Extruder Driver

Attached is a quick picture of my filament drive for the extruder I am working on. The center wheel is attached to the stepper, which is hidden. The upper wheel is the idler pulley. The arm is a pressure arm. The screw at the top, which is a little hard to see, adjusts the pressure on the filament.


The circuit board is the stepper controller. It uses an FTDI 245R, step genie controller(sticker was removed) and 4 MOSFETS. The FTDI chip and step genie are powered by the USB interface and the red/black wires supply power to the stepper.

Where the two holes are is where the extruder barrel mount will go. I will get that finished tomorrow and post a pic with everything together.

I was wondering if that kind of set up was possible, glad you are experimenting with it before I have to make lots of mistakes getting it right!

You have used quite a large diameter drive wheel, looks about 25-30mm which gives it a circumference of 80mm ish. With a 200 step stepper this is quite a large feed per step. Do you think the stepper will have enough torque to drive it?

Well done, good luck and hope to see if it works!

... my first thought were too: - "... would it have enough torque and resolution?"

I have a nema23-stepper wit a 1:10 gearbox and 1/8- and 1/256-microstepping drivers, so this would change to max. 16000 or 512000 steps per revolution what should be more than enough

But i think without gearbox it's not enough power for extruding the molten plastic properly, even with microstepping ...

Viktor

Ahh, I thought you were driving it directly!

Like the circuit your using, have you any more details?


Phil

Hi Phil,

... i'm not damonb - but i'm going similar ways ...

My different stepper-drivers are some selfmade IMT901-drivers and a SMC11 from Naotec with 1/8-microstepping and max 2Amps and 3 drivers from IMS with 1/256-microstepping and 3Amps continuous, 4Amps max.

Viktor

Edited 1 time(s). Last edit at 07/03/2009 06:57AM by Viktor.

I knocked up a variation of one I found on the web using MOSFETs and some quirky logic that drove unipolar motors in wave mode, then realised that I would be better having half stepping with bipolar motors so I bought one o fteh reprap stepper drivers. Ive just ordered three more but the cost of these plus the sanguino has really racked the total cost of the project up. Being a Yorkshireman and having to account for my expenses to "the missus", it has been a difficult decision!

Phil,
The drive is direct drive. I will know soon enough if force and resolution are good enough. I think the force will be enough, but not sure about the resolution. I will know soon enough.

What other details did you need to know about the drive board? I think I included everything in the intial description. The step genie chip(the DIP) has half stepping mode and is a unipolar driver. The FTDI 245R is really nice compared to previous versions of their USB chip. Everything in the chip including the clock. Just need a usb connector and some decoupling capacitors.

If there is a place to put it, I would be happy to supply the eagle cad files for the circuit.

Thanks, I google Step genie and found the web site you gave us! I must learn to read things more carefully!

It looks a nice circuit, but I made the mistake of buying a bipolar motor as I only had two motors. I dont think the Step Genie works with bipolar motors?

Looking forward to hearing how youve got on!

I think the step genie is just a programmable logic device. I thought about using a CPLD to generate the step signals, but I wanted to get the extruder built and not get sidetracked on logic programming. In a future version of the board I may go the CPLD route and then the board should be able to handle bipolar or unipolar.

I finished getting the heater barrel mounted. A picture is attached.

As some had suspected, the stepper I had did not produce quite enough to torque to extrude on its own.
Actually I was sort of surprised it did not work because the radius where the the filament contacts the drive wheel is about .4 inches. This means I should have seen about 8 pounds of down force. It did not take a lot of hand force to get the extrusion started. So 8 is not quite enough to start of sustain.

So with some hand assistance, some ABS came out as can be see at the bottom of the picture.
The stepper is a 53 in-oz according to the sticker. The stepper is pretty old and I think I have seen some in the same size that are about triple the torque.

On the plus size, I had no problem with slipping. I used the suggestion of using a screw tap to cut notches into the pulley.and I had no problems with gripping.

Also by the time I finished testing, the whole assembly was getting rather warm to the touch. So I need to modify my barrel and add in some stainless tubing to cut down on the heat conduction. Also it probably would not hurt to get the bracket made of stainless as well.

I will also take a look into gearing the stepper down.That would help with the torque as well as reduce the step size.

Thats all for now.

The extruder portion can be fussy and really contribute to excess force requirements.

Nophead did a number of experiments that he blogged about and messured fource required indepenent of the drive mechanism.

Any idea of the fource required for you extruder?

I am not sure of the force my extruder requires, but look at the charts at

[hydraraptor.blogspot.com]

it looks like my setup is just under the threshold to start extruding going by the rating on my stepper.
Though that is holding torque. I suspect that turning torque is less than that.

I was just sitting here taking apart an old cordless screwdriver I have to see if that could be adapted to be driven by my stepper motor. I am not sure how much gear reduction there is in a cordless screwdriver, but it is probably more than enough to drive the filament with the necessary force.