Model Boat Mayhem
Mess Deck: General Section => Chit-Chat => Topic started by: Klunk on August 13, 2023, 06:31:44 am
-
As above.
I've tried the crown version from CMB.
RUBBER joint version, and huco ones. All have problems with crap alignment or smashing to pieces, huco and crown. I was getting some from Germany as they were solid couplings, and very good, but pricey at £30 a throw.
Any ideas where to get some uk ?
Otherwise I might have to buy a lathe!
-
Another lesson this morning in why huco couplings are garbage…
(https://www.modelboatmayhemimages.co.uk/images/2023/08/13/IMG_1310.jpg)
-
Plastic cardan couplings work fine provided they're used within their limits. Not suited to high speed fast scale or fast electric craft
Have you tried a constant velocity dogbone type e.g. https://raboeschmodels.com/product/coupling-101-01/# (https://raboeschmodels.com/product/coupling-101-01/#)
Also-
https://www.cornwallmodelboats.co.uk/acatalog/Amati-Coupling-Assembly-A6561_04.html#SID=740
-
I have just got some of those red couplings, there is nothing on them to show they are HUCO as huco have they name on the side. So these must be the usual rip offs. I had to use a vise to get the ends home in the housing. If I was using one in a brushless set-up I would have put shrink wrap over the centre. The last time I used brushless, I was give some stiff tubing, hydraulic oil pipe? and the brass ends were forced into it and it all worked fine, looked neat as well. nemesis
-
Those are some impressive (old?) capacitors that you have there. :o
-
All have problems with crap alignment or smashing to pieces, huco and crown. I was getting some from Germany as they were solid couplings, and very good, but pricey at £30 a throw.
Probably a very stupid question but what is the difference between solid couplings and alignment thingys at £9.60? {:-{
-
Those are some impressive (old?) capacitors that you have there. :o
They’re absolutely not mine. I’d not be dim witted enough to use a huco coupling and the motors are missing pistons %)
-
Any idea what these 'crown' couplings are. New to me.
-
Any idea what these 'crown' couplings are. New to me.
That is a Private Group. Unless you are a member of the group you cannot see anything.
-
No skin off my nose, sunbeam.
-
There are metal ones. But I don’t know if they make assorted sizes
https://www.amazon.co.uk/6x4mm-Universal-Coupling-Coupler-Connector/dp/B01GPTUVRG (https://www.amazon.co.uk/6x4mm-Universal-Coupling-Coupler-Connector/dp/B01GPTUVRG)
-
There are metal ones. But I don’t know if they make assorted sizes
https://www.amazon.co.uk/6x4mm-Universal-Coupling-Coupler-Connector/dp/B01GPTUVRG (https://www.amazon.co.uk/6x4mm-Universal-Coupling-Coupler-Connector/dp/B01GPTUVRG)
Those come in many sizes and from many suppliers eg:
https://www.aliexpress.com/item/1005005052868873.html?spm=a2g0o.productlist.main.1.205b7sVB7sVBYj&algo_pvid=d54cb591-b41b-47cb-bf6e-075440d7db1f&algo_exp_id=d54cb591-b41b-47cb-bf6e-075440d7db1f-0&pdp_npi=4%40dis%21GBP%213.72%212.23%21%21%214.58%21%21%402101e9d516919963982248959e4de0%2112000031464737495%21sea%21UK%210%21A&curPageLogUid=CJztzsmC6w5i (https://www.aliexpress.com/item/1005005052868873.html?spm=a2g0o.productlist.main.1.205b7sVB7sVBYj&algo_pvid=d54cb591-b41b-47cb-bf6e-075440d7db1f&algo_exp_id=d54cb591-b41b-47cb-bf6e-075440d7db1f-0&pdp_npi=4%40dis%21GBP%213.72%212.23%21%21%214.58%21%21%402101e9d516919963982248959e4de0%2112000031464737495%21sea%21UK%210%21A&curPageLogUid=CJztzsmC6w5i)
-
I have recently bought an all-metal UJ from Prop Shop but I haven't used it yet - boat not finished! But if it's up to normal Prop Shop standards, it should be fine. The website does say it's not for fast electrics, but a speedy scale model (MTB, Riva, etc.) should be fine unless you go way, way overboard on your motor and prop.
(https://modelboatmayhemimages.co.uk/images/2023/07/27/motor-in-place.jpg)
Greg
-
'scuse me but a dog bone coupling is a free floating centre dog bone just held within 2 sockets. I have some old plastic ones from SHG, not suitable for the thrashing I can see in above piccys.
