thereprapkitstore.com Prusa Mendel construction Notes/Discussions

Pictures of how I wired my head

1

2

I've put about 50m of filament through now and dismantled the head once and everything seem OK

Edited 1 time(s). Last edit at 06/01/2012 05:39PM by MotoBarsteward.

I received my batch 4 ABS Prusa on Saturday and I'm generally impressed, with exception to the missing Linear Bearings which are hindering my progress. I'm not sure if there is an issue with the supplier or if it was just in error but I'm yet to hear from James with it being bank holiday weekend.

I managed to get the frame together in an afternoon's work and spent the next afternoon putting the fiddly bits together. I'm now stuck without the Linear bearings but I'm sure they'll turn up. I adjusted the incorrect measuremnt of 70mm between the bar clamps and the vertex to 60mm in the wiki. I kindly ask that people edit the wiki if they spot an error (ensure you're looking at the right wiki!) to ensure future builders are given the correct information and avoid unnecessary rejigging.

Pics can be found here

Differences I've spotted in this batch are:

-The motors in my kit are all black
-The kit comes with Melzi electronics for solderless wiring. I'm not sure what electronics were shipped previously.


I had a problem with the large extruder cog being buckled and rubbing the motor screws so I filed the hole for the bolt a little and the cog is now dead straight. I also had the problem already mentioned with the threaded rod ends being damaged while being cut but I just used a combination of a small angled file a bolt screwed all the way up the rod and off again to clean the thread.

As I'm sure you're all aware, the wiki instructions are incomplete. Is somebody here with a finished ABS Prusa able to finish the instructions page? Because I don't think James is going to.

Also can anybody provide a link to wiring instructions for this board? I've only managed to find instructions for a Huxlery so far but I can't imagine the two are much different in their wiring.

Is anybody also able to advise on a cable management method? I've been looking at this wrap-around cable braiding which I could wrap around the threaded rod frame to tidy up all the wires.

I must add that James got this kit to me within 2 days of ordering as I only live about 20 miles from him which I'm very grateful for.

Edited 3 time(s). Last edit at 06/04/2012 12:11PM by remondo.

If you look carefully at the top of this picture: [reprap.org] you can see the labels for all the connectors. Unfortunately that text is missing from James' boards.

Edit: I just noticed your pictures have the connectors labelled. What more wiring information do you need?

Edited 1 time(s). Last edit at 06/04/2012 12:18PM by nophead.

---

[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> If you look carefully at the top of this picture:
> [reprap.org]
> you can see the labels for all the connectors.
> Unfortunately that text is missing from James'
> boards.
>
> Edit: I just noticed your pictures have the
> connectors labelled. What more wiring information
> do you need?



Well I don't know which wire goes where. The stepper motors have 6 wires, 2 of which are shorter and presumably not required. I've determined which wires are pairs based on resistance on the motor but there are no markings on the terminals. Would it be ok to follow this guide for the Huxley?

I'm also a little confused by the 'LEDs' supplied in my kit for the PCB heated Bed Mk2. They look like grain of wheat bulbs to me, do I still need a resistor for these? Because there wasn't one in my kit. If so which one?

Edited 2 time(s). Last edit at 06/06/2012 03:10PM by remondo.

Those are thermistors, not LEDs.

It is similar to the Huxley but you probably want to wire the Z motors in parallel instead of series. If you have six wires and you are ignoring the centre taps then you already have two coils in series and you are on 12V rather than 19V so parallel is likely to give you more speed.

Connect one coil pair to the first two pins and the other coil to the second two. If it spins the wrong way swap the first and second wires. It is possible to work it out given a datasheet but there is 50% chance of getting it wrong anyway. Make sure the power is off when connecting motors.

Edit:
Also the RepRapPro Huxley bed is unusual as it has the MOSET on the bed and not on the Melzi, so that wiring is different.

Edited 1 time(s). Last edit at 06/05/2012 04:51PM by nophead.

