A physically instructive toy.
Heavily inspired by Lego Ninjago Airjitzu toys and Beyblade (all trademarks are the property of their respective owners).
The spinning top consists of 4 parts. The axis with the gear is compatible with the Lego Ninjago Airjitzu toys. The disk consists of two identical halves that allow you to insert up to 6 coins (5 Euro-cent) for more momentum. The bottom cone should fit tightly on the axis, but could also be screwed on with a M3x30 screw or you could just use glue.
Warning: If you put in some coins you might want to be careful near valuable furniture!
The launcher consists of a box with handle and lid and the starter strip.
As an arena we used a lid from a big pot, turned upside down and placed on a bowl for stability, but of course you can use whatever you want.
The gear was created with the library by GregFrost: http://www.thingiverse.com/thing:3575
The gear and starter strip are the crucial parts. If their teeth come out fine the rest shouldn't be difficult. With the standard printing speed the teeth were truncated, but with half the normal speed they turned out nicely.
For the starter strip the shell thickness should be reduced to 0.4 mm (one nozzle size). For all other pieces 0.8 mm would be fine.
The laucher box is easy to print, but if the axis doesn't turn easily in the hole, then you could use a file to widen the hole a bit, or you can adjust the parameter "gearHoleR" in the "spinning_top.scad" file.
Also be aware that different printers and different materials have direct impact on sizes.
(I've used PLA.)