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The RMax is my first printer, got it up and running in Feb, and since day one I've had this problem with the EZ-Struder and haven't pinned it down yet what it is. I would like to know if others have had the same issue, and what to do to resolve it.

By kicking back I mean that the filament is extruding forward without slipping, but, once in a while, randomly as far as i can tell (in relation to other steppers, heat, etc), the stepper will jump backwards by 1/8 to 1/4 turn. This is NOT a programmed retraction, retractions are smooth and turn slow compared to this. This just jumps back in a single step. It has to be some sort of glitch that causes the stepper to jump back in one big step backwards. When it does this it jumps back so fast the filament generally doesn't move back, rather, the filament stops and the teeth grind into it. After the stepper jumps back it goes on from where it jumped back and continues forward. But, if it starts doing this repeatedly, which it does at times, then it starves the filament from going forward and print gets messed up. One time, 2 hours into a 2 1/2 hour print, it ground down the filament to where the teeth couldn't grab it and even though the stepper kept going forward, the filament didn't move. Print ruined.

It has had this issue from day one. But, lately it seems to have gotten worse (or maybe i am pushing the speed too fast? I most try to run at 30 nn/sec on PLA - and it used to be fine most of the time. But, now i can rarely print that fast without too many kickbacks. I've even pushed it to 40mm/sec when it is running smooth but, then it is almost for certain it will start kicking back. At times, though, it goes into a Spasm and starts kicking back every few seconds, and if i slow it down to 60% (60% of 30mm/sec is about 20mm/sec), it generally stops the kick backs. But, there are times that even slowing it to 12 mm / sec doesn't stop the kick backs. The spasms generally last 1-2 minutes, then it goes away and will print fine again at faster speeds, so it comes and goes, as far as i can tell, randomly.

Also, it is a current related or too much force needed issue, if i do a dry run, heated head and bed, just no filament, it never kicks back. And, if it is acting up and kicking back a lot, if i push the filament into the EZStruder (I have a top mounted EZStruder, so if i push down on the filament going into the EZStruder), then the kickbacks stop, let off and it will kick back again. By pushing down I am taking some of the load off the motor. So, it seems to be a current issue, too much current causing a spike or glitch to go back in to the Rambo drivers or logic, and a bad code sent to the stepper causing it to jump back. Remove some of the load off the stepper, and the jumping goes away. I have though of buying a snap-on ferrite core to see it that might help?

When not printing, with the head hot, I can press the release on the EZStruder and push the filament through the nozzle fairly easy, so, it isn't a jam causing it. (I've taken out the nozzle and plastic tube and checked and cleaned them, that isn't the issue, the filament flows properly, as far as i can tell, but this is my first and only printer - i have nothing to compare it with. )

I sent email to Support, and was told it was probably too much current to the stepper, to turn down the current. In the configuration.h the default was 175,175,175,200 (0-255), the first 3 are the x,y,z steppers and the last, 200, is the extruder stepper. I set it to 175 as well and there was no change. I will try lower, but, i'm afraid of going too low and it will start slipping.

When i first built this I had run the Z axis home switch wires down the same channel as the extruder stepper, and the extruder was giving me false Z homing inputs, and was throwing off the print linearity. I re-ran the home switch down another channel and resolved that issue, thanks to input from the forum.

I'm wondering if there is some other similar interference going on with this issue? Right now the extruder stepper wires go down the Z axis channel, in the center, so, if there is interference i don't know where its coming from? Rather, it seems to be the motor itself sending a glitch back into the Rambo card. I do have another stepper, maybe I'll try swaping it. I just got through swapping out the Rambo card, due to the USB port stopped working - a known issue, SeeMeCNC sent me a replacement card, but this problem remained unchanged, so it isn't a bad Rambo board.

Anyone one else have this issue, or know where else i can look to resolve it? Thanks. BTW, I am running .91 Repetier on the Rambo/Arduino side, and 95F on the host, using Slic3r if that makes a difference.

I forgot to mention, I put the 40 mm fan pointed at the stepper drivers on the Rambo, problem still there. But, that fan lasted less than 3 weeks and the bearing went out. It still turns, it just sounds like a little Harley running inside the RMax. I then put a 120mm fan running at full speed, like a leaf blower, and still the problem didn't go away.

There are LOTS of posts here about this, please read those. This is called "skipped steps" and there are several contributors. I've documented them all but let me list them here and you can then search my and other's posts for the remedy.

1. Too MUCH current to the stepper - this overdrives the stepper causing it to heat up.
2. Too LITTLE current to the stepper - the stepper does not have enough power to push the filament. I suspect this more than 1. I have my ezStruder current set to 230
3. Overheating stepper driver on your RAMBo. This causes it to momentarily shutdown. I had this problem, easy fix, use a fan to cool it.
4. A problem in the extrusion path. This can include a deformed PTFE tube - the Bowden or the PTFE in the hot end, snags through the PTC fittings, plugs in the hot end - remember that orifice is small. Pieces of lint on the filament make their way into the hot end and can eventually cause problems. All of these are easy to test - heat up your hot end, depress the red lever on the ezStruder and push the filament by hand. If it won't extrude out the nozzle or is very difficult to push, then concentrate on the items in this list first.
5. Oversized filament or filament that is ovalized
6. The "teeth' on the ezStruder gear can be very sharp and aggressive. They can leave a deep impression in the filament. This increases it's effective diameter and raises the likelihood that the filament can snag at the PTC fittings, in the hot end, etc. Check this along with the previous point.]
7. "Hydraulic jamming" when printing with PLA. My personal favorite. This raises its head when you have retract speed too high. Use 20mm/s and 2-3 mm retract. Any faster and you can run into this.

