stepper motors and lots of general questions

Okies thinking of making one of these the first won't be pretty to say the least, after which I will make parts for a more put together one,
Several questions
A. #1 looking at the whole thing I see there are two motors to lift/sink the bed so for the z axis I need 2 matching motors, question is looking at the designs I dun quite know if I have this right but do you use the threaded rods to move the bed up and down by rotating it?
#2 while using stepper motors I'm thinking of using salvaged ones the problem is that I can't find exact data sheets on many printer salvaged motors I read about the rewrap using 1.8 degree motors and printer usually using 7.5 degree motors but I dunno what they were talking about when they said micro stepping.
#3 I was thinking of using gears to be able to use the 7.5 ones, but the question is if that is feasible I mean I read the 7.5 have 48 steps while the 1.8 ones have 200 steps if I translate this into gears that would be only a ratio of about 4 to 1 so if I have the gear in place how easy is it to program to account for the differences? is it just a matter of plugging in numbers into the software?
I mean gearing like this would mean also that the motor would exert 4 times the torque on whatever is actuated, which means I could get away with smaller less powerful motors.

B. As of now I have salvaged the following motors
#1 An Astrosyn P/N EM-297 type 17PM-K017-P1S What I did find under the type I found an nmb one that is a 1.8" motor but when I twist this one it feels like it has about 50 clicks but I dunno if that is even a valid measure
#2 A Shinano Kenshi STP-42D163 The wedsite does not have a pdf for that series anymore now there are only stt's
#3 And A really small NMB PM42L-D48-EPD8 Doubt this thing would be any use unless it is a 7.5 degree motor in which case with a 4:1 gearing it might have some use but I dunno
I will be looking for trashed printers to try to salvage more steppers in the future I might just get lucky and find the ones I need.


D. As for the controller I see you guys use an arduino micro controller and you use stepper driver chips to translate the signal what would be the cheapest possible option to get this part done? especially if I'm working with salvaged motors and well honestly a slapped together frame, until I can print parts to slowly replace the made-up joints etc.

I am on disability so I really don't have much money to spend right now, but I would like eventually make use of this tech in the cheapest way possible.
I know some of you have quite a bit more experience than me and maybe you can help me get started by answering some of these questions. I can solder, but I'm not a whiz when using IC's I definitely use sockets, because my hands are not that nimble anymore but I usually manage to solder in transistors without frying them.
So any hints on any of the above would be greatly appreciated.
terramir

A. 1. Yes
2. Micro stepping is where the stepper does a fraction of a step per pulse. A 1.8 degree motor takes 200 pulses to do one revolution. At 1/8 micro stepping it takes 1600 pulses per revolution.
3. Yes. Set the number of steps per mm in firmware.

You could use 7.5 degree motors without a problem on the Z axis if you can get enough torqe. Z is geared way lower already due to the threaded rod arrangement so no real need to gear those down even at 7.5 degree steps. With 1/16th microstepping you might even be OK to use them on X or Y but You only get 80 steps per mm using 1/16th stepping on 1.8 degree motors so you'd be down to around 10 steps per mm with 7.5 degree motors unless you gear them down more (likely not worth it due to lash, not sure) . If the motor is really small it likely doesn't have enough torque for any of the axes.

D. what about the electronics what is the cheapest way to get away with that proposal ?

E. Still need to find some more trashed printers to get my motor's together. Can someone tell me how to test the motors they have four wires but I really don't know how I could test them without a stepper driver.

F. does anyone know the stepper motor's listed up there so maybe I can get some data on them like voltage torque etc.

thanks for the answers so far every little bit is helpful
terramir

G another quick question how do you remove those pressed on gear things without damaging the motor's themselves ?
and still asking what is the cheapest electronics solution

Edited 1 time(s). Last edit at 12/28/2011 08:30PM by terramir.

for z axis the lower torque motors will have an easier time if you use 1/4 threaded rod instead of 5/16. I could not get my mendel to do more than 100mm/minute then another user suggested the threading trick, now i can go over 600mm/minute but the belt starts to rattle around so much i limit speed to 300mm/minute. bottom line the 1/4 inch threaded rod would be worth trying if you are using lower torque motors on z axis. i would still use a high torque motor on x and y and purchase extruder motor with highest torque you can find


asked:
another quick question how do you remove those pressed on gear things without damaging the motor's themselves ?
and still asking what is the cheapest electronics solution

i just use a pair of bolt cutters, digging in the direction of the shaft, and cutting into the gear on the motor about 2/3 out so when bolt cutter cuts the gear off the shaft is not damaged.

cheapest electronics solution - the best advice on these forums suggests fewest issues and cost with using ramps.

The absolute cheapest solution is likely to be a Gen7 board you etch yourself and scrounge as many parts as you can from your junk box. Next cheapest is likely Sanguinololu, buy a board and populate it with scrounged components. You'll still have to buy the pololu drivers, but that is common across nearly all the DIY electronics solutions. With RAMPS you have to buy the arduino and add the RAMPS board to it, so it will likely be $30 to $40 more than a sanguinololu or Gen7 setup. That said, RAMPS may be more reliable and is surely better tested and has more resources available, and all firmwares should run on it.

I've seen the pololu drivers and I have a stupid question and it's something I dun get, How come has no one came up with a compatible solution that uses dip packaged stepper drivers I know wouldn't be pretty and I assume the boards would stick out on one end, but it's easier diy and well the only other solution I see to get them more cheaply is to do a group buy, well 100 of these things are like 9.71 a piece if 10 people bought 10 (2 spare and for two reprap's ) we could save some money :p
Anyways

reprap firmware is biased towards ramps and reprap drivers. none of the current firmware properly supports the timings required to work with optically isolated boards which are standard outside of this community.


if you go this route you will need to go into the firmware and modify the do_*_step()'s to have delayMicroseconds(10) after each LOW/HIGH change to a pin. somehow that change is not working by setting delayMicroseconds in configuration.h sprinter firmware. Also you would need to invert enable pins as repraps hardware are backwards.

if you are worried about costs, it is far simpler and cheaper to get it right on the first try. purchase a ramps board pre-built, populate with pololu drivers.


i have a machine I switched with the TB6560 3 axis driver so i could have 1/16 step and it works great with advice above.

but why not use a setup that people understand and can help you with troubles? lots of people on this forum understand ramps, and if you blow a channel the part can be replaced easily.

ymmv, my humble opinions, not endorsed