RepRap RAMPS Build Continued

The world can delay me, but it can’t stop me. (huzzah)

I got some v2.1 opto end stops from the guys at Makerbot and a stepper plastruder from MakerGear. It actually didn’t take all that long to get them put together. It also didn’t take much time to start testing the printer and realize that it wasn’t doing what it was supposed to do. Then I got frustrated with programming (black magic) and then other things got in the way.  Anyway, I got the programming problem solved and now have a Mendel that at least pretends to do everything it’s supposed to do. I’ll share any secret tuning tricks as I run across them.

BTW, what made my Mendel do stupid things was apparently having the end stops inverted in the firmware. If you get everything hooked up, and the end stop LED lights up when you break the beam, but your axes won’t move in both directions, try switching the inversion of the end stops in the firmware and re-uploading it to RAMPS. I guess the controller thought that on was off, or off was on, or something like that.

Before you do that, however, you’re going to have to get those end stops built and hooked up.

NOTE: There are some incidental parts and tools necessary to finish this build. I suggest reading through it first and figuring out if you need some random part like a single 2.54mm connector and its associate crimps. It can be pretty frustrating to realize you need to wait a week to get the right 0.05oz part.

1. Get out your end stop PCB and take a look at it. Not too complicated, right?
   
2. Go ahead and put all the components in place. I suggest just buying the kit, but if you want to track them all down individually that’s your prerogative. I didn’t use the RJ45 jack because that’s pretty old-skool (also it doesn’t work with RAMPS).
   
3. Solder them so they don’t go anywhere. You might as well do all the boards at once. I got 6 so that I could have min and max end stops if everything went well, and if I broke any of them I could use the maxes as spares.
4. Here are some other resources for opto end stops: Makerbot and RepRap.
5. The best way to connect the end stops to RAMPS is to use servo cables. At least, it’s easier than building the cables from scratch using 2.54mm (.1″) hardware. You can do that, but it’s a pain. We’ll get to that later.
6. Hopefully you thought that was all really easy…cuz now comes the hard part. The RAMPS board has two of the end stop connectors reversed; something about squeezing thicker traces on the board. This change means that you can’t just plug the end stops in to the board. First, you have to reverse the two appropriate wires in the connector. To do that you have to get something pointy into the back of the connector and pull up the tab that holds the crimped connector in place.
   
7. Be gentle. You don’t want to damage the tab.
   
8. Now you can switch the two wires. Which two wires, you ask? That’s a good question. As you can see on the PCB, there are three pins labeled VCC (+ voltage), SIG (signal) and GND (ground or – voltage). Basically, you’re going to want to switch the wires that are connected to SIG and GND. You can do it at either end of the cable, but try to keep it consistent so it’s easy to check your work. The connectors are labeled on the opto end stop board and on the RAMPS board, so check each a couple times.
   
9. Do that for every end stop you’ve got. Then I suggest making a big loop of tape (sticky side out), and using it to line all your components up side-by-side for a final sanity check. If you bought a weird color of cable because it was on sale you might want to draw a chart or something to keep track of which colors are which.
   
10. It might be at this point that you discover your cables aren’t long enough. Tough.
11. No, but seriously, if that’s the case you’ll need an extension cable. One way to accomplish this feat is by grabbing a scrap rail of headers that are long enough to go into both female 2.54mm housings. The 90 degree headers are good for this.
    
