Sunday, June 10, 2007

 

It's ALIVE! (sorta)

Well, I finally completed all of the soldering and building for Lamarck... Now I just gotta do the calibration and troubleshooting, and I'll be extruding! So far I have been successful in getting all three axes to work (though the X axis is reversed - anyone know how to get it to go the other way?), but the extruder controller is giving me problems. I seem to have basic communications with the board, but when I try to run the extruder exerciser for testing, it gives me errors. My main task for tomorrow will be trying to figure out what's wrong there.

Pictures of Lamarck as he stands now:
Lamarckian overview

For testing, I have attached all of the PCBs to an old cutting board I had lying around. Once I have everything working perfectly I'll think of a little nicer way to arrange them and their 200 billion (or so it seems) wire connections.

Since I ordered the wrong optical sensors for the endstops, I decided to go with limit-switches for the endstops for now. I was able to pick up some nice lever switches from Radio Shack which seem to do the trick (Radio Shack part #275-017A if you are interested). You can see one of the switches in the picture below, attached to one of the simple brackets I made by bending and drilling some flat steel bar:
lever switch

For those of you that are planning on converting a Sherline mill to a RepStrap, here's some info on how to connect the official Sherline motors (data sheet at http://www.sherline.com/stepspec2.pdf):
The motor connector has 6 wires: Red, Black, Yellow, Blue, White, Orange. Snip the Black and White wires - they won't be needed. Connect Red to pin 1 on the stepper controller board, Yellow to pin 2, Blue to pin 3, and Orange to pin 4. You will also need a pair of large 1.8ohm resistors, one in line with the Red wire, one with the Blue (or one with Yellow and one with Orange - you need one for each coil, but it doesn't matter which lead of the coil you connect them to). This is to compensate for the electrical differences between the RepRap motors and the Sherline ones.

Well, that's it for now. Hopefully tomorrow will bring some insight on my extruder issues and I'll actually be able to extrude something!

*UPDATE* - Thanks to help from Jonathan Marsden, I was able to fix my extruder controller issue - apparently it was an issue related to Sun's java communications library, and switching to the rxtx library and Jonathan's 0.8 RepRap release on Sourceforge, I was able to get my extruder talking! Today I've been fiddling with it, calibrating, and making CAPA filament. I was actually able to get it to start extruding a minimug, but I ran into a few issues - mostly communications errors after one of the axes' motors had been running a while. I suspect it is heat related, so I will concentrate on making the heat sinks more efficient tomorrow. I'll post pics and video as soon as I have anything remotely interesting to show. :)

Comments:
Eric,
You can reverse a stepper motor by reversing either one of the coils, but no both. You can also reverse it by swapping the two coils over.

Chris
 
Your extruder problems may be caused by electrical noise from the DC motor. You should have a ceramic cap across the motor terminals but I can't see it on the pic.
 
So for reversing the stepper, I can just take pins 1234 on the stepper controller and either make them 2134 or 3412 and that will do it?

I don't think the extruder problems are caused by noise on the DC motor, since I haven't gotten it to turn yet, but is any particular size of cap needed, or will pretty much ay work?
 
I don't have the pin numbers to hand but as long as you swap two wires that go to the same coil it will reverse.

I am not sure what the official RepRap value for the cap is but I would imagine anything from 10n to 100n would be OK.
 
Your assertion of 1234 -> 2134 would be correct assuming 12 pairing and 34 pairing. The other flip would have been 1234 -> 1243. I think 1234 -> 3412 doesn't make any change it just shifts the order of things without making a directional difference IIUC.
 
Thanks guys... I tried swapping pins 1 and 2 and that seems to work fine.

Also, it appears that the extruder issue I was experiencing was due to a software bug (Jonathan Marsden would have more details on this), and using Jonathan's release files from SourceForge and the rxtx libraries fixed it! I wa actually able to get CAPA to extrude a bit, and tonight or tomorrow night I should be able to drink to victory!!
 
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