Motor FAQ
Introduction
This page tries to answer most of the frequently asked questions related to the choice and operation of stepper motors used by the Reprap. There is a good article on wikipedia explaining the technology behind stepper motors. The physical size of stepper motors are usually described via a US based standard called Nema, the reprap site has an article explaining the standard.
The pages related to building a Mendel has a list of suppliers of stepping motors.
The power of a motor is usually proportional to the physical size of the motor, The Darwin version of Reprap primarily used NEMA 24 motors, whereas the Mendel version is designed to use either NEMA 14 or NEMA 17 motors. The more commonly used size is NEMA 17 as it is easier to find NEMA 17 motors with sufficient torque compared to NEMA 14.
Torque
The Mendel officially requires 0.137Nm torque (1400 g-cm or 1.215 lb-in) for the X, Y and Z axis. Recent designs for extruders almost exclusively require stepper motors as well, but no requirements for torque has been given in those designs.
Power and current
All stepper motors will have a certain specifications for voltage and current, typically 2.8V and 1.68A, as long as the stepper driver/controller does current control you can use any supply voltage greater than the motor's rated voltage. In fact, a large difference is advantageous to the top speed of the motor. If the motor dirver/controller does not do current control, you must use a supply voltage fairly close to the motor voltage (no more than 2x the voltage specified by the manufacturer) or the motor will overheat and burn out its winding insulation or demagnetize its rotor.
The 2.3 version of the Reprap axis controllers do have current control.
Stepper drivers
Sourcing stepper motor drivers can be a bit difficult, the 2.3 stepper drivers for the Reprap is very hard to purchase pre-assembled, sourcing the individual parts and assembling the controllers can be done with just a little bit of skill, for those without skills or materials to assemble the boards, generic stepper controllers purchased from the web. In Europe it will usually be more cost-effective to purchase pre-assembled boards compared to purchasing the individual parts and perform a DIY assembly.
| Manufacturer | Verified | Location | Comments |
| [Sparkfun] | No | US | Slightly underpowered, at only 750mA/Phase |
| [Polulo] | Yes | US | Can get very warm, active cooling is needed |
| [quality-gadgets] | No | GB | |
| [DIY CNC] | No | GB |
Micro stepping
Microstepping between the pole-positions is made with lower torque than with full-stepping, but has much lower tendency for mechanical oszillation around the step-positions and you can drive with much higer frequencies.
If your motors are near to mechanical limitations and you have high friction or dynamics, you won't receive much more accuracy. When your motors are 'overpowered' and/or you don't have much friction, then you can transfer the higher positioning accuracy to moving accuracy too.
