Tuesday 31 July 2012

Melzi mod

In my previous post: StepStuck I described how Pololu stepper drivers (and the open source equivalent StepSticks) are not configured optimally for the typical motors used for RepRap. Not surprisingly Melzi suffers from the same problem as it just has the same circuit on board the single PCB.

This video is a good demonstration of the effect of enabling the A4988's "low current micro step mode". The Z axis is stepping slowly and you can hear a buzz with pauses in it. When I short out R20 it sounds a lot smoother, but still not perfect.

So I replaced all the ROSC resistors with 0R links.

Mendel90s at Manchester Mini Maker Faire

There were people asking questions non-stop on Saturday. We didn't even get time to eat or drink all day! Sunday was a little less manic and I managed to take these pictures in a rare quiet moment.

From the left a Dibond Mendel90 with 200mm build height, my acrylic Mendel90, Richards's Emaker Huxley and on the far right his polycarbonate Mendel90 printed by the Huxley: -

Mary points out the differences between Mendel90 and the Sell's Mendel opposite: -

Richard brought a large collection of printed objects which went down well lots of children: -

Most visitors hadn't seen 3D printing in real life before but a reasonable number had heard of it. All the people that inquired were pleasantly surprised how affordable it is.

More pictures of the rest of the faire can be found on Tony's blog.

Friday 27 July 2012

Sanguinololu fan hack

I needed to add a fan drive to my Sanguinololu in a hurry so I did this: -

It is just a 6 pin female connector with three of the pins bent out of the way and a protected logic drive MOSFET soldered across two pins. The fan wires are soldered to the tab of the MOSFET and the 12 V pin.

The connection details can be found here: http://www.thingiverse.com/image:131081. The gate of the MOSFET is pin 1 and it connects to the pin labelled PWM B12. It is actually digital pin 4. The source of the MOSFET, pin 3 connects to ground.

I used a BTS134D but pretty much any protected logic drive MOSFET will work. 

A plain MOSFET needs a series gate resistor to not exceed the maximum output current of the logic pin (and to prevent possible HF oscillation due source pin inductance), a pull down resistor to prevent it floating before the pin is defined as an output (during the bootstrap) and a diode for back EMF protection. That requires a small circuit board as in this Thingiverse thing.

I found that adding the FAN_PIN definition to Marlin corrupted the bed temperature reading unless I commented out #define FAST_PWM_FAN.

Thursday 26 July 2012

Manchester Mini Maker Faire

I will be showing a couple of Mendel90s at the Manchester Mini Maker Faire this weekend, including this taller one made from Dibond.

Richard Gain will be showing his polycarbonate Mendel90 and the RepRapPro Huxley he used to make it.