- increased passage size for FSR tails. Printed and tested that they fit. Also tested FSR operation in assembled mechanism; it works!
- added nut slots for rod connections. Each rod now has its own screw and nut, although there is still the option to use a single large screw if you wish (for each pair).
- clamp and plunger now reduced in size, with the top of the E3D/jhead now inserted into the upper plate of the plunger. Plunger is now effectively flush with base of the effector, allowing a standard fan mount to be used on E3D.
17/Nov - This is going to need a bit of a re-think for attaching fan mounts, as they will need to be stationary with relationship to the J-head. Either mounts need to come off the top of the plunger, or the bottom. Probably the bottom...
16/Nov - I have added a WIP SCAD file called BooDeltaUpsideFSR which moves the FSR to the top (undersurface) of the plunger, and places a sloping channel for the FSR tails to exit inwards and up through the plunger, exiting around the pushfit. The reason for this change is that this allows the wiring of the FSR to be tight; the FSR now move with the plunger, which seems to make more sense. I haven't printed this one yet. Also I've been working at reducing the width of the arm connectors, so I'm not sure if the clearance is there for full movement. I may go for one bolt per arm... watch this space....
This is an effector/print head assembly with three embedded force-sensitive resistors (FSRs) set into an effector, with spring-loaded 'plunger' to enable z-depth testing using the hothead. It's gone through a few iterations now, and I don't anticipate major changes.
I have successfully printed this, as shown in the pictures, and the head-suspension spring mechanism works well. I'm still building the printer it's to be used on, so actual performance is unknown. I will say, however, that the print head is embedded very firmly into its mount and doesn't shift at all relative to its mount. Also, the 'plunger' is firmly held in place and it's only movement is the up/down axis when pressed on a firm surface. It works exactly as I expected. The mount clamps can be printed separately in ABS if required, as they are screwed on to the plunger.
The other bits and pieces are shown in one of the pictures. You need 3x 3mm diameter long screws (say, 44mm), 3x springs (I sacrificed 3 ballpoint pens for these), 3 x 3mm washers, 3x 3mm nuts. The black screws are M3, 25mm the longest I could find locally. They're almost perfect, and the nuts beside them were not needed. There was no drilling required; fresh off the printer I just screwed it all together. The screws simply screw in to the holes with a screwdriver and make their own threads. The hole fit is excellent.
Per the earlier comments, it may be true that a FSR should not be "always on" as it reduces lifespan. However, I don't know that for sure and this is a more elegant design than the alternatives I can think of. In any case, FSR embedded below print beds are also "always on" so clearly it's a reasonable thing to do.
If you have previously downloaded this, I suggest another download and grab the latest version because there have been some minor size and position changes of stuff.
I've recenlty (2/Nov/2014) updated the files with minor changes to hole sizes and placements. Specifically, the 'unused' holes are now positioned so that they have good clearance from everything, and the nut traps are correctly sized and flush with the effector base, so mounting anything underneath the effector won't have any obstacles.
Print the STL file BooDelta_PRINT_THIS.stl
This gives you four pieces; the effector, the plunger, and two clamps. First thing is to insert the effector over the E3D jhead. The hex hole should be big enough to allow you to slide it right down. Next, you want to push the top of the E3D into the bottom of the plunger. It should be a tight fit. Next the clamps fit around the E3D neck, flush with the bottom of the plunger. The wider ring faces downard; it should be pretty intuitive. Now you need to screw in the 6x 2.5 (25mm long) screws from the top-side of the plunger, going right through and grabbing the clamps. The clamps should be holding the E3D pretty tightly once you've done that; no lateral movement (or up and down either!).
At this point you may wish to mount your FSD into the 3x grooves set into the top of the effector, and glue them down. The tail of the FSD point outward and sit in the little groove placed there for that purpose.
Next, you want to slide the effector up so that the plunger and effector are against each other. The hex hole of the effector will fit nicely over the hex tail of the plunger (and the clamps). There's a bit of slop there so that they don't rub against each other too tightly; movement should be easy. The 'buttons' on the bottom of the plunger's head will be resting against the FSDs.
Now it's time for the 'spring' screws. Take a spring (I scavenged from ballpoint pens for mine) and insert over the long M3x44mm screw (or whatever you use; the actual length is unimportant). Put a washer over the end so that the spring doesn't slip down the rather wide hole on the top of the plunger, and screw down through the effector. Put a nut in the bottom nut insert of the effector, and make sure it's deep enough to be flush with the effector underside. Screw the screw until it's just peeking out the top of the nut. You may wish to put some loctite on that, but IMHO the screw is going to be held nicely by the spring. After you've done all three screw/springs, you should now have a functional unit; you can slip the head up/down and the plunger and effector will de-mate and re-mate, with the buttons activating the FSDs as this happens. Remember to be careful/fair and push in a vertical direction only, as this is how the actual real-world usage of the thing will happen and best for evaluating its function/effectiveness.
The strength of the spring you choose makes a huge difference, so play with different screw lengths/springs to adjust the 'bounciness' of the assembly. I find that ballpoint pen springs are about right for the screw length I chose.
Finally, screw the push-fit connector into the centre hole at the top of the plunger. That's it, you're done.