Pete you have cracked and near melted that red U/J plastic coupling! Plastic won't do much for you there. I have the ball, with a bar, and socket metal couplings but they always seemed to cause electrical problems.
Anyway these days I can't run fast enough for anything over 30 watts!
Regards
Roy
-
Are these any good?
Are they robust enough?
eBay item number:283138679258
eBay item number:283783204646
eBay item number:284997911742
(https://i.postimg.cc/zbxwj0Cg/Screenshot-2023-08-14-224652.png) (https://postimg.cc/zbxwj0Cg) (https://i.postimg.cc/9RmtZv72/Screenshot-2023-08-14-224836.png) (https://postimg.cc/9RmtZv72) (https://i.postimg.cc/JDzZGZf4/Image4.jpg) (https://postimg.cc/JDzZGZf4)
-
Klunk - what boat and motor do you have which is eating couplings!
I've got some of the better quality Huco type for use in low powered/slow models and wouldn't touch those red plastic ones with the proverbial.
I've pretty much standardised on the alloy/rubber/alloy sandwich ones, which are supposed to be heavy duty so I hope I dont have any problems.
Chris
-
I have been using all metal disc couplings of industrial use for my 1m (40 inch) class cabin cruisers
with no problems regarding the strength. Bench test of the coupling in my Najade showed 24100RPM for 10 seconds.
Another reason is its calmness when rotating at higher speed. :-))
1; A disc coupling installed in my Najade. Screw shaft is 4mm dia. The brushless motor is 1800W 2050KV.
2; 24100RPM with 3S lipo in Najade
3; Another pic of dic coupling in my Jupiter F-99. Screw shaft is 4.5mm dia. The motor is 1200w 2200KV.
4; The Jupiter in the rough water sailing with 3S lipo.
I ordered the couplings from Misumi (a Japanese company ). They carry wide range of couplings for industrial use.
See ; MISUMI – Configurable mechanical components – buy online (misumi-ec.com) (https://uk.misumi-ec.com/)
Enter "coupling" "disc coupling" or whatever you like for your needs. !! :-))
-
Nothing adequately compensates for miss alignment. It generates noise power loss. Never had a problem after correct alignment and use of the 'Rip Max' U/J which was steel and could be classed as a half Dog Bone, ONLY type to isolate end thrust between drive/driven shafts unless we play with the disc and pin drives.
Regards Ian
-
Tony H's question is a good one for many of us. Just what is the difference between an alignment coupling and a solid coupling?
-
Hi BB - which type are you using please? there are many different types on Misumi's website.
thank you Paul.
-
Hi the Huco couplings are not constant velocity joints, which may be part of the trouble. I am using for no more than 40 watts thick wall plastic or neoprene tubing fitted over the Huco brass parts. Normal alignment is dead straight (the only time the Huco C.V U/J's are CV).
Have been interested in the posts of different options.
Roy
-
Ian, disc and pin - I bet there are a few people who have to look it up in Vic Smeed's Boat Modelling book - unless of course you are as old as us :-)
On page 74, fig 161 in Vic Smeed's Boat Modelling revised edition for those who want to know %%
John
-
I've always used the Huco couplings but typically two of them on each shaft which effectively makes them constant velocity joints and takes care of any slight linear misalignment but to be fair they are not designed for very high speeds and power which is where the problem lies. With brushless motors the speed is very much higher and they are just not strong enough at those speeds.
Also the actual clearances to get them on to the shaft takes effect at very high RPM along with the imbalance of the grub screws which causes vibration and can destroy the couplings. Also some modellers tend to have two speeds, full power and off, which puts a huge strain on couplings. Some people I know are very guilty of this and don't seem to understand its best to work up to maximum speed.
Just my experience here but to be fair I tend to model scale craft so excessive speed is not a problem.
Cheers
Geoff
-
'scuse me but a dog bone coupling is a free floating centre dog bone just held within 2 sockets.
If you follow the link it's actually how they describe the coupling. I suppose if you want to be precise then half a dog bone perhaps, just trying to give a description folk will understand.
-
A simple technique that works exceedingly well is to solidly couple the motor to the shaft, but have the inner bearing in the stern tube flexibly mounted with a piece of silicone tube.
