Tuesday, May 03, 2011
Important Lesson About Stepper Motors
Torque! Specifically, holding torque.
Before you order your 5 stepper motors for the RepRap Prusa Mendel, you should read the RepRap wiki about stepper motors.
Here's what tripped me up: I'm using the Wade's Extruder design, which recommends a motor with a holding torque of 5 kg*cm. If you read the above article about stepper motors, you'll know what that means. So, when you go shopping for your Nema 17 stepper motors, you need to make sure they are 24 x 24 mm in size, with a 21 mm shaft length, and a 5 kg-cm holding torque. My mistake was to believe the parts list that came with the printed plastic parts, which was WRONG and recommended a Pololu stepper motor of the wrong size and power. Instead the RIGHT stepper motor is something like the Kysan 1124030 Nema 17 Stepper Motor offered by UltiMachine. A helpful tool while shopping is the torque conversion tool online.
I believe the seller of the parts was trying to be helpful, but just googled for Nema 17 stepper motor and picked one without realizing the significance.
Project Update: Today I just went nuts online and started ordering everything left to order. I even bought a 5 lb spool of the plastic filament to print with. Obviously, I'm in an optimistic mood. All that's left to buy, then, is the electronics. UltiMachine is currently out of stock on the RAMPS complete pre-assembled kit. I'm going to be doing good just to get the mechanics together, and I don't even want to try the soldering. Total for the day $555.09!