Am I doing my Servo Math Correctly?

[noahc]

Using this servo just as an example http://www.rcplanet.com/ProductDetails.asp?ProductCode=FUTS3104&Show=TechSpecs

Speed: 0.21 sec/60° @ 4.8V
Torque: 128 oz-in @ 4.8V (9.2 kg-cm @ 4.8V)

So lets say we have 5" wheels on these and we take 128/2.5  which equals 51.2 oz of torque per wheel.  If you had two of these they'd be at say 100 oz of torque so you could haul roughly 6lbs.

How do I calculate speed from there?  With this: Speed: 0.21 sec/60° @ 4.8V ?

[Razor Concepts]

Unfortunately those values are the maximum values, so the servo can just barely move 128oz-in. With the speed, it is .21 seconds for 60 degrees when there is no load on it. If you put the maximum load on the servo, it will barely move.

[noahc]

What is the best way to move 7-10lbs?  Large servos?

[sonictj]

What is the best way to move 7-10lbs?  Large servos?

dc gear motors

[noahc]

What is the most weight I can do realistically with servos? 3lbs or so?

[SmAsH]

wells, it depends on the servo now doesn't it?
but with hobby servos it would be around that mark.
but a servo is just a dc motor with gears and a driver circuit...
sonictj is right, dc motors geared down will give heavens of power.

[Metal Slug 2]

thats completely dependant on which servo you buy.  For example, the HS-311 servo can only support up to 49 oz/in (4.5 kg/cm) operating at 6v.  And then there are other servo's like this one: http://www.tonegawaseiko.co.jp/pro/e_pro02.html   which can supports up to 380kg/cm!!