12. Just bend them and cut off chunks of 3.
    
13. At this point things get hard to define. Mounting the end stops isn’t all that complicated, but you can run into weird interference issues. The more true to the Mendel build materials and process you stayed the less problem you should have. I used 6-32 socket cap screws instead of 3mm (USA! USA! USA!) because they were cheaper. They are almost 3mm, but they’re big enough that I had to drill out the end stop mounting holes. Then I realized that one or more of the end stops liked to wiggle around, so I had to create a tiny little brace to keep it immobilized. Just do whatever seems to work for you.
14. I suggest using aluminum flashing for your opaque opto end stop triggers because it’s easy to twist into the weird shapes necessary. It’s cheap, abundant (can pick it up at any hardware store) and most importantly it’s a nice raw material to have around the shop. You can cut it with regular scissors and drill it, so no special tools required. Before you unroll it for the first time, take note of how it’s got that tape holding it together; you want to maintain that (it doesn’t like to roll back up again). Try to keep it from unrolling with one hand while you cut off a thin strip, then tape it back up again before it can pop loose.
15. You’ll have to move the axes around to test fit the end stop triggers. X and Y are easy…Z not so much. You’ll have to get the axes working properly before you can figure out what shape to make the triggers for the Z-axis. I set mine so that the min end stop is triggered just AFTER the extruder touches the build surface. I figure it’s on springs for a reason.
16. The MakerGear plastruder build is already documented pretty well over at Makergear.com. I got the 1.75mm version, and the associated PLA, because I wanted this Mendel to err on the side of accuracy. However, many of the parts in the plastruder are still sized for 3mm filament. Because of this I had a bit of trouble getting the 1.75mm filament to work correctly, but I have been assured that it’s supposed to work just fine. Make of that what you will.
17. Pay particular attention to the steps that involve crimping connectors onto the ends of wires. It’s a delicate operation that is guaranteed to frustrate. Unless you’re already good at it or you have a special crimping tool (in which cases you’re probably only reading through this for a laugh). When you solder the crimp onto the wire be careful to keep the solder from wicking up in between the guides on the “top” of the crimp. If that happens, the crimp won’t go all the way into the connector and you’ll have to get that solder out of there (yes I did that and no it’s not fun).
18. I suggest using different sex connectors on the thermistor and heater wires (one male and one female) that way you can’t get them mixed up in the future.
19. When you’re all done building the plastruder you’ll probably discover that the motor Makergear supplies doesn’t have a connector on it, just loose wires. What you want to do is install a 1×4 2.54mm connector on the end of those wires, because that’s the spacing of the headers RAMPS uses for connections. I had one of those, and the appropriate crimps, left over in the RAMPS kit I got from Ultimachine.
    
20. Install the crimps on the wires, then apply just enough solder to secure them. Take a look at the other motors on your Mendel to figure out what order to install the wires.
    
21. Make sure the crimps are all oriented the right way (so the tab will catch them) and shove them into the connector. You might have to get creative with a pair of needlenose pliers to get them to lock in place. Keep in mind that there’s not much space in there, so if they’re not going in all the way you might want to mash the crimped part into a narrower profile. See how the crimped part of that red wire is kind of wide? Just squeeze that into shape. (don’t deform the part of the crimp that goes into the front of the connector…that would just break it)
    
22. Now you can hook the plastruder up to the appropriate locations on the RAMPS board. The motor connector goes next to the extruder Pololu board, the thermistor goes on the T0 pins, and the heater wires go into the D9 terminals (or whichever ones show 12 volts when you try to turn on the heater). I suggest not bundling the thermistor wires with the heater or motor wires since that might cause noise in the temperature reading.
23. Now enjoy the unique feeling of having all the mechanical and electrical work done because you’re looking forward to a long period of time messing with the software trying to get the machine to do what it’s supposed to do.
24. I’ll put together another post on just that subject…whenever I conquer it myself.
25. I like round numbers.

RepRap RAMPS Build

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.
2. Solder them into place.
3. Get out the 10nF 100nF capacitor and LED.
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.
5. Get out several double stacked headers.
6. Cut them into seven 2X3 units.
7. Place them in their respective locations.
8. Use tape to hold them in place. Now solder them drama free. 
9. Get some single headers.
10. Cut off a single 1X4 unit.
11. Place it in the T1-T0 location. Use the tape trick to solder it in place.
12. Get out four 1X16 female headers.
13. Place them in the appropriate locations.
14. Use a couple long strips of headers to keep the female connectors aligned and in place while you solder them.
15. Get out the power terminals.
16. Also, the little push button switch.
17. Solder them in place. Be generous with the solder.
18. Get out the Arduino Mega and associated headers.
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).
20. Insert the headers into their respective locations on the Arduino Mega board.
21. Put the RAMPS shield down on top so that it seats nicely.
22. After you’ve soldered all the headers in place, they’ll be perfectly lined up with the Arduino Mega.
23. Get out one 100uF capacitor and two 10uF capacitors.
24. Solder them in place. The polarity is marked on the board.
25. Get out the three N-channel mosfets.
26. Solder them in place. The proper orientation is marked on the board (a thick white line).
27. Get out the fuse and diode.
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).
29. Make yourself four 1×4 header units.
30. Insert them in the appropriate locations next to the female headers.
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.
32. Insert the eight 1×8 header units into the 1×16 female headers on the RAMPS shield.
33. Set the four Pololu breakout boards on top. Now you can solder everything together with the correct alignment.
34. Remove the four stepper drivers and get out twelve jumpers.
35. Install three jumpers underneath each stepper driver for 1/16th stepping (default).

