Printed stepper motors
This is a nucleus for the development of and gathering info about 3d-printable stepper motors.
Reason for 3D-printable stepper motors
Popular Reprap 3D printer designs include from 4 to 5 NEMA-17 stepper motors, which are as for April 2017 priced at around 10$+ per unit (ebay). Thus stepper motors create a considerable part of a kit price.
In theory, price of stepper motors can be reduced greatly by making them printable and otherwise DIY-able. Thus, development of printed motor designs not only helps a Reprap community, but also enables cheaper manipulators for industrial applications thus lowering industry entry barrier and making production more available for everyone.
Accuracy of a stepper motor is crucial for printing and pick-and-place applications an is characterized by a motor's step angle.
Usual NEMA 17 step angle is 1.8°.
Practice shows that using low-torque motors can cause troubles during printing, so torque is one of the main goals as well.
For printing-aimed NEMA 17 acceptable torque range appears to be 30-50 N*cm. (Note: research is needed on minimal torque req. for different schemes, like it probably varies between delta, XYZ, SCARA etc.)
There are at least 3 ways to achieve high enough torque.
- Reduction. (Two gears of different sizes R and r. Interaction forces are X and -X in their contact area (Newton III-rd), but torques are X*R and -X*r, so they are different in absolute value.)
- More current in motor coils and/or larger coils will obvously help, but it will also cause more heat production.
- Adding more than one motor to a single shaft, consequently or in parallel. Viable if elementary motor price is very low.
Heat is one of the main concerns for printed steppers because ABS softens at about 80°C and coils tend to become fairly hot during work. There are at least several theoretical possibilities to overcome this:
- Use more thermostable plastics (it will require hotter hotend to print it though)
- Use glass 3D-printing like one that was achieved by KIT (a special polymer-matrix material with glass particles that becomes glass in oven). It is not only thermostable, but also fireproof and can be printed by standard means. Downside is the cost of material.
- Make motors bigger in size, make vents in them and possibly include fans or other cooling systems.
- Don't encase coils - make them external.
Note that plastic is less thermally conductive than metal so plastic case is cooling-wise worse than a similar metallic one.
In theory big and even very big motors are still usable in printers and arms via different mechanical connections, but for compatibility with current Reprap models it is better to keep them standard NEMA 17-size or close to it. Redesign is not really a bad thing though.
Projects and progress
Some examples of seemingly working designs from around the world:
NEMA 17 -sized motor built around diametrally-polarized cylindrical magnet, 4 coils and planetary reduction. By Idea Factory
- Teardown, characteristics and explaination. https://www.youtube.com/watch?v=1d73Quuqk54
Simple and large steppers (but still usable in theory if reduction is applied etc.)