Saturday, January 28, 2012

Makerbot Upgrades Part 2

As I mentioned in my previous post, one early print on the machine was ruined when I touched the Z-motor while it was running, giving the machine a static zap that locked up the Z motor control board.  No permanent damage was done to the machine, but the part being printed was ruined.  The Makerbot ThingOMatic does not incorporate any static protection in its design.  It is made from a mix of wood, plastic, and metal, with several large metal pieces (including the motor housings) that are ungrounded and electrically floating.  As I found out, it can be easily crashed by static electricity.  In theory, it may even be generating its own static, as there are a lot of places in the machine where conductive and non-conductive materials are rubbing against each other.

This page has a guide to installing static drain lines.  The instructions are meant for the MK5 extruder, rather than the MK7 we are using, but what needs to be done is essentially the same.

There are five points that really need to be grounded on the printer.  The three motors, the extruder, and the print bed.  I started by preparing five lengths of wire with crimped ring terminals on the ends.  Green with yellow stripe is traditional for grounding wires, and we had plenty of it on hand anyway.  First was the Z axis motor, which I had already learned the hard way needed a static drain line.

The Y axis motor doesn't really need grounding as badly, since it's buried down in the base of the machine, but for completeness I connected it while connecting the others.

The X axis motor is tricky, since there's very little space where the wire can be attached and run without interfering with the X axis travel. I think I've managed to install it without reducing the X axis travel, but to be really sure I may go back and drill a hole to pass the wire through.

Grounding the print head is easy, as there are multiple unused holes on the mounting plate and no clearance issues with the wires.  There is some controversy as to whether this part should be grounded.  Some people have had their extruder temperature readings go off when they connected this wire, possibly as a result of shorts between the nozzle thermocouple and the frame.  I was careful to make sure that the thermocouple was electrically well-insulated from the nozzle when I built the printer, and I haven't seen any problems with the temperature reading after installing this ground lead.

The last grounding wire connects to the heated build platform.  We have installed the aluminum heat spreader, which makes connecting a ground wire easier as I don't have to figure out how to connect a wire to metal foil.  I have rearranged these wires a few times since this photo, as part of the ongoing challenge of dealing with the HBP cable.  I'll get into that more in the next post.

The five grounding wires are run down to the power supply in the base of the printer, connecting individually to mounting holes on the metal frame.  These are static drain lines, not power grounds, so even though they are theoretically electrically connected to the ground lines in the power connectors they need to be run separate from the power ground lines and from each other back to the chassis ground.

With these in place, the sensitive control electronics should be protected from static zaps to the motors, extruder, or heated bed.  I haven't had any prints fail due to static lockup since making this modification.  I have found a persistent issue where the Z axis sometimes randomly reverses direction while homing after a print, but I suspect that's a software rather than hardware issue.

While I was making this modification, I also made the modification described here to all four stepper motor controllers.  The power supply provides 12V and 5V on each connector.  The stepped drivers only use the 12V, generating 5V locally through a linear regulator.  I cut the regulator off each board, and then added a jumper to draw local 5V from the power connector instead.  In theory this should make the stepper controllers more reliable.  I haven't noticed any obvious difference, but it seemed like a good precaution to take.

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