Installing prop shaft and motor

[StruttyParticipant @strutty]

Hello all, I hope someone might be able to help me please?

 

I am a complete beginner to model boat building and am just trying to install a 500 electric motor into a wooden hull. The prop shaft is a 10″ x 4mm solid shaft running in a brass tube with a universal joint to connect to the motor.

 

I have installed the prop shaft, have packed it with vaseline, and it runs nice and freely when turned by hand (although with a little end to end movement). When holding the motor in position, it sometimes runs well and quite quietly, but at higher speeds, it emits a loud shrieking noise. I have lined up the motor and shaft as accurately as I can.

 

I would have thought an electric motor with a well set-up prop shaft should run almost silently, so I assume I’m doing something wrong?

 

Any advice would be appreciated!

 

Thanks in advance.

 

Paul

[StruttyParticipant @strutty]

[ashley needhamParticipant @ashleyneedham69188]

Paul, very difficult to advise at a distance, as it were. If there is no obvious vibration at low to medium speeds then one could assume that the shaft and motor is line up reasonably well.

 

First things first, you need to secure the motor properly to see if it vibrates when fully secure. Does the motor run smoothly on its own? try another motor, buy or borrow one.

 

My money would go on the prop shaft flexing, or indeed being very slightly bent . 10″ is quite a long length for a shaft unsupported in the middle, my opinion. I would take the shaft out and roll it on a bit of glass or something to see if its straight. Further to this, end-play should be adjusted out. Could try a drip of oil on each bearing to see if the lubrication is sufficient.

 

It is not unknown for the coupling brass inserts to be less than accurately drilled and possibly changing on or `t other might effect an improvement. A double coupling, if you have room, would give added smoothness, or at least, make up for any slight mis-alignment.

 

I have a very annoying vibration period on my TBD, runs luvvly at low speed but at around half throttle it buzzes, and then smoothes right out at full speed. I changed the prop-tube and it got a lot better (slack bearings I think it must have been), but is still present. I have a feeling it is something, a fitting or whatever resonating at a certain engine speed.

 

Ashley

 

Edited By ashley needham on 23/10/2011 20:46:38

[StruttyParticipant @strutty]

Hi Ashley

 

Thanks for the quick response! I also wondered about the shaft flexing in the middle.

 

The motor seems to run smoothly on its own.

 

One of your comments puzzles me though. You refer to bearings. All this arrangement consists of, is a brass tube with a s/s rod down the middle, which I have to say, seems a bit of a sloppy fit. Each end of the rod is threaded and has a washer and nut to lock it up to the prop and coupling insert respectively. I’ve added a couple of little fibre washers to take up the slack, which was quite a lot – probably 3-4mm.

 

How could I support the shaft in the middle?

 

Thanks again.

 

Paul

 

 

[Colin BishopModerator @colinbishop34627]

Your prop tube should have a bearing inserted at each end so that the shaft is only supported at the ends by the bearings. If it hasn’t then it isn’t a proper prop tube. Just running a shaft directly in a tube is only feasible for very small models and short shafts.

 

If you just have a shaft and a tube it is asking for trouble, (and lots of leakage!) get yourself a proper unit, they are not very expensive. The noise you are experiencing will be the shaft binding on the inside of the tube.

 

Colin

Edited By Colin Bishop, Website Editor on 24/10/2011 10:18:46

[StruttyParticipant @strutty]

Ah, that makes sense. Clink! (sound of penny dropping!) I did wonder how a bit of grease was going to stop water coming in.

 

Will check out a couple of suppliers to find a better unit.

 

I did tell you I was new to this, didn’t I?

 

Thanks for your prompt help on a Sunday evening.

 

Paul

[ashley needhamParticipant @ashleyneedham69188]

I bought an all-in-one outfit originally for the Sunderland, it was a 2:1 geared 400 unit ..but the propshaft was simply a bit of tube, no bearings.. I didnt realise at the time and it was very noisy.

 

As it happens I took it out as not required, but I used it on the sailing Herald, as it is very compact, and you are not constantly using it, so the noise factor is bearable.

 

Ashley

[StruttyParticipant @strutty]

Hi all

 

Thanks for your input earlier. Quick update…

 

I bought a Raboesch prop and shaft to replace the existing one. Nice bit of kit, with proper bearings and watertight too.

 

I had a heck of a job to get the old prop shaft tube out though. The previous owner had been very generous with the glue, so I had to grind it all away, then bash the tube out with a hammer. Luckily, the boat wasn’t damaged (much) in the process.

 

I installed the new shaft, but had to fit an additional universal joint as the new one was a bit shorter. No real harm in that though.

 

Anyway, the hull has now undergone successful bath tests and no longer makes the dreadful racket!

 

While doing all this, I fitted a smart new brass prop, and the hull has had 5 coats of Plastkote. All the wiring is in now, including a loom for 6V and 12V lighting for when I come to fit it out. Looking forward to trying it out on the local boating lake soon.

 

Whilst writing, does anyone know where you can buy 1/12 scale modern clothes to fit a Heidi Ott doll? Most of the available ones seem to be very old fashioned.

 

Cheers

 

Paul

[Gareth JonesParticipant @garethjones79649]

I have had to remove a couple of old prop shaft tubes and rudder bearing tubes from boats and found that the best method is by applying some gentle heating using a soldering iron or small gas blow torch.

 

First remove the prop shaft and, to make the job less messy, as much as possible of the residual grease or oil in the tube. Then insert a soldering iron in to the tube and allow it to heat up. Position the soldering iron bit as close as possible to the glued in section where the tube passes through the hull. If you don’t have a suitably sized soldering iron a small gas blow torch applied to the exposed part of the tube is equally, if not more effective. Try and twist the tube to free it, using a pair of mole grips with a piece of cloth or card around the tube to protect it if you wish to reuse it. This method has worked for me where the tube is held in place with araldite and if done carefully allows the tube to come free without damaging the hull (as long as you do not set fire to it with a blow torch!)

 

Gareth

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