i had posted in temp forum but ill repost it here and do a build thread.
I’ve always fancied having a go making my own water jet, yeah I know you can buy them and there’s even a really cheap eBay one but it defies the point of what I’m trying to achieve, a complete bolt in unit just won’t cut it for me. Now I have read threads on mayhem and other places about the attempts and regular failings of people trying to make your own jet unit by mounting a propeller inside a piece of pipe and then trying to make a stator which counteracts the swirling affect of the water at the output. I have tried this method myself before so I know first hand just how difficult they are to NOT make as such but make affective. So knowing what I’m up against I’m going to attempt a different approach fit it to a model then see what happens.
A toy battery operated boat of my sons has a jet pump inside it. I remember when I was a kid having lots of these small bath boats and also remember the transition from a standard propeller to these internal impeller style crafts. You don’t see many battery operate toy bath boats these days with a propeller no more. One of those things health and safety slammed down on. Anyway here’s the little boat:
and heres the jet unit:
with the cowling off:
The motor is mounted onto a vertical axis at the stern. My idea is to incorperate this basic pump design into a larger scale and power it by a 540 or hopefully a brushless motor. Its principle is allready used in bait boats and even some types of outboard motor:
So Its not the first time this has been done. Using a 540 27t motor ive designed and fixed a centrifugal pump on the end too see what would happen:
The impeller rotor is 34 mm in diameter and the hole unit is contructed from plastic card. A plate goes over the top to complete the impeller housing and simply bolts togeather. Ive done a test run and heres a youtube link of it working:
http://www.youtube.com/watch?v=nZ1gJeuas7M&feature=channelFrom what i can guestimate using the kitchen scales the thrust is about 2 lb's, which i think which move a fairly small boat relatively nippy. ill have to see.
The combined height of the motor and pump is a fairly lofty 3 inches. I dare say the boat it will be built into will be no more than 16 inches long. Big enough to incorperate the weight and size of the jet unit and its ancilleries but not to so large and heavy that the jet wont have any affect on it. The draw back is that at that length and this motor height the chines on the side of the boat would look rediculously tall!! I need to get the overall height of the pump down so as to bring the profile of the hull down too. unless i have the top of the motor sticking out the deck inside a box or something, which id reckon would look pants!!
I was thinking maybe a low profile 2200kv outrunner to replace the standard 540 motor. Does anyone know if this would work or would the pump overload the outrunner?