Re: [CAD_CAM_EDM_DRO] Encoder count selection for G320

Denis Casserly wrote:

>HI Art,
>thanks for the info, that's just what I was hunting. I looked for Turbocnc
>maximum step pulse rate but can't find it. I will try posting in CNCPRO and
>EMC2 user groups also unless I find the max step pulse rate for them too.
>
>

I don't know what the limit for TurboCNC is. I think it's CPU dependent
though, so there may not be a single number that they could publish
(other than "about 500 kHz" which is the absolute limit the average
parallel port can handle)

As for EMC2, it also has no set limit - the actual limit will be
dependent on the PC you run it on. Note that faster CPUs don't always
translate to higher step rates. There are a lot of factors that
influence timing in a PC. The best thing to do is download the EMC2
liveCD from <http://www.linuxcnc.org/> (download link on the left
side). This is a bootable CD that you can use to test computers,
without installing to the hard drive first.

As a ballpark number, I'll say that most PCs can handle 50kHz stepping,
and you may be able to get into the 100 kHz range with the right PC
hardware. Also note that there are PCI and parallel-connected devices
(starting at $79, going up to $250 or so) which can increase the step
rate into the MHz range, far beyond what any motor driver is likely to
support. Some of these devices can also generate PWM output (for analog
spindle control or some servos alongside your steppers) and have encoder
inputs, which can significantly increase the resolution and speed of
spindle feedback and/or position tracking.

- Steve

>regards
>Denis
>
>On Saturday 14 February 2009 11:39:26 Art Eckstein wrote:
>
>
>>Denis,
>>Mariss sent this to me a few years ago. I think it is what your looking
>>for?
>>
>>"Determine what is your software's maximum step pulse rate. It'll be
>>published somewhere. Convert your motor no-load RPM into revs per
>>second (divide RPM by 60) and divide that by 4. Divide that into
>>your software's max step frequency. The result will be the maximum
>>encoder line count. Pick the next lowest standard mfg encoder line
>>count. In other words, if your result is 566.66 lines, pick a
>>500-line encoder. "
>>
>>Hope this helps.
>>
>>Country Bubba
>>
>>At 02:25 PM 2/14/2009, you wrote:
>>
>>
>>>Hi Dan,
>>>I meant 30 ips not 30 ipm. Encoders arm mounted on motors. I got
>>>some feedback
>>>that mentioned about 18 ips would be a better target and that's the range
>>>I want to target. I'll use a gearhead to divide the speed down by 7 to 60
>>>revs per second.
>>>There is a relationship between PC software output pulse generation and
>>>encoder line count that has a bearing on top speed. I can not find
>>>the article
>>>that mentions how to decide whether the line count is a good choice.
>>>Would you
>>>have any information on how to make that choice?
>>>regards,
>>>Denis
>>>
>>>On Tuesday 10 February 2009 08:00:01 Dan Mauch wrote:
>>>
>>>
>>>>You must have made a mistake when you said that you wanted 30 IPM I
>>>>think you meant 300 ipm. With a 4200 RPM motor and a 3/1 reduction with
>>>>a .891 pitch diameter of the 14xl pulley you would have
>>>>4200/3X(piX.891)=3918 IPM negating other factors. That is a tad too
>>>>fast. You should look to increase the reduction to at least 6/1 . You
>>>>can also lower the top runaway speed by using a lower voltage power
>>>>supply. With your current setup and the encoder on the motor shaft I
>>>>would say that the resolution using a 250 line encoder would adequate
>>>>and give you plenty of speed and not a high number os steps per in that
>>>>the programs you mention would be fine with. Dan Mauch economical 3D
>>>>scanner software and kits
>>>>low cost stepper and servo motors.
>>>>cases for Gecko drives
>>>>kits and assembled 3-4 axis drives
>>>>www.camtronics-cnc.com
>>>>www.seanet.com/~dmauch
>>>> ----- Original Message -----
>>>> From: dcassyc1
>>>> To: CAD_CAM_EDM_DRO@yahoogroups.com
>>>> Sent: Monday, February 09, 2009 9:15 PM
>>>> Subject: [CAD_CAM_EDM_DRO] Encoder count selection for G320
>>>>
>>>>
>>>> Hello all,
>>>> I want to use homeshopCNC servo motors on a router. The motor is
>>>>rated 72VDC and 4200 rpm no load speed, 850 in oz peak torque, 170 oz
>>>>in continuous torque. My plan for the gantry drive is to go from the
>>>>motor through a 1:3 reduction and drive a jackshaft with 14 tooth XL
>>>>gears on each end, which rack over stationary belts fixed to the frame.
>>>>I calculated the gantry mass at 175lbs aprox. I'd like to achieve 30
>>>>ipm traverse speeds for the gantry and carriage. Is that an unrealistic
>>>>speed?
>>>> I don't know how to make the choice between 250 or 500 line
>>>>quadrature encoders. The 'files' sections servo motor files were empty.
>>>>From what I remember, top speed depends on pulse throughput from the
>>>>PC. The control software is CNCPRO, Turbocnc, and EMC. Would the 500
>>>>line encoder provide greater precision?
>>>> Would anyone care to show me how to make the line count selection for
>>>> the Gecko G320 and advise on the PC speed/performance requirements?
>>>> TIA
>>>> Denis
>>>>
>>>>
>
>
>
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