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[hopeitfloats]

reversing bucket is the answer Alex. or if you can put sides on your flap would help. I don't think water fanning out the top is causing your problem. more like its running out the sides

[IKB]

Hi Guys,

Managed to get another testing session down on the lake today with the following results:

• Reversing flap, although it works, I will be producing a more traditional bucket type design, although I am glad I gave it a go
• Intake drill was suspected to be too restrictive,so after breaking most of the bars out, I was proved right with an increase in speed and an audible change in motor pitch at full power, less labored
• Did some more filming with the GoPro on board, but tilted the camera down to try and see if there was any water coming out of the cooling outlet and there was! 
• Achieved longest full speed run on lake to date, due to there only being a couple of other club members today, downside of this was, when I came to disconnect the batteries, I discovered to my horror that the pins inside the Tamiya connectors had become so hot, that the surrounding plastic had melted into the pins and fused everything together.  I am currently running a brushless motor from two 7.2v 5000mah Tamiya type NiMh packs in series to give 14.4v, according to the elapsed time on the GoPro footage, apart from some gentle maneuvering in the harbor, I only managed 60s at full power, at which point the boat stopped because the water jet had ingested air and couldn't re-prime due to the new trim I was trying out. The current setup has a HobbyKing 80A ESC and a ZTW Black Mantis B3660 Kv1900 inrunner,  any suggestions anyone?

Alex

[tsenecal]

IKB,

the tamiya connectors are incapable of handling more than 10 amps max load.  replace them with connectors that can handle 30 to 60 amps, either Deans or PowerPole or EC3 or larger.

[IKB]

Hi tsenecal,

Thanks for your reply, I had not realised that Tamiya connectors had such a low rating, I use XT60 connectors on everything else, which according to some quick googling, can take 60 amps, so will swap to them.

I am also going to look at a different motor spec, which will hopefully give me more torque but fewer amps, as I suspect the one I have is cavitating quite badly

Alex

[IKB]

Hi Guys,

Finished the design for my new jet drive, will be printing the parts out tomorrow, more to come in the next few days

Alex

[IKB]

Hi Guys,

Jetdrive MK3 done and ready for testing.

On order is a Tornado Thumper V3 4260/06 500KV outrunner, at the moment I am running a ZTW Black Mantis B3660 Kv1900 inrunner on 14.4v which gives 27,360 Rpm, a tad excessive for the upper rev range of 20K for this type of jetdrive.
The other issue that I seem to be having, is that the current motor is struggling under full load, so I am replacing with the Tornado Thumper, which is slower revving, but has more torque, I can compensate for the lack of RPM with three blades on the impeller.
Well that is the theory, we shall see when I do the lake testing, but this is the fun of it. 

Alex

[IKB]

Hi Guys,

Well, success is how you determine it I suppose, on the one hand I learnt a lot and have several ideas about how to progress forward, on the other hand, not a great deal worked. 
I have also made a couple of small additional changes since my last post, as well as installing the new motor, I have also added a proper nitrile shaft seal to hopefully stop the suspected water increase into the hull through the prop shaft, along with a new new steering nozzle, which has a 3 degree down angle, which should help the boat up on the plane, as most real jet drives do.
A new less restrictive intake grill, with integral scoop has also been fitted to replace the hacked about old one, I have also decided to conduct all of my future tests using 3S Lipos, as these will more than likely be the power source for my Stolly, so everything need to be compatible with that.

• First run with new motor and three blade impeller, well, the new motor can turn a three blade impeller without breaking a sweat, but as I suspected, it is just not turning it fast enough to make any real ground
• Second run, new motor with 2 blade impeller, with less to do, the motor span faster but the performance is still lack lustre
• Third run, as I only had one motor with me, I decided to up the voltage just to see what it would do and did a run at 14.4v, I also moved the batteries way to forward to try and get the boat on the plane. Having an excessive down bow angle means the drive won't self prime at the beginning of the run and if it stops, it also won't re-prime; the higher voltage gave me an RPM boost from 5500 @ 11.1v to 7200 @ 14.4v, this helped, but it was still slow, to make matters worse, I hit my own wake, lost pump prime and had to be rescued. 

