There are so many different types of DC and AC motors you cannot generalize, for e.g. there is as @cuyler1 mentions, RC brushless which are essentially BLDC motors fed off of Lipo batteries.
Also BLDC are used now in washing machines and HVAC systems.
For robotic use I would consider BLDC or DC brushed, 1ph AC induction are generally out of the question due to poor rpm control, even Universal which are AC/DC but poor candidates unless feedback is used.
If something is needed that is larger than RC style motors, there are several industrial Servo types to pick from, both BLDC and DC brushed.
Max.

 

Hey Guys, I read the replies and they seem a bit abrupt. No one really seemed to want to help with understanding the difference between the AC and DC motors. To his credit, tcmtech did mention that there are three general types. I have not looked at the circuit tutorial being used by sidcircuit, nor do I really have a feel for the physical size of his project. I suspect that the DC motors he is using are PM. If they were wound rotor, the field strength could be varied to change torque. Also, as was posted, DC motors are very easily reversed. With the advent of IGBT controllers, the same is true for AC motors but I have no clue as to the budget for this project. The variable frequency controllers have an abundance of programming capabilities about which some of you may be interested in learning. I use them extensively in my home machine shop.

I still don't follow what you are implying or after?

Yes both DC and AC motors can be controlled with a IGBT based switching circuit but that does not make a Dc and an AC motor the same. A Dc motor can be reversed with a basic four device H-bridge but to drive an AC motor the motor has to be a multiphase and have6 or more switching devices all working in a very specific cycle and timing sequence to work.

As for VFD units, a number of us have worked with them for years and have a very intimate understanding how they work and I as one of those people I can assure you how they work to drive a three phase motor is nothing like how a DC motor is controlled.

To me saying that AC and DC motors are basically the same because they can be made to run off of just two wires is like saying a Diesel and a gasoline IC engine are basically the same because the both have similar layouts and can b e interchanged in most applications.
Just because they share basic similarities and functions does not make them the same.