The M-Jet 35 development has been finished! Buy the files here and make your boat fly: www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-35-3d-printable-jet-pump-for-rc-boats
Today I added a single blade impeller mod to the M-Jet 30 files, I will probably add it to the M-Jet Sprint mods as well. It is not tested for these pumps so that just needs to be kept in mind, but definitely worth trying it out
Finally bought the M-Jet 30 STL and noticed that you have included the single blade impellers with the purchase. Which was a neat detail, I look forward to seeing if it's gonna be better for my application.
Okay, good luck! I have not tested single blades on M-Jet 30 but it is expected that it should give maybe a little bit less thrust, but much lower amp draw, creating better efficiency and runtime.
@@mjetdevelopment How much volume in a minute do you reckon the 30 pumps at full chat? I have got a priming pump, but it peaks at 1l/min and I am afraid that won't be enough to supply the jet with water consistently. A litre a minute is about on par with the SuperSoaker CPS 2000, a PRODUCTION water gun. Which is the most powerful production water gun in history, but still. I could maybe stagger two pumps in parallel to increase flow to 2 litres a minute.
@@ProtonFilms_Mark The M-Jet 30 pumps over 3 liters per second... 180 liters per minute lol. For a water gun this is probably too much right? For a water gun, you need less flow rate but higher pressure converted to higher velocity
You could dramatically reduce the exit nozzle, or add a pipe with small diameter, to get much lower flow rate and higher velocity. But then plan your setup for lower RPM
What if you reduce the number of vanes on the exit nozzle? Your nozzle design creates an amazing laminar flow but my guess is that at the same time there's a significant back pressure that's lowering the system efficiency. thoughts?
Thanks for the idea, I am still testing different combinations and the main thing is, the leaving jet stream needs to be straight so I cannot reduce the vane length too much anyway. But its on the list to test:)
Please forgive the ignorant question (I'm not an R/C boat person), but why are you measuring the thrust with the nozzle out of the water? When the drive is mounted in your boat, isn't it going to be submerged?
Hi, not an ignorat question at all:) The reason is, at first the nozzle is submerged when the boat is sitting still, but as soon as the boat gets some speed, it "gets on plane" and mostly comes out of the water. Only a small area is fully submerged. This is the state in which the boat will run most of the time.
@@mjetdevelopment -- ah, thanks for the explanation! I don't know squat about R/C boats, but my intuition was that in full-sized jet boats, the output would be below the waterline, since water would provide a more suitable medium for the jet to "push" against, than just air. However, after reading the Wiki on jet boats, I see that I was mistaken, and apparently so was everyone else until William Hamilton thought to raise the output above the waterline, in the '50s. Cool -- I learned something new today! Thanks again.
@@roberthaines4221 I understand your idea behind it, however the jet does not work by pushing the water "aganist a medium". It works like a gun shooting a bullet, and producing a recoil force on your shoulder - the water is like the bullet. The recoil, or here the thrust force is generated because the pump is accelerating the water backwards. Actually, raising the nozzle above waterline is benefitial for efficiency, because it is easier to shoot the water into air than into dense water, where it would generate a lot of turbulence.
@@mjetdevelopment -- yeah, I get the distinction; it's Newton's Third Law all the way. One thing I find surprising is that in every video I've seen of RC jetboats, the intakes are simply flat along the bottom of the hull. I'm surprised that at speed (especially in any kind of a chop) they can manage to draw enough water in to keep the impeller(s) constantly supplied, and prevent a loss of efficiency due to the introduction of air. I would've expected to see some kind of an adjustable scoop / spoiler / trim tab that at-speed could direct more water in (without adding drag or disturbing the laminar flow). Perhaps this is already being done, and I just haven't encountered it.
@@roberthaines4221 Yes, this effect is hard to understand for me as well. The curve upwards into the intake is quite steep and I would also expect the water to separate from the surface and create vacuum or turbulence. But I dont have any way to properly find out what is happening there, because cavitation is important in this case and that is hard for me to capture in cfd. I have not tried a scoop yet but I dont want to put possibly vulnerable things under the surface of the hull. Anyway, maybe one interesting thing is - the intake in my boats and most similar boats is so big, that the boat is travelling forward much faster, than the water into the intake. This means, from the water perspective, the water has to accelerate in the direction of boat travel to pass through the intake - the opposite way from the case where the boat sits still, if that makes sense.
