Update: Nothing has happened

Since my last post over a year ago (gasp!), nothing much has happened on my RepStrap. I got stuck at trying to mount the Z-axis threaded rod in such a way that it wouldn't just fall down, and then suddenly I got hired by Google and moved to München. Since I haven't had the opportunity to get all my stuff down, no further development has happened.

However, München does (now) have a maker group, FabLab München, of which I am planning to become a member once the last moving woes are over.

Motor testing (with several digressions)

I'm starting to collect motors and getting more ideas for what to do with them. Most of them I have no idea what the characteristics are, so I'll have to experiment with them. This page and this page gives some useful information on how to test unknown motors. Testing methods include turning the motors at known RPMs and measuring current/voltage and running the motors at known voltage and current while measuring RPMs. To measure RPMs, I would have to build a tachometer. There's an Arduino-based test at Instructables. Preferably one that gives a nice output, e.g. with 7-segment LCDs. I just happen to have a bunch of those lying around, so why not test them all?

This is how my projects typically progress, or rather digress.

On with the testing. A cute way of testing can be found on Instructables, using only components that I already have (yay electronics conspiracy!)...
Or so I thought. Turns out my big mess of resistors did not in fact contain the required one. Now, at least my resistors are sorted so I don't spend an hour every time I start a project finding out that I don't have the resistor (except I haven't labelled them all yet for lack of good label).

Actually, I didn't have the resistors. Instead, I just took a larger resistor onto my breadboard, gave 5 V through it, and tried all combinations until a light went on. From then on, it was easy enough to map out the segments. All but one worked nicely.

Problem now is that it would require 7 pins per display to run it, or a driver (e.g. 4511) to decode and latch them. I don't have enough pins to drive more than one, and I have no 4511. So I can't use that for a display. Instead, I'll just read output on the Arduino, adding a potientometer if needs be.

Fiddling around a bit, I now have a little board with a 220 ohm resistor going to a high-power LED that points at the light detector. There's a 1K ohm resistor on the other side of the reading wire. The analog reading with full light is 800ish, with light blocked it is 550ish. Enough difference that I can use it! That's enough for tonight, it's time to go to bed.

Motor testing (with several digressions)

I'm starting to collect motors and getting more ideas for what to do with them. Most of them I have no idea what the characteristics are, so I'll have to experiment with them. This page and this page gives some useful information on how to test unknown motors. Testing methods include turning the motors at known RPMs and measuring current/voltage and running the motors at known voltage and current while measuring RPMs. To measure RPMs, I would have to build a tachometer. There's an Arduino-based test at Instructables. Preferably one that gives a nice output, e.g. with 7-segment LCDs. I just happen to have a bunch of those lying around, so why not test them all?

This is how my projects typically progress, or rather digress.

On with the testing. A cute way of testing can be found on Instructables, using only components that I already have (yay electronics conspiracy!)...
Or so I thought. Turns out my big mess of resistors did not in fact contain the required one. Now, at least my resistors are sorted so I don't spend an hour every time I start a project finding out that I don't have the resistor (except I haven't labelled them all yet for lack of good label).

Actually, I didn't have the resistors. Instead, I just took a larger resistor onto my breadboard, gave 5 V through it, and tried all combinations until a light went on. From then on, it was easy enough to map out the segments. All but one worked nicely.

Problem now is that it would require 7 pins per display to run it, or a driver (e.g. 4511) to decode and latch them. I don't have enough pins to drive more than one, and I have no 4511. So I can't use that for a display. Instead, I'll just read output on the Arduino, adding a potientometer if needs be.

It moves!

Just got the pieces fitted together for the Z stage for the first time. It moves! It lives! Surprisingly, the stepper motor driver worked right off the bat, unlike the two previous ones, both of which needed some fiddling. Probably the better soldering iron is to blame.

One bolt is about a millimeter too long, I figure I can dremel it down. Bigger problem is that one of the two inner pieces that hold the rail on is so short it can flip to the wrong side, plus the nail is loose. It will have to be redone, and I'm not sure I have a proper piece of acrylics for it. Also am missing two tube flanges. Once that is done, I am ready to mount the first tool!

My tool mounting is with some tie-down strap I got for DKK 20. I have 2x4 long holes they go through (nicely unsharpened with dremel and sandpaper) and they can be used narrowly or widely as befits the tool. It looks primitive, but I think it's good for flexibility and pretty damn solid.

Progress in the 3rd dimension!

I have declared March to be "get the RepStrap running in 3D" month. With some help from Buro Detours, I have assembled the third stepper motor driver, and subsequently cut and drilled the pieces for the Z stage. It helps a lot to have a good hacksaw and a drill press, this one has gone a lot faster than the first two.

One difference between the Z stage and X/Y stages is that there is a plate under the rails that anything sticking too far down will hit. I had to change the spring-loaded wheel holders a bit to be as flat as possible, including cutting the bolts down to minimum size.

I should have a flange today or tomorrow so as to mount the whole thing together. The next interesting part is what to put on in order to hold a head, and how to avoid the whole movable part falling out when there is weight on it.

My first drawing is complete

In an act of utter self-glorification, I made the first thing to be written by the 2D repstrap be the first letter of my name (also, it was only orthogonal lines). After some as just unexplained problems with the Y stage refusing to start, and a slightly wobbly fastening of the Sharpie, it indeed made a letter L (in Blocky Outline 83 point or so). I have now successfully programmed and output something with my RepStrap! Woohoo!

The next thing should be a fractal. Just because.

It moves! It lives!

Having mostly dealt with the problems from last post (Flimsy wiring? Get the right jacks. Overheating driver? attach driver directly to frame. Loose coupling? Tie down coupling with hose tightener (which required dremelling a hole for the screw to rotate through), I have been able to make both X and Y stages move! The whole setup also looks much tidier now.

The stages can move for a seemingly arbitrarily long time, but they still overheat if standing still for about 30 seconds. Have to find a solution for that. I don't know if thermal paste will change much when I've already bolted them tightly together.

Major problem: Both stages have a tendency to switch between running smoothly and getting stuck, depending on exactly how the rod is aligned. I'm guessing the guiding bolt is a little loose, and can change between perfectly aligned with the rod and not quite perfectly aligned.

After cutting off superfluous edges and cutting a notch on the Y stage for the tube tightener screws, I have about 11x16 cm of writeable area. Not a lot, but enough for tests and for a RepRap, should I go that way (requires a plastic extruder, though. First some 2D tests!)

Softwarily, I have refactored the little test program to where I have two functions: move(dir, axis, len) and pauseSeconds(seconds). The move() functions is almost calibrated to move in cm.

For playing around, I am tempted to hook up three three-way switches so each axis can be controlled independently. Or maybe get a mini joystick controller:)