Hi Guys,As you may or may not of noticed I have been very quite of late, but this is just down to the pressures of the real world interfering with my hobby time, but testing has been taking place and I am just very behind on my right ups, three to be precise and a lot has happened, as always, some good, some bad and some stonkingly awesome, but more on that later.We pick up our tale of Jet Drive exploration on 24/06/18...Configuration: 5065 270Kv - 1:2.94 Gearbox - 8S – 23506 RPMFirst Run- Old radio installed kept producing same cutting out issue as last time
Second Run- Radio changed over
- Short half throttle run achieved with a current draw of 30A
- Attempted full power run failed at a current draw of 43A with motor cutting out / stalling
This did not turn out to be one of my better testing sessions: - Radio Loss - This is an annoying fault, my favourite TX has developed a fault and so I am forced to use my secondary handset, usually used for the rescue boat
- Motor Cutting Out - Every time I tried for full throttle the motor would give out a high pitched shriek and die, now I am by far from an expert on brushless motors, but I have encountered this before, shortly before the motor in question let out all the smoke... fortunately that didn't happen, but I have read elsewhere that this can be a sign of timing, ESC frequency issues or pulling more current than the motor is happy with, whatever is causing it, it ain't happy and to be honest I am not really surprised, I wanted to test on 8S, but there is way too much gear in it at the moment, forcing the motor to work much harder than it should do, next time I will change the gear set to try and achieve a better ratio
- Overheating - This 270Kv motor is great, but it does have one flaw, it runs very hot, now this is always going to be a problem as there is no air flow inside the prototype and these motors are more commonly found on skateboards and other such outdoor devices, hanging in the breeze with all the cooling they need, in my case, this causes even bigger issues when using a 3D printed motor mount, which sags under the heat and weight of the motor, causing mesh to be lost in the gearbox, on the second run, anything over 50% throttle towards the end just resulted in nasty noises of gears grinding
Next instalment - 15/07/18…
First configuration: Tornado Thumper V3 5055/06 580Kv – 1:1 – 8S – 17168 RPM
First Run- Thinking I had fixed the old radios problem, I set off with gusto across the lake and the boat performed well… for several seconds until it cut out displaying the same symptoms as before
Second Run- More radio problems
- Mystery loss of drive and then no loss
- Half throttle run achieved with a current draw of 15A
- Static shore power pull produced 27A @ half throttle & 80-85A @ full throttle
- Back on the old radio, after much troubleshooting I had traced the issue down to a broken aerial, which folds away for transportation on the TX, the cable inside was looking decidedly
Second
Configuration: 5065 270Kv - 1:2.08 Gearbox - 12S – 24975 RPMThird Run
- Changed over to alternative powertrain
- Short half throttle run achieved with a current draw of 19A
- Attempted full power run failed at a current draw of 49A with motor cutting out / stalling
Fourth RunSome good, some bad, but a lot more positives to take away than last time:
- Radio Issues - With the backup radio installed once again, (this is a real pain swapping over radios as I have to reprogram the ESC each time to accommodate the new throttle calibration) I set off across the lake and… immediately ran into another problem, I very quickly discovered that both TX were setup differently, so left was right and right was left, easy fix, flip a switch to reverse the channel, until I mistakenly reversed the throttle, which then went from 0 – 100% instantaneously, it doesn’t half shift from a stand still!
