Model Boat Mayhem
The Shipyard ( Dry Dock ): Builds & Questions => Pleasure boats, Sports, Race, Power and Leisure Boats: => Topic started by: gregk9 on May 01, 2012, 10:55:06 pm
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Can anyone recommend a u/j joint, capable of taking the higher rpm off a brushless motor please?
I am stuck with the originally fitted solid propshaft in the boat, but to get a brushless motor in, complete with cooling jacket, I will have to angle the motor up slightly, hence needing a u/j. YES I appreciate a flexishaft is the way to go, but I dont wish to damage the hull, trying to remove the original propshaft.
Tried a "huco" type and it lasted seconds !
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use the huco brass inserts then use a peice of rubber tube to join them togeather. Mark might sell you a bit of tube that he uses for his couplings, ask for the heavy duty coupling tube:
http://www.marksmodelbits.co.uk/
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Thanks for the reply, but don't think a rubber tube type coupling will take the continual angle loading I have with this setup. if the angle between them was lesser, it would probably work. But I cannot reduce the motor to shaft angle, as I am restricted by the previously installed prop shaft as mentioned.
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What about something like this, a coupler with a piece of flex in the middle.
http://www.offshoreelectrics.com/proddetail.php?prod=grp-3344 (http://www.offshoreelectrics.com/proddetail.php?prod=grp-3344)
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gregk9, hi
Sorry to be a pain, but I think that we/you/us are solving the wrong problem! :}
I fully understand that the BL motor cant fit in the same location cos there isn't radial space available
But (and I'm a professional mechanical engineer) UJs are not really for what you propose!
Unless they are designed for the job they are unhappy, hot and lose a lot of power by friction (oh, yes, and fail fast)
~~So with some lateral thinking.
A Leave the prop shaft as is, but fit a new longer "inner" which is long enough to reach where your BL motor is the right diameter
B fit belt or gear drive so that there is no need a big diameter
<<taking the higher rpm off a brushless motor please>>
Why is the BL higher Rpm - this must be your choice?
C How about a BL with smaller diameter and cooled mount?
Photos, please!
andrew
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Huco couplings are only designed for UP TO 1000RPM. When is this going to get into modellers heads?
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Huco couplings are only designed for UP TO 1000RPM. When is this going to get into modellers heads?
That's not nice....
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Torque is the big killer of couplings. Huco or equivalent Hardy-Spicer type couplings work reliably well beyond a 1000RPM providing they're not too heavily loaded- they're only plastic remember, plus they do not like being misaligned heavily, because the design means they accelerate and decelerate as the coupling revolves and this is what causes them to vibrate and eventually fail. They're also only designed to take out a degree or two of misalignment.
The toughest kind of U/J is a ball and cup design made from steel. You can get those from Prop Shop. Ideally you should use two together, in the way they set-up propshafts on model cars.
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I use the heavy duty couplings from Mobile Marine Models, good couplings with a heavy duty rubber, uses the shear pin method, never had a problem in my Lifeboats with brushless...
Russ
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To "aid" your suggestions along, heres a few pictures of the hull in question.
its a "Cen Aqua". the hull is very flat bottomed, so even by lengthening the inner shaft, I stand no chance of putting the drive motor further forward, as no height gain on the shallow angle of the original prop tube, if its sitting at 2 degrees, thats it!
I barely have 10mm under the shaft inner, so chances of putting a pulley on and its supporting bracketry is very limited [but not a discarded option I will add].
(http://s17.postimage.org/85ud6gz3f/P1010083.jpg) (http://postimage.org/image/85ud6gz3f/)
(http://s14.postimage.org/3nalxy5b1/P1010086.jpg) (http://postimage.org/image/3nalxy5b1/)
(http://s17.postimage.org/apq00kmnf/DSC03375.jpg) (http://postimage.org/image/apq00kmnf/)
(http://s17.postimage.org/i89597e0b/DSC03376.jpg) (http://postimage.org/image/i89597e0b/)
(http://s18.postimage.org/eb5mor9sl/DSC03377.jpg) (http://postimage.org/image/eb5mor9sl/)
(http://s16.postimage.org/u3kegtawh/DSC03378.jpg) (http://postimage.org/image/u3kegtawh/)
I too have been in the mechanical trade for many years [far too many to number] so would not like to even try a huco type coupling as I do appreciate their limitations, but wondered if anyone knew of an other option, as this type of hull/boat is not normally my cup of tea, it came up cheap and likes the look of it, but was minus its drivetrain, only the motor mount [see pics for mounting holes for bracket.]
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If that's an inner hull I can see in the pics, can you not cut away a small amount (just enough to remount the motor) without causing a problem?
Rich
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Have you considered direct gears or toothed belt drive.
The motor could be mounted on top of the shaft or offset to one side.
Bob
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the "inner support piece" you can see is moulded to the keel and is bonded to it, so no air space underneath it at all, i did think of that to be honest, but where the motor sits, its plastic against plastic.
the original instructions suggest a 550 or 777 series brushed motor, but though as try and fit a 700bb turbo or similar id go brushless for simplicity and smaller/lighter size of motor.
I always like a challenge [ha ha].
as for gears, im struggling here as i said earlier, ive only got 10mm under the shaft "free space", thats not a lot to get a gear in, let alone a drive beltt as well/ And then of course, make sure the prop gear is bigger than the motor gear as i dont want to put bigger gear on the brushless now do I? that would be way over speed
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Why not just run 1:1
CLICK (http://www.mfacomodrills.com/timing_belts_timing_pulleys/timing.html)
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Maybe something like this may be more to your liking
http://www.cornwallmodelboats.co.uk/acatalog/graupner-flexshaft-couplings.html
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Is there any reason for not using a double pin and slot coupling?
These are well proven and take several degrees of misalignment.
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Why not do as I do use a solid brass coupling made for me bu Marc MMB no issues with breakages
Dave
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These were the standard for I/C moons ago.
http://www.puffinmodels.com/product.php?prod=1706
Regards Ian.
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I used to sell the CEN range of boats and If I remember correctly there was an upgraded ball and cup type uni available as a spare if you wanted to upgrade from the factory 550 motor to a 700 series motor and run 2x 7.2v packs, might be worth a look, I think marine modelling had an article on this upgrade
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Maybe something like this may be more to your liking
http://www.cornwallmodelboats.co.uk/acatalog/graupner-flexshaft-couplings.html
That's the same one I linked to in post #4. It would work fine.
Graupners black u-joint would hold up fine as well I have them on a 16.8volt deep vee with no problems.
No need to make this more complicated than it is.