small printer, runs off of 5v, fits in a backpack.

ok so ive got this idea, what if a small delta printer could be made small enough to fit in a regular school sized backpack. im just sort of putting my ideas out here so if have something constructive to say go ahead. and if i cant get this to work fast, so be it. here is an example of someone using these motors to make a cute little xy table [letsmakerobots.com]. he used a shift register to make the motors work with only two control bits, a direction bit and a step bit. i hope to do the same thing.

it would use these cheap 28BYJ-48 stepper motors, which come with stepper drivers, although not terribly suffistocated, they run off of only 5v and the motor and the driver only cost 3 bucks each so no one is complaining. these could easily run off a usb phone charger or portable 5v backup battery(haha like i have it has 16,000 mAH.) it would be cool to run it off an arduino uno too, but we will get to that later.

One problem with the little motors is they are very slow, because they are 64 step motors, they are geared down 1:64 so basically 4096 steps per revolution. now having said that people have been able to run them at over 35rpms using 12v, and around 15 rpm using 5v.

Now this can be good and bad as it will have very high accuracy, but very low speed. personally, i have a big printer thats very accurate, and if this thing is going to be portable, it might as well have decent speed, i dont want to have to wait like 5 hours to print a little dude or whatever to show it off to my friends.

So i was thinking whats a way to increase the speed? well lets say the average pulley like the 8 tooth t5 was attached(im not going to use t5 belt) now that has an effective circumference of 40mm so we can get a maximum speed of 10mm/s, which is not that bad really

well one approach might be to use large pulleys. say we want to get 60mm/s a reasonable max speed, we would need a pulley of 240mm circumfrance. for example a 48 tooth t5 pulley or a 120 tooth gt2 pulley, and thats just too large to be reasonable.

another approach would be to bypass the gear reduction and use something like a threaded rod directly on the motor shaft. while another approach might be to modify the internal gearing to something a little bit faster. so basically if do a little math 15rpm*64=960 rpm, or 16 rotations per second, not bad you say, but with an m6 threaded rod thats only 16mm/s and there is increased friction from the screw so not really an option.

so a third option, attach the pulley directly to the motor and toss the gears. so again t5 8 tooth we get 40*16mm/s = 640mm/s. i dont think thats going to work haha. well what about with a smaller pulley, say if you were to use fishing line you could use a very very small pulley so if we use a pulley with a circumfrence of say 6.25mm and a diameter of ~2mm we get a travel rate of 100mm/s and that gives us a resolution of .1mm

now a fourth approach would be to gear up the stepper, but then you get slop and that sort of sucks.

the final option would be to remove the gears and replace them with a different ratio.

so just a little project im working on, there are probably better ways to do this, but hey the motors are super cheap and its just something to mess around with. and if i cant get to be fast ill just attach a little motor and it can be a mini mill.

Edited 1 time(s). Last edit at 04/08/2013 04:23AM by aduy.

If your are gone using fishing line, then have a look at block and tackle [en.wikipedia.org] normaly it is used for down gearing, but you could use it in reverse for up gearing, just conect your motor to the "hook" side

i thought about that, but doesnt it need something to pull it back the other way?

Yes, but you could just add another reverse-block-and-tackle on the motor which pulls if the first loses

oh i see, thats a good idea! thanks. if i cannot get this to be fast ill just make it into a little pcb mill, that would be pretty handy.

ok so look i found a picture of the insides of the stepper, and it looks like it would be pretty easy to modify the motor to be direct drive and then it could be attach to a small pulley that fishing line could be wrapped around. also it looks like i could mess around with the wiring of the motor to make it bipolar if i wanted, or perhaps switch up the wiring to get more speed! also the motor is not even geared down 1:64 its 25792/405, which equates to 63.68395, giving an odd 4075.77 steps per revolution.

ok so i finally got my motors in, and made a prototype last night. does anyoneone know if its possible to drive these directly using repetier firmware, it doesnt use a normal step direction enable bits, it would have to have to send 4 signals to the driver to make it step. i think this could be done by making a class in the firmware, but i forgot all of my c++ during my c++ class. any help would be appreciated.


