Duplo 31070

[Peter Blomberg]

Do the underside 'hollows' need to be modeled on each of the radiating bars?

They do not appear to have any function and would only add size and complexity to an already complex part.

Round Duplo brick with radiating bars (31070) BL link.
Picture of underside can be found at ebay link.

[Rene Rechthaler]

No, but it looks like the part is rotational symmetric...
Means you only have to do one Side (dent) and 3 cylinders as a Subpart and then use that 4 times rotated in the main part.
These Cylinders in the Subpart can get intersected with smaller ones to create the cutout.
If the "logs" itself are also identical, they could be subfiled even further.

[Gerald Lasser]

Although they do not have a function except from keeping the ABS used at a minimum and help cooling the part after molding, I would model them.

As Rene mentioned the part ist roatational symmetric (1/4) it will help reduce the file size

I don't know if you have got it, but here's the (rather rough) BI mesh as well