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Author Topic: Rowing machine  (Read 7425 times)

Tim_M

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Rowing machine
« on: September 27, 2015, 06:46:39 pm »

Sadly, I get fascinated by certain topics. I was looking at Krishna's rowing boat and the discussion of how to steer without a rudder. Got me thinking. Here's my contribution:


In reality, rowing boats are steered by lengthening and shortening the stroke of the oars. Taking the 'brief' of achieving steering without a rudder (rather than creating a realistic rowing action) I came up with a simple concept. Rowlocks  {-) .


I've got two ideas here. The first part is to create a non-circular motion for the oars (there are many ways to do this). The second is to change the stroke of the oars. That can be done very easily by moving the rowlocks relative to the driving mechanism. Simples!


I have one mechanism that creates the non-circular motion by using and elliptical guide slot and a slotted rotor. The rotor traps the ball in the slot. The second mechanism has the rowlock offset vertically from the rotor and uses a simple ball joint. I have modelled the rowlocks with an radius on them; this could just as easily be a spherical bearing. You need a pin in the rowlock running in a slot in the oar to stop the oar from twisting. I suggest a worm and wheel would be a good way to drive the rotors.


To steer, you simply move the rowlocks left or right as a pair (or keep them still and move the drive mechanism). As the stroke gets shorter, the speed of the oar gets lower too because the oars stay in sync. The stroke on one oar gets longer as the other gets shorter so I don't think you would need too much movement on the rowlocks.


I reckon with a bit more work, you could make the rowlocks rotate too so that the oars would feather on the back stroke. The ellipse could be pretty much any shape (that would not jam up) or the rowlock could be offset vertically to distort the elliptical action and get closer to real rowing.


I don't have the tools to make these mechanisms or any plans to build a row boat in the foreseeable future but if somebody wants to turn the concept into reality I'd be happy to help design the mechanism if help is needed.


It may have been done before but I could find anything quite like this on the net. (Mind you, I get bored very quickly doing 'prior art' searches. Done quite enough of those at work!)


There are some animations on Utube:


https://youtu.be/ndIpSqvaZY0
https://youtu.be/nZLZashracM
https://youtu.be/cFAvfME79QU
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Martin (Admin)

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Re: Rowing machine
« Reply #1 on: September 27, 2015, 10:29:29 pm »


Elliptical 2 look realistic!
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essex2visuvesi

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Re: Rowing machine
« Reply #2 on: September 28, 2015, 12:12:55 am »

Interesting.


Would you be offended if I took you idea and run with it on my 3D printer?
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Tim_M

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Re: Rowing machine
« Reply #3 on: September 28, 2015, 06:25:15 pm »

I should have put a bit of explanation with the video link.
Elliptical 1 and elliptical 2 are the same except that the rowlock is further away from the rotor in elliptical 2, hence the shorter stroke. They are running at the same speed (or should be). Martin, if you think elliptical 2 looks best, I reckon you need to pull harder!  {-)


Somebody has probably spotted that the 'simple' mechanism could also be turned through 90 degrees to give a flat ellipse.


Do feel free to use this concept in any way you wish - I'd love to see somebody make a real mechanism (or print one  :-)) )[size=78%]. [/size][/size]The CAD models I knocked up are only to show the concept. I rather like the elliptical style actuator. The slot could be any shape you like. The important part of the concept is the moving rowlocks; that's what gives you steering and that was the challenge I set out to meet.[size=78%]
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Martin (Admin)

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Re: Rowing machine
« Reply #4 on: September 28, 2015, 07:01:46 pm »


 Martin, if you think elliptical 2 looks best, I reckon you need to pull harder!  {-)


2 looks like it spends more time in the water. Isn't the center offset upwards?
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Tim_M

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Re: Rowing machine
« Reply #5 on: September 28, 2015, 07:57:15 pm »

Optical illusion. On the elliptical versions, the rowlocks are on the same centreline as the rotor so the action is symmetrical. It was just easier to model it that way. Now, you could easily offset the rowlock downwards a bit and then the action would be skewed; going down more than it goes up. (I had to think about that to be sure I'd got it the right way round!)
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Jerry Hill

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Re: Rowing machine
« Reply #6 on: September 28, 2015, 10:23:00 pm »

Interesting.