-
A simple technique that works exceedingly well is to solidly couple the motor to the shaft, but have the inner bearing in the stern tube flexibly mounted with a piece of silicone tube.
I don't really understand what you are doing. Where exactly does the silicon tube go?
-
Klunk , Have you checked out the various uj offerings from Prestwich Model Boats ? Trevor.
-
Thing is (as I’ve said countless times on this forum), electric motors do not need a flexible coupling. The model should be built so that the motor and shaft are in perfect alignment to enable the use of a solid coupling
-
Didn't even mention the I/C engine version with the pins inside the flywheel and the shaft coupler slotted (Like a BIG ball and socket) John. There were heavy gauge Neoprene sleeve type couplings with the straight knurled brass fittings for motor and prop shafts back in the fifties. ABSOLUTELY useless when one end connected to an ED Racer but totally solved with the ones supplied by Max Coote.
Alignment and solid couplings, same beast in my book but don't solve the end thrust on the motor unless shaft end float carefully adjusted to eliminate motor float limits being exceeded.
Regards Ian.
Forgot the fibre disc and two white metal castings supplied in the Adamcraft Sea Plane Tender John.
'Search' facility should highlight how many times this subject as been beaten to death.
-
Brushless motors nearly always have ballraced shafts so can deal with axial thrust well enough I find.
I think the main snag with a solid coupling is that parts aren’t always made accurately, and you can easily end up with some runout that is a little too much for a smooth result. So you have to be careful where you source parts or your own fabrication if you make them yourself.
-
I don't really understand what you are doing. Where exactly does the silicon tube go?
Basically the silicon tube replaces the inner bearing so the shaft can move around in case the coupling is not completely in line. The shaft for the old Sloopy fast electric only used an outer bearing on the tube with a solid coupling on the motor. The inner end of the tube was open and allowed for slight misalignment of the motor and shaft. Worked well using a narrower shaft than normal, I think 2mm with an adaptor fitted to the end to take 4mm threaded props.
Jim
-
It’s not quite like that. The silicone tubing doesn’t replace the bearing, it acts as a flexible attachment for the bearing, so that it’s not rigidly pressed into the stern tube. Effectively the metal bearing becomes self-aligning through compliance of the silicone tubing.
-
On a side note ....... Glynn Guest provides a definitive guide to installing motors and running gear.
http://www.modelboats.co.uk/news/article/drivelines/27166
-
Interesting point that Glynn makes about the alignment of parts.
I'm just completing the installation in my Fairey River Cruiser and I'm using a Raboesch prop shaft with a ballrace bearing at the motor end. I'm using a Huco type coupling, also Raboesch, made from what looks like Nylon and well made.
This model is only going to be used at moderate speeds so I have no concerns about the coupling. The motor was installed, connected using a solid alignment connecter and then the prop tube epoxied in place, so I have used my best efforts to ensure alignment is as good as I could get and the motor was left in place.
It could be argued that the exposed prop shaft is a little long at around 50mm but I don't think it excessive. Anyway, once the flexible connecter was fitted and the motor run you could see it running out of true slightly where the prop shaft goes into the connecter. Whether it's the connecter being slightly out of round or the prop shaft not being quite straight I don't know.
But it turns nicely and no excessive noise or vibration so I'm not concerned.
I've used the same method in all my builds and did wonder about just leaving the solid alignment couplers fitted but decided not to.
Chris
-
It's always possible for the alignment coupling to be slightly out and yes it has happened to me >>:-(
-
Fair enough, quite a few people have complained out these Huco 'Red' coupling, but personally, I never had an issue with them, including on an
OS 40FSR powered offshore race boat! Well, actually, one did explode on that boat .... but only after something broke, it flew up the bank 10 feet and got caught in the long grass.... the coupling didn't like that much! {:-{
https://www.modelboatmayhem.co.uk/My_models/05%20raving%20mad.htm
Another lesson this morning in why huco couplings are garbage…
(https://www.modelboatmayhemimages.co.uk/images/2023/08/13/IMG_1310.jpg)
-
You're a brave chap and lucky Martin!
We spend quite a bit on our boats so why risk it with cheap connecters? Ok on cheap and or slow boats where if they do fail not much damage would be done.
Chris
-
Klunk - what boat and motor do you have which is eating couplings!
I've got some of the better quality Huco type for use in low powered/slow models and wouldn't touch those red plastic ones with the proverbial.
I've pretty much standardised on the alloy/rubber/alloy sandwich ones, which are supposed to be heavy duty so I hope I dont have any problems.