On the plus side I have learnt much today and there were some small successes, I have a better understanding of brushless motors and the 3D printed fan attachment I made for the new outrunner seems to be working really well, with the motor staying nice and cool throughout testing.
But what of the new reversing bucket I hear you all cry? Well, yeah, that too is on the re-deign list, it is great at throwing water directly downwards, but there is not enough reach on the bucket to throw the water under the boat. But whilst chatting to a friend at the lakeside, we came up with a simple redesign which should do the trick, so watch this space.


Alex

[IKB]

Hi Guys,

MK4 Reversing bucket is designed and will be lake testing on Sunday, high hopes for this design, but I have been wrong before!

Alex

[PeachyPM]

Very tidy Alex  , but wouldn't a closer fit when closed (where the inside surface at the top of the bucket meets the out-pipe/jet) be more efficient? or is this a test to see if the bucket shape works first?

[IKB]

Hi Chris,

Yes, this is very much still in development, the cross section view shows the reversing bucket almost in the fully down position, it is very much at a, "get it to work" stage in the development before moving on to a more polished final product.

Alex

[IKB]

Hi Guys,

So, mixed results again at the lake today, good news is, the reversing bucket design works like a dream and I am so happy with it, I don't think I am going to change anything, bad news is I somehow managed to launch the boat out of the lake and break the motor coupling the process. Going back over the on board GoPro footage, everything is going well, crossing the lake at full power, boat is sitting nicely and the tweaked jet nozzle is producing a good pattern, then the motor suddenly stops for a few seconds; the boat is now traveling without control of direction and covering quite a bit of ground, this is really bad, as we all remember from the sinking in the harbor, no power, equals no steering, finally the motor kicks back in, but I am too close to the bank and launch off one of the tires onto the dirt.
Thinking about this, I am really unclear as to what actually happened and probably never will know, I think the coupling exploded as the boat left the lake, excessive torque not being the culprit, but excessive RPM as the motor at full throttle went from full load to no load in a split second, causing the plastic arms to splay out due to centrifugal force, allowing the spider to escape.

On the plus side, the boat performed very well with the 1900Kv motor on a 3S Lipo, this has lowered the RPMs and as the video shows, produces a jet stream with less cavitation bubbles in it, which is backed up by the video audio as well.

Overall I am pleased with today's results and will return to the lake next weekend with a new coupling to do more thorough testing of the new setup.

Alex

[Stavros]

Hi Alex been there had the tee shirt with those couplings sorry to say this but get rid....contact Steve Tranter of Model boat bits and get a PROPER coupling....I will gte you it was already damaged before you launched it out of the lake.....those coupling if truth be know are not designed for RPM over 5k....if you really want to persist with that type of coupling then simply wrap some insultaing tape around it or even use some electrical shrink wrap over it BUT your alignment must be 100% if you use such tricks

Dave

[PeachyPM]

Dave is quite right Alex, bin the plastic couplings, they're ok on a tug, but that's about it, I've even had one go on a Club500, it robbed young Jim of his first victory! Also I might be wrong but it looks from the photos that your motor is mounted squarely to the bulkhead? Does the prop shaft then dip down slightly? If it's even a degree out with a fast reving brushless that coupling was gonna go sooner rather than latter and a straight replacement will do like wise I'm afraid!
BTW great job on your first race day and well done for keeping your cool when you got black flagged! 

[IKB]

Hi Guys,

Thanks for the comments, GoPro video from the test sail:

https://youtu.be/iEJILl3cvS8

Alex

[PeachyPM]

Dude! Awesome footage, really showed the reversing very well. Great POV manouvering in our harbour, & what can I say about the ski jump? Superb!

