Mendel Prusa needs 5 no. NEMA 17 bi-polar stepper motors. These seem to be easy enough to find, and can be bought super-cheap on eBay from a number of Chinese sellers, but I found the ones I contacted were not too responsive about realistic postage costs when you ordered more than one. (The quoted cost of postage for 5 steppers was 5 times the cost of posting one - I don't think so!)
In the end, I bought them from my regular Australian supplier of all things Arduino, Little Bird Electronics for $17.19 each
http://littlebirdelectronics.com/products/stepper-motor-with-cable
They arrived about a week after I ordered them - very nice units!
I have played with stepper motors before, but I had never had two (or more!) identical units to play with, nor have I used steppers with this much torque. Interesting to test them out by joining the ends of each set of coils together to feel the inductive load, and how when you close BOTH coils the inductive load gets even higher, but the stepper motor action becomes quite smooth (instead of "jumpy"). Also fun to hook two steppers together so that when you turn the shaft on one, the other follows with identical rotation as a "slave" unit - without any power hook up. (The motor you are turning effectively becomes a stepper driver for the "slave".)
Oh well - as they say - "little things amuse little minds"!
Hi, just found your blog.
ReplyDeleteGood to hear that there are more repraps appearing in australia :)
Hate to say this, but those motors are fine for printers and PTZ, but crap for reprap.
from little bird site you linked,
Rated Voltage : 12V
Rated Current : 0.33A
Holding Torque : 2.3kg*cm
You want a motor rated 1-4v, 1.5A, 4.4kg.cm (62 oz.in) or more. The ones from http://ausxmods.com.au are excellent.
You could probably print with them, but you won't be able to go fast without losing steps, and it may just plain not give enough torque on your extruder without getting so hot that the mount deforms.
Having said that, see how you go.. they should be fine for Z!
Hi! Thanks for the comments - I hope I haven't goofed on the Extruder Stepper!
ReplyDeleteMy kit includes the RP'ed parts for a Wade's Extruder, and also came with a parts list for the "vitamins". It recommended 5 no. Pololu http://www.pololu.com/catalog/product/1209 with a holding torque of 20 oz.in (0.15 N.m or 1.5 kg.cm), which the Little Bird Steppers should comfortably exceed.
According to the Wade's Extruder RepRap page http://reprap.org/wiki/Wade%27s_Geared_Extruder , the Wade's Extruder is "good for use with a low torque/cheap Nema 17 motor" and you need "1 X NEMA17 StepperMotor - 5 kg*cm works well; Kysan 42BYGH4803 is what I used." I read the bit about "low torque" and "cheap", but missed the comment about "5 kg.cm"!
Once I get the electronics assembled and wired up, I'll report back here on my results. If worst comes to worst, I guess I'll be buying another higher-torque stepper!