Hi, very nice and interesting work ! Und straight forward design development. I like to see such work. But one question: How do you calculate the jet efficiency ? With measuring the power consumption of the motor and the produced thrust it is not possible. I assume that you are somehow estimating jet velocity or flow rate, correct ? And if, how ? Thanks for your answer in advance.
Hi, great question. There is no estimation involved. You are correct that I measure thrust and power consumption. But the one more thing which I know is nozzle diameter. I can modify the thrust equation (thrust = mass flow*exit velocity) to a different form (thurst = water density*exit nozzle area*exit velocity squared). From this I can calculate the exit velocity (it is the only unknown). Then I can easily calculate many other parameters including mass flow. Then, the output power is equal to kinetic energy the water receives per one second. And at the end I get efficiency. Mainly, there are only two small errors involved: 1) this method estimates the water velocity is the same at every point of the nozzle which is not true, 2) I estimate efficiency of the brushless motor itself based on my previous measurements on a water dyno (in my older video) with similar electronics and load.
Ah, yes of course. That’s a simple and possible way based on an ideal world. But for me it is a kind of estimation because it is not measured somehow. Why I ask ? I did some extensive measurements with my jet sprint boat from KMB with the corresponding 28mm jet unit. I measured power consumption, rpm, static thrust and boat speed at different throttle positions for different impeller and nozzle configurations. Now I updated my Excel sheet with your prediction of jet velocity and jet efficiency. With this I get efficiency value from 40-45% for the jet unit. Interesting to see is, that the calculated jet velocity for low throttle values is higher than the reached boat speed (as it should be), but for full throttle it is the same or even lower with the smallest nozzle I have test. This shows that this way of prediction of jet velocity/ efficiency is somehow insufficient, at least for my case. Therefore, it would be interesting, if you could also measure the speed of your new boat with the new jet unit for a comparison of jet exit velocity and boat speed.
@@SharkV60 Yes, the boat speed can exceed the exit velocity. That is because we are calculating the exit velocity for a stationary jet unit with a static test. As the boat goes forward, the water is forced into the intake faster, helping the pump to push more water. Therefore flow rate increases (by the way rpm should also increase and amps should decrease) and exit velocity increases. So the boat is not going faster than the exit velocity, it is just that the exit velocity is higher when boat is running.
@@SharkV60 I am very surprised by the 40-45% efficiency you measured on the kmb. I also did my old 28mm kmb test previously, not very "properly" that time, but it definitely was not over 30%. May I ask what your resulting output power of the KMB was? Just curious. You can see what I measured for my unit in my "M-Jet 35 Performance" video.
@@mjetdevelopment Jet and normal propeller propulsion are completely different. Typical for jet propulsion is, that the power consumption is more or less independent from the boat speed. Water entering the waterjet inlet is accelerated to ship speed, consequently, exerts a momentum drag on the boat. I can only advise you to do some measurements on the jet in a running boat. By the way, this effect also applies to EDF units for model airplanes.
Interesting mod! I printed your M-Jet 60 and it came out really well. I prefer captive nuts to those brass inserts, but otherwise it was beautifully designed. I notice that both stages have the same impeller pitch and same area, so the 2nd stage just unloads the first a bit rather than creating more pressure or velocity. Could the 2nd stage be pitched a bit higher and have the "squeeze" start early (via hub expand, not outer tube), or is it always better to have constant velocity in the impeller parts and do all the squeeze at the end? I'm also considering designing a single stage version with a cupped impeller and expanding hub. The final stator tunnels (not fins in reducing tube) will stay at tunnel width but with total volume = existing inlet-nozzle ratio. Seems less straightening is required that way, and it allows your steering gate idea to be done easily. Thanks for your work!