Would an oblique straight oval give a more realistic action?
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Tim_M

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Re: Rowing machine
« Reply #7 on: September 29, 2015, 07:41:53 pm »

To be honest, I haven't given much thought to the rowing action itself. My aim was to get steering. That said, the guide slot could be pretty much any shape. I chose an ellipse 'cos it was simple to model in the lunch hour. Obround would work but I'm not sure how realistic that would be. Apart from getting steering, a neat thing about this concept is that you could tune the shape of the stroke by moving the rowlock off centre (in any direction). For example, moving it up would give a flatter stroke in the water - but you might need to angle the rotors to actually reach the water.


I can see I will end up doing a bit more with this when the weather turns cold; maybe even design a practical mechanism if I get the time (the rarest commodity in the world, in my experience). It's many a year since I rowed a boat so I guess the first thing to do would be to research what a good rowing action is. I'm sure somebody's put that on the net somewhere. Just imagine, line up a few of these in a long, slim boat and find some blue paint.....


Anybody got a scale Thames in their shed?? O0
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Jerry Hill

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Re: Rowing machine
« Reply #8 on: September 29, 2015, 09:59:51 pm »

I like 'obround', I've not heard that before.

Another little lightbulb moment. If the length of the obround could be adjustable the stroke length could be varied that way.

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Tim_M

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Re: Rowing machine
« Reply #9 on: September 30, 2015, 06:57:27 pm »

Go on then, let's see you do it   {-)
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TheLongBuild

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Re: Rowing machine
« Reply #10 on: September 30, 2015, 07:13:48 pm »

HI
Have just uploaded a video of a rowing boat on the pond at the Boat Convention, not sure if its what you have in mind but still a nice little clip.

https://www.youtube.com/watch?v=y5j4fHh3e1s&feature=youtu.be

Larry

Tim_M

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Re: Rowing machine
« Reply #11 on: September 30, 2015, 07:37:53 pm »

That's cute. My guess is that the rower conceals several servos, That would take some very clever driving or programming but it certainly does the job!
I especially like the cox in the back giving the orders  {-)
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Re: Rowing machine
« Reply #12 on: September 30, 2015, 07:43:11 pm »

Just saw the video and have to agree that not only is it a well built boat but very cleverly done, well done whoever did it. I love the monkeys face as he looks around {-) {-) ....... U2
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Re: Rowing machine
« Reply #13 on: September 30, 2015, 08:51:35 pm »

I am trying to find out which club / Individual the cheeky chappies belonged to, I do seem to remember that it was controlled by 2 people.

Jerry Hill

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Re: Rowing machine
« Reply #14 on: October 03, 2015, 10:29:00 am »

Go on then, let's see you do it   {-)

No thanks, I'll watch  :}
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Bob K

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Re: Rowing machine
« Reply #15 on: October 03, 2015, 01:59:14 pm »

By far the best RC rowing boat I have ever seen is the one built by Frank Hollis and regularly seen on Black Park lake.  With animated passengers and gramophone it plays lovely music too.

See  https://www.youtube.com/watch?v=l6m-cyclMq8
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Re: Rowing machine
« Reply #16 on: October 03, 2015, 02:45:28 pm »

The rowing boat action is very lifelike. A  superb piece of clever engineering. I cannot see how the mechanism works.
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Bob K

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Re: Rowing machine
« Reply #17 on: October 03, 2015, 03:37:59 pm »

I cannot see how the mechanism works.

That's the really clever bit IMO.  The brass rods and levers etc are so well disguised inside and underneath the rower.  I see it almost every week yet have never seen more than part of its workings.
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Re: Rowing machine
« Reply #18 on: October 05, 2015, 06:21:45 am »

Absolutely fantastic, it looks great and works very realistically. Well done that man...... U2
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Bob K

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Re: Rowing machine
« Reply #19 on: October 05, 2015, 07:14:37 am »

Sorry I am not able to give any helpful information on how it's done.  I understand that the majority of the actuating mechanisms are concealed underneath the two lady passengers.  You would need to ask the builder.
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