any disadvantages of a non-linear delta robot compared to the linear extrusion-based models?

I was wondering why don't we see more non-linear delta bots being developed, a la Firepick/IcePick Delta or this project I stumbled upon while searching on the web. I was impressed with the firepick delta and hoped I would see much more of its kind being played with/ developed. Is there any design flaw that makes it improper for 3D printing?

From my pov it is a concept much closer to the rep-rap beliefs than the aluminum extrusion-based deltas around. No linear rods, no alu extrusions, no linear bearings. Wat can be asked more of a a rep-rap bot ?

Thanks.

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Quote
realthor
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What can be asked more of a a rep-rap bot ?

Thanks.

- A working (i.e. that prints its own parts, for example) prototype or two.
- Good documentation (sources on GitHub, page(s) in the wiki, detailed BOM, Thingiverse, etc)
- Reproducible design at reasonable cost.

All the widespread RepRap designs fulfill these requirements, AFAIK.

One of the advantages of the linear delta over the nonlinear delta is that it is easy to get a large build height. The nonlinear delta makes that harder to achieve. Another reason may be that RepRaps normally use stepper motors for precise positioning because it is easier than the alternatives; but to use stepper motors in a nonlinear delta, you would need either geared motors (with potential backlash issues) or a belt drive reduction, in order to get enough motion precision.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I considered building one for quite some time, but eventually dropped it on favor for linear delta. Large amount of torque is needed, although I can't calculate how much even if my life depends on it.
The academic papers available online quote some scary numbers of tens of Nm for average sized robot. Working volume calculation is tricky. The inverse kinematics equations include trigonometric functions in addition to square roots if I recall correctly.

I would assume, both, repeatability and positional accuracy are not very good on these types of machines.

I simply believe, that the key factor in having a reliable 3D Printer is both, rigidity and having play-free linear axis.

Of course the concept of non-linear movement might be apealing and fot the sake of the "doability" it can certainly be a nice proof of concept,

but for the real-wordl daily use, I would want to have a machine as rigid as possible.

I think of my 2020 minikossel as flimsy btw. and am in the process of building one using at least 40x40mm extrusion, if not bigger, combined with 15mm linear recirculatinglinear rails.

Weight is not an issue at all - if the weight increases, simply use bigger motors or hybrid "servosteppers"

One could understanbly argue, that this is getting further and further away from the "true" reprap thought, but using only "standart" engineering parts which are widel available my perosnal opinion is, that such a machine can very well
be still a true DIY machine and be easy to reproduce.

I would be eager to see some movements, the speeds it can achive and more importantly the repeatability and reliability of the accuracy of it`s movement.

Alex

Quote
dc42
Another reason may be that RepRaps normally use stepper motors for precise positioning because it is easier than the alternatives; but to use stepper motors in a nonlinear delta, you would need either geared motors (with potential backlash issues) or a belt drive reduction, in order to get enough motion precision.

Cycloid gears are already 3d printed and can offer 100+:1 reduction ratio. They are nearly backlash-free and are very unobtrusive basically just an extension to the stepper motor.

@Alexander1984: I agree that repeatability and reliability are some of the most important features a 3D printer must have. I also believe that, if we have solid open-source rep-rap-style designs that nowadays use alu extrusions and linear rails because the plastics of the moment can't provide the before-mentioned must haves, when those plastics will be available, these designs would simply switch the materials and print those parts.

However, when using the "readily?" available alu extrusions, linear rails/bearings, timing belts and what not, not only that the rep-rap-ability of the design decreases dramatically but the cost goes up dramatically to the point when it doesn't make sense to have a home printer. Prices of 1500+ make this a niche for the very passionate that have the money to indulge. By no means an 1500+ printer makes sense from the cost pov when you consider what most people can really print on these machines. What if such devices get damaged in less accessible locations. How would they be repaired?

My point is that such designs, like the non-linear delta, should be developed and researched even by using expensive metal parts because when plastics would provide the properties needed, the switch would be instantaneous. Otherwise the software to run these machines will not have been developed and their issues, observed while running them, would not have been ironed out by that time.

I guess this is a moot issue now because i can't really help neither mechanical design or software writing, this is merely a "sigh" for the somewhat lost opportunities.

Thanks for your responses.

Edited 2 time(s). Last edit at 07/12/2015 07:37PM by realthor.

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RepRap Lander concept on Concept Forge
RepRap Lander concept on RepRap Forums
My Things, mostly experimental stuff