carriage, 3 or 4 wheels?

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Hi all,

I can't seem to figure out whether to use 3 or 4 wheels on the vertical carriage for my Makerslide based delta 3d printer. In what case would someone use 3 wheels, in what case 4?

[regressedEE]

Most deltas seem to use three wheels -- the idea seems to be that vertical carriages only need three whereas horizontal ones need four. This design for kossel carriages looks like it would be easy to adapt for makerslide and does not require an eccentric spacer: kossel mini rails to wheels kit. There are several variants on Thingiverse, just search for kossel carriage. It looks like Bart's design uses three wheels as well.

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Thanks regressedEE!

So not too much theory behind...

[r691175002]

Your question is essentially the same as asking why a tripod would have three legs.

Three wheels is enough to fully constrain the slider on its track. Having four wheels would require making two of them adjustable. Furthermore, it adds the additional requirement that all four wheels lie on the same plane (whereas 3 wheels will always lie on a plane) which could pose a problem for a relatively low accuracy system.

Adding wheels increases load capacity, which isn't usually a problem for 3d printers. Adding more wheels makes it harder to adjust since you will want all of them to be under even tension. It can be difficult to determine whether a specific wheel is loose/tight relative to the others when adjusting using an eccentric bolt.

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thanks r691175002!

Yes, I understand the tripod analogy. Maybe the question was more, why would someone use 4 wheels instead of 3, in which cases is that useful? So load capacity is the answer.