step losses like a regular stepper so the engineers told me to run right at the default 256 setting resulting in 51,200 steps per rev...I have calculated screws at .314961/inch resulting in 162,559.8...sound about right???... Motor btw is 1.8x200

    Thanks!

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    Last edited by jmm2020; 11-17-2018 at 10:41 AM.


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    Default

    Quote Originally Posted by jmm2020 View Post
    .I have calculated screws at .314961/inch
    It that right.....

    I revolution is approx 3" of movement?



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    Activation process jmm2020's Avatar
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    Default Re: Check my math Please

    actually 8mm or .314961"



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    Quote Originally Posted by jmm2020 View Post
    actually 8mm or .314961"
    200 X 254 = 50,800 steps per revolution

    For metric
    50,800 / 8 = 6,350 steps per mm

    For imperial
    6,350 X 25.4 = 161,290 steps per inch

    ___________________________________

    I have to ask , why do you want a step accuracy of
    1/6,350= 0.000157480315mm

    Or
    1/161,290=6.2000124e-006"

    ???

    Human hair thickness is between 17 to 181u meter
    (IE you machine can step less than a hair thickness ... Why?

    https://hypertextbook.com/facts/1999/BrianLey.shtml

    How much backlash does your system have?
    What is the accuracy of your leadscrews?

    Maybe consider adjusting your microsteps accordingly and save the wasted steps of accuracy that does not exist in your system



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    Default Re: Check my math Please

    I in fact asked a similar question of the manufacturer and in the end we decided simply why not...the motors are said to be that accurate and maintain the encoder internally and default to 256 MS/S...by the way your math above is based on 254 MS/S but the setting is 256 MS/S (51,200) in the software...did I miss something...backlash and several other factors can be directly monitored and compensated for internally off the encoder count with these drives so again...an exercise that does require some finite resolution...they are a very interesting little piece.
    Anyway I wholeheartedly agree overall accuracy is an aggregation of quite finite variances from a number of possible error sources but it will be interesting to dial things in and see where it goes...it's a toy for me no doubt about it...I got about 17 of these drives on a random pallet of items in an auction and never paid much attention to them as I was mainly focused on the heat exchangers also on the pallet but I saw a video on YouTube of someone using them for this and thought heck this looks like fun and I had most of the bits.
    Thanks!.



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    Default Re: Check my math Please

    ok,

    254 or 256 sorry, just substitute the right number (it was late and I was typing on a phone....)



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    Default Re: Check my math Please

    I thought so...I am the very king of technical dyslexia as I stated previously...just wanted to be sure...lol...Thanks!

    I checked everything yesterday though not completely and it was right on the money in thou's...for a first general runout it was pretty impressive with the drives but I did notice in the incremental jog of .0100 I would get a bit of a hitch on the very first jog...

    At first I thought perhaps backlash but if I did say 6-7 jogs.... .0700 on Mach4 DRO I would miss the first .0100 but it would actually catch up and then on the return to .0000 it would do the inverse...basically starting off with what seemed a miss but 6-7 jogs would agin result in .0000 or .0700 again...very odd...going to hog a small something and see what the tolerance margins are and go from there.

    I want to play with the backlash settings a bit and see if that does anything as well...



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    Default Re: Check my math Please

    Is that .01 inches?
    The catch up could be due to static friction. What kind of machine is it? Dovetail ways or linears? Static friction issues are more likely on dovetail or box ways than something with ball bearings.



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