Determining the number of gear teeth?

[Isaac_DB19]

I have a system that consists of a shaft and two selected gears.

I want the shaft to be rotating at 250 RPM and to deliver an input power to the system of 850W.
The input torque at the shaft is 71Nm.

How can i use this information to determine how large my driving and driven gears will be, as well as determining the number of teeth that i would use on each gear.

 

[Merlin3189]

[I think you need to provide more information. A diagram or maybe a flowchart showing the inputs and outputs marking known requirements with their values and any known inputs.]

Edit: Oops! Misread your Q.
You want 850W at 250 RPM and have 71 Nm available.
Your output is about 33 Nm, so your gear ratio can be up to 71:33 depending on losses. Maybe 2:1 would be enough?
Your input shaft would therefore rotate at 125 RPM with atorque of 66 Nm + losses

 

[CWatters]

I want the shaft to be rotating at 250 RPM and to deliver an input power to the system of 850W. The input torque at the shaft is 71Nm.

That's not at all clear and looks inconsistent..

You say you "want the shaft to be rotating at 250 RPM" and the torque "at the shaft is 71Nm" ? That means you need a load on the shaft of 1860W.

250rpm = 26.2 Rads/S
Power = 26.2 * 71 = 1860W

 

[Merlin3189]

Edit: sorry my spaces have not worked. It was tabulated.
I don't know how to delete the whole post, so I've deleted the mess! And I don't have time now to re post in another form.