by makeme

How Low Can You Go

In Uncategorized on 20, Nov, 2011 at 14:34

When it comes to 3D printing, the most expensive part of the system is the electronics.

Makerbot wants $370 for their Gen4 electronics. With their Gen6 stepper extruder (and the driver for it) costing $165, and a set of X-Y-Z motors costing $105, that puts the complete cost of electronics at around $640. I figure this is a good upper bound on what 3D printer electronics should cost since Makerbot’s electronics are probably the most professional and full-featured. I’m not going to include a heated bed in this comparison because it’s not strictly necessary to get started, it’s just a performance upgrade.

Obviously, when there are complete 3D printer kits starting at $500, $640 for just the electronics is unacceptable for my purposes.

The confounding thing is that when you move away from Makerbot (and complete kits in general) you start to have to source from multiple vendors. There is not, as yet, a clearing house for open-source 3D printer components. Sellers tend to focus on one or two options. Additionally, they tend to be located in Europe, so that whole “You want HOW MUCH for shipping?!?” thing gets reversed.

RAMPS and Gen6 are mid-range in terms of performance flexibility and cost. So, you know, whatever. All the electronics kits I know of use pretty much (if not exactly) the same stepper drivers, and they all use USB, and these days they all have an SD-card option, so unless one of them tends to spit out errors more often they all have the same 3D printing performance. 

Sanguinololu seems to be the strongest attempt to whittle the electronics down to just the bare necessities. eMakerShop sells the whole thing (including drivers & firmware tested) for about $170 shipped, they want $95 for the motors (shipped) and $75 for the extruder (shipped). That all comes to around $340. Solidoodle sells the whole thing (without drivers) for $105 (shipped), but doesn’t sell anything else. LulzBot can make up the difference with four Pololus for $65, four motors for $75, and a 12V 25A 300W power supply for $35. They have a hot end that they want $75 for. That all comes to around $350.

There are rumors of people pushing the electronics cost even lower. For example, something called GenL offloads most of the computation to the host computer by using more USB bandwidth. Another example is Repic by Mark Feldman, but I can’t find much information about it.

As you can see, the electronics is the most expensive part of the printer and the stepper motor/driver combination is the most expensive part of the electronics. The need for four bi-polar steppers and four microstepping drivers demands $120 minimum. You might be able to get that down under $100 if you get really lucky on sales or start salvaging parts. The biggest barrier is that these particular parts can’t be made much cheaper. The Sanguinololu board can be brought down to around $60 if you buy the bare PCB, then the components, then burn the bootloader with something you already had (or maybe you can find a chip that’s already burned). But the motors and driver prices aren’t going anywhere.

Some blue-sky ideas for lowering the cost even further involve basically starting from scratch and creating a new family of electronics. The primary reason steppers are so popular is that they don’t require any feedback for accurate positioning. It’s possible that coupling a feedback mechanism (linear resistor, optical encoder, whatever) with a standard DC motor to create a servo would be cheaper. It would also be possible to simulate the entire electronics board on an FPGA for a one-chip solution; just a PCB with the FPGA, its interface, and a bunch of transistors for amplification. Maybe the motors, and their complicated drivers, could be replaced with solenoids and some clockwork. Running all the high-power functions off of AC (out of the wall) might eliminate the need for a power supply (get logic power from the USB).

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  1. There was a discussion on Reprap-dev recently about closing the control loop. The best idea that came out of it was probably the one about using tape from an audio cassette as a linear magnetic encoder strip, which should have sufficient resolution, though most of the conversation was about feedback for steppers, which would work with a lower resolution encoder such as an opto-interrupter reading the teeth on the belt.

    I also played around once with the idea of replacing a stepper with a radial engine with solenoids instead of pistons, which is wildly impractical but has the benefit of not requiring precision-manufactured multi-pole permanent magnets, and thus may be easier for build from raw materials.

    Considering that a decent stepper driver also requires current-sensing, I’m not sure that an FPGA would obviate that many external components. It IS possible to do microstepping from a microcontroller using only a pair of h-bridges externally (and in unipolar mode, you can replace those with four transistors), but a good driver regulates current rather than voltage, which would require more external circuitry to replicate. Also, AFAIK, a single FPGA costs more than a complete sanguinololu with stepper drivers (though I haven’t done a lot of searching to find the best prices).

    • I like the idea of a servo-driven set of electronics, but I don’t know if it would be better to use hobby servos or fab together DC motors with encoders. It doesn’t seem worthwhile to add feedback to the steppers. They’re already plenty accurate open-loop.

      Currently I’m playing around with that same idea of using solenoids to create the axial movement. I’ve got some pretty well formulated ideas for reducing the cost of the physical structure itself, but the current electronics (steppers and drivers) can’t be made cheaper. They just cost what they cost. The only way I can see to bring down the overall cost of the system is to move to a fundamentally different actuator: either servos or solenoids. The solenoids look like they’d require some fancy clockwork, but they’re cheap and the electronics to control them should be cheap too.

      Yeah, I don’t know much about FPGAs. I got a Basys 2 board so that I can start learning, but it looks like it’s gonna be a slog. There aren’t any open-source ways of using FPGAs, yet. You can already see the OS3DP community starting to have an effect on vendors, tho. For example, Pololu has a big list of Black Friday deals, one of which just happens to be on no more than 5 stepper drivers. That’s got to be a nod to the community that’s been buying up their entire supply. If we can start to utilize FPGAs we can drive the open hardware movement in that direction.

      • We could save some of the cost of steppers by switching from NEMA17 steppers to “tin can” steppers, but they have a lower resolution (which could be compensated-for mechanically) and are not nearly as standardized in their physical dimensions and mountings.

  2. Hi! I’m quite a noob about reprap and such but I would like to build one someday! You say RAMPS is mid-range in performance. What do you mean? What’s your performance metric? Thank you!

  3. Well, I didn’t do a house of quality or anything like that. I just figured Makerbot’s electronics were the high end because they’re more expandable than anything else. I figure Sanguinololu was the bottom end because it’s specifically designed to use a cheaper chip and it’s not associated with a stand-alone Arduino board. RAMPS, then, would be somewhere in the middle because…actually never mind. I see what you mean now.

    I probably shouldn’t have used the word “performance.” As far as I know all of the electronics kits “perform” to the same level. Makerbot would probably still be on top if for no other reason then that buying their electronics means you get customer support and can RMA if necessary. Maybe some electronics tend to lose steps more often? I don’t think anyone’s ever compared them.

    You’d be just fine using any of the electronics listed in this post. I suppose since they’re all pretty much equal in terms of performance (as far as I know) that’s why I was comparing them on price and room for expansion.

    • Thank you for your reply! Now I’m less concerned about RAMPS. I plan to buy an Arduino Mega board so in the future I’ll use it as the base for RAMPS electronics, in the mean time I’ll be experimenting a little 🙂

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