Edited 2 time(s). Last edit at 04/27/2013 12:26PM by aduy.

if you are trying to provide direct pulses to motors, i have code that can help. my code was for quatro board. it has bipolor pull downs and worked only with 6 wire stepper motors. however the code will work if you have power on both positive and negative side of pulse on 4 wire stepper.

this code can be placed in marlin, and in sprinter. only need to change setup to enable pins, and modify do_motor_X, and y,z,e, and change do_step() to include increment/decrement of steps.

keep in mind that the max pin power drain is 50ma, and 100ma per port.

here is for x motor . i changed the pins to programmable names pina, pina_minus,pinb, pinb_minus


//this code steps in sequence from 0 to 7 for motor control
void Do_motor_X () {
X_AXIS_MOTOR_COUNT=X_AXIS_MOTOR_COUNT&B00000111; //HALF STEP

if ( XENABLE){
switch (X_AXIS_MOTOR_COUNT) {
case 0: WRITE(PINA,LOW); WRITE(PINA_MINUS,LOW);WRITE(PINB,LOW);WRITE(PINB_minus,HIGH); break;
case 1: WRITE(PINA,HIGH); WRITE(PINA_MINUS,LOW);WRITE(PINB,LOW);WRITE(PINB_minus,HIGH); break;

case 2: WRITE(PINA,HIGH); WRITE(PINA_MINUS,LOW);WRITE(PINB,LOW);WRITE(PINB_minus,LOW); break;
case 3: WRITE(PINA,HIGH); WRITE(PINA_MINUS,LOW);WRITE(PINB,HIGH);WRITE(PINB_minus,LOW); break;

case 4: WRITE(PINA,LOW); WRITE(PINA_MINUS,LOW);WRITE(PINB,HIGH);WRITE(PINB_minus,LOW); break;
case 5: WRITE(PINA,LOW); WRITE(PINA_MINUS,HIGH);WRITE(PINB,HIGH);WRITE(PINB_minus,LOW); break;

case 6: WRITE(PINA,LOW); WRITE(PINA_MINUS,HIGH);WRITE(PINB,LOW);WRITE(PINB_minus,LOW); break;
case 7: WRITE(PINA,LOW); WRITE(PINA_MINUS,HIGH);WRITE(PINB,LOW);WRITE(PINB_minus,HIGH); break;
}
}
}


//this code increments and decrements step amount per pulse
void do_step(int axis) {
switch(axis){
case 0:

// WRITE(X_STEP_PIN, HIGH);
if( x_axis_motor_dir)X_AXIS_MOTOR_COUNT--;
else X_AXIS_MOTOR_COUNT++;
Do_motor_X ( ) ;
break;
case 1:
if( y_axis_motor_dir)Y_AXIS_MOTOR_COUNT++;
else Y_AXIS_MOTOR_COUNT--;
Do_motor_Y();

break;
case 2:
if( z_axis_motor_dir)Z_AXIS_MOTOR_COUNT--;
else Z_AXIS_MOTOR_COUNT++;
Do_motor_Z();
break;
case 3:
if( e_axis_motor_dir)E_AXIS_MOTOR_COUNT++;
else E_AXIS_MOTOR_COUNT--;
Do_motor_E();
break;
}
steps_taken[axis]+=1;
// here is where we execute steps
//WRITE(X_STEP_PIN, LOW);
//WRITE(Y_STEP_PIN, LOW);
//WRITE(Z_STEP_PIN, LOW);
//WRITE(E_STEP_PIN, LOW);
}

Edited 2 time(s). Last edit at 04/27/2013 09:10PM by jamesdanielv.

ok so i sort of understand, im not exactly sure how to put it all together, but i will try to figure it out. thanks a bunch. i need to remove the slop before i start messing with the code.

Edited 1 time(s). Last edit at 04/27/2013 10:41PM by aduy.

If you want I can send you the entire build I used. Just give me an email to send it to you.

Hey David,

Just came across this topic as I had a similar idea and thought to search if something similar had been done before. I'm curious, how did you go with this project? Did you finish it or make any progress?

Edited 1 time(s). Last edit at 05/16/2013 01:14PM by HaniC.

