anyone still use dc extruders? help answer a question

I have both stepper and dc motor geared driven extruders. the main reason i went to stepper was slow speed control.


it seems the wider the dc motor pulse the more torque it has. having the lowest pulse width time be a time of 350 microseconds per 1-255 of pwm allows a setting of 15 (5.25milliseconds) and above that to be full power. meaning a setting of 15-255 as workable speeds for extruder motor. this means a few complete pulses a second, using filament to keep back pressure.

I can now using very slow pwm (software, not pwm hardware) have a more full range for dc extruder, without using a quadrature encoder.


does anyone understand why i have full power if the pulse width minimum power time is 5.25milliseconds, and below that power starts dropping off rather quickly? is it that the motor is geared and this is the minimum time required to get past the
90 degrees from the stator poles where torque is zero???



dc motor wiki info


I don't have an issue getting it working, as it does work well. the issue is it puzzles me. I can't explain it!

Edited 2 time(s). Last edit at 08/29/2011 03:10AM by jamesdanielv.