Consider yourself lucky Pat, I go on holiday for a few days without internet and the score plummets. Must be more ruthless and avoid holidays at all costs, exceot where fully connected !!

Like I said Pat "It is the joy in taking part...."😁😁😁
Roy

Bloody hell - I was struggling to get above the 6th position now having got todays wrong I am down to 7th position 😭😭😭😭😭

Here is the story of how the dolos was invented and how the inventors boss claimed the recognition for the invention.
Nowadays you will find them on most South African breakwaters an in most harbours you will find the metal moulds to make them.
The idea has spread world wide.

https://www.facebook.com/100064355032692/posts/pfbid024W4HJ7BsxBptPRJKcL9WroChx32SQyiX2sxBsDfbLKZoX3iBPo8tzBcSg1Ar4Aral/?

Same here Pat. I thought it was a Caisson as I had never heard of the answer at "A". I should have Googled it..😁

Dreary me got that one wrong

Oh well got this one wrong today. Dropping fast, hopefully I will do better tomorrow 😊

Another move down today after a move up yesterday dispite getting todays question right 🤔🤔

I got this right today but I didn't have a clue, until I read the question a couple of times. The answer again is in the question 😉

Should you need to shorten a screwed shaft use a metal saw. But first run a nut onto the thread and then saw the screwed end to size.

A gentle clean up for swarf on the end and then unscrew the nut and this will clean up any damaged thread.

Roy

Personal view:

As I mentioned elsewhere on this site, I spent 29 years on snowplow duty in Canada (somedays it could be as crazy as you can imagine). The equipment we used were 4 x 4 pickup trucks. The front wheel drive was using CV joints between the front turning wheels and the front axle. As explained by Roy and Alessandro, the extreme angle between the axle and a front wheel during a turn made the CV joint feature a requirement. If the CV joint failed the hammering coming from the front end would quickly let the driver know. When someone would ask where the CV joint was on the truck, I would know to point to the in side of the front turning wheels. Until today, I never knew WHY they worked so well👍

When alining the Huco coupling I used a short length of old gas pipe tube, not the current type but if removing the old stuff, put some by as it is slightly greater diameter than current gas tube.

The biggest problem is to get the brass ends sitting absolutely squarely on the shafts. The screwed shafts are the more difficult. With a clean threading on a prop shaft I would place a thickish washer over the thread but too narrow to go over the shaft plain tube.
Then lock this up squarely with a tight fitting nut forcing it against the washer face.

Then place another washer to fit against the tightened nut, then screw the Huco coupling onto this to form a locknut.
This should keep the Huco coupling parallel with the screwed shaft.

There is less problem with the smooth fit of plain hole locating as tightly as possible over the motor shaft. But when doing up the grub screw make sure it does not distort the true fit of the Huco brass part. It can cause the brass part to hump.

A possible solution is to file a slot on the motor shaft and screw a grub screw down and just touching the shaft and then screw a second grub screw down to lock it in place.
It will seem a little loose but it will not come off the shaft.

If any part of the plastic fitting over the splined part of the coupling is waving about when rotating there will be vibration and noise.

As I said earlier I use a plastic tube insert which reduces the effect of misalignment and decreases vibration.

Roy

Graphs? At 11 o clock at night? I can barely write my name at this time of night!😁😁😁

Sorry the animations do not animate.
Tomorrow I will correct any errors. Take what is written with a pinch of salt there may be translation errors.

Good evening to all the
naval modellers of the question of the day.

Your answers are to be considered all correct, however I will give what seems to me the most accurate correct answer.
I will first provide the concise answer and then the explanation (avoiding the mathematical formulas that many do not like), finally a summary with the practical aspects for modeling.
Since it is a forum if I write inaccuracies anyone can correct them or integrate the text with other information.

The single or simple joint (what in Italian we call a "cardanic" joint but that Google persists in translating incorrectly as a universal joint) is the one in images 1, 2 and 3.

Be careful, many sellers (especially online) call the cardanic joint a universal joint. This is wrong.