Chris
German e boat. Cannot remember the motor size off hand. But a 540 brushless equivalent with a 120 esc (what I had to hand)
At full speed on 7.4v lipo she develops a nasty torque roll.
-
Are these any good?
Are they robust enough?
eBay item number:283138679258
eBay item number:283783204646
eBay item number:284997911742
(https://i.postimg.cc/zbxwj0Cg/Screenshot-2023-08-14-224652.png) (https://postimg.cc/zbxwj0Cg) (https://i.postimg.cc/9RmtZv72/Screenshot-2023-08-14-224836.png) (https://postimg.cc/9RmtZv72) (https://i.postimg.cc/JDzZGZf4/Image4.jpg) (https://postimg.cc/JDzZGZf4)
Left pic used ok but problematic on larger brushless
Middle used 15 seconds of life
Right pic not used so will get one to try
-
What RPM are you running at? Balancing becomes very important at higher RPM’s, and a lot of these couplings aren’t with those offset grub screw fixings.
-
Roughly 17000rpm
-
From M-Jet RC Jetboats ( Facebook )
(https://i.postimg.cc/Z0C0bgQY/370178930-122099054156069310-5890021339389328245-n.jpg) (https://postimg.cc/Z0C0bgQY) (https://i.postimg.cc/YjZ0hRc6/385863704-122099054138069310-7807544569021748534-n.jpg) (https://postimg.cc/YjZ0hRc6)
-
Hi Pete, are you sure you are spinning a propellor at that speed?
That is 280 turns per second! I did have a small boat with a high speed engine and it just sat in the water, the prop was like a mixer, nothing happened and then you give it a push and it was off like a rocket.
My old Steamlinia when converted to electric planed very nicely, the 45mm. prop was running at 2000 rpm and the motor consuming 30 watts. All measured and calculated, Malcolm will bear me out as we were first of all trying to get a steam driven boat to plane.
How many watts are going into the motor?
All the best
Roy
-
Hi all, in post No. 33 Chris F mentions the coupling end running out of true.
I have a PT boat and the builder being an aeroplane man had not noticed that the thread at the prop end was actually running in the bearing of the prop shaft.
I decided to replace the bearing and shaft from stock. This did not work as my calipers were measuring several different shaft diameters among my prop shafts, also the prop tubes had different wall thicknesses.
The threads all fitted onto the Huco coupling but some were a bit slack or floppy. A good fitting nut then a couple of tight fitting washers and then the coupling did help straighten out the coupling connection.
The most likely cause is the 'looseness' of the thread assuming it is screwed in place and the same would be true for a plain end where the brass part would screw onto the shaft.
As most of you will know it is easy to knock out the bearing from the shaft but do not do anything else until you have a bearing that is the correct diameter and is a pressure fit into the tube as a replacement. I wondered if the different diameters were due to BA and metric sizes but none reached 4mm diameter
I must have spent a day on the combination of shaft length to diameter and the right coupling, most frustrating. It ended up a compromise but we shall see, and I am not looking for high speed.
Lately I have used the brass parts of the couplings and fitted a thick walled tube between them, it has to be in line but is very cheap and best of all, it works.
In a previous thread on this forum there was an analysis of the speed of the driven end of the Huco or any other U/J joint. Briefly if you are running at an angle although the rpm is the same the angular velocity is different the whole time, i.e. it jerks while rotating!
To test this hold the U/J in your hand and bend to 50 degrees or so and you can see that the rotation rate is different as parts of the coupling change their relative angles. I have found that the old half inch water pipe copper tubing is a close fit over a Huco coupling and might be used to align the motor to the shaft.
Regards
Roy
-
https://www.technobotsonline.com/mfa-motor-re-380.html
Mines a brushless motor running on 7.4v lipo. Above is s standard 380 size motor. Rpm is stated, but drops under load and weight, by 5 to 20% depending on hull performance etc
-
You could only drive a small prop with that motor spec.
What boat and prop size are you trying to run?
-
It's a German s39 eboat. Runs on a 25mm prop. I don't trust huco couplings on brushless as have seen several blow, including ones meant for brushless.
-
I think some of the problems are centred around a few things:
- The standard Huco coupling will only work with a very slight miss alignment in both planes - you need two in line to make it a real constant velocity joint. Other metal joints with discs have the ability to flex in both directions and as such are better if more expensive. This is important for smooth running.
