by makeme

Posts Tagged ‘pololu’

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).

Advertisements

A 3D Printer Under $250

In Uncategorized on 23, Oct, 2011 at 22:22

All the coolest gadgets are too darned expensive; especially when they’re brand new. 3D printers are no exception.

Even the dramatic reduction in price that the open source hardware movement has managed to produce only brings 3D printers down to just over $500. That’s amazing compared to the commercial options (which start at $10,000) but it’s just not good enough.

I think the goal should be $250. That’s right around the pro-sumer line so anything under it is legitimately obtainable for the average person. You don’t have to worry about how much profit you can generate with the thing when it’s cheap enough.

A printer that cheap could become a practical option for STEM education. It would be a good introduction even if it didn’t have impressive performance.

Based on some research it looks like that price point is obtainable, in theory, today.

The most expensive part is always the electronics. Well, eMAKERshop sells sanguinololu electronics, fully assembled (and flashed), with the pololu drivers, for $125. They also sell a mechanical endstop kit for $10. Nema 17 stepper motors are around $15 from Kysan (4 of those). A 12v 5a power supply goes for around $10 on Amazon. That’s the majority of the electronics right there for about $200.

Now we just need to build the frame and linear motion systems. A 1/4″ x 2′ x 4′ piece of pine plywood can be about $10. Home Depot lists 16″ keyboard sliders for about $15 (3 of those). Assuming you could make the printer out of cabinet supplies, that’s about $55. If the extruder could be made out of a bolt with some nichrome wire (old school I know) it wouldn’t add much to the total, which is now around $255.

There are some crucial assumptions in there like a dirt-simple extruder and no need for timing belts. At any rate I think this demonstrates that the idea isn’t as far fetched as it might at first appear. A big piece of the puzzle will be getting around the need for metal pieces, printed pieces, and laser-cut pieces.

Lower Entry Barriers For 3D Printing

In Uncategorized on 12, Oct, 2011 at 22:36

The basic technology required to make a 3D printer work isn’t particularly groundbreaking, so it’s nice to see a brand new design as opposed to yet another copy. Origo is a project (company?) started by Artur Tchoukanov and Joris Peels with the goal of producing an $800 mass-produced 3D printer specifically for kids. It looks like they’re planning on using a double swing arm for the X Y motion, which greatly simplifies the physical construction, lowering the cost. They are also integrating the software so that kids can design things in 3DTin and then have their creations automatically printed. Also, a recycler, but I doubt that idea will work.

More 3D printers, particularly cheaper ones, is great. However, I would like to see the cost and complexity drop even farther. Here are some ideas for how that might happen:

  • The printer itself shouldn’t require powerful or precise tools.
The Thing-O-Matic achieves precision with laser cutters, the Mendel achieves precision with another 3D printer, and they both use special steel rods. The designs depend on expensive and difficult-to-maintain manufacturing tools.
I think it’s possible to avoid the use of things like laser cutters, precision ground steel rod, and pre-existing 3D printers. Anything that’s going to be expected to recreate precise movements is going to need some precision parts and assembly, but that’s almost entirely about the layout. For example, instead of laser cut parts one could print a template on a desktop printer, attach it to the wood, and cut/drill by following the guide. The typical solution to linear motion is some kind of bearing riding on precision rod, but some things like aluminum angle and drawer sliders are nearly as precise while being far cheaper.
The real barrier to entry, however, are the precision manufacturing tools. You CAN download the blueprints for a Thing-O-Matic, but they are specifically designed to be produced on a laser cutter. For example, the T-slots aren’t something you can accurately reproduce on your own. Likewise, while you CAN download the parts files for the Mendel, good luck carving them. “Many of the mendel parts are quite difficult to make from wood, and could do with a re-design. They are all created with 3d printing in mind, so there is no consideration for access to internal spaces, or grain or any of the other things to keep in mind when working in wood.” Designs with these requirements create a speedbump which sucks down money, time or luck. Instead, the goal could be for the printer design to require nothing more than a hand saw (cuts) and an electric drill (holes).
  • It doesn’t actually need a .5mm nozzle.
Creating sub-millimeter holes is kind of a problem. The only really reliable way to do it is to put the nozzle blank and drill bit into a lathe. If you allow the nozzle diameter to rise you start to run into pre-manufactured components like needles. Or, at a minimum, things like 1/32th (.8mm) drill bits that are cheaper and easier to obtain than .5mm bits (at least in the States). Even 1/16th (1.6mm) bits would be small enough to do something useful (probably equate to a 2.7mm wide track) and are pretty much free.
More importantly, moving up to something like a 1/16th bit wouldn’t require any special tools to use. Even holding a sub-millimeter bit requires a special tool. A 1/16th will fit into a standard drill chuck. Sure, you CAN get sub-millimeter bits that have expanded shafts, but that’s starting to raise the barriers again as people need to special order them and they can’t be easily replaced.
  • Make each part do more than one job.
The Mendel (and derivatives) is a good example of not doing this. As great a design as it is, there are metal rods being used for the structure and then different metal rods being used for the linear motion. Using the frame material for linear motion would create more synergy (do you have your innovation Bingo card?).
  • Simplify the positioning system.
The reason 3D printers tend to use linear motion is that it’s really simple to program for. 3D files record things in XYZ Cartesian coordinates, so it’s just a matter of calculating the steps. That’s great for the programmers, but not so great for the mechanical engineers. They have to figure out how to create a 3-axis linear motion system on the cheap. Switching to something more like the Origo (a double swing arm) would make the bot a lot easier to build. All you’d have to do is slap a couple arms onto the shafts of a couple motors. The programming would be more complex, and maybe the motors would be more expensive, but the physical construction would be much simpler.
  • Reduce the number of electronic components.
Electronics are expensive, even when you build them yourself. The electronics package is around 1/4 of the cost of a Thing-O-Matic, for example. It might be possible to create a “board on a chip” design inside a Field Programmable Gate Array (FPGA) that would literally do ALL the calculations. It could even replace the stepper boards. FPGA’s, instead of running software, are reconfigurable hardware. You program their logic gates and then they just do what they do. They have hundreds of I/O ports, allowing all the windings of the stepper motors and all of the sensors and all of the heaters to be controlled directly by the FPGA (via some form of amplification). Also, and this is important, they are truly parallel. If something needs to happen on one I/O pin it doesn’t have to wait for the software to get to that part, it just goes in and right back out.
FPGAs aren’t exactly main stream, and there aren’t any open-source solutions yet, but you can get the software you need to program them for free (just sign up for a license). I’m not sure how many gates you would need to replace an Arduino and four Pololus, but seeing as how you could do it with a single chip it’s worth looking in to.
  • Why not design things without a computer?
Origo is on the right track in terms of making it easier for people (kids) to design the 3D models that 3D printers construct. Why not make it even easier? OpenSCAD, a program that has already proven itself in the open-source 3D printing world, already has support for generating 3D models directly from 2D pictures.

