gears problem

[Roicha]

Hello everyone, i got a question about gears.
i have 2 inputs and 1 output.
the radial speed for input number 1 is W1.
the radial speed for input number 2 is W2.
I the create a gearbox, that the outputs radial speed will be 8W1-4W2.
also, the output can act as an input,
please help me, if you can post a sktech as answer it will be great!
thanks!

 

[zeusfaber]

What's the question you're asking?

We won't design your gearbox/do your homework for you - but if you've got a specific question about it, we can probably help.

A.

 

[Roicha]

I am asking how to make the output radial speed 8W1-4w2.
If i use a differential i can combine the radials speeds.
i have sktech it untill i got the a gear with radial speed of 8W1 and a gear with radial speed of 4W2, but if i use a differential the output radial speed of the differental will be (8W1+4W2)/2. which isn't helpfull.
How do I get to 8W1-4W2?

 

[LionelHutz]

By differential, you mean the inputs go into the what are typically the output shafts on a car differential?

Think about it this way.

Hold the W2 input shaft locked. When the W1 input shaft turns 1 revolution, the carrier turns 1/2 revolution. So, add a gear to make the output 8 revolutions.

Now hold the W1 input shaft locked with the new gear setup. When you turn the W2 shaft 1 revolution you now get 8 revolutions on the output. So, add a gear set at the input of the differential to get 4 revolutions instead. A gear set also reverses the shaft direction.

 

[zeusfaber]

It feels to me like you've already done the difficult bits.

What's the actual difference between +4W2 and -4W2? Can you think of a way of converting one to the other?

Once you've found a way to get (8W1-4W2)/2, think of two different ways to get what you actually want instead. Which of these is better?

A.