Thanks for all the suggestions so far!
I'm trying to connect the dots now.
- Stepper motors seem to be a good solution. They may miss a step here and there but overall they can be controlled quite precisely and (hopefully) eliminate the need for encoders. From what I read online it may be a good idea to get a stepper motor with a step angle of 1.8 degrees (200 steps per rotation). This will deliver a resolution of about 1mm on a wheel with 60mm diameter. A 64-step motor seems too unprecise to me (3mm resolution on a wheel with 60mm diameter). I am not sure what motor to choose exactly, though. There are different sizes, (NEMA 4, NEMA 7, NEMA 8 …). Bigger sizes seem sturdier and stronger. What motor would you choose so that two of them can move and steer a vehicle that weighs approximately 300-500g in the end (rough estimation)?
- I need some way to attach the motors to my chassis, right? Can you tell me what the part is called that is needed for this? Or do the motors come with holes so I can screw them directly onto the chassis?
- The stepper motors are controlled by controller boards. Some of you suggested using one board for each stepper motor, but would it not be easier to use something like this shield? It can control two stepper motors at once which means fewer parts. The shield's wiki says that to use it you need a special library. Is this a plus or a disadvantage? Here is another one but it doesn't say if you need a library: Adafruit Motor/Stepper/Servo Shield
- A question about connecting the Arduino with the motor controller and the controller with the motors: What kind of cables do I buy? Is soldering needed or do I use the kind of cable that you can plug in?