That was my thoughts on the number of vanes as well, since the impeller is so small. I wonder if more "curve" on the vanes helps or hinders. Maybe I should just make the vanes a tad taller to start with. It would be super easy at that point to mill down the impeller vanes and housing to reduce assembled height and capacity if it over performed. At least then I wouldn't have to remake anything.
Up to a point, higher is better than greater diameter.As one increases the diameter, the speed of the tips of the vanes goes up, and as the blade tip speed goes up, you get closer to _cavitation_, where the low pressure generated behind the blades dips below the point of vaporization and makes bubbles in the water. This is bad for a number of reasons (more noise, erodes the blades, etc), but most important for our purposes is: the pump will pump less water. More cavitation, less water moved. So making the impeller blades taller increases the swept volume (more water moved) without coming closer to cavitation. I said 'up to a point' because if you make the blades too tall, it will start to cause pump priming issues. I have not had trouble going up to 1/2", and the POW-pump had 5/8" tall blades, although POW had no trouble getting plenty of water in the hull to drive flow if you know what I mean... An Orfey would NOT want that 'advantage'. *The point where cavitation starts reducing pump output varies by impeller & volute design, and even the throttle curve on your ESC. What I do is spend a little quality time (you DO love quality time, don't you?) by the pool with my transmitter, pump, ESC, and battery. Basically, you ramp up the speed that the pump goes to [(using the adjustable endpoint on the pump channel (I use 'Gear')] and watch the stream get higher/further. At some point, it should start to get weaker. If it doesn't, that's fine, you aren't cavitating. If it does, lower the speed until the stream is at its strongest. Your pump is now in its sweet spot. TiP: Using a servo tester to get in the ballpark is much faster than using the endpoint adjust on the transmitter! This concludes me running off at the mouth.
Run off at the mouth anytime you like, I appreciate and even encourage it. It is usually very educational when you do. You are absolutely right about not wanting that advantage in a tiny boat. I'm still afraid it will sink itself from it's own weight as soon as I attempt some quality time with it by the pool this summer.
I will be posting some pics soon of the pump I'm making for Othar. It is a hair over 1/2" in diameter, and about 1.5" tall. Brushless, even
The impeller blades are generally curved backwards in full size pumps because this decreases the tangential velocity of the water. Full size pumps have to convert all that velocity to pressure and the conversion process is very inefficient. So the less velocity you start with, the less you have to convert. Pumps will work with straight blades or forward swept blades, they will just resulting in the water speed increasing and probably more energy for any given pumping rate. I like the first impeller on the second row. The middle should be open and the outside edges curve back slightly. There is a number that is used to design impellers, the name of which I forget right now, which is generally kept within a certain range. When running the numbers for our sized pumps, the lowest number of vanes I could use and still get a good number was 5. Does the number apply at our scale? I don't know, but I would not use a two blade pump.
Actually, in the study I read on very-high-speed centrifugal pumps, the rotor that they got the best results with resembled the rotor 2nd from left on the top row... The blades looked like right triangles, tallest point obviously towards the middle, with the middle open. Someday I will try one. I still think more than 2 blades is of questionable value in our scale, but then the study's pump was like 10" dia or something in that range.
Humm... I had been playing around with this shape today... swept backwards... just to help me visualize. My thought was that the shape of the vanes, coupled with centrifical force would generate higher pressure at the periphery (assuming clockwise rotation of impeller as shown in top drawing). Maybe I'm overthinking this?? Almost anything with vanes or paddles or whatever will move water, just not as well as it could under optimal design conditions. I extruded the 3D view with the solid disc on the wrong side of the vanes, my intention was for the vanes to be oriented as shown with the disc on top, and rotating clockwise. I'll check and see if I made the same oops on the other one. So it seems you guys are liking the vanes disconnected from the center hub better than the ones that connect to it as on this one?? Seems to make sense if the intake is located at the center of the impeller.
Very interested to see your pump, I'm still deciding on which brushless motor, so I can't wait to see what you have come up with.
After I built this and held it in my hand it struck me that it looked much funnier in the real world vs in cyberworld on a CAD screen. I thought it might be interesting to play a guessing game and see what kind of funny, intriging, thoughtful, insightful, and downright scary answers I get . Sooooo............Try to identify the function/ purpose of this part or what it might be part of the assembly of, or just for fun, tell what it reminds you of. It is a major part in an assembly that is made up of only a few pieces. Let's get the obvious out of the way right off the bat........ It is NOT my rendition of one of the creatures from that fun and popular vintage Arcade/ Atari 2600 game Space Invaders(the younger generation is probably thinkin.... whaaaaa?????)
Neither of the above, but you guys are giving me some good ideas! I will try to post some more pictures of the other parts as soon as I get a chance, including the latest rendition of the part I already posted. I think I'll call him Invader 2.0
I'm all excited because I just got my pump assembled and ready to test . But then..... when I started tesing it...... it pumped the ever living crap out of some water!...... until the motor got wet and stopped running. Anyone have any ideas why? Its a small c10 brushless from Hobby King. It runs awesome when it's not submerged or soaked. If I submerge it, it starts "sputtering" and jerks around. When I take it out of the water and shake it out it runs fine again... Inability to get wet isn't the most desired attribute in a pump motor . I can post a pic of the current pump later.
That doesn't sound right - I have two brushless outrunners on pumps and have not had a problem. The first possibliltiy that comes to mind is that the water is increasing the amperage draw and engaging the over-amp cutout. Assuming you have at least a 10 amp controller, this should not be a problem. What it sounds like is a loose or possibly uncovered wire that is conducting when wet, causing problems with the back EMF measurement and confusing the controller.
