Hello Guest it is May 19, 2019, 05:08:07 PM

Author Topic: Stepper Motor slow down then speed up along curves/arcs  (Read 3647 times)

0 Members and 1 Guest are viewing this topic.

Offline nava

*
  •  45 45
    • View Profile
Stepper Motor slow down then speed up along curves/arcs
« on: February 10, 2013, 03:14:09 PM »
a little of my system specs
96000 baud 8 bits, 1280 per mm, vel 850 accel 160
16microsteps with 2x reduction with belt drives
4.2 amp drivers and steppers.
windows 7 32

look ahead of 20

Ive been trying to reconfigure my stepper motors to get rid of some horrible harmonics so have changed the default setting they came with from 5 micro steps and 400 pp mm to 16 micro steps and 1280 ppmm. This has seemed to help so far however if I bump up the feed rate on a test arc cut (200%) of the feed rate which was 300mm/min I get a strange pulsing every second or so, I tried to play around with baud rate and the frequency which seemed to have no effect.  Its like the motors go through a slight speed reduction and then increase.  If I use the standard 300mm/min feed from the Gcode then I dont have that problem.  I have searched the forums and other places but cant seem to come up with much.  I thought perhaps it was just a lack of speed of my cpu but its not above 15%.  I didnt get to try and change the look ahead but maybe i need more than 20.  I thought also maybe its a problem of power though my pre built system says it can do up to 150 microsteps and I get no problem moving all 3 axis at the same time at the highest speed while jogging. 

Anyone experience something like this before?

Offline Hood

*
  •  25,811 25,811
  • Carnoustie, Scotland
    • View Profile
Re: Stepper Motor slow down then speed up along curves/arcs
« Reply #1 on: February 10, 2013, 03:39:12 PM »
Not really sure what the baud is referring to?
Can you attach your xml and code and I will check if that is ok.
Hood

Offline nava

*
  •  45 45
    • View Profile
Re: Stepper Motor slow down then speed up along curves/arcs
« Reply #2 on: February 10, 2013, 03:48:00 PM »
sorry 1 to many 0''s in the baud rate its meant to be 9600 8 bit 1stop
Ill have to get the xml and gcode file in the morning as im not in the workshop anymore (its 10pm in Sunday  Austria)

edit: I think also I will do a quick video tomorrow as well as upload the files and the rest of the system.
« Last Edit: February 10, 2013, 03:54:56 PM by nava »

Offline Hood

*
  •  25,811 25,811
  • Carnoustie, Scotland
    • View Profile
Re: Stepper Motor slow down then speed up along curves/arcs
« Reply #3 on: February 10, 2013, 04:03:17 PM »
I still do not understand where the baud is coming into things. Mach connects via the parallel port and baud and stop bits etc do not matter as they are for serial ports, unless of course I am missing something?
Hood

Offline nava

*
  •  45 45
    • View Profile
Re: Stepper Motor slow down then speed up along curves/arcs
« Reply #4 on: February 10, 2013, 05:02:59 PM »
by baudrate I mean the serial output settings under the gerneral tab..or does this mean nothing for me in this case..I somehow thought that they were related.
Its was just there as information in regards to my system specs,  In some other robot projects we have increased the baud rate to improve some servo response times and I thought it may matter here.

And just so there is no confusion about it I am using a parallel port
« Last Edit: February 10, 2013, 05:08:58 PM by nava »

Offline Hood

*
  •  25,811 25,811
  • Carnoustie, Scotland
    • View Profile
Re: Stepper Motor slow down then speed up along curves/arcs
« Reply #5 on: February 10, 2013, 06:56:39 PM »
Serial is only used for special functions, ie if you are using a basic serial interface to communicate with some external hardware of some sort, you wont have that, not many do as its not that great anyway. It is nothing to do with motion control and cant be used for it.
Hood