MakerBot Industries

In my case, I think it was because I was using oozebane in skeinforge while at the same time allowing the makerbot's hardware to try and compensate for oozing. The net effect of which must have been that the Gcode was expecting the extruder to be running; however, because of the hardware settings, it was not. If you are using replicatorG 0016, go to Machine->onboard preferences->set extruder parameters. There will be an area titled "reversal parameters". I set "time to reverse" to 0 and "time to advance" to 0. This effectively disables the hardware based ooze control and seems to have fixed my particular issue. Now that skienforge has complete control over the extruder motor, it seems to be able to correctly adjust ooze without causing skipped threads.

Another cause might be power stability issues. Other posters here have been talking about how the heated build plate puts too much load on the cat5 cable that delivers power to the extruder. I can see how that might cause "logic" glitches on the extruder board. You could try to modify the extruder PCB to get power directly from the PSU, but make sure that it doesn't cause the z-axis to get hung up as it moves up and down. A less risky solution would be to use a "relay mod" to power the heated build plate.

Although I have gotten my machine to work fine without the relay mod, I wasn't satisfied with how long it was taking my custom build plate to warm up so I added a second string of nicrome wire. Since it doubled the amp load, I didn't want to run it off the tiny extruder board mosfet anymore. Relay contacts will probably have a short lifespan for something like this because they will arc every time it switches on. I opted to try a solid state relay that I got for free from work. I'm hoping that the solid state relay will offer a higher switching cycle count than relay contacts will. At the moment, I think I'm experiencing problems with leakage current that "latches" the relay on. The build plate continues warming up for several minutes after the extruder board switches off the relay. If I disconnect one of the output wires from the relay then re-connect it while the relay is switched off, then the build plate starts cooling like it should. I think I just need to add a resistor to bleed away leakage current. If I were using a ssr built for a 12vdc output instead of 480vac, I might not have this problem at all.

Unfortunately, if you can't find someone who would give you a solid state relay, you will find that they are more expensive than regular relays. I haven't watched the retail prices all that close, but our OEM pricing at work for a relay is $2.50 and we pay $13 for a solid state relay. Also be aware that solid state relays require a heat sink and thermal paste when used with high amp loads. At ~3.5 amps, I'm not sure if the heated build plate qualifies, but I am using one anyway. I just drilled two holes in an old CPU heatsink and mounted the relay to it using a few sheet metal screws. The passive cooling it provides should be sufficient so I did not use a fan with it. I only suggest the solid state relay because of its longer lifespan, but as you can see, it involves more rigging than a standard relay will and you could certainly make the case that the extra cost/work isn't worth the extra lifespan given that a relay will probably last 2+ years anyhow. If you use a relay socket, replacing the relay is a trivial operation too. The relay just snaps into the socket and you don't have to remove the wires.

One last fix you might try is resetting the makerbot if you see that the red debug light is flashing when you notice the problem. I don't know how or why, but I have seen my debug LED flash in the middle of a few builds. I did not see any problem with the printed part though. It doesn't seem to indicate any significant problems for me, but its worth experimenting with if neither of the above works for you.

You can't use solid state relays on DC. They only switch off when the current falls to zero so they rely on the AC doing that every half cycle. They also drop about 2V so are not suitable for low voltages as they waste too much. The best way to switch DC is with a low RDSon MOSFET with adequate gate drive.

I had the same problem with the temperature. It was always ~20 degrees lower than what was in the gcode after I changed something. From what you just said I'm thinking replicatorG must overwrite the PID settings with default values that don't match the firmware's defaults. Apparently when you wrote the new reversal parameters, it also changed the PID to whatever replicatorG thought it was supposed to be. The same thing happened to me despite never once touching the PID stuff. I had to go hunt for the true default settings. Here is what I found:
P: 7.0
I: 0.34765625
D: 36.0

Try applying the settings then switching off the makerbot's PSU. I think I also had a problem where I lost communications or the extruder kind of locked up or something like that after I changed the reversal settings. It was going on 1:00AM though, so at that point I just shut everything down (PSU and all). It was working fine the next day.

Nophead: Thanks for the warning about the relay. I knew DC opto couplers and the like couldn't be used for AC power, but I have managed to use AC opto couplers while controlling a DC output in a pinch. I was thinking this solid state relay was basically an over sized opto coupler.

OK, finally got the settings close.
It does indeed seem to have fixed the missing layer problem I was having. Prints are much better now.
thanks a lot!

dazeddnc,
Solid state relays are opto isolated triacs with a circuit to ensure they only switch on at the mains zero crossing point and a snubber to suppress inductive switching transients.

About the RDSon, how low is low? I found one in my stash that has an RDSon of .2 ohms.
I found the datasheet here.

0.2Ohm is low for a 500V MOSFET but is very high for a low voltage device, which can be as low as 0.005 Ohm. At 0.2R you would need some heat sinking.

Just have to add: The Rds is 0.2 Ohm at 10V gate voltage, so if you drive it only with 5V, it will be even higher.
If you want a FET that works good at 5V gate drive, you should look into "logic-level" FETs.

