Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Lucas on June 12, 2006, 05:09:45 PM

Hi. I am retrofiting a flatbed (around 5' x 3') plotter into a cnc router. I bought 4 gecko 340 and i intend to use the Mach software.
My DC motors are 24V 140w. They have 125 steps/rev encoders, but i plan to change with US Digital 500 steps/rev encoders.
The gear boxes are 1:20 reduction and at the end i use rails. 20 revs of the motor corespond to around 4 inches of travel.
Can anyone tell me what can be the max linear speed that can be achieved with Gecko/mach combination ?
Also what is the maximal (if there is a limit....?!) rev/min of the motor for the correct reading of the encoders (500 steps, 2 inch diameter) ?
Any help is appreciated. Thanks.
Lucas

You are limited to a 45Khz Step rate and that works out to about 1300RPM of the servo motor. You say there is a 2" Dia pulley driving so that works out to about 408IPM if you have a 20 to one reduction and the resolution is about .000157 per step... I would think about getting 250 count encoders and you will not have to stress the software and computer as much :) That will give you more IPM and the resolution will be about .000314 ish...
That was a nice break form the code :) Hope it is a help!
Brian

Brian, thanks for reply !
Can u explain this more: "You are limited to a 45Khz Step rate and that works out to about 1300RPM of the servo motor. "
I made my calculations as follow:
45Khz means 45.000 pulses/ second.
An encoder with 250cpr will give 1000 pulses/rev in quadruature.
45kz/1000=45 rev/ sec = 2700 rev/minute (rpm)
Next question: 45Khz of the Mach (called "Kernel"....don't know why...?) is for one axis or for alll axis ???

Sorry the calcs that I did at first were all based on the 500 line encoder :)
The 45KHz is per axis so you are okay...

Thanks a lot !