2 Questions about hall effect sensors and steps per mm

I am currently in the process of buildiung a 3DR, and am looking for some advice. My first question is about using these (Link: [www.amazon.com]http://www.amazon.com/Sunkee-A3144E-OH3144E-Effect-Sensor/dp/B00ATNJH20/ref=sr_1_3?ie=UTF8&qid=1424879851&sr=8-3&keywords=hall+effect ) as endstops. My biggest question is what way the magnet needs to be facing (north or south pole) to trigger the sensor, and if it will even work. Thoughts?

Here is a pic of my setup

My next question is How many steps per mm should I have for the x y and z axis if I am using 32 micro stepping?

Thanks!

Edited 1 time(s). Last edit at 02/25/2015 11:18AM by Ggalisky.

Yes, it should be possible to use those Hall sensors. Strangely, the datasheet I found for the A3144 does not say which way round the magnet needs to be. You will have to try it and see.

Are you using 32-bit control eelctronics? If not, then you may find it difficult to get good speeds with 32-bit microstepping. Calculate the steps per mm like this:

steps_per_mm = (microsteps * steps_per_rev)/(mm_per_belt_tooth * number_of_pully_teeth)

where steps_per_rev is 200 for most stepper motors.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I do not think the RUMBA board is 32 bit, so I will use x16 micro stepping for the x,y, and z axis's, and x32 micro stepping for the extruder.

In terms of caculating steps per mm, I am using fishing line to drive my printer, so is there a separate formula for that? Maybe I missed something in RichRaps how-to for the 3DR.

Quote
Ggalisky
In terms of caculating steps per mm, I am using fishing line to drive my printer, so is there a separate formula for that? Maybe I missed something in RichRaps how-to for the 3DR.

Calculate the travel in mm per motor revolution (which is basically the pully circumference), then use: steps_per_mm = (microsteps * steps per revolution)/mm_per_revolution.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].