On Mon, May 29, 2017 at 6:58 PM, mike.valk@gmail.com mike.valk@gmail.com wrote:
I remembered an post from Hackaday. http://www.doublejumpelectric.com/projects/core_xy/2014-07-15-core_xy/
oh wooow _that_ post, yeahh i remember reading that aages ago. learned so much since then. not least, i *really* do not like the non-coplanar aspect of that original experimental corexy design: i've seen so many people be misled into thinking that you can misalign the belts and everything will be hunky-dory.
in a corexy design the belts coming off the pulleys at the ends of the moving beam *must* be in-plane and *must* be at exactly right-angles. anything other than that is just f*****g stupid. not only do you end up with non-linear motion but the offset corner idlers (out of plane) means that the belts "ride".
the simplest way to achieve good corexy kinematics is to have the X and Y belts stacked one above the other. that also has the advantage that the belt termination points can be in the *middle* of the carriage, which, if you have dual rods (or a single linear rail) results in zero twisting of the carriage, even under high acceleration.
in the diagram shown in that post, under high acceleration one end of the belt will become slightly slack whilst the other end is under increased tension: that in turn torques the carriage which in turn places torquing (side-loading) on the rail (or rods).
the best carriage arrangement i saw was the fusebox. everything _else_ about the fusebox was questionable but the belt arrangement at least was superb.
anyway the double pulley arrangement i am going to try out will have a 4x reduction in the amount of force on the belt (traded for a 4x increase in speed, which i will have to think through the consequences of).
l.