RepRap Stepper Extruder Problem

Problem:
My stepper driven extruder will not rotate properly when turned on. It's like it tries to fight itself on which direction it wants to go.

Video: [www.youtube.com]

Background info:
I have the stepper driver wired straight into the extruder controller. 1A - Black, 1B - Green, 2A - Red, 2B - Blue. I tried updating the firmware through replicatorg (the one that is designed to run steppers) and when that didnt work I tried the Arduino hack where you alter the arduino slave extruder file and copy the libraries. Same outcome. The shaft will spin but not continuously in the same direction. The stepper is brand new, it works fine through the stepper boards, i'm just having problems with the extruder board and/or software part. Ive been on forums all day and watching videos and none of the suggestions have seemed to work.

If only one coil is driven it can move randomly in either direction at certain speeds and vibrate on the spot at others. If the direction signal is floating that might get a similar effect as well.

To diagnose the first fault disconnect the black and green as see if it changes. Then repeat with the red and blue disconnected. If one of your driver outputs is dead then one test will behave as it does now and the other will not move at all.

Always turn the power off when connecting or disconnecting the motor.

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[www.hydraraptor.blogspot.com]

I had the same problem. I was told that the chips for on the extruder board were designed for DC motors and don't work well with steppers. I now use a regular stepper board for my extruder and the works great.

The dc chips seem to work OK for me, but I have done a couple of things to help that.
I found that the drive strength seemed to be pretty variable. sometimes it would work great and other times it would have almost no power. I think this is down to the fact that the software can send commands that control the PWM (which affects the strength of the drive). So depending on the sequence of things that I had done (e.g. first heating with reprap host and doing test extrudes versus just loading g code and printing, the order of power-up, etc). My motor windings are about 30 ohms, so there is no real risk of be blowing drivers up even when there is no current limiting. As a result of both of these things, I hacked the firmware so that it ignores any PWM commands and always sets PWM to 255 (which I think represents the maximum). Since then, my extruder has always had good strength using the DC motor drivers.

i was using my extruder board to drive a stepper and it worked fine under the reprap host software, then when i tried replicatorG (with the new stepper firmware) and i had the same symptoms as you describe, so i just went back to reprap.

To Nophead,

I did the test you suggested. When red/blue are plugged in the motor behaved like its usual sporadic self. When I had the black/green plugged in, nothing happened. Now I need to know where to go from here. Does this mean I need a new EC board or is it fixable?

That depends on your SMT soldering skills.

It looks like you need to replace one of the A3949 chips. Carefully inspect all the connections first, as it may have an un-soldered pin or a bridge. They are easy to destroy though. If you set the current too high or disconnect the motor with the power on, or simply have a loose motor connection.

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[www.hydraraptor.blogspot.com]

Alright, thanks everyone for your suggestions. I got scared when you started talking about my soldering skills and went ahead and purchased a new EC board, along with a stepper board, so we'll see if that works.

OK, update. I got my new EC and stepper board. I've followed the steps in this wiki:

[wiki.makerbot.com]

I've jumped all the wires between the EC and stepper board. I've done the tweaks for replicatorg so that it shows rpms in the control panel. The extruder part is what I have trouble with.

Under "driving it under a dedicated stepper driver" option B, it says something about the v2 firmware. I have it downloaded in the makerbotG3 bundle but I dont know what to do with it. The wiki on that doesnt appear to be windows friendly and I'm not sure what it's talking about doing.

If this isnt the right firmware can someone please point me to the right one, and if it is, can you tell me what to do to it.

As is, when I get in the replicatorg control panel I set pwn to 140 and rpm to 10 and nothing happens. I can tell that the EC board recognizes the command because the lights come on but there is no movement from the motor.

I had this same problem when upgrading exturder firmware as well, I had to roll back to the latest one that had "stepper" in the title of the firmware.

Are you talking about the 2.3 EC firwmare in repg? Thats for a stepper extruder with the motor wired to the H-bridge connections. I'm wanting to run it from a dedicated stepper driver.

Oh and by the way, back to my first post, I did try wiring the stepper to the H-bridge connectors and running the 2.3 EC firmware to see what the results would be. They were just like the video I posted at the top of this thread, very sporadic and not in definite direction. Careful precautions were taken while wiring up the motor to the H-bridge connectors, the power was turned off, etc, so at this point I dont think its the EC boards, I'm not sure what it is though.