Getting started building a Mendel, yet again

I know this is a FAQ kind of question on the forum, but people have different skill levels and means available to get started.

I'm located in Denmark, my soldering skills are sufficient to do simple soldering tasks, SMT soldering is definately out of my league. I do a bit of woodworking from time to time, but again, I'm no ace. I've done a tad of programming on ATMEL processors before, so thats where I feel most comfortable doing any tweaking. (I'm a software guy)

I've been looking around, and come up with the following plan, which I believe is withing my capabilities, but I'd like to know if this is a bad idea, if there is anything I have overlooked etc.

First I plan to build a McWire Cartesian Bot v1.2, and then the Mendel, my plans for the Mendel are still a bit sketchy.

From looking around, I get the impression that the pre-assembled Sanguino motherboard seems to be out of stock on a perpetual/permanent basis, so I'm planning to use the Arduino MEGA, the firmare seems to be prepared for using the MEGA, and tweaking the firmware to use the MEGA as a replacement for Sanguiono. is within my skill-set.

Instead of using acrylic, I plan to use HDF (not MDF) to bootstrap the McGuire, and then use the milling capabilities of the McGuire to create the acrylic plates. Converting to metric will be dealt with as I go along. PCBs/Controllers seems to be be the biggest issue, Makerbot seems to be so busy creating makerbots that there is little time for anything else and reprapsource only sells the version 1.2 and no extruder controller that I can find. So I'm planning to use the 1.2 series.

The extruder is the weakest part of my current plan, my current thinking is to build an extruder the same way Elijah Wood did except that I'll probably be using the 1.2 stepper motor control with 5d activated (I'm not up to SMT soldering and getting a prebuild board seems to be impossible, but I can tweak the firmware)

Once I have the McGuire assembled, I don't plan on cannibalizing it for building the Mendel, since I'd like to play around with the limited milling capability of the McGuire, but I should - hopefully - be able to create the RP parts for Mendel.

With the RP parts in hand, I plan to build a Mendel, using a similar controller setup to the McGuire.

I'd like to know if this sounds like a workable plan, if there is a better way of going about this?

The danish danish equivalent to FCC (IT- og Telestyrelsen) are quite strict about radio emissions and most setups I've seen have no cabinets/boxes for the electronics, are radio emissions something I should worry about?

I'm a sorry for posting something which is almost a FAQ, but this project is a bit daunting for me, so any advice and help I can get will be greatly appreaciated.

/anton

I also plan on going this rout soon. feedback on antons post would help pleanty

Picking up an old radio an putting it near my PC indicates to me that my PC is radiating a far greater RF interference than my any of my Repstraps do.

In fact in the late 80's I had enormous problems with radiated RF from my PC interfering with my 433MHz TNC pkt radio setup. I was adding shielding and ferrite beads on almost every lead to of the PC to try an cut the amount of RF noise it was generating back then its was only clock frequencies of 66MHz. We are now getting all the harmonics starting at a base frequency of say 3GHz with everything else in side the the PC running a little slower.

Generally these interference testing standards only apply to mass produced products.

Any interference made with the Darwin or reprap will be at such a low power they will only radiate a few feet from the source your Darwin Mendel or Repstrap.

This is governed by the inverse square law.. Excerpt from Wikipedia on inverse square law. As the grammar and spelling is better than mine.

If you are still worried about producing interference here are some solutions.

Twist all motor drive wires together as this will help cancel some radiated signal or just use fully screened cable to this you could also pop ferrite bead on each end of the wires.

Just look at any high quality USB lead or monitor lead you will see a big lump at the ends of the wires an inch or so from the connector these lumps contain a ferrite bead.

Free space propagation

In free space, all electromagnetic waves (radio, light, X-rays, etc) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of the distance from the source [3] or:

\rho_P \propto \frac{1}{r^2}.

Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.

The power density per surface unit is proportional to the product of the electric and magnetic field strengths. Thus, doubling the propagation path distance from the transmitter reduces each of their received field strengths over a free-space path by one-half.

Edited 1 time(s). Last edit at 01/17/2010 01:25PM by BodgeIt.

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Bodge It [reprap.org]
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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

Great, thanks for the info about radio emissions, it seems as if I have nothing to worry about.

Ever since a friend of mine got a visit from the authorities, and he had to pay a hefty fine (equiv 1,000$) I've been a bit paranoid about that kind of thing.

I think I'll twist the wires, just to be on the safe side.

Again, thanks for the tip.

Great, thanks for the info about radio emissions, it seems as if I have nothing to worry about.

Not yet. There's another open source project working towards that end:
[gnuradio.org]

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And then there is the controversial new proposal for a hole-making attachment:
[dev.forums.reprap.org]

Oh Yes that GNU Radio link looks interesting!

I think using an EM cutter will cause a few more problems than just local RFI laws.

