Dual disc polar printer support

fma

Hi!

I haven't read you for a while, being busy with other projects...

I plan to build another 3D printer, and started over my CoreXY design (to simplify it). But I just found this nice design:

https://hackaday.io/project/177633-dual-disc-polar-printer

Is such hardware supported by RRF? Or does it need further devs?

Is it complicated to calibrate such printer?

Thanks for your advice.

JoergS5

@fma that's an interesting kinematic, in my understanding it should work with serial scara printer kinematics.

the precision may be high, because a high ratio gear is built in (could be implemented by belts also)
it has a singularity in the middle of the upper big plate (there will be problems to print)
the proximal and distal arms are connected in the upper video, i. e. the upper plate rotates if the lower one rotates. There is a parameter in serial scara to set it
homing and calibration will be easy imho

I am interested in building it also.

The upper video has a weakness. The belt on the big plate is a GT2 belt and when bount outwards, it has too high play. I was experimenting with this types and one approach is to use a belt to make my own teeth by using epoxid at the outside of a wood plate, using belt (teeth inward) as pattern. Or simpler, 3D print the big plate. Or like the RepolaRap video without teeth, if friction is high enough.

fma

@joergs5 Thanks for your answer!

I was also thinking to use belts, as gears will have to much play.
The big pulleys can be laser cut, but it may be better to use 3GT profile (3mm pitch) or HTD5 (5mm pitch).

About the singularity, what will be the issue? Can it be fixed in software?

JoergS5

@fma said in Dual disc polar printer support:

About the singularity, what will be the issue? Can it be fixed in software

It is similar to the singularity of the polar kinematics in the middle, where there is today no solution. But I think it is possible to program that the upper plate's speed is set to 0 temporary when approaching the middle, when detecting to be in this region (for the smallest possible segment of a move). But this must be implemented.

JoergS5

@fma there is probably only the singularity, if the hotend can be at the center of the upper plate like in the first video. So avoiding this is a solution.

fma

@joergs5 Ok, I understand.

I will have a look at RRF Scara config to see how to configure...

JoergS5

@fma the connection was handled in the C parameter, like discussed in https://forum.duet3d.com/topic/9346/mpscara-g28-intermediate-position-outside-machine-limits/15
= crosstalk factor