---

[www.hydraraptor.blogspot.com]

Yes I just realised they're thermsistors and came back to correct myself but you were too quick! I've also just noticed the Etemp and Btemp terminals on the Melzi board.

What are the centre taps? Also I have read that a mosfet heatsink for the hotbed is recommended, what sort should I be using?

Which LED's and resistors should I use for the heat bed then? There are thousands of different types, does voltage matter. Would these do?

Thanks for all your help, sorry for my noob questions but this is what forums are for!

When motors have six wires they have three for each coil, one at each end and one in the middle called a centre tap. If two are shorter it looks like they are the centre taps and the intention is for you to use the other two.

I don't think the MOSFETs on the Melzi need heatsinks. They are have very low on resistance so should not dissipate much power and they use copper on the PCB as a heatsink.

You can use any LEDs that are physically the right size with an appropriate series resistor for 12V, so yes those on eBay will work. You only actually need one if you wire the bed the right way round. I have never bothered with them myself. I fear they would not last long at the the bed temperatures I use. A typical LED is rated for -30°C to +80°C but they are at the edge, so perhaps you will get away with it.

Yes this is what forums are for, but it would be nice if James completed the instructions.

---

[www.hydraraptor.blogspot.com]

MotoBarsteward Wrote:
-------------------------------------------------------
> Pictures of how I wired my head
>
> 1
>
> 2
>
> I've put about 50m of filament through now and
> dismantled the head once and everything seem OK


I'd be a little concerned about the life expectancy of your power resistor/thermistor. The constant movement of the head will eventually break those leads. Better to tape them to the barrel or provide some other sort of strain relief to isolate them from any motion.

---

- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

My thoughts exactly nophead! The instructions thus far are excellent, I can only imagine James is under a lot of pressure to deliver each batch on time and as a result he has not had time to complete them.

I'm still waiting for a response from him regarding the missing linear bearings which have halted my progress on the build. It's getting to the point where I would not recommend him due to his poor communication, despite him getting the kit to me within 2 days of ordering and the overall quality of the kit. I can make an exception due to the bank holiday but if I don't hear from him by the end of today I'm going to spit my dummy out.

I came to the same conclusion last night that I will not bother with the LEDs because as you say, most are only rated to around 80°C and the Melzi board has a status LED so I shouldn't forget that the bed is on.

I've just spotted that the diagrams on the Melzi Wiki page have polarity labelled for the most part so I can begin wiring while I wait for the bearings to show up.

My next problem, however, is that the Melzi board has potentiometers for each stepper motor but I don't have any means of measuring the voltage to determine how these should be set. Is there a general rule for this or should I purchase a multimeter?

One more thing- I have an old 10A power cable lying around which I'd like to recycle to connect the heated parts to my board, would this cable suffice? I'd also like to use it to wire my PSU to the board but I've read the whole setup can pull as much as 17A so is it safer (or more efficient) to get some decent cable like this?

Thanks again for your help.

Edited 5 time(s). Last edit at 06/06/2012 11:49AM by remondo.

You can start with the pots low and increase them slowly until either the chips or the motors get too hot for comfort. I would suggest a multimeter with a thermocouple is pretty much a necessity when setting up a reprap as indeed is a digital calliper.

I use wire taken from 13A mains cable to wire up my machines. 10A is a bit light, mainly because of the additional voltage drop which makes a big difference to the max bed temperature.

I expect 30A is too big to fit the connectors and too stiff for the bed.

---

[www.hydraraptor.blogspot.com]

No problem, I'll get a multimeter tomorrow, thanks. I ordered a digital caliper last night as well as isopropanol. Is it a good idea to degrease the smooth rods with this, as well as clean the glass?

I thought 10A would be a bit risky but the only place I have found 13A wire is on kettles, toasters, hoovers etc and they're all in good working order. I'll have a look around work tomorrow, we just threw 3 dead kettles out though! May they rest in pieces.

Thanks again!

