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Calculating minimum torque required to move vehicle up an incline

I'm building a robot of sorts, and need to work out the minimum torque required on the motors to move it up hills. The robot will weigh 15-20kg, and will need to move up inclines of up to 35 degrees at a minimum speed of 0.5m/s, preferably at 2m/s or more though.

The robot has two motors - one powering both the left wheels, one powering the right wheels. The motor is geared to the wheels in a 2:5 ratio via a chain - 8 teeth on the motor, 20 teeth on the wheels.

How do I work out the minimum torque per motor?
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d-glitch
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The force to move 20 kg up a 35 deg ramp is

        20 * sin(35)  ==>  20 * (0.574)  ==> 11.74 kg


This force acts on the wheel radius to generate a torque.  
What is the radius??

Multiply that number by 2.5 to account for the gearing.
And divide by 2 (the number of motors).
Big wheels require lots of torque.
Little wheels require less.

Speed (for a given mass) is related to power, not torque.

What sort of motor do you think you will be using???
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Wheels will be roughly 10cm in diameter. It'll be an electrical motor driving the wheels.
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d-glitch
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Looks good, but do you know of any suitable motors that aren't steppers? I'm driving my test model with a H-bridge made from power FETs and I don't want the added task of controlling the steppers too.
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