Ive been a little ditracted as im currently working on a large hbot printer, once im done with that I will move to the small one. some thing ive noticed are that electronics are now getting cheaper, for example minitronics with everything included is now 85 bucks, so ive been considering ditching the 3 dollar steppers for some nice strong fast nema 11s which i can source locally for 10 bucks each. also i think an hbot design would yield a more efficient volume.

thanks for the interest, I was actually just thinking about it earlier today.

Ah, it's pretty easy to jump between projects - I know i am :-). I've been working on upgrading my original printer. It's a printrbot and I've basically re-designed each part as well as adding better belts, pulleys etc. Even before the rebuild I got it tuned such that the quality was better then some professional rapid models I've received in the past. It should be super sturdy now with a build volume of 200mm^3.

3D printing and printers is all I'm thinking and messing about with as of late. I don't know why.

I started thinking about designing a small printer a few weeks ago. I had a look at the current cheaper printers on the market and thought about what was still making them relatively expensive. It's pretty clear that a large chunk of the cost is in the electronics and motors. I'm an electronics engineer so naturally this is what I looked into first.

The main motivation behind this project and my main goal is designing an ultra low cost printer. Professional quality prints and super high speeds are not so important. 50- 60mm/s max print speed and 0.04mm theoretical resolution in x and y are what I'm aiming for. If I can forgo using stepper drivers and use cheap 28BYJ-48 or similar I think I can get the motor and electronics cost down to about $20 max.

Only problem with the 28BYJ-48 motors is that I've read the backlash in their gearing system is horrible, up to 3 degrees, and they're slow as hell. I know that standard ones (that flood ebay and the like) generally have 4096 steps per rev and can max out at 30rpm. I've seen variants like that on adafruit that have reduction gearing of only 1/16 and with 7.5deg/step giving them 768 step/rev. I also think that there are some with an effective step count of 1024 steps/rev so speed should increase. These in theory should give the desired speed and resolution I think . Not sure about torque though so I've ordered some for testing. Design so far has also focused on minimizing weight to reduce torque requirements.

I'm probably going to design the electronics from the ground up for this project to keep pcb size and design cost right down integrating the discrete components that will be needed to drive everything including motors. Will reluctantly have to stick to using the ATmega to leverage Marlin firmware as I cant be stuffed porting the code but will look at taking out cost everywhere else. I've got a concept in my mind and I think $20 is achievable UNLESS the motors are totally unusable which is likely so I'm still looking into this - could even compensate by implementing an optical encoder. Even a cheap non-gear reduced 0.9 degree motor that is half-stepped without the need of a Pololu driver can yield adequate resolution so if you see something out there that is dirt cheap, let me know.

Will keep you posted if you like.

Im interested, ill keep you up to date on the hardware design. i actually have all the parts now for my big printer which should be done fairly soon.

*subscribed*

This sounds cool. However I must warn you - watch out for the PrismX mini or micro - haven't reckoned the name yet...I'm usually good at names...

Warn us....? That you've got a kickstarter campaign going where your trying to sell a nothing special printer with seemingly false claims (750mm/s)???

Dude relax, where only messing around and are not your competition

do you feel threatened by my picture of a a non functioning micro delta? also the guy that makes the europa and sg2 hot ends on ebay, bradley fudge, is working on a super small light weight hot end design to be used on a bowden tube, im helping him do some research on materials. I plan on using that for this.

Edited 1 time(s). Last edit at 05/20/2013 09:51PM by aduy.

