difficulty setting steps per unit in mach3

[Josh Leber]

I'm having trouble setting up my steps per unit in the motor tuning section of mach3.

I have a small 3 axis router table with mach 3, Gecko G212 drives and Vexta 1.8 deg steppers.

The drives are set up for 10 micro-step
The Axis in question (first to set up) "X" has a cog belt drive with .200" (1/5th inch pitch belt and a 16 tooth cog. Ratio: 1rev=3.2" x axis travel

My calculations are (stepper) 200 steps per rev x 10uS = 2000 steps per rev / 3.2 = 625

Should be 625 steps per unit (inch)

I have the native units set to inches

When in MDI mode if I tell it to move 1 inch, it moves a small fraction of an inch.

After some trial and error I came to the setting in "steps per unit" of 16,250 to actually get the 1" requested. (measured with a dial indicator)

Its pretty close to perfect if not perfect but my calculations dont support this number.

What could be wrong with this picture?

[Josh Leber]

figured it out...

after setting the steps per unit and saving the settings, mach was not reflecting the recent changes for some reason.

after restarting mach. the new settings were reflected and accurate.

now, to the home and limit switches before I break something....

[HuFlungDung]

I don't see where the pitch of the belt and the number of teeth on one wheel has anything to do with the ratio of the drive. For that you need the number of teeth on the driver/number of teeth on the driven.

[lvanduyn]

The number of teeth has everything to do with it. The pitch dia of a 16t XL pulley is 1.016 inch times pi gives a travel of 3.484 in per rev. It appears that Josh used the outside dia of the pulley of .999 inches times pi which gives 3.138 inch per rev and rounded that up. Assuming that the motor is a direct drive on the pulley, 2000 steps per motor rev should yield (2000/3.484) 574.053 steps per inch. Based on that, I have no idea how Josh came up with 16k steps per inch..

[HuFlungDung]

The number of teeth on the driven pulley alone does not determine a ratio, because no ratio was stated. The drive ratio is definitely not the number of teeth in the pulley divided by the pitch of the belt.

[mxtras]

MACH has a utility that allows you to calibrate your axii.

I can not recall where it is, and I do not have MACH here in front of me at the moment, but I know that you can open up this area of MACH and it will ask for a distance you wish to move, it will move that distance and ask you to measure the exact distance it actually moved (use a travel indicator). Once you do this, MACH will automatically update your Steps/Rev. It's a very handy, time saving thing.

***edit***

Found it - look above the big, honking red "Reset" button near the lower, left corner on the Settings(Alt6) screen. You will see a button that reads "Set Steps per Unit". There ya go.



Scott

[mxtras]

Pitch diameters determine ratio. It makes no difference if the belt has teeth or not.

If it was up to the teeth to determine the ratio then flat belts would have no ratio potential?

Scott

[Josh Leber]

It works great. Dead on accurate!

The 16k number was after a bunch of trial and error trying to narrow it down however, mach was not yet reflecting my changes till the restart.. So those numbers had no repeatable affect.

After restart and entering the calculated numbers, all is well.

The machine has a dirrect drive cog belt for all 3 axises. Mahcine started out life as a epoxy positioning and injection machine for Printed Circuit Boards from the semi-con industry. Very nice cantilevered setup.

now I have all the limit and home switches functioning but can't figure haw to get mach to all a jog off a limit switch while the switch is activated?

[Josh Leber]

LIMIT OverRide... figured it out. thanks anyhow.

[lvanduyn]

Hu apparently is not familiar with cog belt drive. I am currently building a machine with belt drive on both X and Y axes.

Josh..
So what is the final steps per inch number that you came up with?

[mxtras]

Originally Posted by lvanduyn Hu apparently is not familiar with cog belt drive.

Oh, I assure you - he is. As am I.

Scott

[HuFlungDung]

Is this like a 'rack and pinion' gearbelt drive? If so, okay, I can see where you are coming up with that distance per revolution of the drive pinion would determine the steps per inch

I'd still be wanting to know where the calculation went awry, as it is out by a factor of 26. Is there a gear reduction on the front of the stepper, before the drive pinion?