Sum of torque

[EOW]

Now, I drawn forces with one support like I spoke before (the motor is on the Pulley1, it's an example), look at the support it works at 2FRwt. It's possible to compare these 2 cases, one with one support and other with 2 supports. Pulleys1 is at 2w in 2 cases, Pulleys2 is at 4w in 2 cases, support is at w in 2 cases.

In the case with one support, the sum of energy is:

-3FRwt for the motor on the Pulley1
-3FRwt for the support, the motor is on the support is apply a counter torque
+2FRwt for the support, torque due to pulleys
+4FRwt for the Pulley2

The sum is at 0

In the case with 2 supports, the sum of energy is:

-3FRwt for the motor on the Pulley1
-3FRwt for the support, the motor is on the support is apply a counter torque
+4FRwt for the Pulley2

The sum is at -2FRwt

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If the motor is at the Pulley2, the motor need to give -3FRwt, true ?
The Support2 receives -FRwt because the motor apply a torque, ok ?
The Pulley1 turns at 2w and there is a radius 3R, so the energy recover is 6FRwt

[dieter]

I was asking about friction because, as fas as I see, when both pulleys can rotate freely, then the support won't receive any torque or force at all. (?)


Please excuse me, I may seem really stupid here.


BR

[EOW]

You don't see the torque with 2R ? F1 and F2 give a torque 2FR, no ? this is not a torque from friction in the axis. Forces come from the belt and are reported to the axis of each pulley.

And you're not seem stupid, it's not easy to understand ideas from others, and you, you try, it's friendly

[dieter]

I really don't see it, no matter how hard I try..,   


Maybe I should just build it. Maybe as a side project.


BR

[EOW]

Hi Dieter,

With one support: F1 and F2 in the image, no ? The big pulley force the belt to turn clockwise, and drive the small pulley, there is the force Fb on the belt, this force is put on the axis : F2. The belt receive the force Fa, and this force is reported to the axis of the big pulley: F1. F1 and F2 gives a torque with the value 2FR (with |F| = |F1| = |F2|). I think with one support it's logical to have 2FRwt on the support for have the sum of energy at 0, but with 2 supports I don't find the torque.

With 2 supports, I tested today with a simulation for look at the angular velocities and all seems correct.

If you have gears and pulleys, you can test it (I order a package of gears for test).