To the first question: "Using a single joint, what problems could it cause?"
The short answer is:
"The problem is that it causes vibrations. Consequently, also more noise.
The vibrations are greater the more accentuated the angle between the axes and the higher the rotation speed. The vibrations are a direct consequence of the different rotation speed, since the cardanic joint is not a constant velocity joint (homokinetic).
In the cardanic joint, unlike the homokinetic one, the instantaneous angular velocity (note "instantaneous") of the driven shaft is not constant during a complete rotation. Logically, the average rotation speeds of the two shafts are the same."

Let's see why in more detail.

The cardanic joint is an exceptional element because it allows the rotation to be transmitted between two axes that are on different planes and therefore form a certain angle between them (see figure 4).
In Italy we call it "Giunto Cardanico" or simply "Cardano", from the Italian mathematician Gerolamo Cardano (1501-1576), who rediscovered it in 1545. In reality, the invention of this type of joint dates back to at least the 3rd century BC, by Greek scientists such as Philo of Byzantium.
It is based on a fundamental central element with four axes called "cross" (see animation 5).
It has multiple uses: from the joints of mechanical keys to the steering axis. In all uses where speeds are not relevant or where few turns are made, no problem is encountered.
As already mentioned, however, at high speeds there will be vibrations, because the instantaneous angular velocity of the driven shaft is not constant during a complete rotation. Certainly the two axes will complete a complete turn in the same time, but in completing the turn there will be accelerations and decelerations.
Without writing formulas, it is enough to know that the transmission ratio is directly related to the angle formed by the two axes (figure 4), the conductor and the duct (i.e. the motor axis and the propeller axis in our case).
In the first graph (figure 6) you can see the trend over time (x-axis abscissa) of the angular velocity (y-axis ordinate) of two joined and perfectly aligned axes. The straight line tells us that, over time, the angular velocity (revolutions per minute, rpm) does not change, it is constant.
In the second graph (figure 7) you can see the trend over time (x-axis abscissa) of the angular velocity (y-axis ordinate) of two joined axes with a certain angle between them. The sinusoidal curve tells us that over time the angular velocity (revolutions per minute, rpm) changes, it is not constant. In some points it is maximum and then drops to the minimum level in a continuous cycle. Therefore, the angular velocity is different from moment to moment. It is clear that the average of the sinusoid corresponds to the value of the straight line.

Let's get to the second question:

"What could be a valid solution and why?"

The answer is:

First possible solution.
"put a second joint"
but it's not enough.

I've noticed that many recommend it and limit themselves to this.
It is important that the angles of the engine and propeller axes with the central axis (alpha 1 and alpha 2) are equal but opposite. Look at figures 8 and 9.

In this way the sinusoids will cancel each other out.
See third graph, figure 10.
In fact two Cardan Joints constitute a constant velocity joint (I think it can be defined as a double joint or universal joint, see image 11)

Second solution:
Use a constant velocity [ homokinetic ] joint (see figure 12 and animation 13)
The constant velocity joint is the one used for example in the wheel axles of cars (see image 14).
In modeling I have never used them but I think many call them "dog bones" (with quite limited performance and resistance).
It is essentially based on mobile spherical rotations that guarantee constant instantaneous speed.
They need continuous lubrication (the real ones) and allow a lower phase angle than the Cardan joint.

Considerations and practical advice.

1. If we can, it is better to look for a perfect alignment between the propeller shaft and the engine shaft.
In this case, it is better to put a fixed connection (without a joint), because the fixed connection will let us know if we are not well aligned and we will be able to correct the positions (we will act more easily on the electric motor).
The Cardan joint, on the other hand, will adapt to small misalignments (deletive and useless) and we could finally have positioned the axes with a slight (not very evident and visible) misalignment.

2. If we are forced to use a joint, for example because the engine is in a high position and we do not want to tilt the propeller shaft (in short, we want to keep it as parallel as possible to the keel), it is not convenient to use a Cardan joint as in figure 15, for the reasons already mentioned.
We can put two joints in series so that the phase shift angles are identical (Image 16). We will thus create a homokinetic joint.
To create two equal alpha angles is not difficult, you do not need a goniometer. Knowing the geometry and the properties of the angles we will use a universal joint (double joint) and we will make sure that the axis of the motor and the axis of the propeller are parallel (again image 16).