Yes, the M-Jet 60 has same pitch on both impellers. That does not mean though, that the second impeller does not add pressure - both impellers add pressure, even if their pitch is the same. This happens, because the first stage stator vanes should straighten the water before the second impeller. Therefore ideally the second impeller operates in the same way as the first impeller and both add the same pressure. During development of the different pumps, I tested different ideas. The M-Jet 60 got a straight hub, however with my latest experience I think that increasing hub diameter and increasing pitch work better - and this is what the M-Jet 35 uses. The idea with "less straightening required" is one of the reasons why I chose the 4-path nozzle for M-Jet 35. As you described it, I think it will work for you and you can use similar steering indeed, good luck!
@@mjetdevelopment Thanks! I'm guessing that the optimum design would have a mass flow based on the funnel shaped Betz curve, but there are always complications like skin friction and turbulence and gaps between impellor and stator. And there's always scale. It makes sense to me to utilise rather than suffer centrifugal effects, so your M-Jet 35 looks like a great direction.
@@OzAndyify I did not know about Betz curve before. I did a quick search, very interesting. I am not sure if this is applicable to such water pump though.
@@mjetdevelopment You are probably right because the jet is in a different medium (air) to the inlet and is fully constrained, but I think a gradual increase in velocity (area reduction) following a similar curve might be better than constant area & velocity in compressor part, then all the squeeze at once after the final stators. It's all one linked flow with water (not as compressible as air), so I may be way off! Your M-Jet35 work seems positive though, so it's worth playing. I love 3D design because we can make things that a metalworker would struggle with.
@@OzAndyify Yes, 3D printing gives great freedom of shape. The M-Jet 35´s impeller hub has an increasing diameter smooth curve, and this is what worked the best during excessive experimental testing, so I guess there might be some connection to the phenomenon you are referring to.
Hey I tried the single prop mod in the M-Jet Spring 3d mods files and actually had worse performance than my standard prop. I was a bit surprised after seeing how much success you had in this video! Have you had any other feedback or updates?
Hi, thank you for your feedback, you are the first who has tested it! The results can naturally differ depending on the specific pump. It is totally possible that this setup works worse for the M-Jet Sprint. Regarding the new pump you can see in this video, I have already objectively verified the results so many times that this cannot be any coincidence, but I am still only testing the single blade pump static and the results can (unfortunately) change when I put it into a boat. Stepan
@@mjetdevelopment Worked great for me, interested to hear your setup. Motor , battery etc. I am using 4s battery, smallish 2845 brushless motor at 1950kv. Everything stays cool, even when diving like a submarine! LOL .
So far, I am not planning sharing the files for this new pump because it is a different kind of a build, not designed to be easily assembled by everyone. Because I am focusing on making progress right now, I am also not planning to make any big changes to the M-Jet 30. But if you wanted to build the M-Jet 30 and try a single blade impeller design, I can create it and add it to the M-Jet 30 files.
@@mjetdevelopment somehow the math used creates the prop. I saw a few on the cg trader. I don't know how or what programs people are even using to make these 3d printed drawings?
Thats difficult. Given the size of my channel, the amount of people and possibly my sales, creating a patent would probably cost more than the profit it could bring. Also, the single blade design is truly only applicable to pumps of this small scale.
That is great can’t believe one blade is better I have printed a much bigger jet unit I should be ready to test it out soon. Check it out on my channel if you like, I like your test rig too I will do something similar
Hey thanks, you are welcome:) I saw your jetboat video before. Yes, I found the test rig to be very practical way to objectively evaluate the performance, especially if you do some calculations from it.
The M-Jet 35 development has been finished! Buy the files here and make your boat fly:
www.cgtrader.com/3d-print-models/hobby-diy/other/m-jet-35-3d-printable-jet-pump-for-rc-boats
Ha, you are smart. The lumps on the new impaler are there for ballancing
Yes😁
It makes sense to let water flow through better so water can evacuate better
Thats part of the reason too.
On life scale water turbines for example, highdr flow rates are achieved with less blades.
Really interesting! It would be good (if it's possible) if you could maybe also sell an upgraded single prop design for the m-jet.
Today I added a single blade impeller mod to the M-Jet 30 files, I will probably add it to the M-Jet Sprint mods as well. It is not tested for these pumps so that just needs to be kept in mind, but definitely worth trying it out
@@mjetdevelopment Brilliant, I'll try this out soon, thanks!
@@mjetdevelopment Tried it in my Mjet sprint and WOW. It seems faster than before!