- Loss Of Drive – Like always I was too impatient to try a new setup and observe the results, this tends to lead to me making do and crossing my fingers that things will hold together, this time, I wanted to test the 580Kv motor on 8S, but it has an incompatible shaft diameter with the current setup, I did however have a brass adapter I had made previously for this motor out of a length of bar with two grub screws in, not really ideal for something generating in the region of 3.4Hp, but I thought, “What’s the worst that could happen?” Part way into the run, in the middle of the lake, the prototype started to slow down, the motor RPMs started to rise and not being able to hear this at the lake side, started to increase the throttle input, what was actually happening, was coupling had become loose on the motor shaft, which was now eating the brass on the inside, this continued until the two suddenly fused together and the prototype took off like a scalded cat, it wasn’t until later when I tried to remove the motor coupling did I realise what had gone wrong
- 580Kv on 8S – This was a very solid performance, very happy with how this went, current draw is a little high at the top end, but this motor would be an excellent choice for a slightly smaller jet unit, what we clearly need is more power
- 270Kv on 12S – This was a setup I was very keen to test, I know this motor has potential, it is just a matter of finding the right setup, stepping up the voltage from 8S to 12S will naturally lower the current figures, I do however have to compensate for the higher motor rpms by adding more gear into the setup, this led to a bit of a standoff in the design, you see, I can only get certain tooth counts in the hardened gears I use, (sticking to off the shelf only) I also only have limited space within the hull and with the 50 tooth gear this motor was already swinging, I either had to compromise on my final ratio, or make a multi stage gearbox, something which I did start sketching out initial ideas for, but in the end I decided to compromise and ended up with a higher final drive RPM than I would of liked, but it would fit inside the hull and work. Out on the water you can tell immediately the difference 12S makes, throttle response is much snappier and with the high final ratio, at part throttle it is performing just as well as some of the other setups can only manage from half throttle and upwards, the consumption recorded was also a vast improvement, with a half throttle figure of 19A, but at anything above ¾ throttle, it again displayed the same juddering / stalling from last time, cutting out at 49A.
Overall it has been interesting using this setup, but I don’t think I will be taking it any further, at the end of the run the motor had again completely deformed the motor mount and I don’t have the time or will power to investigate the stalling issue any further.
Next instalment - 05/08/18…
First configuration: Gartt 5060 530Kv (700 Size Heli) – 1:1 – 12S – 23532 RPM
Couple of minor tweaks to accommodate the new motor setup:
New coupling, finally ditched the old brass homebrew units and bought an Oldham setup from RS, now for those of you not familiar with this style of coupling, they are brilliant, they lock onto the shaft just like a clamp collar does, one hub engages with a torque disc that then transfers the torque to the driven hub
Whilst giving the drive the once over I discovered a small crack in the impeller, next to where the brass coupling insert slots in, being an old impeller I decided to replace it with a new one, slight modification this time, three blades, I also included a nose cone at the front of the impeller to try and help smooth the water flow through the drive, the blades are also slightly larger on the diameter, as a smaller gap between tunnel wall and blade tip equals greater efficiency in power transfer
First Run- Rumbling at slow speed
- Full throttle not achievable due to induced roll
- Shore power pull ½ throttle @ 15A & full throttle @ 84A
- Batteries ran out
Second configuration: Gartt 5060 530Kv (700 Size Heli) – 1:1 – 8S – 15688 RPM
Second Run- Shore power pull ½ throttle @ 15A & full throttle @ 84A
- Batteries ran out
This is one of those rare occasions where everything came together and just worked:
- Rumbling Noise – Not noticeable from the lake side, but on review of the GoPro footage there is a very clear grumble coming from the impeller, my guess is that the tolerance is a bit out and it is very lightly rubbing on the tunnel wall
- 530Kv on 12S – Lively, frantic, explosive, insane, all good words, but they really do not describe the white and orange missile I let loose upon the lake, on 12S the power is simply ridiculous, so much so that the entire hull rolls to such an extent that air from the Port side is sucked under the hull and interrupts pump prime, so lets calculate just how ridiculous it now is:
o P = I x V
o 84 x 44.4 = 3729.6 W
o Hp = W / 745.7
o 3729.6 / 745.7 = 5 Hp
With this much power on tap you would expect the usual finish here, motor got hot, motor mount melted, but no, with a maximum rating of 100A, this motor isn’t maxed out at all, meaning it runs much cooler than my other setups
- 530Kv on 8S – This is a much saner and more usable configuration, (but who wants that?) full power can easily be achieved and the most exciting thing that happened on this run was the batteries running flat, even on 8S though, it is still not to be sniffed at:
o P = I x V
o 80.2 x 29.6 = 2373.9 W
o Hp = W / 745.7
o 2373.9 / 745.7 = 3.2 Hp
So what now I hear you ask? Well for now I am going to take a break from the jet boat, I have been working on this project on and off for just over two and a half years now and I want to do something different, but fear not, this is not the end of the line, I am still very much going to finish the KaMeWa reversing nozzle properly by building the RC pneumatic system I started, I also have a new second hand hull, one of my favourite designs, which I am going to retrofit one of my slightly smaller units into for some thrashing fun, so as always, watch this space
Alex
Author
Topic: Water Jet Drives & 3D Printing (Read 99675 times)