stepper torque vs. geared extruders August 04, 2015 01:42AM |
Registered: 8 years ago Posts: 5,232 |
Re: stepper torque vs. geared extruders August 04, 2015 02:03AM |
Registered: 9 years ago Posts: 445 |
Quote
o_lampe
Hi guys,
just want to know if there is a "golden cut" regarding decreasing stepper torque at high RPM and the extruder gearing?
I know about current limited BLDC motors, that the torque is constant from 0 to 50% of the RPM range and from 51-100% the torque decreases more or less linear.
How about steppers?
Insanely high gear ratio could put the stepper in trouble, a direct drive slow running stepper might have more torque for printing and a lot of speed reserve for fast retraction.
I´ve seen extruders with as high as 42:1 ratio. Would they still fit the golden rule?
-Olaf
Re: stepper torque vs. geared extruders August 04, 2015 03:00AM |
Registered: 10 years ago Posts: 14,672 |
Re: stepper torque vs. geared extruders August 04, 2015 03:42AM |
Registered: 9 years ago Posts: 445 |
Quote
dc42
Higher gear ratios such as 5:1 should be OK if you use a short motor, so that you can get good acceleration without excessive filament drive force.
HTH David
Re: stepper torque vs. geared extruders August 04, 2015 04:53AM |
Registered: 8 years ago Posts: 5,232 |
Re: stepper torque vs. geared extruders August 04, 2015 06:13AM |
Registered: 10 years ago Posts: 14,672 |
Quote
o_lampe
Thanks David for the elaborated explanation
Wouldn´t it be helpful for controllers with onboard digital current control ( hint, hint ) to implement a dynamic current control?
Winding resistance, max. current and gear ratio are the known parameters to regulate the desired ( speed depending ) torque.
Full torque on high speed retraction / low torque for average extrusion...
The steppers would stay cooler, too.
All steppers could benefit from dynamic current control.
-Olaf
Re: stepper torque vs. geared extruders August 04, 2015 10:32AM |
Registered: 11 years ago Posts: 335 |
Quote
o_lampe
Wouldn´t it be helpful for controllers with onboard digital current control ( hint, hint ) to implement a dynamic current control?
Re: stepper torque vs. geared extruders August 04, 2015 10:46AM |
Registered: 10 years ago Posts: 14,672 |
Quote
691175002
I think there is the potential for too many unintended consequences if you start screwing with Vref at high speeds while a single chip driver is running.
Re: stepper torque vs. geared extruders August 05, 2015 03:46AM |
Registered: 8 years ago Posts: 5,232 |
Re: stepper torque vs. geared extruders August 05, 2015 04:03AM |
Registered: 10 years ago Posts: 14,672 |
Quote
o_lampe
I didn´t say to change Vref at high speed or during an ISR. There is a print cue in FW, where you can look ahead through the g-code and do the Vref calculations beforehand.
Quote
o_lampe
Another feature would be to change the print speed itself according to track length. ( something a very low acceleration would do automatically )
I hate it, when my printer starts to shake, because the print speed is high when the hotend wiggles in tiny moves along the part.
When it prints an arc ( read: lots of short straight tracks ), it should print fast, but at sharp direction changes like 45° zigzag and short tracks, it should slow down.
Re: stepper torque vs. geared extruders August 05, 2015 04:15AM |
Registered: 8 years ago Posts: 5,232 |