The Search for a COTS Nozzle

For anyone interested in improving existing 3d printer designs, or creating new ones, the extrusion nozzle is a real issue. The biggest problem is that the nozzle can’t be made out of the same material the bot prints in; it will either liquify at extrusion temperatures or bond with the material being extruded. Additonally, the nozzle has to meet very particular standards of size, shape and strength.

It’s entirely possible to machine a custom nozzle that does the job quite well. That’s what everyone has been using so far. But the level of machining required is prohibitive. Just try drilling a 0.5mm hole if you don’t believe me.

What we need to find is a Commercial Off The Shelf (COTS) nozzle that is already being mass-produced for some other purpose. It doesn’t necessarily need to be a drop-in product, a little light machining (like tapping threads) would be fine, but it does need to be:

• Resistant to heat. ABS is extruded at around 220*C, and some people run a little bit higher.
• Rigid. It needs to resist quite a lot of pressure from the extruding plastic.

Also, it would be nice if it was:

• Cheap. Duh.
• Interchangeable. Some preexisting threading or method of attachment.
• Doesn’t stick to molten plastic. Infrequent, if any, need for cleaning.
• Variety. A range of nozzle inner diameters would be great.

I don’t think anyone’s found anything like this yet, at least not with an inner diameter under 1mm, but here are some ideas that might work.

• Graphite Ferrule. These things are used in gas chromatography. They’re described as “soft” but they are manufactured with a range of diameters in appropriate sizes and are made out of pure graphite, so they don’t melt until 450*C.
• Capillary Tubes. These things are used in liquid chromatography and other advanced stuff. They can be made out of all kinds of different materials.
• Ceramic Tubes. More of a range of things. What’s important is that they tend to be manufactured in sizes down to and below 0.5mm inner diameter.
• Needles. Again, a range of things. But a few examples for different purposes like veterinary medicine, dispensing materials, and inflating balls.
• Flow Control Orifice. These are used to control the flow of liquids or gases through pipes. They’re all made out of brass or steel, they’re tiny, and they’ve already got pipe threads.

If we can’t find anything that works as-is, then we have to move on to additional steps that take a COTS nozzle from almost right, to totally right. Some examples might be:

• Solder. High-temperature solder (usually lead free, possibly with silver in it) could be used to close up an overly large inner diameter, and then an appropriate hole could be drilled through the solder.
• Cement. Some sort of fireable clay, mortar or concrete type stuff could, once set, resist the temperatures (and maybe the pressures) involved. Maybe it could even be formed around a wire of the appropriate diameter, so when it sets the hole remains and no drilling is necessary.
• Multi-part. Perhaps machining appropriate grooves (.25mm-1.5mm) in two matching surfaces, and holding them together, would work.
• Tapping. Threads are great for attaching one thing to another, particularly if you might want to detach it in the future.

Makerbot Thing-O-Matic Extruder Relay Fix

As I addressed previously: the Makerbot Thing-O-Matic has a few issues. Also addressed previously: why that’s half the fun!

The best way to troubleshoot something is to find where the problem is and gradually work backwards. At each step you try to confirm that a part works the way it’s expected to work. When a part fails a test, you either fix it or bypass it and see if that solves the problem. If it doesn’t, you make a note and continue moving backwards. Of course, it’s always preferable when you can just fix the problem. Or, maybe replace a part, that’s good too.

Plan C is usually to alter the design to compensate for something that simply can’t do what you’re trying to make it do. When it comes to the Generation 4 electronics and the Kysan DC motor on the extruder (all of them) … I’m down to Plan C.

