Kossel Plus FSR Holders

These hold 3 FSR's, which the glass bed rests on, so that you can use the tip of the hotend as the probe. This system works pretty well!

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This FSR holder works quite well.

It is easy to modify it for different diameter or thickness glass beds.

You can place small (approximately 1mm thick 5mm x 5mm) squares of foam between the glass and the key piece which swivels to lock the glass in place.  This pre-loads the FSR so that you can better control how sensitive it is.

I used a drop of rubber cement to attach the round plastic buttons to the bottom of the glass.  This keeps the glass from being able to rotate.

The glass should lightly rest against the heads of the socket head cap screws so that it can easily move up and down.  Tap on the glass to verify that the microcontroller triggers easily -- a red LED will light when it triggers.

The sensitive area is a triangle with the three FSR's at its corners.

I use Wing Wong & Ian Lee's code for the Adafruit Trinket, but you could use this with John SL's board.  With a Trinket, wire all three FSR's in parallel, so that pressing on any one will trigger it.  Note: the Trinket code is not limited by any license.

Someone else also made the Trinket wiring diagram. Note: I found I had to wire 5v from the RAMPS to USB+ on the Trinket.  The BAT+ input is for more than 5v (for example from a battery), and the voltage regulator it is attached to seems to require a little more than 5v to deliver 5v to operate the Trinket.

I have been building Kossel Plus printers (my own design) using these.  They allow the effector to be simpler, because it doesn't have to include a z-probe.  I use RC's Marlin for auto calibration.  Here is a link to my calibration instructions:  http://www.maui-3d.com/kcZeroBacklashInstallation.php#calibration

Materials and methods

- 3 FSR's, for example these: http://www.ultibots.com/fsr-force-sensitive-resitor/
You can also get these same FSR's from Adafruit or TriDPrinting.

- 9 M3 nuts.

- 9 M3x10 socket head cap screws.

- An Adafruit Trinket board or JohnSL's board, for example in this kit: http://www.ultibots.com/fsr-kit/



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Mini haydnlookingoverthepacificHaydn Huntley commented ago

Hi DaveyHi, Not all micro switches are of equal quality. For a z-min probe, it is a plus to have a micro switch which is good quality, has a soft spring, and does NOT have a spring arm. I got some excellent ones from TriDPrinting.com.

You don't want to wire the FSR's directly to your printer controller. Instead use the Trinket Fsr.ino file to program your Trinket, and use TrinketWiring.png as your wiring diagram. Note: I normaly wire 5v from the printer controller to +USB on the Trinket (and not to BAT+). You could wire BAT+ to 12v. On an 32-bit printer controller, usually there is a jumper to select for using 5v (and not 3.3v) for the endstop switches and z-min probe. Also, note that I use a 5v Trinket, and not a 3.3v one.

D6e57563f5f40dfc808fbb5e92aab9f1?default=blank&size=40DaveyHi commented ago

The issue I have with the effector microswitch is that there is inherently slop in the mechanism and my distrust of microswitches. My cheap Micromake Chinese delta came with one that was incredibly sloppy. Even after some hacking to get it stable enough to print its replacement (lol) it's probably still the weak link in the system. It is kinda nice having a spring-loaded hot end though, for the inevitable crashes.

I oedered the 0.25" ones but looks like you used the 0.5". This is the first I've heard of a Trinket. I'll have to look into that :-) I was going to try to wire them straight into the digital in.

My FSRs arrived today but I'm still trying to get this $%#@ to print accurately enough to make new parts. By the time that's done, my AZSMZ board will be in and I'll be starting all over! lol

Mini haydnlookingoverthepacificHaydn Huntley commented ago

I've seen people design FSR into the effector, however you don't need to worry about keeping them independent of bed weight -- the software on the Trinket automatically adapts to the bed weight. I suspect a problem with locating them in the effector is that the effector goes through a lot of acceleration changes, which might trigger it. Believe it or not, but a well designed micro-switch-based z-min probe can actually work quite well.

D6e57563f5f40dfc808fbb5e92aab9f1?default=blank&size=40DaveyHi commented ago

That's good to know. I was thinking of mounting them in the effector as that would solve the heat issue (if there is one) and keep them independent of the bed weight.

Mini haydnlookingoverthepacificHaydn Huntley commented ago

FSR's don't like high temperatures, but with the setup I'm using, there is a plastic "button" and several mm of glass insulating the FSR's from the heat.

I haven't tried printing ABS with this setup yet.

It also probably helps that typically I calibrate the printer once, without heating the bed (using RC's Marlin's auto calibration "G30 A Dnnn.nn" command, and the printer stays calibrated until the next time I change some of the parts.

D6e57563f5f40dfc808fbb5e92aab9f1?default=blank&size=40DaveyHi commented ago

I thought there were temperature issues using the FSRs on a heated bed as the bed temp exceeded the FSR's rating?

Mini haydnlookingoverthepacificHaydn Huntley published this design ago