If I was not clear please tell me.
Anyone can add their personal experience.

I still have to study the behavior and experiment with connections with semi-rigid cables in harmonic steel or other material.

I've been translating the answer for twenty minutes.
It's a very difficult twin birth.

Hi all. I was just thinking (dangerous for me) we are doing a lot of chatting in the Question of the Day section. Would we not be better in the forum section under Chit Chat hobby or otherwise? If we were there would we still get notifications?

After all these decades, somebody finally explained what a CV Joint is. I first meet them in 1989 in the front wheel drive axles in 4 x 4 pickup trucks. Thank you Roy👍
Yes, they were different than the drive shaft u-joints

Regarding post 4272 a U/J is not a constant velocity joint. If you drive it with your fingers and increase the angle you can see that the o/p shaft goes around in jerks some faster than the i/p and then compensating with the slower side.

Since this was brought to my attention I have ditched the centre pieces, and keep the brass parts and now use a thick wall tubing, feels like neoprene.

This is cut to length and first warmed with hot water and then fitted between the brass units the splined shafts make a good connection, and keep the angles as shallow as possible.
The result is also quieter, I agree that this is a solution at the lower end of power but suits my models fine.
Roy

ok then I found some machined type, 3mm to 5mm here in Canada for $19.02 CDN

Hi Ross, it doesn't matter really as I never have a problem these days. When I discovered the problem it was on my 48" Perkasa with a 5mm shaft running a 4084 620Kv motor to a two blade 46mm prop. It has been running fine for at least 10 years now..👍

Simplesailor:

What size shafting are you dealing with?

motor side
prop shaft side

I agree with RossM, and I set my single universal joint/couplings up with a slide over brass tube as well. However I no longer use UJ's made from plastic in anything above 10,000 RPM, and I have never found a good quality precision engineered metal UJ. So now it is flexi shaft or very accurately aligned solid connectors. The reason I no longer use plastic in high speed is because the torque that can be given (On fast starts) by brushless motors can cause the fingers to open and the brass centre just pops out, giving loss of drive. (These were good quality couplings as well) My temporary solution was to put some heat shrink round the centre to stop the brass part flying out. 😀

I may have misused the term DOUBLE UNIVERSAL JOINT. I was thinking about 2 single universal joint, one on each end of a shaft. This would join the output shaft of the motor to the input shaft of the work-to-be-done. This works well in large heavy applications.

This 2 single universal joint system often includes a sliding shaft, where one half of the shaft is sliding inside the other half of the shaft. This can allow for the changes in distance between the end of the output shaft and the beginning of the work-to-be-done shaft caused by twisting of motor or work-to-be-done

SimpleSailor wrote: " I assume this was a rhetorical question and you don't actually need help ".
Of course, when we ask the question, we need to have the answer ready.

Hi SimpleSailor, in the question I asked I am referring to the single joint (simple universal joint NOT double universal joint), which is the one that gives problems.
What are these problems and what are the possible solutions is the question.

I hope I was clear and did not make a mistake with the translation.

Hi Alessandro. I assume this was a rhetorical question and you don't actually need help 😂

In the past I have used a short length of brass or plastic tube that is a snug fit around the coupling, holding it in perfect alignment whilst the motor/motor mount is fixed in place. Once all adhesives have cured, the motor can be removed, the tube slid back off the coupling and the motor refixed...

Alessandro

BEST solution??

Align the well supported shafts PERFECTLY and join with a solid connector. That would be the least amount of power loss and wear.

Real life? Universal joints. At this stage, one would have to know the variation in the torque and rpm of the application. For example, an electric power generator with constant rpm and torque would use a lighter duty coupler than a racing hydro plane boat that has high variation in torque, load and rpm.

Do you have a specific application in mind?

Hi Alessandro.

Item 3. Are you talking about a Double Universal Joint (Huco) or a Dog Bone Drive ?

A rubber/neoprene coupling, transmits the power through a smooth curve..

Hi RossM, your answer is correct.
However, there is a more specific reason.

