Easy question on measurement

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  • August 3, 2014 at 10:05 am #6561
    contacttodd
    Member

    Hi. I am generating GCODE with a program that is output a sample such as this:

    G01 X1.00 Y1.00

    It seems like the tiny g is interpreting the numbers of, for example X1.00 as (I have it in G20 or inches) as 1 foot instead of 1 inch.

    How do I get the tinyg to look at that in a 1″ measurement instead of a 1 foot measurement?

    August 3, 2014 at 1:31 pm #6563
    cmcgrath5035
    Moderator

    Hmmm, I think something else (e.g. calibration parameters) is wrong.
    In my experience, from (X0, Y0), G01 X1 will move 1 mm or 1 inch depending on G20.

    Try mm mode; still off?

    Are you sure tinyG “knew” where it was (was zeroed properly)?

    August 3, 2014 at 2:55 pm #6564
    contacttodd
    Member

    Thanks for the reply. In mm when I try X1 I get about 3 inches (not measured, but at a glance that looks to be about correct). When I specify G20, inches, and try X0.01 I get one inch. When I try X0.1 I get about 1 foot. My plotter cannot handle X1 so I’m not sure what that yields. Do you think the issue is in the amount of movement per degree of the stepper could be the issue?

    August 3, 2014 at 2:57 pm #6565
    contacttodd
    Member

    Forgot to answer, I do have X and Y at a zero point so that is not issue.

    August 3, 2014 at 8:21 pm #6566
    cmcgrath5035
    Moderator

    Do you think the issue is in the amount of movement per degree of the stepper could be the issue?

    For sure.

    Tell us a bit about your machine ( e.g. Shapeoko, something else), belt vs screw, etc.

    Think of it this way; tinyG FW does a bunch of computing then sends microstep signals to the steppers. So what you program as the movement per 1 revolution of the stepper is what tinyG uses to compute how many microsteps to issue.

    August 4, 2014 at 7:44 am #6572
    contacttodd
    Member

    Thanks for the reply. I built the makeblock XY Plotter which can be seen here:
    http://cdn1.bigcommerce.com/server2600/4r4weyxd/products/189/images/960/IMG_0107_1__30467.1405403084.1280.1280.jpg?c=2

    It is using the stepper motors which are detailed here:
    http://www.makeblock.cc/42byg-stepper-motor/

    On the tinyg I configured the $1sa to 2.0 as that gave the X0.01 a movement about 1 inch.

    Based upon the reply here, I thought maybe changing the default setting on $1tr to a different value would yield a change in movement but I haven’t noticed anything as of the values I changed it to as of my last modification.

    Based on the information I described here, is there a particular setting I should be adjusting to get this movement of X1 = 1″?

    Thanks for your assistance.

    August 4, 2014 at 9:23 pm #6577
    cmcgrath5035
    Moderator

    Wow, cool picture, looks sorth of tike a 4 rotor drone!

    Quick look, pulleys (therefor, movement per rotation) much larger than, say, a Shapeoko.

    Your steppers are 200 steps per rotation, 360/200=1.8degrees per step.

    So $1sa=1.8 is the correct setting.

    Motor specs don’t make it obvious what microstepping they support, I would guess setting $1mi=8 would be ok for the X and Y axis, seems sort of standard.

    The big factor in movement is $xtr, where x can be 1,2,3,4(motor number) when using tinyG.

    From the picture, tour pulley’s look huge when compared to, say, a Shapeoko.

    So you need to review the machine documents to determine travelper rotation, which might come down to belt pitch (distance between teeth) x teeth on the pulley.

    To be more specific, you will have to tell us whta motor is connected to what tinyG driver.

    August 5, 2014 at 7:40 am #6579
    contacttodd
    Member

    Thanks for the reply and the feedback on my XY plotter. It’s a fun device and the hardware, when compared to the cost was a good deal and an enjoyable build. However, the electronics on it were a poor fit and buggy. I used that as a chance to get involved with the tinyg and what a GREAT IMPROVEMENT. I really love the tinyg.

    I looked at the tinyg documentation and noticed, deductively, that $xtr (or $1tr for the X and $2tr for the Y) seemed like the right value to adjust. I put in guesses for numbers that seemed to ball park the figure they might need and had fairly accurate movement (around 1.5″ instead of 1 foot) when using the following values:
    Default Adjusted
    $1tr = 0.0039 in. . Modified = 5.0
    $2tr = 0.0492 in. . Modified = 5.0

    The only thing I noticed was that the speed reduced dramatically and the movement became very jittery when traversing along the X or Y movement. Any thoughts as to why it would do that?

    Thanks again for your feedback and I really enjoy this hardware!

    August 5, 2014 at 5:24 pm #6580
    gagandeep90
    Member

    I am currently facing a similar issue as contacttod. I was previously using a gshield v5 on the OX CNC and decided to upgrade it with a tinyg. My motors are 1.8 degrees Nema 23 and were working perfect with 8 microsteps and the tr rate was set to 26.772 on the gshield. However, once i connected the tinyg i noticed if i enter 10mm it would go a lot more than 10. Then I decided to use a calculator online to fine tune the tr settings and it turned out that if i reduce the tr the machine travels even more than before. If i increase the tr rate then it goes lesser. Eg : X10 goes 100mm on 26.772 tr and X10 goes 10mm on 59.86 tr.

    After i made these adjustments my machine jog speed has become a lot slower and if Im correct if the machine travels more than the command given a reduction in the tr rate corrects it. But currently its the opposite. A increase in the tr rate is correcting it.

    My X Axis is connected to motor 4, Z Axis to Motor 3 and both Y Axis to Motor 2.

    Here is the link to my $$ Dump :

    https://www.dropbox.com/s/94y96i42e93w8ad/DUMP.txt

    August 5, 2014 at 9:44 pm #6583
    chmr
    Member

    gagandeep,
    tinyg’s $xtr setting works differently than in grbl: In grbl, you configure (micro)steps per mm; tinyg wants mm per motor revolution. For the Ox, the thoretical value is 60 (60 teeth on the pulley * 3mm per tootn on belt). If you had $0=26.772 on grbl, on tinyg $1tr shoul be = 200 steps per revolution (1.8 deg motor) * 8 microsteps / 26.772 steps per mm = 59.764 mm per revolution. Seems pretty close to the theoretical value.

    contacttodd,
    calculation for your machine is the same: $1tr = number of teeth on pulley * distance of teeth on the belt. I just don’t know the actual values for your plotter.

    First amend the $Xsa (step angle, 1.8 for both) and $Xtr settings, then you can adjust the speed ($Xvm and $Xfr).

    August 5, 2014 at 10:57 pm #6585
    alden
    Member

    Thanks for the detailed explanation. See also this section on the wiki:
    https://github.com/synthetos/TinyG/wiki/TinyG-Configuration-for-Firmware-Version-0.97#motor-settings

    The step angle is a motor parameter, typically 1.8 degrees for most motors. It’s an independent variable. It just describes your motor.

    The microsteps is also an independent variable. Set to 1, 2, 4 or 8.

    For screw axes the travel for revolution is the pitch of the screw, e.g. 1.25mm thread pitch is = 1.25mm per revolution.

    For belt machines the travel per revolution is approximately the circumference of the cog wheel. Which is somewhat less precise way of saying the number of teeth on the pulley * distance of teeth on the belt as chmr said.

    Once you get the tr set you can dial it in with calipers and some measurement.

    August 6, 2014 at 6:06 am #6590
    gagandeep90
    Member

    Thank you chmr and alden for your detailed explanation. This cleared up all of my issues. Thank you once again.

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