It is probably a good idea to polish the smooth rods and clean them well. Once the bearings run on them they deposit a little oil so don't clean that off. It is sometimes necessary to add some if the bearings dry out.

You could try the 10A wire. I don't think it will overheat as it is usually generously rated and normally runs inside an outer sleeve. In free air the rating should be higher. The bed only takes 10A when cold and the current soon drops.

You could also double it up if it isn't too thick to fit the connectors.

---

[www.hydraraptor.blogspot.com]

Thanks for your concern. Actually, in practice, there is no movement in the leads. I have heat shrink after the terminals and it is rigid enough to prevent the resistor or thermistor leads moving independently of the head.

akhlut Wrote:
-------------------------------------------------------
> MotoBarsteward Wrote:
> --------------------------------------------------
> -----
> > Pictures of how I wired my head
> >
> > 1
> >
> > 2
> >
> > I've put about 50m of filament through now and
> > dismantled the head once and everything seem OK
>
>
> I'd be a little concerned about the life
> expectancy of your power resistor/thermistor. The
> constant movement of the head will eventually
> break those leads. Better to tape them to the
> barrel or provide some other sort of strain relief
> to isolate them from any motion.

MotoBarsteward, would it be ok to include your photos on the J-Head wiki page? The current images are outdated and I'm sure people would benefit from a visual representation of your tidy wiring. Your images would of course be accompanied by credit if you so wish.

Would it be ok to use some Thermal Compound for computer CPUs to ensure optimal heat transfer from the resistor to the nozzle?

Edited 3 time(s). Last edit at 06/07/2012 05:53AM by remondo.

I've also built the ABSPrusa and I'm really fed up with the lack of instructions.

I thought the PSU he shipped was faulty until I found out about the green-black connection to turn it on. However, now I have the PSU working but no response at all from the Melzi board. Someone mentioned an LED on the board, where abouts is it? I can't see it, should it be showing as soon as power is applied?

Oh well off to Maplin for a multimeter.

I noticed a PCB jumper in the kit, presumably this is supposed to go on the board somewhere, any idea where?

There is a jumper right in the middle that selects whether the power comes from USB or the 5V regulator. If you leave it off it will not work. I selected the regulator.

There is also an auto reset jumper at the end. Put it on for flashing firmware and remove it if running from SDcard.

Edited 1 time(s). Last edit at 06/07/2012 11:37AM by nophead.

---

[www.hydraraptor.blogspot.com]

The LED is under software control so it depends on what the firmware does with it.

I am not sure where it is but it will be a small rectangle made from transparent plastic.

---

[www.hydraraptor.blogspot.com]

Cheers nophead, with the jumper installed my laptop now recognises it needs a USB driver. Another step along the way.

Yes, no problem. I think I set it up to be free to download. When I get back of scout camp, I'm going to take a load of photos of the machine for reference.

PS I'm a scout leader not a scout!

remondo Wrote:
-------------------------------------------------------
> MotoBarsteward, would it be ok to include your
> photos on the J-Head wiki page? The current images
> are outdated and I'm sure people would benefit
> from a visual representation of your tidy wiring.
> Your images would of course be accompanied by
> credit if you so wish.
>
> Would it be ok to use some Thermal Compound for
> computer CPUs to ensure optimal heat transfer from
> the resistor to the nozzle?

Thanks to nophead I am printing now, but my hot bed doesn't heat up. I've checked the voltage at the bed and it's almost 10V (lost nearly 2V on my cables)

I didn't include the LED; should I have soldered in something to replace it?

No you don't need anything to replace the LED. If you are really losing 2V in your cables I would expect them to be smoking. Also 10V across the bed should get it hot, but not hot enough for ABS.

The most likely cause of getting 10V is that PSU voltage has dropped. if so it needs a dummy load on the 5V rail.

Have you soldered the wires to the bottom of the board? I don't think the top pads are connected.

