For my godchildren, I developed and 3D-printed a Marblepump. The marble pump is compatible with Lego / Duplo bricks and designed to use with Hubelino marble tracks.
I made a short Video, where you can get a first impression. https://youtu.be/UdZP1RB9AnA
Affiliate Link to the Hubelino marble run: http://amzn.to/2gon6T8
As explained in the Video, I designed two versions. The differences in the feeding of the marble to the marble pump.
Version 1 (feeding with generic Hubelino track)
Pump housing V1
Version 2 (feeding with optimized marble track)
Pump housing V2
Feeding slope V2
Common parts (version 1 and 2)
top outlet right
top outlet left
I recommend that you first print the following sample brick to tune in the printer settings for a perfect fit to the generic bricks.
generic brick for testing
I made a test print with a brick. Then I compared printed one to the generic brick.
With the scale function of the slicer, I adjust the error of the pitch of the knobs.
With this, the shrinkage of the part can be compensated. For PLA I have to scale by 1.005.