garageFab.cc

To investigate the plotter stalling problems that were encountered during recent tests, I had ordered Keling stepper motors - one of the official choices of the Reprap project. They are rated for 166 oz*in of holding torque (vs 60 oz*in in Alltronics). They also cost about as much more. When the Keling steppers arrived, I assembled the plotter again. 

For some reason, the maximum feedrate that Keling steppers gave without stalling was 300 IPM, and that was on single-axis movements (like "G1 X10" or "G1 Y6"). Alltronics steppers could do about 600 IPM on single-axis movements in previous tests. I thought this was strange and decided to install Alltronics back to compare.

After I modified the XY plotter design to use new linear motion components, increasing the work area along the way, I needed to actually assemble and test it. During the build, I had to add a couple of shaft mounts with bearings, supporting the middle section of the threaded rods - they were bending too much. These changes are reflected in Sketchup files for the XY plotter. I also used version 1.2 of stepper motor driver boards. The good thing is that SMD v1.2 uses IDC header with 10-pin ribbon cable for Arduino interface as opposed to CAT5 in SMD v1.1 (which is soldered directly to the board and can break from bending). Unfortunately there is only 8 inches of the ribbon cable included with the SMD v1.2 kit, so I was constrained in where I can place the SMD boards and Arduino. This resulted in the weird "Γ" arrangement of heatsinks, as seen in the pics.

I haven't posted in a while, but have done a few things:

Taken apart the drilling contraption since I didn't really need it when the angle no longer had to be accurate; enlarged to 1/4" the holes on the angle from drilling contraption. This created a nice pile of Contraptor parts, ready for the next project. Made several sliding elements of different sizes - full, half, "quarter", installed Delrin nuts in some of them. Revisited the whipping rod/nylon couplings problem and decided to switch over to 0.250"ID aluminum tube for couplings. Tried to couple this tube to 10-24 rod, unsuccessfully. Searched for more powerful but still cheap steppers with lower coil current. Plotted the next contraption to be built.

The package from Mouser.com arrived on Friday, and on the weekend I put together the stepper board using detailed instructions on RepRap wiki. Hooked it up to Arduino, loaded Zach's stepper exerciser sketch and after I set the trimpot (R9) to about 1 o'clock on the dial, voila - it worked! The steppers I used are rated for 2.3V, 2.3A. Oh yeah, spent some time to figure out the stepper wiring - basically the midpoints on the coils of unipolar steppers are not used at all. The 4 outputs of the board are to be connected to the 2 pairs of the endpoints.