Manipulate Voltage Output to Control Extrusion

I am working on a custom 3D-printing setup where I could change my extrusion speed by changing voltage output to a DC motor. I basically want to run two wire leads to an external control board and vary the voltage across them between 0-10V. I am trying to find a simple way to modify a RamBo printer board, so the printer can change the voltage based on the amount of material to be extruded, just as conventional set-ups vary the number of motor "steps" to achieve this control.

So here are my main questions,
Would it be easier to somehow convert the 4 lead extruder stepper signals to a 2 lead voltage manipulation, or use one of the PWM heater outputs?
If I use the stepper signals, would I need to run the stepper wires through an additional controller, or just modify the RamBo firmware?
If I use a PWM output, how would I achieve a variable voltage gradient as opposed to a simple on/off effect? Additionally, is there a simple way to modify Slic3r gcode to account for this change in the "E" commands?

Those are the methods I came up with, but I might be making it too complicated. If there is a simpler way please feel free to share.

I am also open to building a printer board from the ground up to accomodate this functionality if that would be easier, but I figured working with existing firmware would be beneficial.

I should mention that this extrusion would be termperature independent, because I have a separate set-up for that.

Any advice or comments would be greatly appreciated.

Zernebog

Just make a frequency to voltage circuit, hung off the 'step' input to the stepper driver.

[www.google.com.au]

Edited 1 time(s). Last edit at 12/09/2015 12:01AM by nebbian.

The power of a DC motor has highly exponential relationship with voltage, while the step signals and the corresponding extrusion is linear.

You would better put a encoder to the DC motor and control the extrusion in a closed loop. There are several fresh threads about this topic.
-Olaf

Thanks for the responses,

Quote
nebbian
Just make a frequency to voltage circuit, hung off the 'step' input to the stepper driver.

[www.google.com.au]

Nebbian, could you elaborate on this setup? I am looking at your link, and I am seeing a number of different pre-constructed circuits on the market out there. Do you know of one that is specially made for this application?

Quote
o_lampe
The power of a DC motor has highly exponential relationship with voltage, while the step signals and the corresponding extrusion is linear.

You would better put a encoder to the DC motor and control the extrusion in a closed loop. There are several fresh threads about this topic.
-Olaf

Olaf, I already have closed loop control of the DC motor setup on a separate control board. This is how I know that I have a linear relationship between my voltage and motor speed; however, maybe there is a simplified way to construct the control. Could you point me to some of the fresh threads you are referencing?

Thanks again,
Zernebog

Sounds easier to make the external board take STEP and DIR pins, no?

I'm curious, why would you want to do that instead of the tried and tested stepper method?

JamesK: He's using DC motors. Lots of advantages and disadvantages, and they may just be experimenting.