I tried replacing the old Extruder Controller (EC) circuit board with a new one that Makerbot was kind enough to RMA (thanks Ethan!). I also tried replacing the actual motor driver chip (A3949) on the old board with a new one from Digikey (no joy, also, I’m not sure how happy support was about that). The closest I got to a solution was that the totally new EC would drive the motor for a little while (the old one wouldn’t put out any voltage at all). I backed out the delrin plunger’s thumb screw on the extruder so that there was no load on the motor, and just watched the multimeter. Sometimes it would work fine (11.98v), sometimes it would try (~7v) and sometimes it would give up (80mv).

For what it’s worth, by running through this failure mode several times I was able to find that when the motor stopped turning its resistance was basically shorted out  (1.4 ohms). When it was turning fine it was resisting fine (30-45 ohms). So, I suspect that it could very well be a problem with the motor (a bad winding maybe) that’s causing a problem with the motor driver. My guess is that the motor is basically shorting out while it’s spinning, which dramatically increases the current in the circuit, triggering the A3949 to shut down. It’s probably turning back on a microsecond later, applying 12v again, and shutting down again. Repeating that over and over again is probably what produced the 7v-ish reading.

At any rate, replacing the broken part didn’t fix the problem. It merely illustrated that the new part would probably break too. Several people seem to agree that the current design is beyond fixing. Time for Plan C.

“… I’m using the motor just fine to push plastic , powered from the 12v rail of the power supply in the TOM, using a relay connected to the usual motor control to turn it on and off. There hasn’t been a single glitch in this setup.” – ScribbleJ

“Instead of connecting [the EC] to the motor (which fails just as described in these posts), I connected it to a couple of relays. This works in both directions…” - MakeALot

“The relay kit did it for me. Motor started working perfectly.” – g00bd0g

I didn’t feel like waiting for  support to maybe send me a relay kit, so I cobbled something together from Radio Shack. I am happy to report that I just got through 20 minutes of printing without a single problem (that hasn’t happened in weeks). What I did is basically like what rwensley did, but with only one relay (forward or stop).

Parts list:

• Relay (SPDT10A 12V M RLY) $4.99
• Perf Board (23/4x6x1/16 MICRO) $2.99
• Diode (PK2 1N4005 DIODES) $ 0.99
• Terminals (PCB TERM 2P 5MM) $1.99
• Molex Connector (DISK DRIVE EXTCABL) $3.99

Steps:

1. Figure out where to mount the new components. I cut a small piece off the perf board and drilled 1/8″ holes so that I could mount it in between the EC and stepper driver using the existing mounting points.
2. Test fit the components. I then elongated the holes because I’d mounted the board too close to the edge of the bottom panel. Remember that the outside edge of the electronics are butted right up against a wall when the bot is closed.
3. Mark the perf board. I suggest, if you mount the DIY relay board underneath the two existing circuit boards on the same bolts, that you mark it with a sharpie to show where you have room for components. Remember to connect the RJ cable.
4. Cut the female Molex connector. I left a couple inches of wire, then stripped a half inch off of the end of each.
5. Drill holes for the Molex connector wires. I used a 5/64″ drill bit to enlarge four of the holes (at least one hole apart).
6. Hot glue the components in place. You don’t have to do that, but the perf board I used didn’t have any copper on it, so I wanted a better mechanical connection then just soldered wires. It doesn’t take much hot glue, tho.
7. Wiggle everything. The idea is that things aren’t going to fall apart when you start connecting/disconnecting things and trying to stuff them inside the bottom of the bot.
8. Wire it up. Wiring a relay is pretty straight forward. Remember to put the stripped end of the diode on the positive wire.
9. Test it. Not strictly necessary, but it’s good to make sure you got polarities right. I plugged everything in like it was finished, except that I left the two control wires free and just hooked them up to an external 12v source. This simulated the motor controller sending 12v to the motor (actually the relay now).
10. Connect everything and close the bottom. Yay!

Is Makerbot Going To Make It

CES has come and gone, and as usual a lot of people have done “journalism” on topics they don’t understand. For example:

Glen Stantos of Geeky Gadgets seems to be unclear on the concept of a “work in progress,” describing the Thing-o-matic as “working exactly like your trusty printer.”

David John Walker of Seer Press News took Makerbot a little too literally at their word in describing just how “maintenance free” their extrusion system is.

Gizmag managed to get their description right by simply parroting Makerbot’s description.

