Longboat Prusa - please help me with what i need to do

Hi

I have bought a Longboat Prusa from www.thereprapkitstore.com. I have one from batch 1.

Because of the instructions being incomplete and the fact i am new to 3d printers, i am stuck with what to do! can anyone tell me how to:
- wire the heat bed to the power supply
- attach the electronics
- and get the right software

thanks
simon

Hi Simon,

I also just got one of the Longboat Prusa kits, and have been busily assembling it this weekend.
And it's now at the stage where it moves under its own power!

I agree that the instructions are a bit vague regarding the electronics, but I found that most of what you need to know is covered elsewhere.

If you have a read of the Sanguinololu page, particularly the Wiring Diagram, it all becomes much clearer.

I did wire up the MOSFET on the heated bed as shown in the instructions, and tested it by connecting it to the 12V power supply and manully toggling it on/off.
But after that I changed my mind, and think I'll try the direct connection as shown in the diagram above, to avoid having to modify the Sanguino board.
(Is there a downside to all the power going through the Sanguino???)

It comes with the Sprinter firmware, to allow you to check it is working.
But you'll need to be able to build it with your own 'Configuration.h' to tune it to your machine. I didn't have much luck getting this to work on my Windows machine, but on Linux it works just as described in the README file.

One last thing. One of my stepper motors kept jittering when stationary, and after a bit of swapping things around I narrowed it down to one of the Pololu units. I then noticed that the potentiometer was not in the same position as the others, so tried setting it the same and the problem went away.
So it looks like the Pololu units are not necessarily calibrated correctly as supplied.

Mark

I wondered about all the heater current going through the Sanguinololu board - but it seems to work fine, so seems not much point in fiddling about with an external FET.
The main PSU connector is right next to the heater FETs on the PCB, so there's going to be very little drop across the connecting PCB lands - and as long as you have good chunky wire from the PCB to the PSU, in particular the ground wire (the heater +12v side does not need to go thru the PCB - the FETs switch the ground side - so the main 12v current thru the PCB is for steppers) then it doesn't seem to affect the other electronics.
I used heavy speaker wire for the main PSU feed.

Got myself up to the heated bed wiring bit and am a bit confused. The ARCOL blocks are mounted in a different orientation as in the instructions ("circle" vs. "star") so I'm wondering what's the best way to go about it. Anyone care to post pictures of the alternative way of setting this up? Feeling a bit jittery about modifying the Sanguinololu board.

Here is a picture of the way I wired it up, minus the MOSFET.
As long as you make sure you wire them in parallel it will be OK.

Bloomoo Wrote:
-------------------------------------------------------
> Here is a picture of the way I wired it up, minus
> the MOSFET.
> As long as you make sure you wire them in parallel
> it will be OK.

How much power should the heated bed produce? I've updated [reprap.org] with some notes from what looks like a mistake on the original instructions (shows resistors between source and ground instead of between 12V and source, resulting in a lot of heat in the FET), but will now be producing 100W onto the heated bed (12V onto 4 5.6R resistors in parallel, which may be too high? I'd guess we want a stable temperature so it's better for the heat to match the power loss and also needs to be within spec for the supplied PSU to put out 8A on its 12V output.

An alternative is to run the bed from the 5V supply, but then power would be down to 20W total, not sure if that would be sufficient?

Has any thought gone in to insulating the heated bed on the underside so it doesn't need so much heat and stays more evenly heated? Is the heat only turned on when the bottom layers are being printed, or does it stay on all the time?

The power question is I suppose only related to how fast the bed heats up as the temperature is the key thing. I am running the bed from the main board and it works fine. You need to put a thermistor in the centre of the bed * and take the output back to the connectors on the main board. The temperature should then be regulated and remain constant throughout the build. Either manually set it via your controlling software or put it in the gcode. See my post about missing Sprinter codes here.
Haven't tried any insulation of the bed, I suppose it would decrease the time to reach a stable temp.

*I attached the thermistor with HT silicone and Kapton tape.

One other thing I forgot to mention is that the mainboard power transistor driving the bed gets quite hot so I put a heatsink on it.


my blog

Edited 1 time(s). Last edit at 02/17/2012 08:27AM by glyn.

I've got my machine up and running now, and can confirm what glyn says.

Running the heated bed directly from the main board work just fine without any problems.
(The Arduino that comes with the kit is built using STP55NF06L MOSFETS, and I checked everything would be OK before wiring it up)

However, it does run a bit hotter than I would like for long term use. Probably around 50-60C.
So like glyn, I'll be adding some heatsinks and/or a fan in the near future.

I also used some HT silicone to attach the thermistor to the bed, but also drilled a small blind hole to accept the thermistor head in the same way as the head heater block.
(I've attached a picture of them waiting for the silicone to cure)


And a quick note for anyone assembling the extruder unit.
When it came time to set up the extruder with some filament in it, I found that the bolts were just barely long enough to get the wing nuts on, and required considerable effort and swearing to compress the springs at the same time.

I couldn't easily find any longer ones to replace them, so to save myself future pain I decided to disassemble the extruder and deepen the hex shaped holes for the bolt heads.

I did this by heating up one of the bolts so it was hot enough to melt the plastic and pushed it in, head first, about 2-3mm deeper.
Most of the plastic gets forced into the long 4mm hole, so you'll need to drill it out afterwards.