# Homework Help: Torque calculation, torque calculation over some axis

1. Jul 22, 2008

### papermate

1. The problem statement, all variables and given/known data

Actually this is not a homework or course question, but I think it’s quite simple. So maybe it’s suited to post it here.

I’m designing a machine that rotates a big object round its own axis. The object has a diameter of 2,7 meter and needs a torque of a least 105Nm to meet the demand of the angular acceleration. The big object is a cylinder. This cylinder is supported by two axis with a diameter of 0,3 meter. The big cylinder is driven by those to axis by means of friction.

I’ve calculated the force that is necessary on the outside of the big cylinder to give it the required torque. This total force is according me equal to 78N. (105Nm/1,35m=78N)

The total force that the two axis supply to the big cylinder should be at least these 78N. So each axis should supply 78N/2axis=39N to the big cylinder.

The torque that the axis should have; T= F*r = 39N * 0,3m = 11.7 Nm.

These two axis are driven by one electric engine. The outgoing axis of the electric engine goes to a reducer with an unknown ratio. This axis first goes to a 3-way gearbox with a ratio of 1:1. One outgoing axis is directly fixed on an axis that drives the cylinder. The other axis of the 3 way gearbox goes into a 2-way gearbox with ratio 1:1. The outgoing axis of the 2 way gearbox drives the other axis.

2. Relevant equations

My “inquiry form”;

- Is the calculation of the torques correct? I’m not sure but I think they are ok.
- The torque that is marked with pink, in the drawing below, is this correct? Or needs this axis a torque of 23,4Nm (23,4 = Torque axis one + Torque axis two = 11,7 + 11,7)
- If I can be ‘sure’ that my calculations are right I can go on looking for an engine with reducer. Has anyone some advice where to pay extra attention on by choosing the right one?

If you have some notes, remarks, solutions, or questions, please react!

All assistant is more than welcome ;)

3. The attempt at a solution

Please check the part above and the drawing
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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2. Jul 23, 2008

### nvn

papermate: (1) Your calculation of torque T2 = 11,7 N*m is correct. (2) Torque T marked in pink at the bottom of your diagram, between the reducer box and the three-way gearbox, needs to be T = 23,4 N*m, not 11,7. (3) I don't have comments regarding the engine.

3. Jul 23, 2008

### papermate

nvn: thank you for your post.

I see and understand my mistake...

Thank you