At least the Tested guys , who have been running Makerbot products for a while now, were coherent.



Here David M. Ewalt of Forbes thinks that 3mm ABS filament only costs $5 per pound, when the Makerbot store he linked to actually sells it for $10-45 per pound. Makergear sells it for more.

Anywho, that stuff’s not the point. The point is that Makerbot is starting to approach that time in the life-cycle of successful startups when they go from small to large. Or, at least when they have the chance to go from small to large. All this press, and it is well deserved press even when it is inaccurate (reporters overstating something is par for the course), is a good indication that Makerbot has “made it” and needs to seriously consider their business model.

The way I see it, Makerbot can remain true to the open-source “maker” idea they started with and keep putting out a product that appeals to DIY enthusiasts. A big part of that model is continuing to let their customers do a lot of their testing for them. This ongoing extruder problem is a perfect example. Since they can get a dozen bots to print for days without any problems, and there aren’t hundreds of people crowding the forums asking about their dead extruders, this failure mode is reasonably rare … for a DIY project. But (and I don’t have any numbers) it seems like this failure mode is too frequent for a larger enterprise. If Makerbot starts selling an order of magnitude more bots they are going to run out of early adopters. While they might be able to get the general public to assemble a Thing-o-matic (at least a full day of work) they are going to have a really hard time getting them to be patient when it doesn’t work or gradually stops working over a couple of weeks. But even ignoring the assembly time (maybe they sell them pre-assembled), you can’t sell something for $1500 that only works for a few weeks. Not to the general public at least.

Which brings me to the alternative business model. Makerbot could go for the expansion that interest in their product supports, but they’d have to dramatically change the way they operate. Selling thousands of bots per quarter will require an obvious expansion of physical and personnel resources, which (since they’re in America, more specifically New York) will start to cost an awful lot. There’s a reason so many things are manufactured in China. The DIY, early adopter, solder fume addict community will pay a premium for something they can hack … the general public won’t. Also, Makerbot’s current clients will “pay a premium” in the extra time and effort required to make the product work properly … the general public won’t. In fact, selling something designed to be hackable to the general public pretty much guarantees that the first people to buy it will be the members of the general public who THINK they can hack, but actually can’t. These people will probably just poke it until it just breaks, and then demand a replacement. Additionally, since Makerbot’s business is based on open-source designs, if they start to create a new market they will find themselves with competition. Even more fun, they’ll find themselves with their first lawsuit as soon as someone leaves the bot printing overnight and their kid reaches in to grab the extruder nozzle, or someone opens their bot up and leaves it lying on the carpet with the z-motor powered up and starts a fire, or someone sticks their eye under the extruder to see if it’s clogged.

I don’t think it’s practical for Makerbot to actually pursue that second option. Not only do none of the founders seem interested in the corporate mindset, there are already tons of pre-existing corporations that can fill up the consumer marketplace with plug-n-play 3d printers. The fundamental technology really isn’t particularly complex or expensive, so as soon as a demand exists it will be supplied. But that does put Makerbot in an interesting position. They can run full speed to become a large corporation and fill the consumer market’s demand for 3d printers, or they can stay where they are with the open-source early adopter thing. They already pretty much guaranteed that they can’t get their company acquired (bought out) since they release all their IP to the public for free. If they wanted to do that they’d pretty much have to rely on the value in their brand.

What they could do, and what I think makes the most sense, is they could expand the “Makerbot umbrella” to include more products. Whenever they get their 3d printer’s mean time to failure low enough, they can start on something else. We can already see that they’re sort of pursuing this strategy since every now and then they mention that they also sell other things like a 3d scanner and an egg plotter. However, I’m unsure about how long that strategy could last. It seems to me that it would only work if they came up with a new flag-ship product that attracted just as much DIY community interest as the Cupcake/TOM did. See, once someone has a TOM, they don’t need a second one, and the market is just too small for them to continue to run a business off of consumables like plastic.

Basically, I think Makerbot needs to stay in the DIY market, but to do that they need to come up with a new flag-ship product. If they don’t, I fear their initial success will be short-lived rather than sustained. An initial expansion followed by a long, slow contraction. And my intuition tells me that the kind of guys who would start something like Makerbot are not going to stick around when their business becomes boring and gradually shrinks, but they can’t really sell it to someone else since all the information someone needs to copy their business is available for free. So, if they don’t come up with a new Cupcake-type-thing in a year or so they just might call it quits.

