Motors for Robotic Arms

Depends on the accuracy requirement and use.
Is it for a serious engineering application or is it more of an eductional toy/project?
You don't say wht continent you are on.
Rotalink do some nice cheap motor gearboxes, some with feedback on the motor.
Mostly brushed DC, but that's your best bet for low cost.
Del

...and how fast do you want to move bits? If relatively slow, you can take a small motor with a gearbox, or use lead screws and small motors......servo motors are best but cost more and you need more control electronics, but accuracy is far, far better......

Cheaper is stepper motors....software is also cheaper for stepper motors and there is a lot of free stuff around.

Some use stepper motors with optical feedback as a check on the movement of the stepper motor, which is somewhere in the middle with regard to price....and software requirements...I personally have no experience with this combination though....

You need to learn to specify a lot better than you have up to now......then we can help you specifically.....

thank you for your answers...!!!

the robot actually is more educational, but i want to do it more "strong", putting 2 motors, one at the base and the other at the first arm. Primary i had a problem with that, i put 2 servos to the base and 1st arm but it is not enough strong, so i had problem with the motion.
now i am interest in accuracy and speed. (i use the basicstamp2 micro controller for my robot brain)

i send you a picture to understanding my construction and maybe it is more easy to help your opinion

http://rs450.rapidshare.com/files/194179426/P2110061.JPG

and sorry for me, i do not introdused my self before, i am from greece.

i wait your answer

What I personally would use (I am not an expert) would be small to medium steppers with either gearboxes or threaded rod, to allow for high strength movements with reasonable speeds and easy control hardware/software.....limit switches are also quite easy to organize......

I am sure that you will get some better advice from more experienced Robotics engineers shortly......

Also its easy to interface to a PC with either USB or a parallel printer port.....Software is also easy to find for such connections.....

haha, in the new year, you seem to get more modesty. not an expert, otherwise I shall jibe again at

Some use stepper motors with optical feedback as a check on the movement of the stepper motor

In the new year I find I can still visit and post a thread. wow, its pity. not banned.

you can select anyone of the 3 type of motor you listed above. the stepper motor recommanded by Andy G is also good one to conside.

in fact, dc servo motor can be either brush or brushhness. so that the 3 types would be one sort.

do you assembly 3 or 4 motor in the arm joint to lift the load?you can calculate the torque and then select the motor for your use.