openscad 2D to 3D

With just colored lines and some labels OpenSCAD can generate a water-tight 3D model. Kids (anyone) could use crayons or colored pencils to draw a blueprint of their design, scan it, and have it start printing automatically.

RepRap RAMPS Build

In Uncategorized on 11, Feb, 2011 at 12:00

I’m building a RepRap Mendel because one bot just isn’t enough.

The brains of my new bot will be a RepRap Arduino Mego Pololu Shield (RAMPS) because it’s a design that manages to be small, powerful, and line-replaceable. The biggest plus I can think of over the Makerbot electronics is that RAMPS fits the same functions into a much smaller package. That’s not entirely fair, because the MBI Gen 4 electronics are designed to be more flexible in potential applications than RAMPS, but I’m not looking for flexible at the moment. The biggest plus over the RepRap Generation 6 electronics is that the most important pieces are easily replaceable.

So, lets get to it. I found the Arduino Mega (2560) on Amazon, got the DIY RAMPS kit (v1.2) from Ultimachine and found some Pololu stepper drivers in stock at Robot Shop.

[update: I can confirm that this build works for running steppers from the Repsnapper control panel, but I’m still waiting for endstops, so I haven’t tested that function yet.]

[update: I can confirm this build works for running steppers, using min and max endstops, and sensing/controlling the extruder temperature. I don’t have a heated build platform, or a build cooling fan, so I can’t test those features.]

  1. Get out two 4.7K resistors and seven 100K resistors. IMG_0130
  2. Solder them into place. resistors
  3. Get out the 10nF 100nF capacitor and LED. IMG_0133
  4. Solder them into place. The LED’s polarity is not marked on the board, but the RepRap wiki instructions say the short lead goes closer to the bottom of the board. cap & LED fixed
  5. Get out several double stacked headers. IMG_0135
  6. Cut them into seven 2X3 units. IMG_0136
  7. Place them in their respective locations. IMG_0137
  8. Use tape to hold them in place. Now solder them drama free. IMG_0138
  9. Get some single headers. IMG_0139
  10. Cut off a single 1X4 unit. IMG_0140
  11. Place it in the T1-T0 location. Use the tape trick to solder it in place. thermister connection
  12. Get out four 1X16 female headers. IMG_0143
  13. Place them in the appropriate locations. IMG_0144
  14. Use a couple long strips of headers to keep the female connectors aligned and in place while you solder them. IMG_0145
  15. Get out the power terminals. IMG_0146
  16. Also, the little push button switch. IMG_0148
  17. Solder them in place. Be generous with the solder. IMG_0149
  18. Get out the Arduino Mega and associated headers. IMG_0150
  19. Cut one 2X18, one 1X6 and 5 1×8 units (it doesn’t matter if some of them are made out of multiple pieces). IMG_0151
  20. Insert the headers into their respective locations on the Arduino Mega board. IMG_0152
  21. Put the RAMPS shield down on top so that it seats nicely. IMG_0153
  22. After you’ve soldered all the headers in place, they’ll be perfectly lined up with the Arduino Mega. IMG_0154
  23. Get out one 100uF capacitor and two 10uF capacitors. IMG_0155
  24. Solder them in place. The polarity is marked on the board. capacitors
  25. Get out the three N-channel mosfets. IMG_0157
  26. Solder them in place. The proper orientation is marked on the board (a thick white line). IMG_0158
  27. Get out the fuse and diode. IMG_0159
  28. You have to install the fuse, but the diode is optional. According to the RepRap wiki the diode connects the RAMPS power terminal to the Arduino mega board. Without the diode you can theoretically run 35v through the steppers (more torque). With the diode you are limited to the 12v the Arduino is happy with (theoretically 20v, but don’t push it). IMG_0160
  29. Make yourself four 1×4 header units. IMG_0161
  30. Insert them in the appropriate locations next to the female headers. stepper connections
  31. Grab four Pololu break out board kits and make two 1×8 header units. Hopefully you don’t end up with 3 out of 4 kits containing 1×15 strips of headers instead of 1×16 (like I got). But, if you do, you should be able to make up the difference with some scraps from the RAMPS kit. IMG_0164
  32. Insert the eight 1×8 header units into the 1×16 female headers on the RAMPS shield. IMG_0165
  33. Set the four Pololu breakout boards on top. Now you can solder everything together with the correct alignment. IMG_0166
  34. Remove the four stepper drivers and get out twelve jumpers. IMG_0168
  35. Install three jumpers underneath each stepper driver for 1/16th stepping (default). jumpers