Repairing the RapMan 3D printer:

So the RapMan started to misbehave a while ago... The parts being printed weren't very strong and the layers would separate with very little force.

With a bit of sleuthing I worked out the the 200k Ohm thermistor in the extruder nozzle was drifting out of tolerance in a big way.

A quick email off to BFB and Michael kindly sent me out four spare thermistors.

Let the rebuilding begin!

The extruder heater, nozzle and thermistor assembly are all held together by fire cement, this necessitated a little exhumation of the nozzle :)

I soaked the nozzle in hot water to soften the fire cement (I more than once very nearly took a swig of cementy water thinking it was coffee...)

After a little persuasion the cement was removed allowing the replacement of the thermistor :)

The printer has just this minute successfully completed a test print :D More to come.

Replacing the Magic Smoke

So I've been doing a lot of work with the Rapman Printer lately. The present mission is to print a set of spare parts for a complete machine. Said parts are going to be assembled into a replicating mashup of a machine, stay tuned on that one :)

The upshot of it is that running the printer for extended periods caused a very well documented manufacturing fault in the electronics to rear it's head... There is no real protection for the ADC of the microcontroller reading the thermistor in the extruder.

Now when you have:
A machine made of insulating plastic brackets supporting a metal frame.
Hot molten plastic flowing through a conductive extruder nozzle.
And a fan continuously blowing air over the nozzle and work piece.

The above is a very good recipe for static electricity :) Whenever the relative humidity droppled below about 50% the machine would start crashing randomly. Throwing away three or four hours worth of printing was starting to get a little frustrating so I went in search of answers.

The recommended fix in the BFB forums is to run a steam humidifier next to the machine. I did try this and yes it worked...

However I have some fundamental engineering, ethical and financial issues with this as a fix:
The machine as it is uses about 50W and the humidifier uses another 250W, Ethically I have an issue with increasing the power consumption of a machine by 6x just because of a design flaw. From an engineering point of view a lot of humidity around electronics and bearing surfaces is never good. And it makes the room damp in winter!

So I started poking the machine with  combination of zener diodes, capacitors and LEDs when something went pop. A wayward multimeter probe let the smoke out of the $25 extruder motor driver IC, bother. (feel free to insert non PC substitutions for bother which I may or may not have used at the time)

Above is the smoked 28pin T-SOP device sitting on my fingertip, it was removed with the judicious application of hot air from my SMD rework station.
The new IC was attached using solder paste, said rework station and a little swearing.

With the machine working again, my attention turned back to fixing the crashes.

On the right is a rather mediocre hand drawn circuit diagram on what I came up with to solve the problem.

The 220nF capacitor serves to soak up any high frequency noise and spikes while the 3.3V zener copes with overvoltages. The LED serves to increase the forward voltage and leakage resistance of the zener to a level that doesn't affect the temperature measurement accuracy. It also flashes whenever there is a decent static discharge to the thermistor :)

So far the machine has run for about 30 hours without any signs of crashing or glitches, long may it last.

Again on the right are the zener, capacitor and led soldered somewhat crudely to the extruder connector for now. Also of note in the picture, the extruder motor driver IC.

Freeze Motion Water Droplets

James at Work spoke to me the other day about a clever lab idea involving a strobe light and a special kind of water pump.

The idea is that the pump squirts a stream of water droplets on a regular basis which are synchronised with the mains power frequency. A stroboscope is then shone on the stream of droplets which depending on the flash frequency will freeze or slow down the motion of the droplets.

Below is a video of a similar apparatus at one of MIT's museums:

After more sleuthing on the internet I found a web page owned by Professor Derin A. Sherman he has a demonstration using the same principles.

Here is the video from Professor Derin's lab demonstration:

My Lab Demo:

Initially I was unsure as to what sort of pump would be available here in New Zealand however that was short lived. Espresso coffee machines use a oscillatory piston pump to achieve the 10 to 15 bar extraction pressure required. My mate Hamish aka b45h4 has a dead coffee machine sitting in his garage just begging to be "hacked" :D

Thats all for now - check back in a couple of days for pics and videos.

Torque and Moments

Introduction to Torque:



Introduction to Moments:

Engineering Mechanics Statics

As promised here are a couple of youtube videos that may help you with the mechanics problems we're doing at present.

Introduction to Basic Trigonometry - Take a look at some of the other khanacademy videos while you're at it:




This one is part of a lecture series by IIT - It starts right from the beginning of mechanics:



Introduction to Vectors, Vector Addition and Multiplication:

SHIHAD - Sleepeater

When Sam Peacocke approached me about doing some effects for a Shihad music video I had no idea how apt the title was going to turn out :-D

I was given a ten page PDF of how the video was to play out... It required a spinning shaking chair, water cannons, smoke machines and a wind cannon. For me it simply read: Lets make some cool stuff :-)

The pNuke:

This cannon resulted from my initial "more power Igor!" approach to the water cannon idea. The pNuke is a 9kg gas tank fitted with a 2" solenoid sprinkler valve. The tank is pressurised  with an air compressor, activating the valve dumps the tank with quite some violence.

Thanks to: Greg at work for helping me out with the welding and James at Deeco for the valve.

Testing the pNuke with no nozzle:

The water is thrown even further when you fit the pNuke with a nozzle:

The following video shows why we decided to only use the pNuke as a wind machine... It's simply too violent when shooting water:

My Dad being pNuked:

Smoke Ring Cannon:
We did initially want to shoot smoke at everyone in the video... Software glitches filling our tent with smoke made us decide at about 1am on the saturday morning that smoke was a bad idea.



The Gentle Annie Water Guns:
These were used for generating the streams of water than fly behind and into each person as they spin on the chair.

A bank of 3/4" solenoid valves fill a bunch of polypipes with water and then use compressed air to "empty" them in a hurry.


Valve Bank:

The Gentle Annies required two different air supplies in order to achieve the desired effets. The pNuke was also supplied with regulated and filtered compressed air.

Air Supply Manifold:

The Final Result: www.sleepeater.co.nz/

Check back soon :) This is a work in progress...

Driving the RapMan rapid prototyper

The following is a few pointers on driving the RapMan prototyper WelTec purchased in late 2009.

Destruction Manuals:

All the documentation is online in PDF format, the build manuals are 3d PDFs meaning they're best viewed with adobe reader. All manuals are on the Bits From Bytes download page. The version 3.0 manuals apply to our machine.

The build manuals should only be needed if something breaks.

Information on machine setup such as setting the Z axis height is all in the operations manual.

Skeinforge:  The application that slices STL files into layers and generates the gCode tool paths.

The Skeinforge Wiki has information on how to install and configure skeinforge.

Skeinforge announcement and trouble shooting blog

Skeinforge settings for different plastics:

Polyactic Acid (PLA)

ABS

More to follow...

Building a Part:

Start by generating an STL file from your 3d CAD package of choice.

Open Skeinforge and select the material profile you want to use.

Click the Skeinforge button to open the file you wish to process.

Skeinforge will appear to "lock up" until is has finished generating the tool paths.

Once Skeinforge has finished there will be a YourFileName.bfb file in the directory the STL file was opened from.

Copy the .bfb file into the root directory of a FAT32 formatted SD card.

Insert SD card into the machine and refer to operation manual on how to run the file.