I can deliver 6700ft/lb to a 600mmdia drive wheel. I would like to gear this wheel up from 6rpm to 1000rpm. Before I build this machine what Hp/Kw can be expected at the 1000rpm shaft on a direct drive?. Or is there a formula for loss in gearing up?

This might help you, although I'm not sure if it takes in account any friction losses etc. that might occur - but it should give you a good ballpark figure. https://x-engineer.org/graduate-engineering/mechatronics/mechanisms/how-to-calculate-a-gear-ratio/

direct drive efficiency 98% But you will definitely use the reduction gear, so you need to multiply this by the efficiency of your gearbox and the efficiency of the electric motor, then as a result you will receive a correction factor for the all of the mechanism. You will also have wheel bearing losses, but these are very small values that can be neglected.

Thanks John12, that site gave me the information I needed, basically if I gear it up at 4:1 It will reduce the input to a quarter each time, keep going and there would be nothing left, thanks for your interest GoodCat.

So if you if you go 6x4= 24... x4 = 96... x4 = 386... x4 = 1536rpm. So you have to gear up by 4:1 four times, so I guess your power would be reduced by the same? So that's... 26ft/lb? I'm not really sure what that is in Metric, can you do anything useful with that? You might be able to gear up with a greater ratio though, then you reduce the steps? Also, you might find this video interesting, just as a related thing :

Thanks John12, I didn't know that stuff existed, you are right about the big loss at the end, and that has put that my gravity motor in the shelf for a while