Hi Sundogz, I've attached some pics so you can see that the flex shaft is supported from the inside of the jet body behind the rubber seal right up to the back of the impeller. I don't know where you heard that the flex shaft in my setup is unsupported but as you can see, you're quite mistaken. The flex shaft in the brass tube is a much closer fit than the stock shaft in the stock unit and as my flex shaft is fully supported there is no vibration, whereas you will always get some vibration with a solid coupler and solid shaft because the motor shaft and impeller shaft will never be perfectly aligned. With my setup, at the motor end there is about 10mm of flex shaft between the inner end of the brass sleeve and the motor coupler, this 10mm length of flex cable is the only part that can 'flex' and it does so to negate any shaft misalignment thereby eliminating any vibration that would otherwise cause.I don't know why you would say that a brass bush is not suitable to support the end of a flex shaft when you haven't even seen one of my shafts let alone tried one. There is only about 5mm of flex shaft protruding from the back of the impeller and with the flex shaft being dipped in epoxy means that it's more like a steel reinforced epoxy shaft, so there is no discernible wear in the bush.Actual impeller RPM and the thrust of the jet unit are quite proportional. Power and thrust are not at all the same thing. In this scenario 'power' is what you are applying to the shaft from the motor whereas thrust is the amount of motive force generated at the jet units output nozzle.At lower RPM when you're operating well within the thrust envelope of the jet unit an extra 10% of power from the motor will give you something in the order of 7 or 8% increase in thrust. The point of diminishing returns you mentioned is the point where the power to thrust curve starts to flatten out and the extra power you apply gives you less and less added thrust and you quickly reach the point where you can double the amount of power applied and but only gain 10% additional thrust.The amount of additional thrust I get running a 4800kv on 3S motor is obviously not proportional to the increase in RPM but it is noticeable... because the entire drive train is running smoothly.In point 1 of your summary you say that a flex shaft can't reduce vibration... anyone who has used a flex shaft in any drive system will tell you that's exactly why they're used. I agree you should never try to rebore a coupler, I make mine from solid rod on a micro lathe to make sure they run true.As for your point 2, there is a great deal inherently wrong with the amount of tolerance in the stock NQD shaft and bore. It allows lateral movement of the shaft which is any mechanical system is extremely undesirable.And your point 3... hmmm.... not sure how you can say a system is no good without trying it... and your statement that the flex shaft in my system is unsupported and that a flex shaft can not reduce vibration are the only examples of misinformation I can find anywhere in this thread.Clearly we're just going to have to agree to disagree
