Finding the right motors to go with your robot’s can be a challenge. One needs to consider the impact on the system.
Where to find them:
If you go with the wrong ones they maybe under powered or worse overpowered and power hog’s. It’s best to shop around online for surplus motors from sites like http://www.goldmine-elec-products.com/
For a 330mm base it is best to go for 12-24 volt motors that are 72-130 RPM’s (revolutions per minute) on the output shaft after a all metal gearbox. Also try and remember it is more about torque then speed. The robot will need to sense the environment around it and will need to be slow and steady instead of quick. Later when you have mastered a slower robot you can always upgrade the speed.
There are also multiple steps in quality to look for. If you happen to find a Maxon gear motor set that fits the bill for your robot snatch them up as they are one of the highest quality and efficient motors out there.
Look out for Back EMI:
EMI or (Electromagnetic interference) Is created by all electric motor types. It is best practice to reduce it with a 1uF capacitor across the motor terminals, use shielded wires, and Ferrite beads near the motor input terminal and the main cable.