cheapest 3D printer?

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cheapest 3D printer?

Postby tommythorn » Tue Jan 21, 2014 8:48 am

In the Wally-0 thread,
Nicholas Seward wrote:@tommythorn: I can raise my glass to that. Closed loop machines are coming soon to a cheap hobby machine near you. I actually want to one up that. I want to have a machine which is initially unaware of its geometry and may only only have repeatability over a small time scale. The theory goes that you could build your approximate work space map when you start and it can continually refine/correct its internal model during a print. Cardboard 3D printers with $1 DC motors anyone?


Is cardboard much of a saving over printed plastic? Looking to QU-BD's One-Up, clearly the upper limit for the electronics is < $200. Using the list price, it seems that the four steppers + drivers make up about half of that. I have been toying with some ~ $2 28byj-48 w/drivers. Slow as heck and weak too, but delightfully cheap. I find it difficult to imagine that a DC would be much better.
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Re: cheapest 3D printer?

Postby Nicholas Seward » Tue Jan 21, 2014 11:14 am

The only way that makes sense is in the not too distant future. The controller's cost will have to be on the same price scale as the mechanicals. I would say less than $20. The currently imaginary controller would have to have some closed loop scheme that would allow it to transduce the location of the effector with micron precision. I personally want this transducer to be contactless but this can be done with string and spring loaded spools. Anyways, the details aren't the point here. My point is I look forward to the future when someone assembles existing technology into a dirt cheap closed loop controller with the processing power needed.

Let's spec out one possible solution. We will need to control 4 dc motors. We would also need magnetic rotational encoders for the spring loaded spools. We would need a low power hot end and its thermistor. All of that is super cheap to control and interface with including a decent ARM chip if you build your own.

You could mass produce 3D printers like these and they could be essentially disposable. It might not be cheap enough to put in a happy meal but each filament manufacturer would be glad to give one away if you order enough plastic.
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Re: cheapest 3D printer?

Postby TBog » Tue Jan 21, 2014 12:36 pm

There is this kickstarter project http://www.kickstarter.com/projects/122 ... 3d-printer
They say that DC motors are not only faster and more powerful, but also cheaper, smaller and lighter. Most robots in automobile assembly line and highly advanced humanoid robots employ DC motors.
The printer in by no means cheap, but maybe it gives you some more insight in DC motors...
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Re: cheapest 3D printer?

Postby see3d » Tue Jan 21, 2014 2:22 pm

It has always been the precision transducer that is the most expensive part of a DC servo system. A low cost precision transducer needs to be "invented". The low inertia brushless DC motors specifically designed for maximum performance servos can also be expensive, but they do not need to be for a low end bot.
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Re: cheapest 3D printer?

Postby Nicholas Seward » Tue Jan 21, 2014 3:38 pm

They already exist but just not in a cheap complete package.

The actual components for a precision transducer can cost less than $5. You can use many different methods. I am partial to magnetic angular encoders. I recall a cheap one mentioned in the original Simpson thread on the RepRap forum that had 12 bit precision. That is good enough for our purposes.

They usually cost a lot more because you are paying for a more complete solutions and your average joe doesn't have the ability to do the electronics and the firmware. Time for open source hardware to step in.
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Re: cheapest 3D printer?

Postby tommythorn » Tue Jan 21, 2014 6:04 pm

Thanks for the pointer to the Rappy kickstarter. I'm a bit skeptical of their claims as
RC planes and drones use DC motor because of its high power and light weight.
is inaccurate; RC planes and drones (except the Parrot) use Brushless DC motors, which are explicitly commuted, just like steppers.

The DC motors Rappy show are (AFAICT) brushed, which the industry appear to be moving away from for noise, efficiency, and reliability reasons.
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Re: cheapest 3D printer?

Postby Dpharris » Thu Jan 23, 2014 2:13 am

Electronics are getting cheaper, too. 32 bit mpus are plentiful. Eg the Teensy3.1 is pretty sweet at $20. http://www.pjrc.com/teensy/teensy31.html

:o
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Re: cheapest 3D printer?

Postby Jason Fisher » Thu Jan 23, 2014 11:16 pm

http://www.stellamove.com/#!pump-board/c2pi

More pictures of their "PUMP Board" DC motor controller. Are they only using one of these or one per motor?

http://www.stellamove.com/#!auto-leveling/c1609

It looks like they are auto leveling with a marker or pen, but I wonder if that is just there to cause resistance without damaging the nozzle/board (i.e. felt-tipped), that is then measured by the motor controller?
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Re: cheapest 3D printer?

Postby see3d » Fri Jan 24, 2014 1:35 am

The lack of technical information is very disappointing. It also does not look like it will be an open source project. So far, all I got from it is that they use a cheap brushed DC motor with a high gear ratio. Nothing about where their position feedback comes from. Based on the pictures, I am going to say that the position feedback comes directly off the back of the motor, before the gear reduction. That would give the highest resolution, and does not get the feedback whipped by gear backlash or mechanical resonances. They might load the gears, or just accept the gear backlash as within acceptable tolerance. The encoder is likely a quadrature magnetic or optical system. I think the magnetic Hall ones are lower cost. The mechanism looks like a small UltiMaker 2. The KS price is reasonable for a small assembled unit.

The demo of the bot being shaken and still printing was not an indication that the feedback was compensating for this. It just shows that a high gear ratio is stiff.

It would be interesting to know what servo motor they are using, and if they are surplus or new, and what they cost.
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Re: cheapest 3D printer?

Postby cdsteinkuehler » Fri Jan 24, 2014 2:07 am

Nicholas Seward wrote:The actual components for a precision transducer can cost less than $5. You can use many different methods. I am partial to magnetic angular encoders. I recall a cheap one mentioned in the original Simpson thread on the RepRap forum that had 12 bit precision. That is good enough for our purposes.


But what good does an angular encoder do? Maybe you can eliminate some of the slop of a stepper system (belt/string stretch, etc), but what you really want to know is the actual position of what you're trying to control: the extruder nozzle. I was traveling today, which gave me time to think about position sensing while sitting on the plane. I think you want something non-mechanical, or you just push the expense and complexity from one place (the drive side) to another (the position sensing).

So for non-contact sensing, you can do (at least) acoustic, RF, and optical. Optical is probably off the table given the current state of (inexpensive) electronics, but GHz RF (think mm wave radar) and acoustic could probably be managed with fairly low-cost systems. RF will require much more hardware support, but acoustic positioning could be implemented mostly in software (especially if a DSP is available, or perhaps using some FPGA gates). Of course absolute positioning is a problem since you have to account for the varying speed of sound, but it occurred to me this could perhaps be calibrated out by appropriate setup of the transducers and microphones. If one got _really_ crafty, it might even be possible to generate signals and place microphones such that standing waves were produced that could be used to directly sense position error.

I'll keep thinking about this...if anyone has any good ideas for sensing position inexpensively, please share!
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