Rotopods and other kinematics ...
January 14, 2008 04:12PM
Hi all,

... i found a video of a very interesting planar-tripod/rotopod: []

From here: []

*** start EDIT

... and here an even older and very fast demonstration: [www.ifr.ing.tu-bs.de]

From here: [www.ifr.ing.tu-bs.de]

*** end

This seems to be very easy to assemble and could solve the problem of reprapping parts for hierarchical bigger systems ...


Edited 1 time(s). Last edit at 01/14/2008 04:31PM by Viktor Dirks.
Re: Rotopods and other kinematics ...
January 14, 2008 08:33PM
The one problem that I foresee is the complications and inaccuracies from a non-Cartesian robot.

Never mind that, after thinking about it, all you have to do in order to keep track of where the stage is in space is triangulate it from the angle off of the motors. This is quite intriguing actually. Great find!! I might get my dad to attempt to write some simple software for a machine like that. it seems to use 1 extra motor over the Cartesian setup (3 in the XY plane and on for Z), but costs saved from excess nuts and bolts could make this feasible, at least on the small scale.

Re: Rotopods and other kinematics ...
January 15, 2008 01:26AM
... i'll post some more images and infos, when i have finished my 'tripod-toy':

look here [builders.reprap.org] under "Assembling the Tripod..." for more images and a short video of manually playing with the kinematics ...

Actually i'm at optimizing my 3D-CNC-repstrap (in the BuilderBlog-link above under "Got the perfect RepStrap" too), so i can mill the needed parts for the tripod and some equipment for applying the diode-laser- and dispenser-heads ...

Re: Rotopods and other kinematics ...
January 15, 2008 08:59PM
After thinking about it, i think that there is a three motor setup for this type of thing. Imagine a two jointed arm, with a motor in each joint and the stage moves under a stationary extruder which then moves up and down for the layers. The mechanics of getting a straight line would be complicated, but it could defiantly work.

Re: Rotopods and other kinematics ...
January 16, 2008 01:23AM
Hi Jay,

... here: [www.harmonicdrive.de] you have a parallel-scara-robot in a similar setup with two motors for XY and a third motor for Z ...

Orthogonal moving with angular driving isn't so complicated - you have clean conversions, what's called "Inverse Kinematics", where for every point in the working area you have a corresponding position of the motors.

So you have only to brake down your line into elements small enough, so you can draw a straight line with many small arcs too.

With a linear interpolation between the two (or three axes for a 3D-line) you can move as exact as you wish - in this special setup you have an overall accuracy of some microns!

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