Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: writerson on April 02, 2010, 08:39:09 AM
-
Hello i am new about this subject and trying to find a solution about some problems in my mind.. Assume that we have three 3000 rpm servo motor, has 8192 ppr encoders. With using 25.000Hz, 35.000Hz.... 100.000Hz, how many servo motors can run with using mach3 with a P4 2.0ghz processor ? Could you please help me about this calculation ??
-
You are either going to have to use electronic gearing if your drives have that feature or get an external pulsing device such as the SmoothStepper or even DSPMC etc
If you dont then the max RPM you would get from the motor is 732RPM and that is at 100MHZ kernel and chances are you wont get a clean enough pulse at that kernel.
As far as the amount of motors are concerned, that doesnt affect things as Mach can pulse each axis up to the max frequency of the kernel, so it doesnt matter whether you have 1 or 6 axis.
Hood
-
i wonder that, how can you make that calculation ?
-
100KHz kernel means 100,000 pulses per second, divide that by the pulses per rev of your motor which is 8192 so that equals 12.207 revs per second max you can achieve, multiply by 60 and you get 732.421875 RPM.
Hood
-
Thank you very much for the reply.. There's one more thing, whats the relation between the PC's Processor ? i mean which processor speed i need minimum to run mach3 100Khz ?
-
Impossible to say as it is not just dependant on the CPU speed, the parallel port plays a role, the chipset of the motherboard may play a role etc etc.
Hood
-
so is that mean mach3 can drive a servo maximum 732RPM doesnt matter its nominal speed is 1000RPM or 6000RPM (if we are using a 8192 ppr encoder) ? in this case i want to ask you two more questions really important for me to solve the subject..,
1-) if our encoder is 2500ppr and nominal speed is 3000RPM, at 100Khz kernel it will turn 40rpm\s = 2400 rpm\m, how much Steps we need to send from motor tuning to get 2400RPM\m ? (2500 steps ?)
2-) i think This external pulsing devices are working well with mach3.. but i cant understand that how this boards increase the maximum speed of mach's ? (i mean, the source is 100Khz isnt there any delay ??)
-
so is that mean mach3 can drive a servo maximum 732RPM doesnt matter its nominal speed is 1000RPM or 6000RPM (if we are using a 8192 ppr encoder) ? in this case i want to ask you two more questions really important for me to solve the subject..,
1-) if our encoder is 2500ppr and nominal speed is 3000RPM, at 100Khz kernel it will turn 40rpm\s = 2400 rpm\m, how much Steps we need to send from motor tuning to get 2400RPM\m ? (2500 steps ?)
It depends what you are meaning by 2500ppr encoder, most encoders are spec'd as lines so a 2500 line encoder would actually be 10,000 in quadrature.
Because 2500 doesnt divide by 4 to give a normal line count of encoders I will presume you are meaning a 2500 line encoder, so at 2400rpm that would require a frequency of 2500 x 4 x 2,400rpm /60 = 400KHz
If you were meaning a 625 Line encoder then you would need a frequency of 625 x 4 x 2400 /60 = 100KHz
2-) i think This external pulsing devices are working well with mach3.. but i cant understand that how this boards increase the maximum speed of mach's ? (i mean, the source is 100Khz isnt there any delay ??)
The max kernel speed is of the Parallel Port and not Mach as such. The SmoothStepper communicates with Mach over USB via a plugin, Mach plans the trajectory and the SmoothStepper puts out the pulses to the servo drives. The smoothstepper can pulse at a max of 4MHz so for your example of 2500 line encoder at 2400 rpm the SmoothStepper could actually pulse 10x more than you would require.
Hood
-
Thanks hood, now its more clear.. This smooth stepper has encoder inputs ?? for carrying the encoder information to mach3 ?
-
Mach is open loop so if you put any encoder info back to Mach it is really only for user monitoring purposes. With a servo system the encoders go to your servo drives and that is where the loop is closed.
Hood
-
does it works for closed loop operation ? --->
http://www.rogersmachine.net/encoderinfo.html
it says that " Alerts the operator of positioning errors on each axis. "
-
Its not closed loop as it will not correct the position on the fly, only report errors. All servo drives that you can use with Mach will fault out if a following error limit is exceeded so no real need for that with a servos system.
Hood
-
thank you, again and again !! now everything is clear..