Stoked! I got a Blackfoot

[Stoked! I got a Blackfoot]

My boy turns 5, so I got this, but really it's for me.  But he will have fun watching.  Can't wait to paint it and get it running!

[I just got a Blackfoot! What upgrades are critical?]

What does Shimming it mean and how do you do it?

[I just got a Blackfoot! What upgrades are critical?]

Super excited to get a Blackfoot! 

I ordered some Ball Bearings for it, (Fast Eddy) 

and that's it so far.  I'd heard about the MIP ball diff, but I dont want to soak another $60 on this right away.  Not planning on gong brushless or Lipo right away.

 

What am I missing?