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Author Topic: Water Jet Drives & 3D Printing  (Read 16433 times)

derekwarner_decoy

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Re: Water Jet Drives & 3D Printing
« Reply #150 on: April 21, 2017, 04:50:35 AM »

Alex.....you have an interesting issue to resolve ie., “how to eliminate unwanted heat created by the thrust of the impeller being reverse transmitted to the drive shaft thrust bearing and the subsequent heat build up that occurs between the interface of the housing and the thrust bearing”

1. to what temperature does the plastic filament material remain mechanically stable?
2. will the material accept a brass bush being inserted into the housing, during or post manufacture?
3. the brass bush could be spider legged to the thrust bearing to allow air flow between the thrust washer and the bush
4. could sufficient air flow be achieved even with a small finned centrifugal fan mounted to the shaft?
5. could water cooling of the brass bush be an option?....[similar to the water cooling of motor jackets?]

Your CooLRC 4074 motors is listed as a draw of 2800W……..[it also has an option of a water coiling coil]

6. after efficiencies & losses, some of this energy is consumed in providing the rotation power to the rotor
7. some of the energy is the transmitted opposite reaction being the inboard thrust of the rotor shaft and the heat transfer you are experiencing

All of the hypothetical calculations to where this energy dissipates will only confuse you

Manufacture/Print another housing to the latest [as failed] design & install the current rotor & thrust bearing……with a $20.00 digital pyrometer determine, confirm and document  the running temperatures of the thrust bearing, the housing interface and all associated motor/gearbox attachments under full water load conditions ……maintain the full load testing until all temperatures peak and then maintain/stabilise

From there you can progress your thoughts in what and how you will remove this heat from  the housing

Derek
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Derek Warner

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Illawarra Live Steamers Co-op
Australia
www.ils.org.au

derekwarner_decoy

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Re: Water Jet Drives & 3D Printing
« Reply #151 on: April 21, 2017, 11:36:21 PM »

Alex....just a few points to consider :o

1. manufacture the motor mounting plate from aluminium
2. mount the thrust bearing the aluminium mounting plate [as you had shown a week or so ago]
3. install a needle roller bearing in the housing plate [just next to the point of failure which will accommodate the longitudinal thrust movement]

Lubrication of the free floating needle roller bearing may need further consideration, however the aluminium mounting plate should adsorb the heat gradient created from the rotational thrust [bearing] without any issue

Derek
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Derek Warner

Honorary Secretary [Retired]
Illawarra Live Steamers Co-op
Australia
www.ils.org.au

IKB

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Re: Water Jet Drives & 3D Printing
« Reply #152 on: April 22, 2017, 01:29:40 PM »

Hi Derek,


A well considered and thought out response as always, I did look at needle roller bearings but unfortunately they are of no use as at the required size they top out at 5K RPM, which is a bit low compared to the 19.5K RPM operational speed of the jet drive, on closer inspection of the thrust bearing, it looks like the problem had arisen from one half of the race, which is pushing against the 3D printed gearbox is a sliding fit on the shaft, where as the other half rotates freely, this was a complete over sight on my part and is explained in the attached image.
The bearing is designed to be installed with one half of the race supporting the rotational side, in my case, this would be the clamp collar on the shaft, the bearing race rotates with the clamp collar relative to the second half of the race which is stationary in relation to the impeller shaft, this half of the race therefore has a larger clearance to allow free rotation of the shaft within, in short I installed the bearing in backwards, the race locked onto the shaft and friction welded itself to the gearbox  :embarrassed:

So a much quicker fix than I thought, I can print a replacement gearbox part, (got to love 3D printing) ready for more testing down the lake tomorrow! 


Alex
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bfgstew

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Re: Water Jet Drives & 3D Printing
« Reply #153 on: April 22, 2017, 03:25:56 PM »

Nice to see you have found the problem Alex, bearings this small are notoriously difficult at best of times but when you are supposed to fit one way, you need to be on your toes to ensure correct orientation.
Look forward to your next run.
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #154 on: April 23, 2017, 11:23:47 PM »

Hi Guys,


Well, got the prototype rebuilt and on the lake today, on the plus side, the thrust bearing appears to be working, on the other hand, this was one of the shortest runs ever at just under 40 seconds when the impeller exploded!  >>:-(
No idea what caused this, sailing along at half throttle and halfway through the acceleration to full throttle the impeller explodes, now there are a couple of possibilities as to why this might happen:


  • Ingestion -  Even though the intake has a grate on it, not everything is strained out, so ingestion is still a very real issue
  • Torque - I have a lot of power on tap with this setup, it may be that the impeller simply shattered under the sudden change in loading
Whatever the reason may be, it is clear I need another impeller, it may be that the SLA resin I am using is just too brittle to withstand the forces a jet drive imparts, so I will more than likely go back to the PLA impeller which has withstood all kinds of abuse and lived to be abused another day, video from today:


https://youtu.be/-Qb9pNazcqE


Alex
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