Donovan Parks wrote:
>I have a 1 HP motor (= 0.75kW = 553 foot lbs/sec) and need to know how much
>force it can exert.  I am looking for a 'best case' estimate - that is,
>what
>is the most force it can exert if everything were ideal.  What I am
>thinking, is that if I have a load cell fixed to a wall then what will it
>read.

Power is the *rate* at which the motor delivers energy: 750W means
the motor can do 750 joules of work every second. If you like
analogies, power is to energy as speed is to position; it is the
rate at which it changes. So, if we know your motor can deliver
750W of mechanical power, we know the rate at which it can do
work. How much force is this? Unfortunately, there is not a
straightforward answer to this question: it depends on the system
your motor is doing work on. If, for example, you deliver work
to a frictionless test particle of mass m, initially at rest,
then the instantaneous force at time t is sqrt(Pm/2t), where P
is the power of the motor (750W in your case), ignoring any
nonconservative losses (friction, air resistance, mechanical
inefficiency, etc.). As for the force the motor can exert on a
wall, if you think about it for a second, you'll see it depends on
the setup. For example, if you attach a long swing-arm to the
shaft of the motor, then clearly it will deliver more force at the
end of the arm than if you use a short one.

In real life, motors are usually rated by giving the power delivered
at some particular rotation speed. You can use this number to
compute the torque the motor can produce at the given rotation
speed. Is that what you want? If so, the formula is
torque = P/w, where w (usually written as the Greek lower-case
omega) is the rotational velocity. If you have P in watts and
w in radians/second, then the torque will come out in Newton-meters
(Nm).

I'm sorry to give such a long-winded, unsatisfying answer, but
unfortunately your question is not well-posed.

Michael V

Thank you for reading my little posting.


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