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Using FSR delta auto calibration with Duet tutorial

Posted by mhackney 
Using FSR delta auto calibration with Duet tutorial
January 24, 2016 01:41PM
I've been using FSR "z probe" on all of my deltas and a TAZ printer with great success. Now that I've made the switch to Duet I'll share my learnings with the community. You can find the details on my blog post FSR Auto Calibration Setup for Duet

Some folks have great success with FSRs and others not so much. I have a few suggestions to help make sure you have great success and some ideas on why those who have problems, have problems. In addition to the blog, here is some more info.

Firstly, it is very important that the FSR mounting system is very rigid. I suspect that beds consisting of a borosilicate plate with a silicone or Kapton heater, especially larger diameter beds of this sort, are the cause of some problems due to their flexibility. All of my beds are mounted on 1/4" melamine "snowflakes". This serves two purposes: 1) it makes for a very rigid bed setup and 2) it provides thermal insulation for the FSRs.

Another critical area is the FSR triggering/mounting system. I spent a lot of time designing and testing a 3D printed mount system that has been very reliable on Rostock Max, Mini Kossel, Kossel 250 and Lulzbot Taz printers. The key is to NOT over constrain the mounts. The bed needs to float on the FSRs (typically 3 of them) while being constrained in the X - Y plane. Plunger systems using pistons in cylinders are very difficult to align to minimize friction in the Z axis and are overly constrained in the X - Y plane. I suspect this is the #1 cause of issues for folks.

It's also important to have a pad of some sort on the FSR surface to distribute the triggering force. Dense silicone or neoprene pads work very well and help insulate the FSR from the heated bed.

I futzed around with directly interfacing FSRs to the thermistor port but gave that up when the marvelous JohnSL board arrived on the scene. This board takes all of the guesswork out of interfacing FSRs. It makes the FSRs look like a simple mechanical endstop switch to the controller electronics and firmware. It provides sensitivity adjustment with jumpers and can be configured as an NO or NC switch. A great piece of kit!

Hopefully these tips and my blog post will help others.

Edited 1 time(s). Last edit at 01/24/2016 01:42PM by mhackney.


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