HaniC Wrote:
-------------------------------------------------------
> Ah, it's pretty easy to jump between projects - I
> know i am :-). I've been working on upgrading my
> original printer. It's a printrbot and I've
> basically re-designed each part as well as adding
> better belts, pulleys etc. Even before the rebuild
> I got it tuned such that the quality was better
> then some professional rapid models I've received
> in the past. It should be super sturdy now with a
> build volume of 200mm^3.
>
> 3D printing and printers is all I'm thinking and
> messing about with as of late. I don't know why.
>
> I started thinking about designing a small printer
> a few weeks ago. I had a look at the current
> cheaper printers on the market and thought about
> what was still making them relatively expensive.
> It's pretty clear that a large chunk of the cost
> is in the electronics and motors. I'm an
> electronics engineer so naturally this is what I
> looked into first.
>
> The main motivation behind this project and my
> main goal is designing an ultra low cost printer.
> Professional quality prints and super high speeds
> are not so important. 50- 60mm/s max print speed
> and 0.04mm theoretical resolution in x and y are
> what I'm aiming for. If I can forgo using stepper
> drivers and use cheap 28BYJ-48 or similar I think
> I can get the motor and electronics cost down to
> about $20 max.
>
> Only problem with the 28BYJ-48 motors is that I've
> read the backlash in their gearing system is
> horrible, up to 3 degrees, and they're slow as
> hell. I know that standard ones (that flood ebay
> and the like) generally have 4096 steps per rev
> and can max out at 30rpm. I've seen variants like
> that on adafruit that have reduction gearing of
> only 1/16 and with 7.5deg/step giving them 768
> step/rev. I also think that there are some with an
> effective step count of 1024 steps/rev so speed
> should increase. These in theory should give the
> desired speed and resolution I think . Not sure
> about torque though so I've ordered some for
> testing. Design so far has also focused on
> minimizing weight to reduce torque requirements.
>
> I'm probably going to design the electronics from
> the ground up for this project to keep pcb size
> and design cost right down integrating the
> discrete components that will be needed to drive
> everything including motors. Will reluctantly have
> to stick to using the ATmega to leverage Marlin
> firmware as I cant be stuffed porting the code but
> will look at taking out cost everywhere else. I've
> got a concept in my mind and I think $20 is
> achievable UNLESS the motors are totally unusable
> which is likely so I'm still looking into this -
> could even compensate by implementing an optical
> encoder. Even a cheap non-gear reduced 0.9 degree
> motor that is half-stepped without the need of a
> Pololu driver can yield adequate resolution so if
> you see something out there that is dirt cheap,
> let me know.
>
> Will keep you posted if you like.

oh I see are these here the motors you speak of? [www.sparkfun.com]
they look nice and fast and strong, and if you run a small pulley they can be pretty accurate if you half step them, which is achieveable with any basic electronics.also they can be had for 3 bucks on ebay.

also i see these 512 steps per revolution [www.adafruit.com], i would be wary as to the gearing, the 64 reduction ones were not actually 64 they were some wierd fraction

Edited 1 time(s). Last edit at 05/21/2013 07:11AM by aduy.

aduy Wrote:
-------------------------------------------------------
> oh I see are these here the motors you speak of?
> [www.sparkfun.com]
> they look nice and fast and strong, and if you run
> a small pulley they can be pretty accurate if you
> half step them, which is achieveable with any
> basic electronics.also they can be had for 3 bucks
> on ebay.

These sparkfun ones are un-geared so resolution would be pretty crap unless using external gearing or >1/8 micro-stepping. Even with half-stepping and a really small pulley of say 5mm diameter the best resolution you might expect is ~0.16mm [(5*pi*(7.5*0.5))/360] so I don't believe they are usable as is. Speed, useful torque and backlash would be much better than the 28BYJ type though.

The other ones I was thinking of using are also on eBay and they're about $3 each. They're exactly the same motor (28byj-48) except they have 1/16 down-gearing rather than 1/64. This would mean they are faster but have less torque. The resolution would be sub 0.04mm thought.

> also i see these 512 steps per revolution
> [www.adafruit.com], i would be
> wary as to the gearing, the 64 reduction ones were
> not actually 64 they were some wierd fraction

Here's what I've found (from reading and testing the motors I received yesterday). Some are indeed not as they're spec'd. As you said the 1/64 ones are not 1/64 but more like 1/63.68xx. It's like a lucky dip, as some are exactly 1/64 and some are not. But who cares as we have calibration in the firmware for that.

When they specify 4096 steps per revolution with these 28byj-48 motors, you must know that this is with half stepping not full stepping. Full stepping would be 2048 steps/rev. I was suprised to learn this.

Have you done any testing with these motors actually moving a mass on a rail yet?

I haven't and I'm concerned that the speed/torque balance may not be sufficient. I tested the ones I received (that were 4076 steps/rev) without being connected to anything. They are rated to spin at a maximum of 14rpm. I found that with acceleration I could get it to go 28rpm. Also if you overdrive them (i.e. increase the voltage) the speed can get to about 90rpm but there is virtually no torque and they get hot fast.

