Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[flybobby]

I have a torpedo 850 motor to install but it is too fat!!  The inboard end of the prop shaft sits too low inside of the hull, not allowing enough room to line the motor up!! :-[

Is there some kind of flexible coupling or a magic fix so that I do not have to fit a new stern tube, or make adjestments to the existing one?

Any suggestions welcome as i am pulling what's left of my hair out on this one! ::)

[Colin Bishop]

You could try using a double coupling if the misalignment is not too great but this will reduce power to some extent. The alternative might be to go for some form of geared or pulley drive if there is enough room to mount the motor alongside the shaft. If you could post a photo then I'm sure others on the Forum would be able to come up with some possible solutions.

[flybobby]

I will have a go at getting a pic(there is not a lot of room to take one, but I will have a go.)  Thankyou

[andywright]

Any chance of lengthening the coupling and moving the motor forward to a deeper part of the hull. You must try and keep the motor in line to reduce drain on batteries and not to lose power through a slightly out of line coupling. I always treat couplings as a method of reducing wear on the inner bush of the shaft rather than to take up out of line drives.

[Colin Bishop]

I have seen successful installations where the motor and shaft have been out of alignment in one dimension only and a double coupling used. They seemed to run quite freely although some power would have been lost.

[flybobby]

I will try a double coupling.  I don't want any power loss so if this doesn't work I will re-evaluate the stern tube :-\

[Shipmate60]

flybobby,
There are 3 options that spring readily to mind.
1 use a double coupling, bit the motor will still be out of line but will run ok.
2 Mfa do use reduction gearing for this motor, but if you fitted 2 toothed belt pulleys of the same size and of course a toothed belt you would retain the same motor speed with mimal friction losses.
3 Fit a Cardan shaft, which is another propshaft ahead of the main shaft, with a coupling both ends, but this will move the motor forward. This is used quite commonly in Marine Engineering.
I had the same problem, so posted 2 pics of how I got round it.

Bob

[Too Large - attachment deleted by admin]

[wombat]

Hi Flybobby,

If the misalignment is lateral only and not too large you could try an Oldham type coupling. Huco also do a "Uni-Lat" coupling designed to take up both lateral and angular misalignment

Tim the Wombat

[17-21]

I run 4 MFA 850s in my Severn lifeboat but I use a 1 to 1 belt drive. if you have room mount the motor over the shaft and then belt drive it.

[Too Large - attachment deleted by admin]

[flybobby]

flybobby,
There are 3 options that spring readily to mind.
1 use a double coupling, bit the motor will still be out of line but will run ok.
2 Mfa do use reduction gearing for this motor, but if you fitted 2 toothed belt pulleys of the same size and of course a toothed belt you would retain the same motor speed with mimal friction losses.
3 Fit a Cardan shaft, which is another propshaft ahead of the main shaft, with a coupling both ends, but this will move the motor forward. This is used quite commonly in Marine Engineering.
I had the same problem, so posted 2 pics of how I got round it.

Bob

Your solution would fit my problem, where did you get the 'in-between shafts'?   Thanks all for your suggestions

[Shipmate60]

flybobby,
I made it from another propshaft.
Cut off one end and remove the bearing (I used a bolt that slid down the inside diameter) cut the outer shaft to whatever length you require. Dont forget to include length of bearing, lightly lubricate, fit a coupling either end. just make up some supports from balsa and use lots of epoxy to fit and strengthen.
Done.
It took about 30 mins to fit completely and left Epoxy to Harden overnight.

Bob

[Colin Bishop]

This is a very good example of the value of the Forum. Somebody has a headscratching problem and the members readily provide several viable solutions just like that!

Doesn't just apply to new modellers either. We all have an opportunity to learn from the experience of others in areas we are not familiar with. Viva Mayhem!   

[flybobby]

Excellent shipmate60, a real help

[Shipmate60]

I am still nosey, I know some get fed up with "Can you take the top off and let me have a look!"
NO NOT TO LADIES
So many ways of doing the same things.
WONDERFUL!!!

Bob

[cbr900]

Colin,

Thats one brilliant thing about this Forum, it makes the impossible, become the simple, well done to everyone.....




Roy

[DickyD]

"It makes the simple become the impossible"

Very good Roy I will have to remember that.

Must make a note of it.

Oops have already.

Where's that glass gone?

[Colin Bishop]

"It makes the simple become the impossible"

Speak for yourself mate! life's complicated enough as it is....

[flybobby]

I have heard of folks coupling the motor to prop shaft with flexible tubing!! Can this be done?? :-\

[HS93 (RIP)]

Have you thought of using a longer inner shaft moving the motor further back. that if the shaft is on an angle in the first place,it would bring it further forward but higher .flexible tubing on a motor of that size would just knot.  allso if it is not in line there is a lot of wast of energy  .. Peter

[martno1fan]

I have a torpedo 850 motor to install but it is too fat!!  The inboard end of the prop shaft sits too low inside of the hull, not allowing enough room to line the motor up!! :-[

Is there some kind of flexible coupling or a magic fix so that I do not have to fit a new stern tube, or make adjestments to the existing one?

Any suggestions welcome as i am pulling what's left of my hair out on this one! ::)

hi do it the american way and use a flexi shaft that way it doesnt matter what angle you have the motor at within reason!!!you can use the existing tube !!

[HS93 (RIP)]

They dont use reverse as the shaft unwinds  Peter

[martno1fan]

They dont use reverse as the shaft unwinds  Peter

i cant see any electric motor unwinding them as they handle gas engines upto 46 cc ,even more!! ,one small 800 motor wont unwind it im sure!!.in any case you can weld it so it wont unwind using normal solder!!.

[HS93 (RIP)]

What the full lenth??  they allso run in a different type of outer tube, they have a lining made of teflon or similar. Peter

[malcolmfrary]

Its unusual to find a gas engine that reverses, but electric ones do it very easily.  The spring-type drive is normally arranged so that it is trying to tighten up in normal use, especially with high-power motors.  I use ex-lighter flint springs as a drive coupling for small low power plastic kit conversions, but that is a different game altogether.
The cardan shaft or a gearbox/toothed belt drive seem the best ways to go.

[martno1fan]

What the full lenth??  they allso run in a different type of outer tube, they have a lining made of teflon or similar. Peter

some use teflon at the ends of the shafts but most dont they just use grease like any shaft!!ive also seen where a guy has indeed soldered the  shaft where it exits the stuffing tube and joins the engine..in any case there will only be a small length of the shaft not in the sleeve as you can bend the brass tube also so the chances of it un winding is small .the 800 motor in my opinion wont be strong enough to unwind it anyway!!.