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Author Topic: Rack & Pinion step setup  (Read 11007 times)

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Rack & Pinion step setup
« on: March 20, 2012, 10:20:27 AM »
Hello everybody.

I'm using rack & pinion drive system.

I need help from you guys to calculate step per mm correctly  ???.

I saw  calculation example in INCH. I used same calculation calculating steps per mm. But I getting wrong step count.
My calculation:

circle pitch 25.4mm (1")
25.4 * pi = 79.796453
79.796453 / 3 = 26.598817 (reduction)
26.598817 / 200 = 0.132994 (mm per step)
1 /  0.132994 = 7.51913 (steps per mm)
 7.51913 * 16 = 120.30609 (16x microstepping)

I used mach 3 steps per unit calibration, and come out with pretty accurate results - ~ 57.6 steps per mm.
So I'm wondering where I miscalculated ? I need to calculate it accurately :)

Thank you guys for help !

Offline Hood

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Re: Rack & Pinion step setup
« Reply #1 on: March 20, 2012, 11:33:10 AM »
pitch circle is  1" = 25,=.4mm so circumference is 25.4 x pi  = 79.756

Motor 200 steps per rev, x by 3 times gearing = 600 steps per motor rev.

600/79.756 = 7.52294 steps per mm

That would only be a value if your drives were full steping which would be highly unusual and I am guessing they are set to 1/8 step so that would make your steps per mtor rev 8 times more, ie 200 x 8 x 3 = 4800 steps per motor rev.
Because the motor moves the gear 25.4 x pi then your steps per unit would be
4800/79.756= 60.18 steps per mm

Hood
Re: Rack & Pinion step setup
« Reply #2 on: March 20, 2012, 11:43:37 AM »
Thank you for reply.

The steping is set to 16 mircrosteps



my setting is ON / OFF / ON / ON

Offline Hood

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Re: Rack & Pinion step setup
« Reply #3 on: March 20, 2012, 11:54:13 AM »
Ok I see you had that in your post, I sometimes dont read properly when at work ;D

So then it will be twice what I said and I see you have it correct as well in your calcs. Now you say it works out at only approx 57 when you use the Set Steps utility and measure so I can only assume you have a 0.9 degree stepper motor rather than the normal 1.8 degree.
Hood.
Re: Rack & Pinion step setup
« Reply #4 on: March 20, 2012, 12:02:03 PM »
Ok I see you had that in your post, I sometimes dont read properly when at work ;D

So then it will be twice what I said and I see you have it correct as well in your calcs. Now you say it works out at only approx 57 when you use the Set Steps utility and measure so I can only assume you have a 0.9 degree stepper motor rather than the normal 1.8 degree.
Hood.

In motor spec's says that motors are 1.8 degree:
http://www.zappautomation.co.uk/sy60sth883008-nema-stepper-motor-p-24.html?cPath=9_159_42
strange.
is the 0.9 degree motors worse than 1.8 ?

Offline Hood

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Re: Rack & Pinion step setup
« Reply #5 on: March 20, 2012, 12:09:30 PM »
not worse at all, all depends on your application. A 0.9 degree stepper has double the resolution of a 1.8 so it may be a good thing in some applications and bad in others.

If the motor is definitely 1.8 degree then there must something else wrong in your calcs I think, is it definitely 3:1 gearing and not 1.5:1?

As a test set the motor stepping to 1/8 on the drive and see if it moves half the distance, it could be the info on the dip switch settings is wrong, it wouldnt be the first time these Chinese drives have been documented wrong.

Hood
Re: Rack & Pinion step setup
« Reply #6 on: March 20, 2012, 12:22:57 PM »
Actually I was setup'ed 1/8 stepping (settings from pic above: OFF / OFF / ON / ON). I left the steps per mm setting about 120 (as my calculations was with 1/16 stepping). And it was very close to real distance travel  (moved 100 mm and only 2mm's  was traveled more than needed).

So I'm really confused.
Re: Rack & Pinion step setup
« Reply #7 on: March 20, 2012, 12:30:48 PM »
Here is the video recorded today.

Settings:

steps per mm: 57,7
velocity: 15000 mm per min
accelaration: 550 mm per sec

I think I will adjust correct step count only with mach3 steps per unit calibration. I can't see other options.
But I would like to know where is the problem with my calculation or drives or steppers. In that case I will be able to setup everything correctly.