Regarding point 3, I have my own rule.
If I can align the engine to the propeller, I always use a fixed joint (without a joint).
I will look for the perfect alignment (or almost).
However, if there is a misalignment, it is impossible to use a fixed joint.
So the question already foresees a situation in which there is a misalignment of the engine axis and the propeller axis.

What is the best solution then?

Alessandro

1) Loss of power and bad wear from vibration

2) Increased maintenance because of the joint

3) Extra effort required to align output shaft and drive shaft

Solution:

Double joints

These would help absorb the slight misalignments, reducing power required and wear.

Repairs could be easier with smaller sub-sections that will require service or modification

Good morning everyone, I propose a human question for those who want to participate.
This question concerns dynamic rc naval modeling.

To transmit the rotary motion from the engine to the propeller, we can use various systems.
In case it is not possible to use a single and rigid axis, joints can be put in.
Using a single joint, what problems could it cause?
What could be a valid solution and why?

I will say my opinion after the other part of the world (which is now sleeping) will have the opportunity to read.

It's blocked in the UK on copyright grounds.,

Found, ep.2 in Italian. I was already curious.

Hi Alessandro, the French fireships arrived before he could answer...

Hi Nick, I remember seeing some scenes on YouTube.
Nice images but I don't remember the dialogues. A movie question, in short (I took it seriously, hahahahahah).
I wonder if there was a coherent answer or just a theatrical one.

Alessandro, I do not know the answer, the question is from a TV show called Hornblower, it arose as a question in our hero's examination for Lieutenant. (Episode 2). Doug gave a good answer...

Hi Nick, in relation to your last question I believe that a boat that complies with your conditions (close hauled, port tack, wind from the North East) must go east, as already said (see figure 1).
If, instead, it goes north, therefore towards Dover to go close hauled it should be on starboard tack and not port (see figure 2).
In other directions it cannot be possible because all three conditions are not satisfied.
If what was said is correct I will go ahead otherwise stop me.

In answering I imagined that the boat wanted to go to Dover, but perhaps I am mistranslating.
Should it go to Dover or does it want to continue towards the East?
If it has to proceed towards the East my answer will be different.
If it has to go to Dover (even without a sudden change in the wind) it will have to tack to port (changing tack from port to starboard).
So, to recap, I gave my answer considering that the boat wants to go to Dover and that there is a change in the wind direction (from 045 to 049 degrees).
Figure 3.

Dunnage! We used to collect it from the docks when we were kids, for den building, carty making and for burning on Nov 5th. Of course we weren't allowed to take the decent pieces...

I am getting closer😁

Doug, at some point you obviously turned east and ended up in Munich
🤣

Rather than impinge on QoD, perhaps we should start a new board, called something like Interrorgation club or something. Problem with the rapid fire stuff is that timezones preclude our shippers from the US Australia etc. Just a thought.. I remember on Mayhem there was a guess the photo, where photos or crops of photos of all things ships, both full size and model were posted and folk had to guess what it was.

I like this question, Nick:

"You're close-hauled on the port tack, beating up the channel with a north-easterly wind blowing strong, with Dover bearing north two miles. The wind veers four points, taking you flat aback. What do you do, sir?"

but I can't translate it correctly and understand.
If you are on port tack, the wind is coming from the North East (45 degrees) and you are sailing close hauled, then you are heading East (090 degrees), right?

If the wind shifts and comes from 49 degrees you enter the blind spot suddenly.

If these are the correct premises.
I would bear away first (move the bow away from the direction of the wind) in order to immediately recover the close hauled pace.
But immediately after that I should tack to port and go on starboard tack.

I think I am getting a bit addicted to this so I will wind my neck in a bit lol

Have a good night everyone

Nick,
Re The channel question-
You turn due West and take shelter in Folkestone harbour, my home town😁
Cheers, Doug😎

Thanks for that very interesting question and answer (Nick & Alessandro) I never fixed a Decca Navigator but did get a small Decca radar working for a someone. Anyone interested in the Decca Navigator the link is interesting (I thought so 😁)

https://www.jproc.ca/hyperbolic/decca_hist.html

I confirm Decca Navigator System.
But I looked on the internet.

Decca Navigator and , yes, Hornblower, The Examination for Leuitennant episode...