Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Other Technical Questions... => Topic started by: d-jnana on August 01, 2008, 08:30:39 pm
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Hi guys, and gals,
Anyone else find aligning motors and shaft to be really difficult or is it just my beng totally crosseyed?
How do you do it?
GARY
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Hi,
when you say you are having tropuble are you fitting the motor direct to the shaft or are you puting a Universial Joint assembly in between?
R,
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I fit the motor first well fixed in, then use a tube the same lenght as your chosen coupling to join the motor shaft to the prop shaft, then fix in the shaft, because you should have a small amount of movement through the hull. When set remove the tube, insert coupling, and you should (no really you should) have a near perfect line up
Phil
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Set the prop shaft in place and attach the coupling to it. The put a dollop (if the word really exists) of P38 car body filler, or similar where you want the motor. Attach the motor to the mount and then press the motor, which has been wrapped in cling film into the filler until all is lined up. It never fails...
Barry
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Gary
One tip I've seen is to connect a single cell (1.2 - 1.5v) to the motor, with an ammeter in series. Connect up the motor, U/J and prop shaft. Dollop the P38 onto the motor bed and squidge it into the hull in roughly the right place, then turn on the current. If you move the motor around, the current will increase or decrease, which indicates more or less misalignment. When the current is the lowest you've hit the optimum alignment. Let go, turn off the current and let the P38 set.
For big gaps under the motor bed e.g. in a hull with a deep keel I prefer P40, which includes chopped GRP strands.
Works for somebody - although, like Phil, I use a rigid tube to couple the two halves of the U/J while I install the running gear.
FLJ
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A variation of Footski`s is to use silicone bath sealant instead of body filler. I use a block of wood glued to hull bottom that is 1/4" lower than engine mount , sealant dollup is squirted onto block, support the mount ,with motor fitted, till sealant cures (24 hrs). A brass tube is slid over the coupling to keep it solid and the line-up will be automatic, when cured the brass lining-up tube is removed. I also remove the centre block of Raboesch-type couplings and replace it with large diameter silicone tube pushed onto the splines. All this to try and quieten noise. I was thinking of trying sealant to fix the prop-shaft tube through the hull, anybody tried this ?
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I have tried silicon to fit the tuebe through the hull. In time it leakes as vibration makes it let go of the metal tube.
Well thats what I think anyway.
GARY
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Recently I have been fitting a new motor in an old hull. I made a template of the tube angle wrt the keel by placing a bit of wood on the keel next to the tube and scribing along it. I used this to set a motor plate at the right angle. I then packed up the motor to height by sighting up through the tube to see the end of the shaft.
As I haven't glued it in I might give the ammeter test above a try.
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I use the 1.5 volt battery method, but just go by the sound/revs of the motor, the faster the better.
Works for me
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Thanks guys,
I like the idea of using blobs of sticky/squidgy stuff to seat the motor. I take it the blobs go under the motor mount. I'm going to give it a go in conjunction with the ammeter test using milliput so that I can tap a couple if holes in it to screw the mounting plate down firmly.
GARY
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Yes under the mount but you could perforate the mount base and allow the squidge to ooze up through the holes and form mushroom "rivets". Wrap a bit round the edges too while it is still liquid-sh. I just re-fitted the motor in a Springer last night, should have photographed the process, sorry ! The balsa box in photo are just a dam to contain gunge while it cures, can be left insitu or removed to reveal a solid block of silicon "rubber". Also pics of my lining-up tool, simple brass tube push fit over coupling (slots to clear rivets). I now use only the end pieces of this type of coupling with thick-wall silicon tube pushed over the splines. Much quieter. The anti slip rubber is also for same reason and to help batteries from moving.
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A few years ago Bryan Ward at Mobile Marine Models used to sell a gadget for alignment of motors to props, if you are still having problems it may be worth a try.
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I`m sure a block of brass same length as a coupling with appropriate dia hole each end to suit motor and prop-shaft would be a boon.
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Can you take a photo and show the problem Gary?
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An old wooden cotton reel is the same size as the red plastic bit on a coupling and the brass bits will fit nice and snugly inside the ends of the reel.
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Here how I did the same thing in the Puffer....
http://www.modelboatmayhem.co.uk/Builds/Puffer_Jan/Part_4.htm
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I have never built a boat yet but have you guys thought of using 'No Nails' for bonding in motor mounts :embarrassed:
Tony
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I have tried silicon to fit the tuebe through the hull. In time it leakes as vibration makes it let go of the metal tube.
You are using SILICONE?.... the rubbery bath sealant stuff to fit a prop shaft in to a hull?.. :o :o :o no wonder it comes loose and leaks!.
Nooooooo, rough up the outside of the brass outer tube with some sandpaper and EPOXY it in...
If you must, stick the motor mount in to the hull >>:-( , but a wooden block in the bottom of the hull and some small brass woodscrews through the motor mount to hold the mount down is a far more professional job. It also allows you to remove the motor for maintainence or replacement at a later stage.
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Golden Rule: NEVER mount anything inside a hull that you cannot remove at a later date. If you do, you will come to regret it!
Colin
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Well said toesupwa
with your way (and mine) if you change the motor to a new one then you have a pre aligned base to fork of. ie same motor same coupling all fits OK even if you have to use a different motor or coupling the base plate is set at the angle to the shaft.
