Phil Keller wrote:
> -How do I decide what size motor to use? (Assuming a 50 lb car and a 50%
> slope)

Actually the slope has nothing to do with it.  The relevant factors are the
weight of the car, the total height it must be lifted, and how fast it must
get there.  Since you only supplied 1 of the three, I'll make up numbers for
the other two as an example.  The car weighs 50 pounds, which is about 23Kg.
Let's say it needs to be raised up 5 meters in 10 seconds.

The upward force on the car needs to be 23Kg x 9.8N/Kg = 225N.  Times 5
meters lift is 1127 Joules.  Divided by 10 seconds is 113 Watts = .15
horsepower.  Assuming 80% motor efficiency and another 50% effeciency in the
remaining mechanical system, .38 horsepower is needed.  So a 1/2 horsepower
motor can do this just fine.  A 1/3 HP motor is close and maybe OK if the
mechanical efficiency is not as bad as 50% or you're willing to wait a
little longer.  A 1/4 HP motor is enough if you're willing to wait 20
seconds instead of 10.  Of course this all assumes proper gearing is in
place to get the specified lift time at the optimal speed of the motor.


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