So, what could Makerbot work on next? I’d like to hear your suggestions, but in the meantime here are some of mine:

• I suppose the most obvious product is a plastic recycler. It’s a more popular topic in the RepRap forums, but pretty much everyone everywhere is already interested in the idea. Something that could take bulk plastic (even if it’s just failed ABS prints) and turn it back into filament for the printer, would be quite popular. Additionally, a lot of work on this topic has already been done in the open source community, so Makerbot wouldn’t have to start from scratch. That seems in keeping with what made the Cupcake/TOM successful (it was pretty much entirely based on the RepRap). Finally, they might even be able to run the recycler off of the same electronics kit already sitting in the bowels of the TOM. The Gen 4 electronics have extra actuator/sensor connections that aren’t being used. A firmware upgrade, a new version of ReplicatorG, a second power supply, a few wires and you’re up and running.
• They could introduce new models of 3d printers that don’t use plastruders. There are literally several dozen different methods of printing in 3d and not all of them require a million dollars. The most obvious method is ACTUAL 3d printing, where a powder medium is smoothed flat and an inkjet head prints a picture to bind it together.
• A complimentary subtractive manufacturing process might be good. If they could build a CNC machine that automatically took parts the TOM had finished, and cleaned them up, drilled holes, maybe even produced a smooth surface finish, it would probably be bought up by the same people who already have a 3d printer. So, not just Makerbot customers, but also RepRap owners and UP printer owners and whatnot.
• Perhaps they could expand into technologies that would compliment the desktop manufacturing paradigm. For example, I have a wet/dry vac that is totally plastic (printable) except for the motor, switch, and wiring harness. In fact, the limitation of “but what can a plastic part do” is the first thing people think of when I show them 3d printing. ABS is structural. To make it generally useful it needs to  hold electrical and mechanical systems in position. Since their market is (and should be) the DIY early adopter hacker type, they could create a sort of Legos system for DIY projects. For example a pick-n-place bot that could build circuit boards by putting components in position and soldering them, and then put them into a 3d printer to have the housing built around them, would be quite attractive to that community.
• One of the biggest limitations is that everything is in plastic. Metal is much more useful for many practical applications, but machining it is a pain. Building up the shape of the metal part you want in easy to handle plastic, and then casting it in metal, would make the machining of metal nearly unnecessary. Perhaps Makerbot could build a sandbox casting bot that takes the part the TOM spits out, dumps sand around it, melts some metal, and injects it into the mold … turning the plastic part into a metal part automatically.

Makerbot Extruder Mystery

Now that I’m an established blogger I think it’s time to tackle the elephant in the room. I’m referring, of course, to the Makerbot extruder “issues.”

I’m not claiming to have a solution, not yet, I just want to try to inject some structure into the problem solving process. There are a lot of references to this problem spread around the interwebs, most of which are speculation. I’m not much use when it comes to electronics, but I can at least compile everything into a coherent troubleshooting process … and then add my own speculation!

First, lets hear from the community:

“I’d try that, but since my last post, the extruder motor stopped spinning altogether.  can’t get it to spin in a build or in the control panel. Ugh.” – Rich

“Then I was trying some raftless objects and the extruder drive died 1/2 way through my 20mm cube and I was like “WTF”?” - Gabe

“I am experiencing something odd with this motor as well.  I was able to complete about 3 prints without any issues.  However recently, the extruder motor stops responding in mid print.” – GodfatherUr

After Makerbot fixed the stop button bug in ReplicatorG, and after so many people reporting that their extruder motors still spin when they apply an external voltage to them, I think it’s safe to discard the theory that there is something wrong with the motors themselves. So, while that’s the thing that most obviously stops doing what we want it to, it seems like it’s just not getting what it needs from lower down in the chain.

That leaves the extruder controller (EC), the motherboard, or the power supply (PS). Lets work backwards, starting with the PS.

