Aeronaut Classic build prop shaft seizure

[Tim GoldingParticipant @timgolding51028]

Hi All,

Happy New Year. I'm new here but not new to RC in general. I hope you can help. I got into RC boats relatively recently when my wife bought me an RTR. As I enjoy building/tinkering as much as running my many RCs I decided to do an Aeronaut Classic build. It was a joy to do for a relative newcomer to wooden builds and I was really pleased with the results. The maiden voyage was a success. Evidence here;

However, during the second run 2 days later she started to make a noise and slowed to halt (luckily near to shore). It turns out the prop shaft has seized. Apart from the obvious disappointment and realisation that I will need to break into the hull to replace it I am also confused as to why it happened. I had upgraded from the kit shaft to a 7 inch M4 Fineline prop shaft as I am running a 2200kv brushless motor on a 2s lipo and a 30mm 3 blade prop. I also greased the shaft to help prevent water ingress. As I see it there is no point spending time replacing it unless I know why it failed. Could it be too many revs for this shaft? Any help much appreciated.

Thanks

Tim

Edited By Tim Golding on 02/01/2019 16:41:42

[Tim GoldingParticipant @timgolding51028]

[Dave MilbournParticipant @davemilbourn48782]

Tim

That's a fast motor, even on 7.4v. I use either 750 or 1000kv outrunners in my models – both on 11.1v. I would suggest you de-rate the motor to one of no more than 1500kv if you want to carry on with the 7.4v battery. I don't know anything about the type of prop tube you've fitted, but SHG Model Supplies can supply new bearings for 4mm shafts in 8mm OD tubes for not-a-lot. The bearings are on Page 22 of their catalogue. These might save you from having to dig out the tube from the hull. You might also check that the prop you're using isn't a 'racing' type i.e.with a coarse pitch.
Good luck, m'duck!

Dave M

Edited By Dave Milbourn on 02/01/2019 17:06:38

[Chris FellowsParticipant @chrisfellows72943]

As Dave says that is a very high revving motor and at max revs with that battery will be doing over 16k. revs which is well beyond what most (unless a racing prop shaft) prop shafts are designed for.

A quick Google didn't find what the Fineline prop shafts max revs are but given the price I'd guess that it is well below what you've been revving it at! I see it has bronze bushes which have probably been damaged – unfortunately you can't go for Dave's suggestion as the Fineline tube is only 6mm and so unless you can get and fit new bushes you are going to have to fit a new prop shaft and a lower revving motor.

Chris

Edited By Chris Fellows on 02/01/2019 17:30:08

[Colin BishopModerator @colinbishop34627]

The Caldercraft Fineline range is really intended for moderate speed operations. As the name suggests, the construction is relatively lightweight to reduce the outside diameter of the tube to give a scale appearance for scale models. For a performance model a beefier tube is needed.

However this model represents a fast sports boat rather than a racing craft and your video shows that it is running at well over scale speed.

If the bearings can't be replaced then you are faced with removing and replacing the tube. However it may be worth contacting Model Boat Bits

**LINK**

who offer a bespoke engineering service and would probably be able to make you a set of new bearings. If you can then extract the existing ones it will save you a lot of trouble but it would be wise to take the advice from Dave and Chris and use a less powerful motor/prop setup. This should still give impressive performance.

It might also be worth contacting Jotika/Caldercraft to see if they could supply you with replacement bearings although these might be relatively light duty ones compared with bespoke ones.

Presumably you can access the outer bearing reasonably easily. If you can get that out then it should be possible to insert a rod or dowel into the tube to drive out the inner one.

If the tube does have to come out then the best method is usually to apply heat which will break the glue joint so that you can twist the tube and extract it. A heavy duty soldering iron will do the job. The biggest problen with getting the tube out is that you need to do it without damaging the rest of the model or the varnish/paint finish.

All things are possible though!

Colin

 

Edited By Colin Bishop on 02/01/2019 18:27:36

[Paul TParticipant @pault84577]

Tim

What type and how much grease did you put into your propshaft as it is possible that your seizure is attributable to hydraulic lock rather than mechanical failure.

Have you tried stripping the shaft out of the tube?

Paul

[Ray Wood 3Participant @raywood3]

Hi All,

Just my two Penney worth, I have never greased a stern tube, just a drop of 3 in 1 oil on each ends Bush before a run 😀 works for me, but I've never used a brushless motor!

Regards Ray

[Colin BishopModerator @colinbishop34627]

I would have thought that hydraulic lock would cease once the shaft/tube had cooled down. But going on from that I assume you have removed he coupling and established that it is indeed a shaft bearing failure and not a seized motor?

Colin

[Paul TParticipant @pault84577]

Hello Colin.

