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RepSnapper - Steps per mm????

Posted by Flackster 
RepSnapper - Steps per mm????
April 23, 2011 03:12AM

I just got my mendel working (hooray!) and want to set my 'steps per mm' (e.g. to compensate for a 100mm move only going 85mm)

I'm using Gen6 electronics and RepSnapper. I'd like to follow the steps given here: [reprap.org]

However, the instructions (I think?) refer to the RepRap software. Or possibly the firmware. So, not applicable to a RedSnapper user?

Can anyone help tell me how I'd change my XAxisScale (or equivalent) using RedSnapper?
Or maybe the Gen6 firmware? (I've downloaded Arduino, etc but I don't understand what files I need to locate/edit or what parameters
- as per here: [www.mendelfactory.com])

Also, I'd like to avoid needing to update/reload the firmware for each change if possible

Any help very much appreciated

(I'll post this on the mendel-parts forum too)
Re: RepSnapper - Steps per mm????
April 23, 2011 03:52PM
This is something you are going to want to address in the firmware. I am not familiar with the GEN6 electronics, but looking at the firmware configuration.h file:

Look in the section that begins with the following comment

// define the XYZ parameters of Mendel - standard pulleys

You will need to increase the multiplier until you have a more precise movement. Before you do anything, make sure your incorrect motion moves are consistent. That is to say, make moves at various lengths, and observe that they are consistently off by the same multiple. If this is not the case, then you are probably loosing steps due to too much or too little current on the stepper drivers.
Re: RepSnapper - Steps per mm????
April 26, 2011 09:06AM
Generally, it's best to calculate the steps/mm for all axises except the extruder, which should be measured because it's hard or impossible to tell what the "effective diameter" of the pulley is due to differences in how much various plastics and pressures squish the filament into the pulley's teeth.

With X, Y, and Z, it's much more accurate to calculate, because it's hard to measure precisely the distance moved, as filament diameter, dropped steps, backlash, etc. can all effect it.

Explains how to do it:
(oops, this one uses an incorrect formula. radius of the pulley doesn't enter into it, just the number of teeth and the belt pitch! see second link for correct formula, which is

Steps per mm = (((360/Motor step size) * (1/Driver microstepping))/Leadcrew pitch)*(Leadscrew pulley teeth count / Motor pulley teeth count))


Steps per mm = ((360/Motor step size) * (1/Driver microstepping))/(Belt pitch * Tooth count)

motor step size is 1.8° for 200 step motors.

Does it for you, though you have to download the HTML file to your local machine first, as it's not longer hosted correctly:

I'm building it with Baling Wire
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