Force required to move a 6 wheel cart

[iamatallone]

I am currently working on an idea of mine and have an issue. I have a car with 6 wheels on it with an estimated weight of 400 Lbs. It will be using 8" pneumatic tires and would like to calculate the how much toque in need in the motor to drive it. I plan on it going no faster than about 1 Foot per Sec. and it will be on a snow covered surface. Any help would be great because i haven't the faintest idea on what i need to calculate it and what research i have done always seems to be inconclusive.

 

[Unrest]

Basic idea would be to find the torques needed to overcome:
1) rolling resistance
2) hill climbing
3) acceleration
Possibly in some worst-case combination.1) Trickiest, check it out on Wikipedia, there are formulas, but you probably need to find data on for your type of snowy situation.
2) Free body diagram, straightforward
3) F=ma

 

[jack action]

By putting the following values in http://hpwizard.com/car-performance.html" :

(transmission) Engine power: 0.25 hp
vehicle mass: 400 lbm
drive wheels: AWD (The site assumes it is a two-axle vehicle, but if your vehicle is also AWD, it should give similar performance)
friction coeff.: 0.25 (typical value for hard-packed snow)

You get enough power to get maximum traction until 1 km/h ( $$\approx$$ 1 ft/s). See the first graph (MAXIMUM ACCELERATION & SPEED; solid line).

The rpm of the 8" tires at 1 ft/s is roughly 30 RPM ( $$\approx$$ 1 ft/s / (8/2) in X 12 in/ft X 30/pi rpm/rad)

Hence the torque for ALL wheels is about 44 lb.ft ( $$\approx$$ 5252 X 0.25 hp / 30 rpm)

That would be my first estimate.