slowing down my robots 12v motors
I have a question I hope someone can help me with regarding my current robot build so I hope this is the right place to ask. I am in the middle of building my own version of a full size K-9 with a few differences that I will be doing an Instructable for when he is completed. I am currently waiting for some parts from EZ Robots to arrive which are due sometime this month (June, 14) and so far I have pretty much completed his body and rolling chassis.
The question I want to pose has to do with the rolling chassis/drivetrain. The parts for the chassis have mainly come from a kiddies ride on car which has two 12v, 30w drive motors which produce two fixed forward and reverse speeds (slow 3MPH and fast 5MPH) and a single speed 12v steering motor, connected to a control/radio control receiver box, controlled by a R/C controller and powered by a 12v 7Ah rechargeable battery. The R/C controller will be located inside the body and 2 servos, via the EZ Robots EZ-B controller, will move the joysticks for the chassis movement (one servo for forward and reverse, and the other for left and right).
I have this pretty much sorted, but hear is where I need the help . I want to slow all 3 motors down a bit. I would like to have the steering motor turn slower so there is more precise movement via the servo control, and would like to be able to adjust the speed of the drive motors so I can have a slower, almost a crawl, speed while K-9 is roaming the house, and then be able to readjust the speed so he can move quicker around larger area or open spaces. The current "slow" speed is about 3 MPH but it is just a bit to quick to navigate autonomously around my house so I'm looking for a hopefully simple solution.
I had an idea of simply splicing through one of the motor wires on each motor and wiring in a 12v potentiometer which I could attach to his control panel and adjust it/them as needed (or even servo controlled, but first things first). Could it be as simple as that or would I need something more? I have also read online about maybe using a PWM but I wouldn't know how to wire it (or them as the case maybe) up. Would using a PWM do what I'm looking to do and would it even work on the set up I have?
I am not really experienced in using or installing resistors or soldering circuit boards ect, so a simple "easy for me to do" solution would be great, so any help and advice or solutions anybody here can offer really would be appreciated, and thanks in advance .