At this point, I'm sticking with the solid state approach simply to learn more. A relay is obviously much simpler and probably more energy efficient since it doesn't expel waste heat. I work with relays every day though… that method bores me.

I thought the heaters operated at 12V? I was just going to use the heater output to switch it on/off. However, I also noticed that the heater mosfet switches ground - not the 12V side. That means I can't directly drive that chip anyhow.

Whether or not it is optimal, I devised a circuit using that mosfet which seems to work. I'm using an opto coupler to switch on/off a 12V line. I followed this schematic when wiring the mosfet. I wasn't sure what value resistor to use between the gate and ground, so I put a pot there. With it set to 190Kohm, that seems to be about right. The other resistor is just the ~4 ohms from my heater wire and of course I'm not driving an LED so I ignored that part of the example schematic. In place of the switch, I use the output side of my opto coupler. I probably shouldn't be putting 12V into the mosfet's gate, but I couldn't find a current rating in order to use ohms law and calculate the resistor I would need to drop it down to 10V. It has worked for a couple of prints so far and seems stable enough, but I'm wondering if the extra 2 volts might cause a loss of efficiency or cause the mosfet to burn up faster.

I have it optically isolated from the extruder, and I have a fuse on the incoming power. Hopefully this will be enough to protect everything in the event of a failure.

The extra 2V on the gate should not matter as long as you are not exceeding Vgs max.

The value of the pull down resistor is not critical. It needs to be low enough to stop any leakage current through the opto from turning the FET on. It needs to be high enough to not take more current than the opto can deliver when it is on. I would use something like 10K.

Hm, thats an interesting, but for me a bit a strange way of driving the FET.
The 12V on the gate will not be a problem at all, Vgs max rating is 20V if i remember correctly (did not check the datasheet again).
I agree with nophead on the gate-gnd resistor beeing a bit too high with 190K. A FETs gate is working like a capacitor. If you have the gate-gnd resistor too big, it would take a lot of time to switch off the FET, becuse the "gate capacitor" has to discharge thru that resistor. Slowly switching a FET is always a bad idea, because it is in the transition phase where the biggest power losses occur. (Thats one of the resons why faster driven power FETs that do switch a lot (motor drivers) usually have a pre-amplifier. To source or sink a big amount of the FETs gate-charge with a short high burst current as fast as possible, thus reducing the losses that happen in the drain-source channel and keep the FET cooler)
10-20K sound like a good choce, depending on what your optocoupler can switch.
Well, ybout the optocoupler, thats what i refered to at the beginning as beeing the strange part. As it is, this does not offer you any protection at all they way you're using the circuit. The optocoupler is a device used to galvanically seperate to circuits. Unless you have two independendent, galvanically seperated power sources for each side of the optocoupler, it does not help you at all in protecting the one side from faults on the other side. The only purpose it has in your circuit is that it acts as an inverter. Okay for me to do it like that if you just happen to have the parts sitting around, but not really recommended as solution for everyone…

I guess my original hope was that the optocoupler - in addition to inverting which side gets switched - might serve as a weak link that would destroy itself before doing damage to other circuits on the extruder. In the event of a short circuit or something to that effect, I wanted it to pop the output on the optocoupler rather than have a short circuit connect back to the extruder terminals.

I know my optocoupler isn't going to filter out noise or anything because all the power still comes from the same supply. Hopefully my vision of how it provides an extra layer of safety is correct though.

your fix with changing the extruder parameters and letting oozebane take over worked for me initially but now it seems my m101 woes are back….

anyone else have this happen?

Are you running a heated build plate directly through the extruder mosfets?

I don't remember seeing this problem until I started running with a hbp. I just assumed it was a skienforge or firmware bug and didn't make the connection to any hardware changes. I don't really know why my fix appeared to work, but after reading what other posters were saying I kind of figured it was just a coincidental fluke or something, not really a true fix. I only ran the HBP on my extruder for three or four days with the new extruder settings applied. I didn't exactly have an opportunity to evaluate it as a long-term solution, it was just the only thing that yielded any results. Nothing else I did got rid of the problem.

After changing the reversal parameters, I never got the M101 problem again, but I still switched my hbp over to a relay system so I could run a higher wattage heater andbring it up to temperature a little faster. This is probably a key difference that explains why you still get the error and I do not. From what the other people were saying, it sounds like the control failure is due to pulling 4+ amps over the cat5 cable's 20-ish gauge wires. With the HBP running on power delivered through relay contacts (or an external mosfet if you like) instead of the extruder board's mosfet, the amp load must be low enough for the cat5 cable to manage.

Try running without connecting the heater in your build plate and see if your extruder does the same thing.

my HBP is powered through a relay as well….I'll try without it at all and see what happens

i'm officially brain-dead. I completely forgot I had just upgraded to a new extruder board and MK5 pulley so internal settings had to be turned off….boy do I feel sheepish. seems to be printing smoothly again

but after reading what other http://www.eluxurybrandstore.com/ posters were saying I kind of figured it was just a coincidental fluke or something, not really a true fix. I only ran the HBP on my extruder for three or four days with the new extruder settings applied. I didn't exactly have an opportunity to evaluate it as a long-term solution, it was just the only thing that yielded any results. Nothing else I did got rid of the problem.