hi,
I am going to build a tracked vehicle and I am wondering wich motors I should use (I am going to put four) between theese:
-GHM-13
-GHM-09
-GHM-04
what is the difference? and what does the stall torque meen? is higher better? 
they are all basically the same, run at 12 volts, its just that they have different stall torques and rpms, which you asked about, stall torque is how much a motor can move…i think until the motor stops correct me if im wrong guys
well if you want your rover to be able to move a lot of weight around then you better off with a higher stall torque, but as you will observe the higher the the stall torque, the lower the rpms so the slower it goes, overall it all depends on wat your application you using your rover for
if you want it faster then you get one with higher rpms, but by sacraficing torque, and if you want a more powerful bot, you get one with higher stall torque, but by sacraficing speed
chunga got it right. The stall Torgues is about of resistance (weight , drag) that the wheeles / tracks have before it will stop.
ok, what i dont understand is that the GHM-13 goes faster than the others and has the highest stall troque of them (16.7 kg-cm).
Sam,
Inside the motor there are windings. The armature, along with the density of its windings, arrangement of the windings, the actual thickness of the wire in the windings and the material of the windings all play a role in the amount of current that can be generated within the windings. Additionally there are other considerations within the motor itself that play of role in determining the speed and power of the motor (i.e. friction of the motor and load).
Voltage = current * resistance
One simple example - for the same voltage provided to 2 different motors the higher the resistance of the windings the lower the available current (thus less torque). If you were to measure the resistance of the windings of the motors most likelihood they are different. Additionally, if you’re able to measure the frictional resistance of the axle of each of these motors, you would find this also to be different. And remember, a slight bit of friction meaured at close to static speed gets multiplied as the speed increases (that little hole in the wing of the space shuttle would not have been much of problem if the shuttle was going 100 mph instead of 18000 mph - in fact, the friction was great enough at 18000 mph to cause metals to molten)
This is an oversimplification but one in which I think you will understand.
PSSSST - go with the GHM-13 (or whichever one has the most torque) because tank tracks generate a higher friction load on the motors than a wheel.
Hope this helped
Chris
thanks o evryone who replied 
i needed the info[/code]
o yea, sry about the mis information on the motors, the ghm-04 is actually 12 volts probably explaning the differnces in rpm and satll toqrue to the ghm-13 
yeah its ok
Um… the GHM-04 is actually a 7.2vdc motor.
The reason the RPM’s are different between one motor and another is because they have different windings. The GHM-01 and GHM-12 are both 12vdc and 30:1 reduction, but the motors are completely different. The windings have different wire guage and different number of turns on the armature.
, thats wat i meant to say, 7.2 for the ghm 04, wow, im on a role 