Good point about checking for motor failure.

Re hydraulic lock, depending upon the viscosity and volume of grease used it is possible for the grease to create a hydraulic lock by 'cooking' and become compacted at one end of the tube then congealing and setting solid around the shaft…..better than superglue.

Paul

[Richard SimpsonParticipant @richardsimpson88330]

The only time I have ever put grease in a shaft the motor would not even rotate and so it had to be removed. What this made me realise was just how much additional load grease in a shaft can put on the motor. This can lead to motor damage, particularly at the performance end of the spectrum you are dealing with.

As already suggested you need to check the motor and then make a decision. If you want the performance you will need to completely remove the tube and fit a proper performance shaft and tube arrangement. If you are happy with a more scale performance then you should be able to get away with rebushing the existing tube, if indeed that is needed. If it is needed any local engineering place should be able to turn you up a couple of bushes from the ones you remove.

As has also been mentioned you might have burned grease between the shaft and the bush however careful application of a little force should get the shaft out in one piece then all you need is a good clean up.

Does your installation include a fuse? This would protect the motor in future and help to prevent a recurrence.

I suspect that the grease has burned in the bushes and you should be able to remove the shaft intact. I would then fit an oiling tube and a smaller motor and enjoy the boat at a much more scale pace. Fill the tube with a fairly light oil and just wipe a smear of grease or vaseline on the rear face of the propeller and the rubbing face of the universal joint.

[Tim GoldingParticipant @timgolding51028]

Thank you all for your detailed responses. Looks like I should have asked a lot more questions before I selected the prop shaft! Oh well, lesson learned there. I used tech grease 300 lithium (extreme pressure) that I use on my RC gearboxes etc. Also the motor is fine as I have decoupled it. I’ve just been trying to get the shaft out and eventually I got there – wasn’t helped by having used thread lock at the coupler. However to my surprise once detached from the coupler it span quite freely. I’m wondering if it was actually binding on the nuts IE they were tightening in use. There is a washer and a nut on the shaft before the coupler. How should I do it? It’s a threaded shaft and threaded coupler. Given the effort to replace the shaft I’m hoping I’ve got away with it somehow.

[Colin BishopModerator @colinbishop34627]

That could indeed be the problem Tim. It is certainly possible for the shaft nut to 'wind up' and lock everything solid unless the nuts at both ends are tightly secured – one against the prop, the other against the coupling. At the prop end the prop itself should screw tightly onto a nut which acts as a locknut. Then the washer of course goes between it and the tube end.

On the inside you need to lock the coupling to the shaft using another nut arranged so as th give minimum play on the shaft. Again, use a washer between nut and tube and a spacer if necessary.. The oher end of the coupling just slides onto the motor and is tightened.

From what you say it appears that the high revs and vibration have loosened the nuts leading to the lock up. Hopefully that is all it is, fingers crossed. However, you will have seen from the advice offered that once you start putting significant power through a driveline there are all sorts of issues which can (and do!) arise.

Colin

[Richard SimpsonParticipant @richardsimpson88330]

You have been lucky and got away with it. Tighten up as Colin says but ensure that you have a clearance to enable the shaft to spin freely with minimum longitudinal clearance. The washers provide a thrust face against the bushes to transmit the thrust into the hull. The one behind the propeller is the ahead thrust face and the one behind the universal coupling is the astern one.

I would still suggest that you replace the grease in the tube with oil and use a smear of grease on the thrust faces only.

Have you got a fuse in the power line? I would also still recommend that you go for a lower powered motor. To me it is preferable to have a transmission that is lightly loaded and capable of many years of reliable operation than one that is highly loaded and potentially unreliable in operation.

[Tim GoldingParticipant @timgolding51028]

Thanks again. I’ve re-attached and it runs freely again. Phew! I really didn’t fancy chipping into that enamel and hull. Replacing the motor sounds like a good plan but actually as I use a computer radio I will adjust the throttle end point to keep revs down for now and may be add some expo to reduce initial torque – even replacing the motor is a bit of a job due the way I’ve mounted it. I don’t have a fuse in the power line. I didn’t consider it as I don’t on other RCs but I might do that presumably to save the electronics if it binds?

[Richard SimpsonParticipant @richardsimpson88330]

Yes, it will protect your speed controller and motor in the event of an overload or overcurrent. As you have already seen an overload could have caused overheating in the motor before failure or even weed around the prop can have the same consequences. It will also protect the model in the event of a short anywhere.