@@JeffJackson86 Very interesting! Power consumption is definitely lower as well.
Wow!!! Nice one!!!
Thanks!
Finally bought the M-Jet 30 STL and noticed that you have included the single blade impellers with the purchase. Which was a neat detail, I look forward to seeing if it's gonna be better for my application.
Okay, good luck! I have not tested single blades on M-Jet 30 but it is expected that it should give maybe a little bit less thrust, but much lower amp draw, creating better efficiency and runtime.
@@mjetdevelopment How much volume in a minute do you reckon the 30 pumps at full chat? I have got a priming pump, but it peaks at 1l/min and I am afraid that won't be enough to supply the jet with water consistently. A litre a minute is about on par with the SuperSoaker CPS 2000, a PRODUCTION water gun. Which is the most powerful production water gun in history, but still. I could maybe stagger two pumps in parallel to increase flow to 2 litres a minute.
@@ProtonFilms_Mark The M-Jet 30 pumps over 3 liters per second... 180 liters per minute lol. For a water gun this is probably too much right? For a water gun, you need less flow rate but higher pressure converted to higher velocity
You could dramatically reduce the exit nozzle, or add a pipe with small diameter, to get much lower flow rate and higher velocity. But then plan your setup for lower RPM
And also I dont know how the pump will behave if you really decrease the diameter a lot
How did you go with this one blade design?? any updates??
Really excited to see some development!!
Yeah there are multiple updates and I am still developing it, check my channel:)
What if you reduce the number of vanes on the exit nozzle?
Your nozzle design creates an amazing laminar flow but my guess is that at the same time there's a significant back pressure that's lowering the system efficiency.
thoughts?
Thanks for the idea, I am still testing different combinations and the main thing is, the leaving jet stream needs to be straight so I cannot reduce the vane length too much anyway. But its on the list to test:)
I'm wondering is he makes the rear blade pump smaller.
Nice work! Single blade or single stage (1x impeller)?
Thanks! It will be a 2-stage single blade impeller design. I even tested some 3-stage designs but then it is really getting too long XD
Please forgive the ignorant question (I'm not an R/C boat person), but why are you measuring the thrust with the nozzle out of the water? When the drive is mounted in your boat, isn't it going to be submerged?
Hi, not an ignorat question at all:)
The reason is, at first the nozzle is submerged when the boat is sitting still, but as soon as the boat gets some speed, it "gets on plane" and mostly comes out of the water. Only a small area is fully submerged. This is the state in which the boat will run most of the time.
@@mjetdevelopment -- ah, thanks for the explanation!
I don't know squat about R/C boats, but my intuition was that in full-sized jet boats, the output would be below the waterline, since water would provide a more suitable medium for the jet to "push" against, than just air. However, after reading the Wiki on jet boats, I see that I was mistaken, and apparently so was everyone else until William Hamilton thought to raise the output above the waterline, in the '50s.
Cool -- I learned something new today! Thanks again.
@@roberthaines4221 I understand your idea behind it, however the jet does not work by pushing the water "aganist a medium". It works like a gun shooting a bullet, and producing a recoil force on your shoulder - the water is like the bullet. The recoil, or here the thrust force is generated because the pump is accelerating the water backwards.
Actually, raising the nozzle above waterline is benefitial for efficiency, because it is easier to shoot the water into air than into dense water, where it would generate a lot of turbulence.
@@mjetdevelopment -- yeah, I get the distinction; it's Newton's Third Law all the way.
One thing I find surprising is that in every video I've seen of RC jetboats, the intakes are simply flat along the bottom of the hull. I'm surprised that at speed (especially in any kind of a chop) they can manage to draw enough water in to keep the impeller(s) constantly supplied, and prevent a loss of efficiency due to the introduction of air. I would've expected to see some kind of an adjustable scoop / spoiler / trim tab that at-speed could direct more water in (without adding drag or disturbing the laminar flow). Perhaps this is already being done, and I just haven't encountered it.
@@roberthaines4221 Yes, this effect is hard to understand for me as well. The curve upwards into the intake is quite steep and I would also expect the water to separate from the surface and create vacuum or turbulence. But I dont have any way to properly find out what is happening there, because cavitation is important in this case and that is hard for me to capture in cfd.