According to Makerbot the Thing-o-matic (TOM) ships with a “500w Hercules ATX power supply” which has slightly different specs depending on where you look (17A or 22A on +12V for example)* mine says 22A on the side. I can’t find anyone who admits to manufacturing the thing, although I did learn just how many products are called “Hercules.” So, I did what I always do … I swallowed my pride and consulted wikipedia. The Hercules claims to have over current protection, which should shut down the whole PS if something drew too much juice. Additionally, I didn’t have any trouble finding +12V at pins 8 & 9 (power and ground on the schematic), even when the motor was failing to spin, so it doesn’t look like there’s too little juice either. I followed (in as much as they apply) some troubleshooting guides like these 1, 2, 3 and didn’t find any problems. Replacing the PS seemed to work for G00bd0g but not for Ryan9. I don’t think the PS is the problem.

Ditto for the motherboard. Mostly, I just can’t think of how the motherboard COULD cause the kind of problems we’re seeing. It’s not responsible for extrusion.

The EC, on the other hand, not only controls extrusion but has its own set of firmware. Hooking the motor up to a dedicated power supply demonstrates that there’s nothing wrong with it. The very next thing in the chain is the EC or, more specifically, the A3949 motor driver. As you can see from the schematics, the motor driver connects directly to the motor, supplying everything it uses to function. More specifically, the motor driver takes in a logical signal (distinguished by two LEDs) and power from the +12v rail, then outputs a PWM signal that controls the motor’s speed by turning on and off really fast. To make a long story short, I could never find anything going wrong with anything besides the part of the circuit that connects the output of the motor driver with the motor. Ergo, I think it’s the motor driver that’s causing the problem.

My suspisions regarding this phenomenon is best explained by James, one of Allegro’s (the A3949 manufacturer) technical support reps. After I described the problems to him he replied, “The symptoms you describe are typically related to electrical overstress in the motor driver chip … One risk area is that some applications will use a connector between the motor driver and the motor.  If the connector is disconnected when there is significant amount of current flowing in the inductive load then there will be an out of spec. voltage spike that will damage the motor driver.  As with an ESD event the device may only be weakened by the voltage spike and subsequently fail after 10-20 more hours of operation.”

When I provided the link for the schematic he observed, “I see from the schematic that clamping diodes are in place to prevent excursions of outA and outB from going below ground.  I do not see similar clamping diodes in place for holding the outA and outB to VBB(+12V).”

That’s what I’ve got. Since I suspect a problem with either the chip or the circuit I’m going to have to lean on the technical expertise of EE guys (more of an ME guy myself). My guess is that the design of the circuit is allowing damaging spikes to come back to the motor driver. I don’t know where the first spike comes from, but it sounds like a single bad spike can degrade the chip enough to guarantee failure eventually. I suspect this would account for the interesting variety of failures (or lack thereof) reported by the community.

Personally, I was planning on moving to a stepper extruder anyway. So now I’m just planning on doing it faster. Maybe better electrical isolation of the ICs would solve the problem, maybe not, but at this point it looks like DC extruders are outclassed by steppers even if the extruder problem is solved.

How To Tell If ABS Will Stick

The Thing-o-matic (TOM) is full of surprises.

Probably the biggest shock I experienced was having my very first build stick like it was supposed to, and then peel off like it was supposed to, on not only the first try but on all subsequent tries. The new belt that Makerbot is including with the TOM kits worked perfectly. It’s a pre-made affair that appears to be two layers of plastic tape that were wrapped around a pipe of the appropriate diameter.

That being said, the belt gradually warped. After a couple dozen rotations (not every build was allowed to progress to the eject stage) the belt had a small section that would lay flat, but was mostly waves so big you could surf ‘em.

It got to where the surface of the belt was rising up many milimeters, which made it useless for printing on. The Makerbot support team indicated that the belt might have been too tight, which put too much force on it and stretched it out into a funky shape. They have yet to get back to me regarding how exactly I’m supposed to adjust the tension of a belt on the Automated Build Platform (ABP).

Since I didn’t want to go back to an old and busted option like the lowly Heated Build Platform (HBP), I took advantage of the old style DIY belts they were kind enough to include with the kit. After fighting with the assembly process I eventually got an ABP with a flat belt again. Unfortunately the belt refused to associate with ABS. I tried sanding the surface (in one direction), and I tried degreasing it with windex and other products … but nothing really worked. I had moderate success with just centering the kapton tape so that the build started out on it. Kapton seems to be a reasonably good build surface.

