Anyone know how to spin a blade fast enough using hand power?

[SeanAngelo]

Not nearly enough. I would say at least 4000RPM.

Just to tell you, we won't actually be putting fruits in and see if it works in order to pass the project. We just need to set a suitable RPM for it work, not too low of an RPM but not too high where you are not able to achieve it using gears. 

[byalexandr]

Just to tell you, we won't actually be putting fruits in and see if it works in order to pass the project. We just need to set a suitable RPM for it work, not too low of an RPM but not too high where you are not able to achieve it using gears. 

Oh then yeah 720 is fine.

[Bean86]

@SeanAngelo Your calculation is correct yes, glad to help. Had to do a similar project when I was at Uni some 14 years ago

[neebuilda]

(Feel free to correct my maths, never was my strong point, but the theory should be sound)

Just to tell you, we won't actually be putting fruits in and see if it works in order to pass the project. We just need to set a suitable RPM for it work, not too low of an RPM but not too high where you are not able to achieve it using gears.

If you could use the 120 tooth and 30 tooth gears you mentioned earlier then you should be able to get 960rpm out of a compound gear train. If the 120 tooth turns at 1rps then the 30 turns at 4. This gear is on the shaft as a 120, so this new 120 also turns at 4 RPS. We then take another 30 tooth gear and if driven of the 4 RPS 120 tooth, it will turn at 16 RPS.

16*60=960

This all assumes you could only turn the first wheel 1 time every second, but realistically you should be able to turn it 2-3 times a second, so that means 1920-2880rpm