I have not tried a scoop yet but I dont want to put possibly vulnerable things under the surface of the hull.
Anyway, maybe one interesting thing is - the intake in my boats and most similar boats is so big, that the boat is travelling forward much faster, than the water into the intake. This means, from the water perspective, the water has to accelerate in the direction of boat travel to pass through the intake - the opposite way from the case where the boat sits still, if that makes sense.
Hi, very nice and interesting work ! Und straight forward design development. I like to see such work. But one question: How do you calculate the jet efficiency ? With measuring the power consumption of the motor and the produced thrust it is not possible. I assume that you are somehow estimating jet velocity or flow rate, correct ? And if, how ? Thanks for your answer in advance.
Hi, great question. There is no estimation involved. You are correct that I measure thrust and power consumption. But the one more thing which I know is nozzle diameter.
I can modify the thrust equation (thrust = mass flow*exit velocity) to a different form (thurst = water density*exit nozzle area*exit velocity squared). From this I can calculate the exit velocity (it is the only unknown). Then I can easily calculate many other parameters including mass flow.
Then, the output power is equal to kinetic energy the water receives per one second. And at the end I get efficiency.
Mainly, there are only two small errors involved: 1) this method estimates the water velocity is the same at every point of the nozzle which is not true, 2) I estimate efficiency of the brushless motor itself based on my previous measurements on a water dyno (in my older video) with similar electronics and load.
Ah, yes of course. That’s a simple and possible way based on an ideal world. But for me it is a kind of estimation because it is not measured somehow.
Why I ask ? I did some extensive measurements with my jet sprint boat from KMB with the corresponding 28mm jet unit. I measured power consumption, rpm, static thrust and boat speed at different throttle positions for different impeller and nozzle configurations. Now I updated my Excel sheet with your prediction of jet velocity and jet efficiency. With this I get efficiency value from 40-45% for the jet unit. Interesting to see is, that the calculated jet velocity for low throttle values is higher than the reached boat speed (as it should be), but for full throttle it is the same or even lower with the smallest nozzle I have test. This shows that this way of prediction of jet velocity/ efficiency is somehow insufficient, at least for my case. Therefore, it would be interesting, if you could also measure the speed of your new boat with the new jet unit for a comparison of jet exit velocity and boat speed.
@@SharkV60 Yes, the boat speed can exceed the exit velocity. That is because we are calculating the exit velocity for a stationary jet unit with a static test. As the boat goes forward, the water is forced into the intake faster, helping the pump to push more water. Therefore flow rate increases (by the way rpm should also increase and amps should decrease) and exit velocity increases. So the boat is not going faster than the exit velocity, it is just that the exit velocity is higher when boat is running.
@@SharkV60 I am very surprised by the 40-45% efficiency you measured on the kmb. I also did my old 28mm kmb test previously, not very "properly" that time, but it definitely was not over 30%. May I ask what your resulting output power of the KMB was? Just curious. You can see what I measured for my unit in my "M-Jet 35 Performance" video.
@@mjetdevelopment
Jet and normal propeller propulsion are completely different. Typical for jet propulsion is, that the power consumption is more or less independent from the boat speed. Water entering the waterjet inlet is accelerated to ship speed, consequently, exerts a momentum drag on the boat. I can only advise you to do some measurements on the jet in a running boat. By the way, this effect also applies to EDF units for model airplanes.
Interesting mod! I printed your M-Jet 60 and it came out really well. I prefer captive nuts to those brass inserts, but otherwise it was beautifully designed.
I notice that both stages have the same impeller pitch and same area, so the 2nd stage just unloads the first a bit rather than creating more pressure or velocity.
Could the 2nd stage be pitched a bit higher and have the "squeeze" start early (via hub expand, not outer tube), or is it always better to have constant velocity in the impeller parts and do all the squeeze at the end?
I'm also considering designing a single stage version with a cupped impeller and expanding hub. The final stator tunnels (not fins in reducing tube) will stay at tunnel width but with total volume = existing inlet-nozzle ratio. Seems less straightening is required that way, and it allows your steering gate idea to be done easily.
Thanks for your work!
