by makeme

Posts Tagged ‘problem’

Time and Resolution

In Uncategorized on 22, Nov, 2011 at 19:36

I was discussing ways of making better prints with a guy in my office. What follows is the result of that discussion.

A big problem for 3D printing is that you have to trade resolution and time. If you want a cleaner and more accurate part you have to wait longer for it. This is because the printers can’t cover a large area at once. Whatever method is used for the smallest areas has to be used for the largest ones. Maybe you can change tools, but that’s got issues.

Wouldn’t it be nice to be able to form an entire layer at once? Yes. Yes it would. Here is a theoretical method for doing that.

Start with a build surface. Fill that build surface with a grid of tiny holes and in between those holes put tiny electromagnets. Next, flip that surface upside down so that the electromagnets are on the bottom. Now when you inject ferrofluid through the holes you can move it around on the underside of the build surface with the electromagnets. By turning the electromagnets on in a controlled order you can arrange the ferrofluid so that it outlines the exact shape of your first layer.

magnetic fluid 3d printing

Now put that into a tank so that the bottom of the ferrofluid, which is hanging off of the build surface, is just touching the bottom of the tank.

magnetic fluid 3d printing 2

Inject the printing substance through the build surface into the cavities formed by the ferrofluid. Even if the substance is liquid, it will be constrained by the floor of the tank and the ferrofluid.

magnetic fluid 3d printing 3

Harden the printing substance in some way. Heat, UV light, catalyst…kind words. Whatever works. Then raise the build surface by one layer height. Fill the tank with enough of a support substance to just reach the depth of one layer height. This support substance needs to be denser than the printing substance.

magnetic fluid 3d printing 4

Inject more printing substance through the build surface surface to fill the cavity formed by the ferrofluid and the previously hardened printing substance. Any overhangs will rest on the support substance.

magnetic fluid 3d printing 5

Repeat this procedure for each layer, rearranging the ferrofluid when necessary.

magnetic fluid 3d printing 6

This process, or something similar, could open up a paradigm in which you don’t have to trade time and resolution. Each area of detail can be resolved at the same time by just controlling all the relevant electromagnets, then the open space can simply be filled with whatever it is you’re using to print. It doesn’t seem like the control electronics would be all that complicated, either. Basically you’re just drawing on an LCD readout. The complicated part of this idea is the various substances. It’s more of a chemistry problem than an electrical problem.

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Makerbot Thing-O-Matic Extruder Relay Fix

In Uncategorized on 23, Jan, 2011 at 19:14

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:

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!

TOM relay

Makerbot Extruder Mystery

In Uncategorized on 05, Jan, 2011 at 18:23

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.