- At high rotational speeds manufacturing tolerances come into play along with grub crew imbalances which cause vibration and noise and eventually joint failure. Brushless motors get to much higher revs than the original couplings were ever designed to take and at those speeds the centrifugal forces on the couplings can make them pop open.
- Where does the thrust go - I've seen lots of pictures of Huco couplings (and others) with the brass inserts fully inserted - this is not good practice and you should allow for 1mm of float so the in line thrust is not transmitted through the coupling. The thrust needs to be taken either with a separate internal bearing (not often done albeit it is typically full size practice) or at the end of the prop shaft with a collet and a couple of small washers so the prop thrust is pushed against the prop shaft casing and hence to the hull.
- If the thrust is pushed against the engine via the coupling it will put a strain on the coupling and can cause a Huco to burst. It will also put a strain on the engine bearings. It is also possible that if the engine is mounted in a typical "L" shaped metal bracket that the bracket will deflect under load putting more strain on the coupling and premature failure and increased current consumption because of friction.
- Solid couplings also need to take this into consideration - the thrust should be imparted to the prop shaft casing.
However having said all this we are making models which are massively stronger than their real life counterparts so we can typically get away with things that would fail in real life.
Cheers
Geoff
-
Yep, a lot to be said for the OLD Rip Max ball and socket U/Js. Better if aligned but NO thrust transmission problems.
Huco have promoted laziness.
Regards Ian.
-
Brushless motors are almost always equipped with ballraces, which will absorb axial loads effectively for the kind of load we're talking about.
When using the motors in model aeroplanes the motors take the axial force from the airscrew, so is there any difference with a boat?
Fullsize Schnellboats hit about 50mph at full crank, so a model will need a good turn of speed, but scale speed will depend on the scale of the model. Also useful to know prop pitch.
To find out scale speed, calculate the square of the models scale, then divide with the speed of the fullsize boat.
e.g for 1:1 50mph, for a 1/32 model-
Square of 1/32 is 5.7
50 divided by 5.7= 8.8mph
Assuming the motor can wind within 95% of its unloaded RPM, e.g. 16150RPM, the pitch is equal to the diameter (a "square" prop), then you're looking at around 15mph with zero slip, which is impossible. In practice prop slip, plus drag from the hull etc. means you can usually halve that figure.
Few commercial model props are "square", most designed for submerged running tend to be about 1.2-1.4 times diameter, some designed for steam power tend to have a very high pitch to compensate for the low RPM/high torque of many steam engines.
In practice most speeds usually need to be increased a bit over scale for very slow boats, else a model will dribble along. Not the case with something like a Schnellboat
Does that help or are you now thoroughly bamboozled?
-
I take your point re axial loads with brushless motors when used in model planes, good point. Are the same motors used in boats, I just don't know but a valid point indeed. However the couplings may not take these axial loads which is the main point.
Cheers
Geoff
-
That would depend on the coupling. A solid coupling will clearly transmit the load. A cardan style coupling would also transfer axial force. A dog and bone coupling would not transmit an axial load, as the two parts are not connected axially.
-
Hi GUY'S,
A bit late on this subject but here is how I make DOG & BONE couplings.
Get a flat used file about 1" wide by 3/16" thk stick about 12" into a coal fire and leave it there until cool in the morning.
Cut off about 5" of the file with hack saw
Drill and form a a hole as shown in pic to suit the size of the ball, hole to be . 015'" dia smaller than the finished ball to allow filing to final dia, make sure that the cut is 7deg to allow swarf clearance.
When completed re harden the tool for cutting the ball.
The driver to the engine is a simple turning job and the final ball has a 1/16" dia rod drilled thro'.
When finished case harden the mild steel components.
All done quite easily
George.
-
An oldie but goody ;) Miles better than the plastic monstrosities
Regards Ian.
-
George, definitely one of the best solutions - the only problem I can see now is - do people know what a coal fire is these days. There probably wont be many around now - by God I would give an arm and a leg to have a coal fire in this house that I live in now - the modern thing with no chimney.
Well, rant over.
John
-
WHAT ,
No Chimly what about Santa
Geo
-
WHAT ,
No Chimly what about Santa
Geo
haven't you heard santa's not woke enough
-
This is what we need! ...
(https://i.postimg.cc/cCgcJbxQ/394740519-723363149827172-3837426051924052183-n.jpg)
-
Wow, That's what I call a coupling.
George