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Building a Darwin

Posted by Anonymous User 
Anonymous User
Building a Darwin
April 24, 2007 05:45AM
Hi RepRappers,

Have you got some advice for someone starting the building of a Darwin machine?
What's the hardest part in this project?

I'm a bit more confident with building electronics than building pieces for the cartesian robot, would it be possible to have something like a market place to exchange parts? Sharing universal board with corner brackets? smiling smiley

If possible, I'd like to show this first built RepRap machine at the Berlin CCC camp next August, is someone else going there?

The documentation on the wiki is great, it allows to have a quick view on each part of the project really easily.
Thanks for all ;-)


Re: Building a Darwin
April 24, 2007 09:43AM
welcome and thanks for your interest in the project.

i havent built a darwin yet, but i've been involved for a while so i can just offer general advice: have patience. we're working with cutting edge technology, and attempting to do it on a budget of $500, when the rest of the world is doing it for 2-1000x that much. sometimes things wont work, sometimes they will. and when they do... it will more than make up for when they dont =)

a marketplace would be an excellent idea. once things really get going, we'll probably open up a marketplace forum for people to offer things for sale/trade. also, in the near future, RepRap as a project will be offering certain hard-to-get parts for sale at, or near, cost. Stay tuned for more details.

i live in NYC, so it might be hard for me to get there. then again, my brother lives in Berlin, so that might be a very cool excuse to go there. please post more info as it gets closer.

i'm glad you like the documentation... we're always trying to improve it.
Anonymous User
Re: Building a Darwin
April 24, 2007 10:25AM
Hi Zach,

Thanks for your answer, I'll keep you posted on advances made during next months, and there will have few fabbing hacker for sure at next CCC camp winking smiley

Re: Building a Darwin
April 27, 2007 08:31PM
I've read through all the building instructions in the wiki, and it talks about using another darwin to create the parts for a new one. Is the current darwin capable of creating it's own parts to a high enough standard to make new darwins or is the wiki talking about once the darwin is finished?

Re: Building a Darwin
June 25, 2007 11:25PM
I'm in NY too. I have access to a couple of metal shops and a wood shop, and I'm thinking of pulling some friends together to make a reprap. I have scant expertise to a mill, but I do have access to one, and maybe this is a good time to learn how to use it properly.

Right now, I'm thinking of the frame and wondering if frame rigidity is an issue. Should I build it out of steel? Or should I go with aluminum?

And I see there's lots of belt driven pieces, which I haven't much experience with. I keep thinking screw drives might be doable. I imagine it's been considered, and I was wondering if somebody has easy answers as to why I should avoid it.

Finally, if anybody in NY is interested on combining efforts, I'm happy to discuss it (just leave a note in this thread).

Thanks much. Looks like a wonderful effort with the potential for a impressive future. Good luck, all.
Anonymous User
Re: Building a Darwin
June 26, 2007 03:58AM
The only page I can find about using a lead screw is this one: [reprap.org]. There the idea of using a lead screw is dismissed because it would take 3.5 minutes to traverse 300 mm. However, there are some problems with the calculations.

These are mine: The steppers do 400 steps per rev, and the M8 studding has a pitch of 1.25mm per rev. The calculation runs the steppers at 100 Khz which is 250 rpm which is 312.5 mm per minute (12 IPM). This is less than what the people at cnczone get when using metric studding. When using acme screws or ball screws they go up to 200 IPM or 85mm/sec!

The goal of Darwin is to extrude at about 10mm/sec, and this is easily done with lead screws. See the Clanking Replicator blog for an example of a lead screw driven RepStrap.

Re: Building a Darwin
June 26, 2007 06:27AM
Um... Clanking Replicator's Tommelise isn't getting 10 mm/sec. I'm looking for 3.5-4 mm/sec in the short to mid-term. Mind, with my previous bootstrap machine, Godzilla, I got up to 15-20 mm/sec it was hugely noisy and I doubt that I could have got the positioning resolution needed to do anything useful.

Mind, I'm not particularly worried about Tommelise being slower than Darwin. For the price of one Darwin you can easily build three Tommelises and run them all off of the same PC. As well, the baby gearmotors that Tommelise require use less than a tithe of the amperage that the steppers on Darwin do.

Edited 2 time(s). Last edit at 06/26/2007 01:30PM by Forrest Higgs.
Re: Building a Darwin
June 26, 2007 08:15AM
I think there are some problems with your calculations.

100 KHz / 400 steps is 250 revs per second or 15000 RPM which is way too fast for a stepper motor.

To get reasonable speed with a lead screw you need to use one designed for the job. These are multistart, have a big pitch and are relatively expensive. As an example my machine uses ball screws with a pitch of 1/2" and 200 step motors. A realistic stepping rate is 1KHz which gives 5 RPM and about 40mm / s. This is with a constant current driver and low voltage motors. I don't think you could get that fast with the constant voltage driver RepRap uses.

If you use cheap studding then the pitch is such that you really need to use a DC motor with a shaft encoder as Forrest has done.

Edited 3 time(s). Last edit at 06/26/2007 08:21AM by nophead.

Re: Building a Darwin
June 26, 2007 09:51AM
hey blerik!

i'm in NY, Brooklyn to be exact. if you're interested in getting involved in the project, i recently received a set of Darwin parts from Adrian that I am now in the process of assembling. if you'd like to get involved and/or help out with that i'd be more than happy to have you involved.

i've got most of the boards assembled, and the machine itself is 50% assembled. now i need to finish the assembly, get everything hooked up. then the calibration and testing begins.

you could even be there when it achieves self replication! =)
Anonymous User
Re: Building a Darwin
June 26, 2007 10:28AM

You're right, forgot to look up the max speed of the stepper. And I forgot to factor in the stepper driver RepRap uses. And using a proper lead screw helps a lot too.

But I'm a stubborn bugger, and so I will continue my experiments with a stepper and an M6 lead screw... (the specs on my stepper say it'll go up to 30 rps or 1500 rpm, I'll probably have to run it at 50V to get there)


I'd love to get involved with your Darwin machine. Too bad I live in Amsterdam, Holland. I'm currently trying to make my own RepStrap machine from scratch. Still working on the first axis, and waiting for my stepper drivers (I found the most beautiful driver board on sparkfun, but it's sold out!).

Re: Building a Darwin
June 26, 2007 11:41AM
blerik... there are actually at least 2-3 people involved in reprap in holland. joost van wiel comes to mind right away. i know because i've shipped a few packages over there =)
Re: Building a Darwin
June 26, 2007 05:16PM

It was James who is in NY, not blerik :-)

Re: Building a Darwin
June 26, 2007 10:52PM
yup, i understand. i met up with him tonight. great guy, very friendly. i was just pointing blerik in the direction of other reprappers in Holland, since i know firsthand that they are there.
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