annajoseph:
THe Johnson motor draws a current of minimum 800mA and maximum 9A
Since your motor has a max current of 9 amps, you need to get an h-bridge driver (for each motor) that can handle that current.
But it isn't so simple as finding one that is 9 amps. Instead, you want to add an extra percentage to that amperage, and size to that. Somewhere around 15-30% - so shoot for a minimum of around 12 amps or so. This is because you never want to drive any component or system to it's max rating, and instead size for above that rating as a safety margin.