Wheel Encoder Blocks
Each wheel motor has an attached encoder, and as the wheel turns, it generates a continuous stream of "ticks". One full wheel revolution results in 192 ticks. By using the tick counts, you can determine how far the RedBot travelled.
These oval blocks accumulate the number of ticks generated as each wheel turns. They are reporter blocks and can be assigned to a Scratch variable.
These rectangular command blocks allow you to reset the tick counts for each wheel back to zero.
These "hat" blocks will continuously monitor the number of accumulated ticks for its associated wheel. When the number of ticks exceeds a user specified value, the blocks attached to this block will execute.
See the "Quick Test Program" for a usage example.