Determine torque required to move load

[lsvaladez]

Trying to figure out how much torque an electric motor would need to move a load of 100lbs on a flat surface. The device would use two electric motors attached to a 8 inch diameter wheel (each motor is attached to a 8 inch wheel).

 

[Baluncore]

Welcome to PF.

Only the energy needed to accelerate the mass must come from the motor.
What is the maximum speed required?
To enable us to calculate the wheel torque required, we need to know how far the vehicle will travel, and how much time does it have to get there?

A cheaper, low-torque, high-RPM motor could be used if the motor has a gearbox, that would slow the wheel speed and increase the torque available to drive the wheel.

 

[erobz]

Trying to figure out how much torque an electric motor would need to move a load of 100lbs on a flat surface. The device would use two electric motors attached to a 8 inch diameter wheel (each motor is attached to a 8 inch wheel).

Are you using the wheels to drive a conveyor belt carrying a 100 lbf load, or something else, maybe this is a buggy carrying 100 lbf? Either way, acceleration and various forms of friction should be considered to determine the minimum output.

 

[jrmichler]

Is this homework? If so, we can move it.

A diagram of what you are trying to do would be very helpful because your description is unclear. If you have no information on rolling friction, you need to provide the necessary information so that we can help you estimate the rolling friction. You need to describe the speed, distance, move time, and acceleration in order to calculate acceleration torque. You need to know the maximum speed in order to properly specify the motor and reducer.

 

[lsvaladez]

Welcome to PF.

Only the energy needed to accelerate the mass must come from the motor.
What is the maximum speed required?
To enable us to calculate the wheel torque required, we need to know how far the vehicle will travel, and how much time does it have to get there?

A cheaper, low-torque, high-RPM motor could be used if the motor has a gearbox, that would slow the wheel speed and increase the torque available to drive the wheel.

Hello,

Let’s say the device needs a max velocity of 5mph, and we want it to travel around 30ft in 10 seconds.

 

[Baluncore]

I assume you must stop when you get there, and have no brakes, so you will use the motor to brake. That makes the problem symmetrical.

Accelerate for 5 seconds, then decelerate for 5 seconds, to get there in 10 sec. 15 feet in the first 5 seconds, then 15 feet in the last 5 sec.
We know; s = ½ * a * t² ; so can calculate the acceleration.
a = 2 * s / t²
a = 2 * 15 / 5²
a = 30 / 25 = 1.20 ft⋅s^-2

The speed limit is 5 mph = 7.333 ft/sec.
What will the velocity be after 5 seconds.
v = 1.2 * 5 = 6 ft/sec.
So it is below the speed limit.

I think I would use SI units for the next bit.

 

[Baluncore]

SI units.
Time, t = 5.000 sec
Dist, d = 15' * 0.3048 = 4.572 m
Accel, a = 2 * d / t^2 = 0.3658 m/s/s
Vmax, v = a * t = 0.3658 * 5 = 1.8288 m/s
Mass, m = 100 lb * 0.4536 = 45.36 kg
Force, f = m * a = 16.591 N, (newtons)
Radius, r = 4" = 0.1016 m
Torque = f * r = 1.6856 N.m
Energy = 0.5 * m * v^2 = 75.8535 J, (joules)