Originally Posted by v0rtex
Diff: Move one wheel forward, other goes backward
1-way: Move one wheel forward, nothing happens other side
Spool: Move one wheel forward, other goes forward too
Just to make it clear...
Diff: Move one wheel BACKWARD, other goes forward
1-way: Move one wheel BACKWARD, other goes backward
Spool: Move one wheel BACKWARD, other goes backward
Basically a spool is like having a solid shaft between both wheels where they move the same direction at the same speed no matter what.