---

[www.hydraraptor.blogspot.com]

I made that mistake. I just assumed that, because the pcb was double-sided, they were through hole plated and they're not. It had me going for a few minutes, I can tell you!

One thing the photos above of my hot end didn't show is that the heater and ptc cables are secured back to the x carriage by a cable tie around the extruder stepper. They are not free floating.

nophead Wrote:
-------------------------------------------------------
> No you don't need anything to replace the LED. If
> you are really losing 2V in your cables I would
> expect them to be smoking. Also 10V across the bed
> should get it hot, but not hot enough for ABS.
>
> The most likely cause of getting 10V is that PSU
> voltage has dropped. if so it needs a dummy load
> on the 5V rail.
>
> Have you soldered the wires to the bottom of the
> board? I don't think the top pads are connected.

Thanks once again nophead, I'd soldered the wrong side.

The reason it is not plated is because plating adds thickness to all the copper areas and normally doubles the thickness of the tracks. The problem is it is not accurate enough to create precise resistances. The original MK1 board that Josef Prusa designed has no holes.

---

[www.hydraraptor.blogspot.com]

I found a better way for the final step to mount the y- and z-axis.
But that i way i noticed, that the z-axis is not vertical.
i do not understand this. everything is symmetric, yet the bottom end of the two smooth z-rods are about 5mm beside the middle.
i have jigged everything again and again and i simply don't understand it.
As you others followed the instructions on the ABSPrusa-Wiki, maybe you haven't notice this.

If someone of you has a sliding calliper, maybe he would like to check this (see attachment image)
Having the the y-stepper in front, just measure the distance from a z-smooth-rod to the front vertex (the M8 nut) and compare it with the distance to the rear vertex.
With my reprap, the difference is about 10mm :-(

And i really would have to use brute force to bend the smooth rod to the middle position.
Very strange, because i do not find the reason for this :-/

roland
www.scriptdoctors.org

Anyone noticed that the parts on thereprapkitstore git hub are different to those supplied in their kit? I noticed the extruder cogs were diferent and I'm half way through printing the wade.stl file now and that's also different to what came with the kit. N0phead, it was rumoured that you supplied the parts to thereprapkitstore. Can you cast any light on this?

I print the parts James asked me to print, which was what I was printing in my own Prusa sets plus some changes requested for LM8UU bearings. At the time they were printed the Github repository did not exist and James has never mentioned it to me.

The only differences I can see are the Wade's parts.Mine are a much older version. I tend to stick with what I know works as any new stuff from Josef usually has holes that are way too big when I print them so I have to get the source and hack it, which takes time. Unless I can see some functional advantage I stick with what I have.

The gears and the idler bracket are in the Mendel90 repository :
[github.com]
[github.com]
[github.com]

I have attached the body. wades.stl

Presumably the ones you are printing will work as they are later versions.

---

[www.hydraraptor.blogspot.com]

> Re: im a stuck :-(

okay, it was late in the night and was to stupid to correctly use my sliding calliper
i have documented my better way to mount the x- and z-axis into my little wiki page: [reprap.org]

ideas welcome.

Roland, I used the original Prusa wiki page to align the z-axis smooth rods. Tie a small nut to a piece of cotton thread to create a makeshift plumb line and place it through the top smooth bar holder and hang it down towards the bottom bar clamp. Now position the bottom bar clamp so that the nut sits inside the opening for the smooth rod, ensuring the plumb line is hanging perfectly vertical.

You will need to file or cut some of the material in the hole where the x-axis smooth rods sit in the pastic parts and ensure the smooth rods are pushed all the way in. Make sure you maintain a snug fit though.

I'm still waiting for my bloody bearings after over a week. Our friendly neighbourhood postman neglected to ring the bell even though I was in, with what I assume was 2 bearings which James sent me (he should have sent me all 10). By the time I get these parts I'll have lost interest in the project.

You shouldn't need to remove any material in the X-ends if they are the ones I printed. The rods should just push in. I just tested one here.

---

[www.hydraraptor.blogspot.com]