[Captain fizz]

Not withstanding the motor glitch, that unit is now looking seriously good

[IKB]

Cheers Captain Fizz,

I am very happy with the unit now, I am going to machine a solid coupling this week and get back on the lake this weekend for some better runs, hopefully get some lakeside video footage as well

Alex

[tsenecal]

the bigger question is why did the motor cut out?  i see that you have water cooling to the motor, do you have water cooling on the speed control as well?  if not, perhaps the speed control cut out after overheating....  i know that you didn't have it running for long, and you have run it on higher voltage, but until that gets sorted out, i fear you might need to reinforce the bow with something like an aluminum sheet :)

[IKB]

Hi Tsenecal,

The motor cutting out is a bit of a mystery, the motor is indeed water cooled but the ESC has no inbuilt water cooling and it is one of the heat shrunk in line jobs that don't really lend themselves to cooling on a plate.
At the moment, I think it was interference, or it could be a dodgy motor connector, I changed the bullet connectors on the motor to match what the other motor is using, so that I could swap quickly between motors if needs be, but I got to the lake and found I had one mismatched bullet connector size, so smashed them together with some pliers and then reinforced it with tape. It is more than feasible that this lakeside bodge came back to bite me. 

Alex

[martno1fan]

Nice work but surely you would be better off using a flex shaft to stub shaft arrangement rather than using a universal joint or at least do away with the uni joint and use a rubber type coupling that can handle the high rpm,if you really want to stick with a uni joint then id go with a stainless one from pmb. Also be a good idea to use a boat esc with water cooling,boats with high rpm need that or things overheat very quickly.
Mart

[IKB]

Hi Guys,

Down the lake this evening and another mixed bag of results, although, I did manage one very positive full power run, which proved once and for all that the nozzle design is sorted, planing flat at high speed across the lake, there are however, some other issues to contend with.
The first problem I had, was the new pumped cooling system, which once primed, worked very well, but getting it to prim was another story, I ended up injecting water into the system with the boat in the lake; a fundamental rethink is required here.
Second issue I am having is a very nasty vibration in the impeller shaft at certain RPM ranges, the noise is so severe that at first I thought the impeller was rubbing on the inside of the housing, but after everything had been checked, it is clear that there is something very wrong when the motor is revved, so much so, that at times, the vibrations disrupt the water flow through the drive causing a momentary loss of pump prime, leading to another rescue by a fellow club member, a full strip down will reveal what is wrong.
Third issue, water ingress, it's getting in some where, I just don't know where.

So now that I am happy with the power run achieved today, I am going to rip out the jet drive and install a new home print version, main tunnel and all that will hopefully fix all of the above problems.

Video of the best run from today: https://youtu.be/iNsUIvYS7KM

Alex
 

[derekwarner]

Alex....we can clearly hear the vibration pulses....17+ seconds, 37+ seconds & 55+ seconds

It does not appear to be water or wave related
For these momentary pulses [less than ~~ 0.2 of a second] we cannot perceive a motor speed increase

In mechanics, many rotating element groups have 'critical speeds' where transient mechanical resonance amplifies itself

Essentially in this high speed scenario, the rigidity of an element in the drive becomes unstable

Just a matter of understanding which element it is & then how to harness the instability without drawing power

On the 11th, you mentioned a new machined motor to shaft coupling........if your brushless motor has sealed ball bearing/s on the output shaft........& you have a solid coupling with no resilient element....the next point of contact is the diametrical clearance between the prop shaft tube & the shaft

You could try using a stroboscope to visually see what is moving when the critical speed/s are reached...using a strobe here is like watching a spoked train when suddenly visually appearing to run in reverse

The questions in the image below may assist 

Derek 

[IKB]

Hi Derek,

To answer your questions:

• Yes, in the propshaft housing is a ball race bearing and shaft seal
• It is not supported as I have very little spare time to make modifications every week and the parts of the jet drive inside the hull are all original, where as everything on the outside has been replaced several times.

The next incarnation of this unit will have a redesigned main body, which will incorporate an integral motor mount, which will shorten the impeller shaft greatly, I will also be swapping to a solid coupling for extra rigidity.


Alex

[IKB]

Hi Guys,

Finished the design for the new jet drive impeller housing tonight, going to print the parts off tomorrow and hopefully be on the lake Sunday

Alex

[tsenecal]

IKB,


don't know if it has been asked or not, but i am curious which 3d cad software you are using to design this? your illustrations of the different mods look very nice, and i was wondering if they are just edited screen shots, or are you exporting "scenes"?