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Bonsai Repstrap

Posted by Sci 
Sci
Bonsai Repstrap
March 07, 2010 08:44AM
I spotted a batch of surplus stepper motors going cheap. 2000 stepper motors.
It immediately occurred to me that this is perfect for a small production run of something.

A few sums and tests later, and I bought them.

The motors are several times weaker than the ones used in Mendel, but I think I can produce a small repstrap machine based on the Mendel design. It'll be stripped down to the bones, and with some simplifications. I'm expecting a resolution of about 0.2mm.

Why do something like this? Because if it works, I should be able to make a couple of hundred of them for sale. Probably in the £150-200 range.
It'd allow folk to print their own parts for the full-size reprap, and have a smaller crude machine they could more easily keep on their desk. Plus it would give folk a relatively low-cost and low-stress taster in repraps.
And it could be broken down for parts for other projects (plastruder should be reusable in a larger machine, motors for small robotics).

Will try and get a blog tag up somewhere to track progress. smiling smiley


--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
Re: Bonsai Repstrap
March 07, 2010 09:19AM
I'd think they'd work fine with a geared extruder. We have to gear the extruder down anyway to get the required precision, and so it's effectively over-torqued. Some similar would work for the axis drives if you wanted the extra precision. It'd be at the expense of some speed, but the belt-driven design is too fast anyway, and we're not using anything close to the real speed it can go.

So at the expense of some additional reprapped parts you should be able to successfully make a perfectly functional full-sized mendel with the cheaper steppers.


--
I'm building it with Baling Wire
Re: Bonsai Repstrap
March 13, 2010 12:16AM
Will try and get a blog tag up somewhere to track progress.

Be sure to post in this thread as well.

A new wiki page for your machine would be good as well.


-Sebastien, RepRap.org library gnome.

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything! grinning smiley
Re: Bonsai Repstrap
March 20, 2010 04:58PM
You can also gear down the stepper motors for the X,Y, and Z stages too. The will slow things slightly, but give more precision. Most of the time, Mendel, as well as the rest of the current generation repraps are speed limited by the extruder, not the motor drives. I would consider making full sized Mendels, but with all the small stepper motors geared down for more torque. These geared down Mendels will also likely consume less electricity than normal ones.

Mike


Team Open Air
Blog Team Open Air
rocket scientists think LIGHTYEARS outside the box!
Sci
Re: Bonsai Repstrap
April 06, 2010 10:14AM
As is wont to happen with my projects, I've been working on this without maintaining a visible record. I have at least been taking photos and will attempt to get a retrospective of work so far up soon.

So far though, some of the changes have been thus:
  • Simplifying construction by using the frame studding as the runners by sheathing them in stainless-steel tube. This has the added benefit for rapid construction that tubes cut to set lengths keep all the parts properly spaced from each other. Less adjustment.
  • To allow easy shipping I also looked at making the frame partially collapsible. However I'm now looking into various cam-lock bolts to see if it would be possible to do this quickly and repeatedly, allowing the lightweight machine to be outright portable.
  • I'm forgoing complex chain or belt drives and going for tensioned wire. Using nylon-coated steel cable seems to be working well, though I need to procure better crimping tubes.
  • Debating simplified end-stop sensors by simply grounding the heater-block (modified Hydraraptor design) and monitoring when it makes electrical contact with pads at the ends of it's runs.
  • To overcome issues of motor power, I'm experimenting with using a counter-weight on the Z axis cable web (redundant cable run to keep axis squared), as well as using a bourden-cable feed to the plastruder to remove mass from the head.
  • Foregoing controller boards for simple parallel-port control with optical-isolation and indicator LEDs.

Still hunting for a friction or cam shaft-lock. Have one doodled up. Rather like the toggles found on coat adjustment cords, only with a nut in the middle.


--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
Sci
Re: Bonsai Repstrap
April 13, 2010 08:54PM
Snagged a brief video of the folding mechanism in action.

[www.youtube.com]

May create issue with running bourdon cable, but something will come to me.

Also, logging day to day progress on my creative blog. Can be followed specifically by following entries under the "reprap" tag.

[sci-starborne.dreamwidth.org]

Edited 1 time(s). Last edit at 04/13/2010 09:01PM by Sci.


--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
Sci
Re: Bonsai Repstrap
April 13, 2010 09:55PM
Also, created wiki page as requested. Will improve as time allows.

Now to bed.

[reprap.org]


--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
Re: Bonsai Repstrap
April 15, 2010 05:34AM
Peter,

What are you casting, and what are your molds made of?

Is this interesting?
[reprap.org]


-Sebastien, RepRap.org library gnome.

Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything! grinning smiley
Sci
Re: Bonsai Repstrap
April 15, 2010 09:36AM
Sebastien: I mostly cast fake claws and animal-style paw pads for people doing costuming, LARPing and so on. (Trying to widen my range ASAP. Over-specialising is not helping!)
I've also used it to make some Mendel frame parts, and make duplicates of some useful pullys and gears.
I use RTV tin-cure silicone moulds, though trying to learn other types that may be of use.

The epoxy-granite is indeed interesting! I already use calcium carbonate as a filler compound in the claws I make to improve impact resistance. It's light enough that it doesn't come out of suspension when de-gassed in a vacuum chamber.
I've also worked with 300 and 150 mesh glow powders. Both of them tend to settle out on degass (tho might be due to longer cure times as well).

I know TOMPS sell a marble filler powder intended to give castings the same feeling of mass. I've investigated it for possibly making ornaments. I'll keep it in mind for future possible CNC use.


--
Peter "Sci" Turpin
London, England

Provider of practical solutions.

(Sometimes stellifying Jupiter IS a practical solution)
VDX
Re: Bonsai Repstrap
April 15, 2010 09:46AM
Hi Peter,

... i used ecospheres from Trelleborg and Omega-Bubbles as lightweight-filler - maybe it's something you can use too?


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
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