[Mechanics] Why delta robots have 2 arms per one motor arm

Other Hardware Motors, Mechanics, Power and CNC
1

Hello,

I am wondering why all delta robots have 2 arms per one motor arm.?
I.e

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Why we have 2 arms for every motor arm?
I think that it should work with one arm and the down effector will still be parallel.

All designs available in internet use two arms but the only reason I can see is if their universal joins are
half spheres and they need a spring between them to hold the joins.

if we use regular ball joints / end rods / it should work with one arm per motor right?

Thanks
Anton

2

Maybe it is easier to get the required stiffness and freedom from rotational stresses with a paired arm.

Try it and see, and report back.

..R

3

Because you need at least 6 pivoted(*) support points to define the position of the head, use less
and the structure is floppy - its position is not completely constrained as an object has 6 degrees of
freedom and each link can only constrain one degree of freedom.

(*) we are talking about freely pivoted at both ends - each link only constrains the distance
between its ends.

Compare to a Stewart platform.