So far, I think this quick'n'dirty prototype has some flaws that I need to restart from scratch:

• 3D printing, no glue
  This must be reproducible, and gluing things make it hard to repair and lacks precision.
  I will probably use another toy to get the wheels but that's all.
• Stepper motor or hacked servo
  The mushroom is quite heavy and with a basic DC engine I don't have any feedback so I have to put a strong current to get it moving and then it accelerates too much. I don't need speed, so I'll either use stepper engine like this one or that one or hack a servo to get a continuous spin.
• Bottomless mushroom
  The mushroom will just sit on top of a platform that will contain the electronics and the motor. It will be easier to test and fix.

I never did any 3D printing so I guess it's part of goals of things to learn for 2018!