I've converted a cordless drill and an ancient pedal from a sewing-machine to work with my cordless powertools in order to have a better drill/screwdriver/polisher/etc and my workbench.
Step 1: What I used .. what you'll need.
1. cheap cordless drill
2. scavenged pedal from sewingmachine
3. misc. screws, cableties, contactcement etc
Step 2: At the heart ..
.. of it is the controller from the drill.
You'll have to take your own apart and there's plenty of information on that so I won't show any.
Step 3: Taking the speed controller apart ..
.. You may need to separate the controller into its various parts but be warned:
The little controller is all surfacemount wierdness and the chances of getting it back together are slim so don't break open any of the plastic. Just separate the switch from the controller.
Also make sure to note position and connections of all cables.
+/- (Black/Red) from the battery/powersource
2 orange from the controller to the forward/reverse-switch
Step 5: Forward/Reverse, battery, motor and testdrive.
It's a good idea to oversize things a bit since you never know how much power you might one day be pulling of this.
The whitesocket is connected like this:
Switch out1 <-> To Motor1
Switch out2 <-> To Motor2
Powe out1 <-> Switch in -
Powe out2 <-> Switch in +