Do you mean the Little things like :-

The effect it might have on EMP warning receivers around the world?

How large the micro chip kill zone will be around the machine?

The amount of power an EM cutter will use?

The price of the Mu-metal required for shielding the build area?

What other emissions are generated?

Like How to get it to pass local radio emission Laws?

To name only a few at the moment.

Edited 1 time(s). Last edit at 01/18/2010 02:57AM by BodgeIt.

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Bodge It [reprap.org]
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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

No, the first thing to figure out is the paper tape reader and gearwork to control it.

Hi Anton,

Seeing that you're in Europe, I thought I'd let you know that I have got some pcbs and components coming in to be able to build up some motherboard V1.2, Extruder V2.2, stepper V2.3 and opto enstop V2.1. I should have some completed motherboards and extruders within 2 weeks and the stepper and opto endstops within 4 weeks (The pcbs for the steppers and endstops are taking a little longer).

If you don't mind waiting a little (I think makerbot are out of stock anyway and it takes a week or more from them) then I can supply you with the electronics you may need.

My site should be up in 2 weeks and I can ship to Denmark pretty fast and pretty economically. I'm located in Belgium.

Let me know if there is anything else you need and I'll add it to some of my other bulk orders (atavrisp mkII for programming your atmel, or usb to ttl cable, or whatever).

Hi Matthew

I'm definately interested, this could be a better electronics solution than my original plan.

2-4 weeks wait time is fine with me, I've just started gathering and assembling the mechanical parts, so I won't be ready for the electronics until then.

/anton

Excellent,

I'll keep you updated on my progress and let you know when I've got stock

I'm from Finland and I'm also interested in building a McWire for repstrapping Mendel.

If/when you get to actually converting the designs to metric units, could you please share them here? Just not to duplicate the effort.

From my point of view, both HDF/MDF and acrylic could work, but please tell me when you get some experience in building a McWire on HDF.

Good luck! =)

If/when you get to actually converting the designs to metric units, could you please share them here? Just not to duplicate the effort.

I think it would be good to start a new wiki page, with whatever name you like, and link to it here.

I've started making this model using MRL-CAD, it is pretty slow going, since I'm using this to climb the rather steep learning curve of MRL-CAD. So far I've only modeled the support frame, nothing more.

Once I have something more substantial than just a few lengths of water pipe, I'll try to setup a wiki page, with my stuff.

I have started a new wiki page related to a Metric version of the McWire. The wiki page is located here.

I'm no ace at editing wiki pages compounding that is a bit of uncertainty about what categories, tags etc. should be used, but at least there is a semi permanent place to store what ever info is available.

I'm currently trying to create a BRL-CAD drawing of a metric McWire repstrapper, and need a bit of help.

I'm trying to locate - preferably in Europe - a source for the aluminum pieces, both the U-profiles and the L profiles. So far I've only found one, [uk.rs-online.com], but their products seems to based on inches, which gives some rather nasty fractional numbers when specifying drilling holes etc.

Similarily the NEMA engine is causing trouble, since NEMA specifies non metric bolts and threads, I've been looking for a source of IEC motors, and dimensions for IEC motors, but have come up blank.

does anybody have links to those kinds of sources?

In the UK we can get metric AL angle and U profile in high street diy shops like B&Q.

I think you are stuck with NEMA as the standard for common motors, but at least the screw threads are metric and also the shaft if you buy them in Europe.

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[www.hydraraptor.blogspot.com]

I am just finishing up my mcwire/mcguire. For the sheet stock 1/4" acrylic or similar is fine and I don't see any reason why it is worth laser cutting. If you have a table saw and a drill press you will be fine. Print out the PDFs' on sticker material, stick that to the acrylic and start cutting. Make the sheets square (they rounded corners are totally unnecessary). One end of the bearing arms needs to be rounded to clear where the bearing runs along the u-channel, I used a dremel with a drum sanding bit (maybe 3/8") and just did it in my hand. Also you don't need to the "special" countersink bit, I used a 1/2 inch hitachi countersink, which was close enough.

The whole mcwire thing is a total hack so there are huge tolerances all over the place, I worried a lot about the little details when I was ordering parts and planning it, it was wasted effort.

I also used little eye hooks and rubber bands instead of springs/nails in the bearing arms. The mcwire is total macgyver stuff and should probably be renamed to that.

At this point I have serious doubts about the mcwire's performance as a general purpose CNC, I just don't think it has the speed or accuracy to be that useful.

Great, it is comforting news that the tolerances are so great with the McWire/MacGyver repstrapper, it gives me hope that I can actually pull this off :-) .. I'm not that great at precision craftsmanship.

Although, with that information, I feel I have probably "wasted" time planning this thing out in meticulous detail. Including changing the size of the support frame, in order to make it easier for me to get some kind of precision.