All this time I was bouncing around from forum to wiki to email trying to figure out if anyone had solved this adhesion problem. The best I could gather was that some people had a problem with the exact same kit and some people didn’t. That implied there was a variable involved in using the kit that was being missed, and so was randomly popping up to cause trouble. A conversation with Makerbot’s support led me to suspect it might be that each side of the DIY belts had a different surface, one was Jekyll and one was Hyde. But, in this case, they both looked exactly the same. How to tell them apart?

What I discovered was that you can find out which side is which with a sharpie. The side that won’t be a good surface for printing also is not a good surface for writing.

the bad mark is on the outside surface

The side that the sharpie ink can stick to is the side the plastic will stick to.

the good mark is on the inside surface

The belt I had put together first randomly had the wrong side facing outwards. It was 50/50. I couldn’t find a mention of this difference between the two sides in any of the build or troubleshooting documentation, let alone a method for telling them apart. If other people try this fix and find it consistently successful we can add it to the build instructions so that this problem never appears again. The last thing anyone wants is a 3d printer that would work if only the freakin’ plastic would stick. I haven’t tried this method on anything except the belts from Makerbot, but it seems to have something to do with the inherent properties of the surface of the plastic, so it might work generally (it verified that the pre-made belt is a good build surface).

Let me know whether or not this works when you try it.

Why I Bought a Makerbot Thing-o-matic

The Thing-o-matic (TOM) is pretty impressive. Specifically, after I put it together it worked pretty much exactly like it was supposed to, and then it gradually stopped working like it was supposed to.

I was impressed because I spent a couple of months waiting for it to arrive, and I filled those months with keeping track of what other operators were doing. Most of what I read about was one problem or another, or another … or another. It seemed 3d printers only worked after one spent a considerable amount of time babying them. So, I was expecting to get the TOM put together, watch it not work, and then slowly tease various functions out of it. Instead I was treated to the spectacle of it not only working, but the default settings producing adequate prints on the first try.

That was then. Now that I’ve been printing for a week or two things are starting to go wrong. BUT I’m not complaining! As an early adopter I fully expected things to require fixing, and I’m actually quite excited about the chance to figure out a solution that can benefit everyone else having the same problem.

What I’m looking forward to breaks down into several basic categories:

• Bringing 3d printers up to minimum standards
• Maintaining those minimum standards
• Augmenting beyond those standards

There are certain basic things any 3d printer needs to be able to do just to be called a 3d printer, let alone make anyone happy. “Things” like not failing unexpectedly. At a minimum it should be able to build a physical structure out of a raw material in a controlled way. There are a lot of things that can go wrong with that process, but the level of technology required to merely meet that standard is modest by modern standards, so purging it of bugs shouldn’t last forever. Once a design meets that minimum standard the focus becomes more about optimization than construction.

At some point in the life-cycle of any design it will work properly for longer than it’s ever worked properly before. This phenomenon increases the chances that a new 3d printer will run into a failure state that is so unusual it simply hadn’t had a chance to occur, in addition to predictable accumulated wear. Solving these issues as they arise allows the design to become something people can build future plans around.

Of course, the world wouldn’t be what it is if people left good enough alone. When we can rely on something to do what it’s supposed to do over a certain period of time we immediately ask “Well, why can’t it do more?” 3d printers, specifically hobby 3d printers, are at that point where we really don’t know what their ultimate limitations will turn out to be.

I got a Makerbot Thing-o-matic because 1) I like their style and 2) Electricity is black magic (software might as well be demon summoning), so it’s nice to buy the right to pester a support team with questions, and 3) because it’s a vaguely standardized product. A RepRap is next on my list (I can print it!) but learning on a TOM means that there are hundreds or thousands of other people looking at the same parts behaving in the same way. The presence of this large group manipulating the same machine means that problems can be diagnosed reliably and solutions are meaningful. If something goes wrong with a RepRap the odds are better that yours is a little bit different from everyone else’s, so they might not have experienced the same problem and they might not be able to reproduce it. Additionally, if you solve the aforementioned problem it might not actually help all that many other people.

Also, it’s cold outside … and there’s nothing on TV.