R,
I have to undo a pair of motors in an Alkabha (spelt wrong I think) and then fit fixed shafts, knowing the owner I will probably need to change the motors at a later stage too. :(
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Got to admit, double / 'cardan' coupling or overshaft gearbox or belt drive every time.
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True having a double cardigan is the easiest way to fit motor to shaft though there is a draw back to that fitting system and that is the length of the installation. Some models are restriced in what you can squeeze in.
Also as a foot note every bend in a drive line = a loss in performance = increase in drag = possible deflection vibration = noise
just my look on things you understand.
R,
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Agreed. in very tight installations, I've used solid coupling to make up an entirely solid drive line.
With a solid drive line, I've mounted the motor in place, assembled the driveline, left the stuffing tube free
while it was glued in place which leaves the the tube to take on the the natural angle.
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Does that allow for any movement in the motor shaft. ie wont the weight of the propshaft put the motor shaft off centre, and wont it still be off centre when you glue the prop shaft in. :-\
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When I done it, the motor is in it's final fixing place which is best alignment as possble and
the tube and shaft are loose in the hull hole. With everything tightened up, it's already lined
up and held in place by itself, all you have to do is glue in place. Only recommended for small
installations, flexy shaft setups or Very confident builders!
On another note, just browsed through Terry Smalls build of the Slipway FSB Tenby Scale 1:32,
he used electrical "choc block" connectors as solid couplings!?!?!? The thing must have shook
itself to pieces in minutes!
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I am currently building my first model, a Hunstman 31 on a GRP hull and have a query regarding the propshaft alignment. I have fitted the electric motor and also positioned and used epoxy resin to fit the propshaft which is joined to the motor using a coupling. I am quite satisfied with the alignement of the propshaft from the stern up to the motor, however I do have one issue. The coupling after attaching to the motor drops slighty for the propshaft to be able to screw in to it. It therefore is not in a totally straight line. It is difficult to measure how much it drops and I have taken digital photo's if this helps should they be needed.
My questions are, should this be something to worry about?
Should I wait until it is powered up until I see whether this causes vibration or has a negative effect on the life of the batteries.
Should I correct this, which would mean freeing the propshaft from the epoxy resin, if this is possible without causing too much damage. I am just finishing fitting out the inside of the hull and I am yet to complete the superstructure before considering any paint job.
Any thoughts would be appreciated. Thanks. Stuart
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It sounds to me as though the couplings diameter is larger than the props shaft. The coupling should have come with an internal collar so that the shaft is a tight fit. If you think this may be the cause, get back to the shop where you bought the coupling from and see if the have a collar for it.
Barry
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Stuart, if you have to move anything it might be easier to move the motor.
Try attaching the coupling to the prop shaft first.
If its a little bit out it shouldn't matter to much, thats why you have the coupling.
Give the motor a run and see if you have any adverse affects.
Good luck. O0
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i fitted my motors to my tug and powered them up in the bath on friday night. Starboard sounded smooth as silk but ironicly you could see clear as day the alignment was MILES out where as the port side alignment looked good but it sounded more like a 12 cylinder diesel engine turning over when i powered it up. So i took everything out on saturday morning then chisled the motor mounts out and totally redesigned the mounts and fitting them using a modified MMM alignment tool and the "dollop" of p38 filler method.
Now all alignment looks good from all angles O0 When powered up this time, the starboard side was as smooth as silk. The port side, which now in theory should have near perfect alignment sounds much the same as before. I can see the end of the coupling which is attached to the shaft bouncing up and down. I notice the nut on the said shaft is very "wonky", it looks like the threads have been very poorly cut. If this is the case, would this be the cause of my vibration. IE the coupling cannot mate to the shaft concentricly because the threads are "wonky".
Has anyone else experienced a similar problem?
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I have had problems with the coupling ends being bored off centre which will give vibration and noise.
Bob
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Or you could have a bent prop shaft!
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I dont think the shaft is bent as it slids in and out of the tube perectly O0
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Take out the shaft and roll it on a very flat surface, glass, worktop etc......
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the shaft is spot on, the problem is the nut. The the tap which cut the thread in the nut did not go through the nut concentricly. I swapped the nut for a good one and there was no vibration atall. Problem sorted ;D
Now i need a new nut, such an inconvenience >:(
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There's always some nut behind annoying problems! {-)
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Just fitted motor coupling etc into my swordsman here's how i did it i bought a shaft and coupling from Mobile Marine which they make themselves the coupling ends are brass one tapped 4mm the othe a grub screwed 3mm hole but both ends accept an 8guage wire on the inside ends so i used a piece of piano wire to line things up smeared th motor mount with vaseline and bedded it onto P38 which i will drill and tap later here's the pics as this explains easier {-)
The coupling the tube can be cut to suit
(http://i127.photobucket.com/albums/p127/bbdave/Swordsman/P1000667.jpg)
8 guage piano wire
(http://i127.photobucket.com/albums/p127/bbdave/Swordsman/P1000668.jpg)
Motor all lined up the back end needs to be supported to avoid the motor hanging on the shaft
(http://i127.photobucket.com/albums/p127/bbdave/Swordsman/P1000669.jpg)
P38 set
(http://i127.photobucket.com/albums/p127/bbdave/Swordsman/P1000670.jpg)
Dave