What size of drive pulley?
Posted by appjaws1
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What size of drive pulley? May 12, 2016 04:12AM |
Registered: 10 years ago Posts: 780 |
Using nema17 stepper motors, what is the best size of drive pulley to use with a GT2 belt ?
How do you calculate the resolution?
What are the advantages and disadvantages of different of different number of teeth?
appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1
How do you calculate the resolution?
What are the advantages and disadvantages of different of different number of teeth?
appjaws - Core XYUV Duet Ethernet Duex5
firmware 3.1.1 Web Interface 3.1.1
Ormerod 1-converted to laser engraver, Duet wifi
OpenSCAD version 2020.07
slic3r-1.3.0, Simplify3D 4.1.2, Cura-4.4.1
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Re: What size of drive pulley? May 12, 2016 09:07AM |
Registered: 11 years ago Posts: 5,780 |
The resolution is a function of the pulley size, the motor steps/rev and the microstepping used.
If you use the typical 200 steps/rev (1.8 degrees per step) motors with 16:1 microstepping, the controller will produce 3200 microsteps (usteps) per revolution of the motor. When the belt moves the extruder carriage moves by the same amount. Typical drive pulleys have 20 teeth. 20 teeth at 2 mm pitch means that in 1 revolution, the belt (and extruder) will move by 40 mm. 3200 usteps/40 mm = 80 usteps/mm.
You can get pulleys that have 16 teeth- in that case you'll theoretically get higher resolution: 100 usteps/mm (that's 10 um per ustep). I say theoretically because the actual resolution you get will most likely be limited by elasticity of the belt, flex in the printer frame and guide rails, slop in the bearings, and basic motor step accuracy (typically 5%).
A larger pulley will move the machine faster (because the extruder will move farther with each ustep), but will deliver less torque. A 40 tooth pulley will move the extruder 80 mm in one rev, doubling the speed compared to a 20 mm pulley by reducing resolution to 40 usteps/mm. The reduced torque may or may not be a problem depending on the moving masses and friction in the system, and your expectations for acceleration, speed, and starting/stopping position accuracy. Oriental Motor has motor torque calculating tools that make it pretty easy to figure out how much torque your motor needs to deliver the performance you want. Once you calculate the required torque (with your drive pulley of choice), you shop for the motor that can deliver that torque.
Maximum speed is limited by motor torque and the maximum pulse rate from your controller board. Arduino/RAMPS boards are limited to 40k usteps/sec (IRIC), Smoothieboard can do 100k usteps/sec, others may have different limits. Using the 20 tooth pulley example above, since it takes 3200 usteps/rev, with RAMPS you can spin the motor at 40000 usteps/sec / 3200 usteps/rev =12.5 revs per sec. Since the extruder moves 40 mm with each rev or the motor, you can theoretically drive it at 40 mm/rev x 12.5 rev/sec = 500 mm/sec. Motor torque drops at high speeds, so you're unlikely to actually achieve that sort of speed because at some speed the torque will drop too low to move the mechanism (the motor will slip) unless you select a motor (and driver and power supply) to deliver the full torque required at that speed.
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
If you use the typical 200 steps/rev (1.8 degrees per step) motors with 16:1 microstepping, the controller will produce 3200 microsteps (usteps) per revolution of the motor. When the belt moves the extruder carriage moves by the same amount. Typical drive pulleys have 20 teeth. 20 teeth at 2 mm pitch means that in 1 revolution, the belt (and extruder) will move by 40 mm. 3200 usteps/40 mm = 80 usteps/mm.
You can get pulleys that have 16 teeth- in that case you'll theoretically get higher resolution: 100 usteps/mm (that's 10 um per ustep). I say theoretically because the actual resolution you get will most likely be limited by elasticity of the belt, flex in the printer frame and guide rails, slop in the bearings, and basic motor step accuracy (typically 5%).
A larger pulley will move the machine faster (because the extruder will move farther with each ustep), but will deliver less torque. A 40 tooth pulley will move the extruder 80 mm in one rev, doubling the speed compared to a 20 mm pulley by reducing resolution to 40 usteps/mm. The reduced torque may or may not be a problem depending on the moving masses and friction in the system, and your expectations for acceleration, speed, and starting/stopping position accuracy. Oriental Motor has motor torque calculating tools that make it pretty easy to figure out how much torque your motor needs to deliver the performance you want. Once you calculate the required torque (with your drive pulley of choice), you shop for the motor that can deliver that torque.
Maximum speed is limited by motor torque and the maximum pulse rate from your controller board. Arduino/RAMPS boards are limited to 40k usteps/sec (IRIC), Smoothieboard can do 100k usteps/sec, others may have different limits. Using the 20 tooth pulley example above, since it takes 3200 usteps/rev, with RAMPS you can spin the motor at 40000 usteps/sec / 3200 usteps/rev =12.5 revs per sec. Since the extruder moves 40 mm with each rev or the motor, you can theoretically drive it at 40 mm/rev x 12.5 rev/sec = 500 mm/sec. Motor torque drops at high speeds, so you're unlikely to actually achieve that sort of speed because at some speed the torque will drop too low to move the mechanism (the motor will slip) unless you select a motor (and driver and power supply) to deliver the full torque required at that speed.
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
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Re: What size of drive pulley? May 13, 2016 02:44AM |
Registered: 10 years ago Posts: 780 |
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