Hello Guest it is October 04, 2023, 02:45:20 AM

Author Topic: Newbie servo question  (Read 6995 times)

0 Members and 1 Guest are viewing this topic.

Newbie servo question
« on: October 09, 2006, 01:24:42 PM »
Hey guys.
Ive tried researching this but came up empty.
I have Pittman 14207S007 Servo's running on Gecko 320's for my X and Y axis.
Im trying to tune the motors but dont know what the heck Im doing  :)
I cant find out from my vendor what cpr I should set up .
It seem's they run smooth when jogging but sometimes stop for a sec and the DRO keeps going ???
Could that be a Accel/ Velocity issue as well as the CRP setup ?
Running the famous road runner it seems fine (Moving Slow)
Its the fast jog where I have the issue.
Re: Newbie servo question
« Reply #1 on: October 09, 2006, 03:52:45 PM »
Think I sorted it out.
Bumped the IPM down to 120 and raised the cpr to 2000.
Smooth as Butta so far.
Re: Newbie servo question
« Reply #2 on: October 09, 2006, 09:26:41 PM »
Glad you have it sussed but I'm curious.  Isn't 120ipm kinda slow for Servos, especially with no load? 

I suppose there are a number of factors to consider like, what kind of a machine (mill, router, lathe, etc)?  How much weight are you moving around? And of course, what are you cutting (wood, metal, foam)?

I run my machine around 200IPM with my underpowered steppers and sometimes I could just scream because it is so arduously slow.

I always thought that one of the biggest advantage of Servos was that they could go so much faster and still give you the torque?

Just Curious.

Re: Newbie servo question
« Reply #3 on: October 10, 2006, 08:20:33 AM »
Im gonna bring it up and see what happens.
Earlier I had it set way up there and it would move that table around WAY fast  ;D
I just want to set it where it wont miss any steps EVER.

I need to figure out now how to set up the table parameters.
Heres a unrelated question.
I have Mach set up in Inches.
Do I set up the table size in inches ??
Also are my DRO's dislaying inches ?
I can move Y 2 inches and thats not anywhere near what the Y dro says  ???
Re: Newbie servo question
« Reply #4 on: October 10, 2006, 09:42:08 AM »
Inches is Inches- everything, the whole enchilada- you need not set anything else.

If you tell the machine to move 2 in and it does not (moves more or less) then you don't have your motor tuning set right.  I also suspect that you have no gear reduction on your servos which is probably what is causing you to lose steps at higher speeds.

Re: Newbie servo question
« Reply #5 on: October 10, 2006, 09:47:30 AM »
Thanks Sid.
My encoders are on the BallScrew shaft and I have a 4 to 1 ratio on the Pulleys.
I'll keep tweaking till I get her right !

Offline chad

  • *
  •  361 361
  • When the going gets weird, the weird turn pro.
    • View Profile
Re: Newbie servo question
« Reply #6 on: October 10, 2006, 02:43:20 PM »
Hi Yoda!   Ok you have to take a couple of steps back before moving forward. The first thing you have to figure out is your steps per unit. The 2000 you entered is just an arbitrary number until you know: how many counts your encoders are, what pitch your ball screw is, your belt reduction. Until you know these things that number won't mean anything, and neither will your velocity or accel.  Look at the top of this screen under tutorials and watch the videos they will help fill in some gaps.

Now if you don't have any idea the encoder count or the pitch of the screws there is a nifty utility to get you in the correct ball park.

Get a ruler and a calipers or better yet a dial indicator and go to the settings page. get your machine in the middle of it's travel and click on set steps per unit button. This will bring up a window that will ask for an axis to set. pick the x.
Next it will ask you to enter an amount to move enter something small to start with like 1". The machine will move what it thinks 1" should be. it will then ask you how far it actually moved, use the ruler to get a rough amount.
So if you entered 1" and the machine moved .25" then enter this number. Click on and do it again. this time try to get more accurate. Put one inch in again and measure the result and enter it when asked, this time it should be a lot closer than the first time.
Once you get in the ball park you can use a dial indicator to get really accurate. repeat this process for all of the other axis. I have a feeling that your 2000 steps per unit (in this case inch) is going to be WAY too low for a servo system with a ball screw, encoders and a 4 to 1 belt reduction.
Once you get this axis calibration down to the point that you enter 1 inch and the machine actually travels one inch you can use that number with a measurement of the pitch of the ball screw, and the 4 to 1 reduction to determine the encoder count.   

Now that your machine is set NOW you can start playing with the velocity and the accel and try to tune your motors for good results.

Re: Newbie servo question
« Reply #7 on: October 10, 2006, 03:37:20 PM »
You a mind reader Chad  !!!   lol
I was out in the shop doing just that when you posted.
Ive been relying on the video's for instruction and decided to actually
read the Mach3 PDF doc .  DUUH !!!    ;D
Its now set at 10,000 step per inch and hitting the Mark dead on.
Wish I had more than 5 inches Y (Bench Mill/Drill) but for what Im going to do it should be fine.
I loaded roadrunner and its now larger than my table size.
Oh well. still tickled to make progress.
Thanks All !!


Re: Newbie servo question
« Reply #8 on: October 10, 2006, 03:45:53 PM »
Ive never used it but I think possibly the scaling  beside each axis DRO might help you do the roadrunner if you so wish.
Re: Newbie servo question
« Reply #9 on: October 10, 2006, 06:03:20 PM »
Hood is right on the money, scaling will solve the size problem.  Insert a G51 coomand at the beginning of your program like this..

G51 X.90 Y.90

This will reduce both axis by 10%

Don't forget to add a G50 at the end of the program to Clear the Scaling factor (otherwise it will remain)