motor selection help

[aruna1]

hi can someone please fill me with how to select proper motrs for your robot?

Biggest problem I have is the torque. I see different torque values in motor specifications.but i dont know which torque is suitable for my robots. is there any relationship between robot and torque? i mean some equation or something to find out how much torque i need to run my robot at specific speed?
thank you

[VegaObscura]

Torque helps your robot to accelerate, and to fight outside forces (most commonly gravity when going uphill, and friction); it does not affect your robots top speed other than fighting these two factors.  You cannot calculate the top speed your bot will have unless you know the amount of friction.  I believe I recall admin saying that a good rule of thumb is to get motors that have enough torque to lift your robot vertically.  Just take the weight of your robot, and multiply by the radius of your wheels to get the required torque.  If you measure in kilograms and centimeters, this will give you the kg-cm torque of your robot.  The same goes for oz-in.

A helpful tool I use for comparing motors that are measured in different units can be found here.

[waltr]

Motor and torque calculations are tricky. Do read the SoR tutorials on statics and dynamics then use the RMF calculator.

Be careful with the specs many vendors list for motors. Most do not have the full motor specs that make choosing a motor difficult. They usually do list the 'stall torque' which can be used. To understand more about motor specs and calculation see the articles on "How to select a DC Motor" and "Motor Calculations" here:
http://www.micromo.com/n42044/n.html