[Peter Brown 15Participant @peterbrown15]

I made the mistake of fitting a brush less inrunner to my aeronaut classic. The coupling and shaft gave up after about 10mins and I lost the prop and inner shaft to the depths of the pond. Subsequently went back to a JP 380 motor and a 25mm brass 3 blade propeller and white marine grease in the shaft. This is reasonably fast. My Aeronaut Diva has a power M400 motor with a 25mm prop and 7.2v battery. It’s slow but never overheats and possibly is more like scale speed than a fast boat. Battery lasted me over an hour and possibly would have continued longer.Classic at Penarth Marina
https://youtu.be/KJpA-MSgCRk

Edited By Peter Brown 15 on 07/01/2019 16:20:44

[Dave MilbournParticipant @davemilbourn48782]

Peter
Grease isn't good inside a shaft because it adds too much drag, especially in cold weather. There are better alternatives e.g. Waxoyl or even plain old 3-in-1 oil. I simply put a little light sewing-machine oil onto the bearings before each outing and leave the "stuffing tube" unstuffed. I may have to resort to some molybdenum grease [Hob-E-Lube] on the lower bearing of Swordsman but that's only to compensate for a crappy bearing. We never stop learning, do we?!
Inrunners tend to be too fast for direct prop drive, except perhaps for exotic fast-electrics [or Harry Smith…], as you've discovered.
Dave M

[Peter Brown 15Participant @peterbrown15]

Dave,I will take the advice on board. Saying that I haven’t had any problems with the Marine Grease as it’s not thick and is syringable. I may be wrong but I don’t think the 2mm brass tube in the Classic or Diva has any bearings.

[Dave MilbournParticipant @davemilbourn48782]

Are you seriously running a 2mm O/D shaft in a 2mm I/D tube – in those models?? If so then it's not at all surprising that you've had problems. At those motor speeds the drag will be phenomenal and the current drain equally so. I'd have thought that the absolute minimum would be a 3mm shaft in a 6mm "stuffing" tube with plain bearings at each end.
DM

[Peter Brown 15Participant @peterbrown15]

Dave, both kits came with the brass 2mm I/d tubes as standard. As I said there are no bearings unless I’m mistaken so it’s just a tube. I’ve no problem running brushed motors in them at scale speed. Obviously brushless is not advisable. The marine grease possibly helps in that there are no bearings. Grease spec -35 degrees to +150. As I run my Classic at above scale speed I do have a fan for cooling and this works for me and the motor is rated at 9.5v.

[Malcolm FraryParticipant @malcolmfrary95515]

Past experience has shown that a lock nut that is not correctly locked can walk along its shaft and pinch both ends. This makes a very effective brake. The usual mistake is to tighten the lock nut against its friend while holding the shaft. the two nuts (or nut and coupler or prop) need to be tightened against each other to lock against the thread on the shaft.

There was a post on RCGroups a few days ago talking about the different grades of thread locking compound, from memory the "Purple" would be the best for our uses. If you can get it.

[Chris FellowsParticipant @chrisfellows72943]

Peter

Using a brushless motor isn't the issue, in fact it's preferable in that type of craft, it's using one with a far too high a kV rating and a weedy prop shaft which you allude to.

As Dave has said, you need something around the 1000kV mark. The one you have could still be used if you restrict the throttle, though higher kV motors are less torquey – try it with the new prop shaft first.

As the prop shaft is pretty short you need at least a 4mm shaft. if you don't want to worry about lubrication you could use one of the Raboesch maintenance free prop shafts (though quite a bit more expensive) with a choice of 10k. or 15k. max revs. available from Cornwall Model Boats etc. the latter being the best bet in a fast boat.

Chris

Edited By Chris Fellows on 08/01/2019 14:05:59

Edited By Chris Fellows on 08/01/2019 14:07:26

[Peter Brown 15Participant @peterbrown15]

Thanks Chris but I actually prefer using a brushed motor. For me the 2mm shaft is not a problem after all it came with the kit. If I wanted to rip up the water then I would get a fast electric with a brushless motor. I think the clue is in the type of boat Cabin Cruiser.

Edited By Peter Brown 15 on 08/01/2019 14:16:36

[Chris FellowsParticipant @chrisfellows72943]

Sorry Peter, now that I've read through the thread again I see that I've mixed up yours and Tim's posts! Most of what I've said is more relevant to Tim.

As regards your boat, if brushed gives you the performance that you want then great. Still reckon you should bin the 2mm prop shaft though. Just because it came with the kit doesn't mean it will be the most suitable or of good enough quality. Kit producers have to save as much as they can to make it viable.

Chris

[S MParticipant @sm83187]

I would do away with the grease as already suggested, instead I would use a silicone oil as this has the benefit of minimal thickening when in the water, unlike greases, even light greases, as they do thicken up in water and create unecessary drag, which creates unecessary loadings.

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