It's going to be a balance of gearing used vs speed vs sufficient torque vs motor voltage to be able to use these motors I think. I'm going to continue my testing by trying to move a mass and see the speed and torque response.

Edited 2 time(s). Last edit at 05/21/2013 07:54AM by HaniC.

see the thing is i can still get actual nema 11s with 1.0kg of torque in town for 10 bucks each, and they are going to be much faster stronger and more precise than any of these little motors will be, so until we find a decent motor with zero backlash and the right gearing im sort of stuck.

Nice little design, aduy. I've received three of these 28BYJ-48 motors too, ordered from China via eBay, and mine aren't 2048 steps either. If you run them in full step drive, they're still pretty powerful though. I don't know if they're powerful enough for a delta bot, but I'm thinking something like a Tantillus could be made with them.

Wouldn't using them in a delta reprap eliminate backlash on the gears because of the gravity pulling down on each three slides?

As long as you don't accelerate downwards at more than 1 G.

---

[www.hydraraptor.blogspot.com]

this is true, and they are pretty slow so i doubt they would be accelerating faster than one g, thanks for pointing that out. what was your way getting rid of the backlash though.

AFAIK Tantillus uses regular NEMA17 motors, I was only suggesting a modified, lower-cost Tantillus model that would use those 28BYJ-48 motors.

If you were asking about my tests, I didn't eliminate the backlash at all.

edit: what about trying the 12V version of that same motor? It should be stronger and/or able to be driven at much higher speeds.

Edited 3 time(s). Last edit at 05/24/2013 11:21PM by Yvan256.

I did a couple of tests with this motor having rigged up a quick linear axis. I couldn't get the motor to move any mass whatsoever let alone with any sort of acceleration or speed.

I had previously been overdriving them during initial testing and got them to spin at over 100rpm when unloaded but now Im thinking I might have fried them a little as I expected at least a little torque at low speeds but nothing.

I'm gonna get a few more to repeat the test but I doubt we're going to be able to use them. I've started trying to source a >10N.cm, 0.9degree nema 14. This should give the necessary speed, torque and resolution when half stepping. Best price so far is about $7. I'm certain I get it to sub $5.

I've also given up on those 28BYJ-48, at least in using them as regular step motors. I've tried to make them go forward 85 steps, pause, (repeat 5 times) and then backward 425 steps and it can't even do that properly. I'm not even talking about the gear backlash, after a dozen runs of that sequence there's an increasing positioning error… it's madness!

I'll keep the three I have for other projects, but I'll have to use switches or photodetectors for positioning.

edit: On a positive note, I've just fixed my old Roland MDX-3 with one bolt, a small plate cut from a part of an old printer, a "12VDC PCB drill motor" from eBay and three LEGO parts. I even need to drive the new motor at only 5VDC otherwise it's too fast!

The best part is, I think the spindle is about two to three times as powerful than before.

Edited 1 time(s). Last edit at 05/25/2013 01:55PM by Yvan256.

HaniC Wrote:
-------------------------------------------------------
> I've started trying to source a >10N.cm, 0.9degree nema 14. This should give the necessary speed, torque and resolution when half stepping. Best price so far is about $7. I'm certain I get it to sub $5.

Can you give us more details?

you know i was also thinking about cheap servos, but the issue is that they can only rotate so much, but if you took the pot inside the motor and then replaced it with a long slider, then it could accurately position itself on each axis. well the only problem is finding long cheap sliders.

After reading about servo motors on wikipedia, it seems there's a lot of types of servos but the low-cost ones would be useless for a 3D printer:

"Simple servomotors may use resistive potentiometers as their position encoder. These are only used at the very simplest and cheapest level, and are in close competition with stepper motors. They suffer from wear and electrical noise in the potentiometer track."

If HaniC can get a source of NEMA14, 0.9 degrees motors for 5$ each and by staying with half-stepping as he suggested, it would be precise enough for an entry-level printer. We could gain precision by using fishing line like Tantillus, using a very small diameter pulley/rod to increase the resolution if needed.

I'm guessing even 7.5 degrees motors could be used if the rod diameter was small enough, say 2mm?