Yes, the M-Jet 60 has same pitch on both impellers. That does not mean though, that the second impeller does not add pressure - both impellers add pressure, even if their pitch is the same. This happens, because the first stage stator vanes should straighten the water before the second impeller. Therefore ideally the second impeller operates in the same way as the first impeller and both add the same pressure.
During development of the different pumps, I tested different ideas. The M-Jet 60 got a straight hub, however with my latest experience I think that increasing hub diameter and increasing pitch work better - and this is what the M-Jet 35 uses.
The idea with "less straightening required" is one of the reasons why I chose the 4-path nozzle for M-Jet 35. As you described it, I think it will work for you and you can use similar steering indeed, good luck!
@@mjetdevelopment Thanks! I'm guessing that the optimum design would have a mass flow based on the funnel shaped Betz curve, but there are always complications like skin friction and turbulence and gaps between impellor and stator. And there's always scale.
It makes sense to me to utilise rather than suffer centrifugal effects, so your M-Jet 35 looks like a great direction.
@@OzAndyify I did not know about Betz curve before. I did a quick search, very interesting. I am not sure if this is applicable to such water pump though.
@@mjetdevelopment You are probably right because the jet is in a different medium (air) to the inlet and is fully constrained, but I think a gradual increase in velocity (area reduction) following a similar curve might be better than constant area & velocity in compressor part, then all the squeeze at once after the final stators.
It's all one linked flow with water (not as compressible as air), so I may be way off! Your M-Jet35 work seems positive though, so it's worth playing.
I love 3D design because we can make things that a metalworker would struggle with.
@@OzAndyify Yes, 3D printing gives great freedom of shape. The M-Jet 35´s impeller hub has an increasing diameter smooth curve, and this is what worked the best during excessive experimental testing, so I guess there might be some connection to the phenomenon you are referring to.
Hey I tried the single prop mod in the M-Jet Spring 3d mods files and actually had worse performance than my standard prop. I was a bit surprised after seeing how much success you had in this video! Have you had any other feedback or updates?
Hi, thank you for your feedback, you are the first who has tested it! The results can naturally differ depending on the specific pump. It is totally possible that this setup works worse for the M-Jet Sprint. Regarding the new pump you can see in this video, I have already objectively verified the results so many times that this cannot be any coincidence, but I am still only testing the single blade pump static and the results can (unfortunately) change when I put it into a boat. Stepan
@@mjetdevelopment Worked great for me, interested to hear your setup. Motor , battery etc. I am using 4s battery, smallish 2845 brushless motor at 1950kv. Everything stays cool, even when diving like a submarine! LOL .
Should I hold out purchasing your M-Jet 30 model, or will it be updated?
So far, I am not planning sharing the files for this new pump because it is a different kind of a build, not designed to be easily assembled by everyone. Because I am focusing on making progress right now, I am also not planning to make any big changes to the M-Jet 30. But if you wanted to build the M-Jet 30 and try a single blade impeller design, I can create it and add it to the M-Jet 30 files.
Edit: The mod is there.
Smooth all those very rough edges and surfaces off of the parts and you'll get even more efficiency.
Try using the fibonacci sequence to make one spiral spiral prop.
I think I might have seen a photo of such thing but I am not sure how exactly you mean?
@@mjetdevelopment somehow the math used creates the prop. I saw a few on the cg trader. I don't know how or what programs people are even using to make these 3d printed drawings?
Just needs a patent
Thats difficult. Given the size of my channel, the amount of people and possibly my sales, creating a patent would probably cost more than the profit it could bring.
Also, the single blade design is truly only applicable to pumps of this small scale.
That is great can’t believe one blade is better I have printed a much bigger jet unit I should be ready to test it out soon. Check it out on my channel if you like, I like your test rig too I will do something similar
Hey thanks, you are welcome:) I saw your jetboat video before. Yes, I found the test rig to be very practical way to objectively evaluate the performance, especially if you do some calculations from it.
I was like what the f***
Me too XD
I subscribed this is my thing and you do fantastic videos
Ty jsi Čech zejo btw já napsal svoje jméno do vyhledávání a ty jse jmenujes stejně jak já asi tomu nebudeš věřit ale fakt
Dobrá náhoda XD