Thursday, April 16, 2009

Nice housing

To make all the electronics studentproof I dicided that it needed a housing. And wouldn't it be nice if it matches the Fabber? So I designed a PMMA housing in Inventor (my 3D program) in the same way the Fabber was build. The only problem is that it isn't possible to make this with a mill because it has some sharp internal corners to make the slots for the nuts.

Last week I went to a Fabtable at the fablab in The Hague ( were the labmanager offered me to use the machines at the lab. One of wich is a lasercutter! So I asked if I could make the housing on this wonderfull piece of equipment and he said yes.

With some PMMA sheets and the CAD drawings I went to the Fablab and this is what happened:

With a thickness of 6mm the 35W laser was just strong enough to cut trough the material at a rate of 3mm/sec. The panel on the picture took aprox. 15 minutes to cut.

Ofcourse I hadn't brought enough material to cover the first f*ckups but a quick trip to the workshop got me a new sheet. In the end all 6 panels came out very good and all the components fit perfectly.
Front: 2 temperature controllers and the switch for the heater. In between the controllers there is a hole for a switch to control a solenoid. The solenoid can raise or lower one of the extruders.
The main circuitboard is the one from the computer power suply. The board on the right (with the blue connectors) hold the resistors for the permanent load and the FET's for the heater.

The back panel is almost the same as it was in the computer. Only the DIN connectors are added to connect the extruders. The wiring will be for the thermalcouple, the heatercoil and the solenoid.

And yes, I know the tag on the fan is upside down...

Lots of thanx to the men at Fablab for letting me use the lasercutter.
Wasn't there someone who tried to install a laser on a RepRap?

Tuesday, April 7, 2009

Temperature controller

Yesterday I decided to stop trying to build a budget heater. For good thermal control I need temperature controllers that measure the actual temperature take action acoording to this and the set value. The way in wich the Reprap does this works good, at least that's what I understand from the stories I read from other users. For this project it would be too much work because the Fab@Home uses a totally different language and I'm not good at all with software. I hope to keep it this way...
For a mechanical engineer I still had to dig in deep in to electronics to find out how to control the temperature. In the end I found a very nice controller. The controller will work with the most common temp sensors like thermalcouples, ptc, ntc, pt100 and some. The ouput varies from a relay to some electronic signals. 
I also managed to make a power suply for a desktop computer suitable as a power suply for the heater. This involved some resistors and a switch because the suply won't work without load. Also it needs to be turned on, same as you turn on your computer. The package is completed by a MosFET between the heater and the powersuply to regulate the powerinput to the heater.
This is no rocketscience elektronics but for a mechanical engineer it's a bit of topic...

Wednesday, April 1, 2009

F***ing powersuply

I tried to spot weld the heatingcoil with four different powersuply's, the first one gave the best result: at 10 amp (max current) the wire welded together but they didn't fuse as much as I wanted.
Another powersuply (22 Amp) had a shortcut saffety so no current at all. With the third I was able to set the current, but when I switched it on it started smoking, without any load connected. Some internal shortcircuit or something, the suply probably hasn't been used for a couple of years so no one knows...
The last attempt was a self build suply. I found an old transformer (240 V -55 V) with coils made of thick wires. This one should be able to give me the current I need. A variac on the primairy coil should give me the ability to regulate the welding current. Unfortunately I blew the fuse...

So, I tried soldering with silver. It was tricky not to overheat the wire with the gastorch but I managed. Unfortunatley this connection broke after some fiddeling.
In other words: I walked a lot of kilometers today to get all the stuff together for nothing. Good thing the sun is shining!