You didn't mention what material you are printing or any information about when this occurs - immediately, in the middle of a print, after a sequence of rapid retracts, etc. These all help diagnose.

My bet is on too little current, driver cooling and/or PLA jamming.

MHackney

I've seen the posts on "slipping". but that and "skipped steps" doesn't really describe what mine is doing. It isn't skipping or slipping, it kicks back suddenly by 1/8-1/4 turn. Maybe it's just the wording that is used, maybe they all mean the same thing?

1-2 But how low or how high should i go on the current? It was at 200 and i lowered it to 175 with no change. I'll try going down to 125 and up to 225 or so in steps and see what happens. Will take a while because I don't have time to do tests for a few days.
3 As I said, i have even put a 120 mm fan blowing at full speed aimed toward the stepper drivers. Rambo overheating shouldn't be the issue.
4 - yeah, i've had isses with the ptc fittings, but, that is it's own problem but, as i also pointed out, it will give the Kickbacks even when the filament is easily pushed by hand through the heated head.
5 I have had one roll of PLA that was a bit larger and caused more kickbacks then the normal sized ones. So, that may lead me to where to look.
6 And, yes, the teeth on the gear definitly leave their mark in the filament, maybe that's an issue, making the filament larger and making it harder to go through, I'll look into it

As far as materila : I have never printed with ABS yet, But this issue has been with PLA and t-glase, that's what i use mostly (I've ran nylon, but too soft for my needs). On the PLA, I've never been able to get past 40 mm/s without the kickbacks going crazy, and generally 30 mm/s is max i can do, sometimes i have to slow down to 20 or slower. I've been running the temps between 185-192 with peek fan at full

It is worse with t-glase I run that between 220-235 But, my head won't get that hot if i have the peek fan at full, so i have to set the peek fan to 150.
The most i can do with t-glase is about 20 mm/sec - and sometimes lower.

I just saw someone else claim with PLA they said they do 40-60 on the perimeters and 80-150 mm/s on the infills. Whoa, i can't get anywhere close to that.... All because of this issue. If i could get up that speed i could finally do some of the larger files i wanted to do.

When this occurs, I said, it's random. If i go too fast it will occur from the start (printing the skirt) to any and every time. Too fast it is constant, so i have to slow down to where it will stop.

I've also run into this 'kickback' recently. Anyone find further solutions for this?

I've had the rostock since January and have had successful prints without any kickback.

The kickback seems to have occurred after two changes:
1) I moved the unit into my garage, in Florida, where temps are regularly in the 80's or higher.
2) I remade the extruder wires with the four pin connectors recommended in the assy guide.
3) I now close the unit door since the extruder wire no longer needed tweaking to work.

The kickback doesn't start initially but occurs after 15 layers on a small print.

kittka wrote:I've also run into this 'kickback' recently. Anyone find further solutions for this?

I've had the rostock since January and have had successful prints without any kickback.

The kickback seems to have occurred after two changes:
1) I moved the unit into my garage, in Florida, where temps are regularly in the 80's or higher.
2) I remade the extruder wires with the four pin connectors recommended in the assy guide.
3) I now close the unit door since the extruder wire no longer needed tweaking to work.

The kickback doesn't start initially but occurs after 15 layers on a small print.

You should add a fan that blows some air on the driver chips on the Rambo. The chip for the extruder is
known to kick out because of heat and the symptoms are as you have described. Some fans will fit in the area
where the LCD is. The fan on the rear of the Rambo helps but sometimes the additional cooling from the front is also needed.

I was thinking this would be my first check from the list in mhackney's post. The move to a non-air conditioned space was a main concern. I'm reprinting some test parts with a good sized fan on the board... we'll see!

EDIT: The cooling fan was the solution, and the test prints were fine. Now, unfortunately, my system is open again until I figure out a fan cooling ocnfiguration... hoping there are some suggestions already out on the forum. Thanks for the help guys!

FWIW the way the stepper drivers are designed to dissipate heat is through the bottom of the chips, not the top, usually boards have copper pads with plated through holes to act as a small heat sink.
So when you point a fan at it, it's better if it's moving the air on the bottom of the board, not necessarily directly over the chips.
I have a 40mm fan that blows at the back of the board when the power is on.

kittka wrote:I was thinking this would be my first check from the list in mhackney's post. The move to a non-air conditioned space was a main concern. I'm reprinting some test parts with a good sized fan on the board... we'll see!

EDIT: The cooling fan was the solution, and the test prints were fine. Now, unfortunately, my system is open again until I figure out a fan cooling ocnfiguration... hoping there are some suggestions already out on the forum. Thanks for the help guys!

Best of luck finding a way to cool the front of the chips. A picture of your solution would be appreciated.