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Author Topic: Trim Tabs  (Read 2738 times)

The Old Fart

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Trim Tabs
« on: January 09, 2018, 12:16:37 pm »

Hi Guys,

I've fitted working trim tabs to my Tamar 1/16 lifeboat.

First trial, with tabs fixed down at 45deg, made a huge increase in speed.

Question 1 is, which size servo to use to control the tabs, standard or mini MG90s?

Question 2 is, Where to position trim tabs, when turning?

Will be using a small Arduino to control servos.

Dave.
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C-3PO

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Re: Trim Tabs
« Reply #1 on: January 09, 2018, 12:32:24 pm »

Hi Dave,

See - http://www.modelboatmayhem.co.uk/forum/index.php/topic,59654.msg627192.html#msg627192

I understand that when turning the trim tab on the side of the boat you are turning would be engaged (down) and the other tab which would without the trim tabs raise up in the air with the turn of the boat is at neutral - no effect.

Are you thinking of having preset control points (matrix) dependant on the position of the throttle/rudder?

C-3PO
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The Old Fart

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Re: Trim Tabs
« Reply #2 on: January 09, 2018, 12:43:20 pm »

Yes I'll be inputting ,throttle, rudder, enable switch into arduino, then control 2 servos. Project for our other site. %)

Theory is then that the inside of the turn is lifted by the tabs?
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furball

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Re: Trim Tabs
« Reply #3 on: January 09, 2018, 12:44:25 pm »

How are you activating the trim tabs from inside the hull?


Don't the stern door hinges get in the way of the top of the dummy hydraulic rams?


(future ideas for 1/12 version...)




Cheers


Lance
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C-3PO

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Re: Trim Tabs
« Reply #4 on: January 09, 2018, 12:49:41 pm »

Yes I'll be inputting ,throttle, rudder, enable switch into arduino, then control 2 servos. Project for our other site. %)

Theory is then that the inside of the turn is lifted by the tabs?

Brill! - good to see you saw an noticeable speed improvement.

Forgot this bit re "neutral" trim tabs - http://www.modelboatmayhem.co.uk/forum/index.php/topic,59654.msg627201.html#msg627201

I do also wonder if there is any merit in trying an active weight distribution concept - imagine a small tray with some lead weights and the using your linear servo concept the tray could be moved quickly to the bow or stern a little to change the COG - worth a try? Could almost be linked (scaled) to your forward throttle position...

C-3PO
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The Old Fart

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Re: Trim Tabs
« Reply #5 on: January 09, 2018, 01:06:52 pm »

The stern door does not open on this model, and the hinges are in the wrong place. Pic shows the trim tab connection. using 1mm brass rod, it didn't buckle in trials so hope it'll be strong enough.
I'm hoping that someone has fitted similar tabs, and draw on their knowledge on servos to use.  The metal geared MG90S are nice and small, but would appreciate feedback.

Did think of moving weights around, but hull full of gear, and think non started. Have seen stepper motors used to balance an aircraft carrier model.
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McGherkin

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Re: Trim Tabs
« Reply #6 on: January 09, 2018, 02:43:02 pm »

Hi Dave,

See - http://www.modelboatmayhem.co.uk/forum/index.php/topic,59654.msg627192.html#msg627192

I understand that when turning the trim tab on the side of the boat you are turning would be engaged (down) and the other tab which would without the trim tabs raise up in the air with the turn of the boat is at neutral - no effect.

Are you thinking of having preset control points (matrix) dependant on the position of the throttle/rudder?

C-3PO


This isn’t normally how trim tabs are used. You would put them down when accelerating (to stop the bow pointing at the sky, and to help lift the stern out of the water) and raise them up at speed to keep the bow slightly up. The only time you would normally alter them seperately is to counter offset loading.


You could adjust trim tabs for turning but it is very rare to never that you would see a real life coxswain do it, usually because trim tabs move very slowly, certainly not quick enough to rely on in a hard turn.
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C-3PO

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Re: Trim Tabs
« Reply #7 on: January 09, 2018, 03:02:22 pm »

This isn’t normally how trim tabs are used. You would put them down when accelerating (to stop the bow pointing at the sky, and to help lift the stern out of the water) and raise them up at speed to keep the bow slightly up. The only time you would normally alter them seperately is to counter offset loading.

You could adjust trim tabs for turning but it is very rare to never that you would see a real life coxswain do it, usually because trim tabs move very slowly, certainly not quick enough to rely on in a hard turn.

Does that apply to all applications of trim tabs or just trim tabs on lifeboats?

C-3PO
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McGherkin

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Re: Trim Tabs
« Reply #8 on: January 09, 2018, 03:28:05 pm »

I’d say a good majority of boats. I’ve never actually come across an automatic system in the wild which does the whole moving in turns thing, and it’s simply unheard of on manually controlled ones. Between operating the throttles and steering wheel there aren’t any hands left to operate them.
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C-3PO

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Re: Trim Tabs
« Reply #9 on: January 09, 2018, 03:46:15 pm »

The backdrop to this is "Auto" adjustment

I guess the value or not will be assessed when Dave implements the system on his Tamar.

I can see some benefit in theory - I have a 1/12th Severn that can make you heart run faster as it turns sometimes!!! If it works I would also put this on my Tamar and Arun

I am sure the "Auto" aspect of trim tabs perhaps relates more to sports boats - have a look at 4:06min https://www.youtube.com/watch?v=sbOInDmFIVE

C-3PO
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The Old Fart

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Re: Trim Tabs
« Reply #10 on: January 09, 2018, 03:51:51 pm »

Once I get the servos sorted, designing 3d printed brackets at the moment, then I'll do the electronics and report back.
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me3

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Re: Trim Tabs
« Reply #11 on: January 09, 2018, 08:40:12 pm »

I’d say a good majority of boats. I’ve never actually come across an automatic system in the wild which does the whole moving in turns thing, and it’s simply unheard of on manually controlled ones. Between operating the throttles and steering wheel there aren’t any hands left to operate them.


You're quite right, tabs aren't used for cornering, they are used to help her on the plane. They are normally left in the stowed position. Ie all the way up as they're not very efficient when down, more drag etc. They can be lowered in rough seas to bring the bow down. As the bow is the sharpest bit of a boat it cuts through the waves better. They can also be used to counteract weight imbalances as suggested. There are some automatic based systems that claim to counteract roll from a beam on swell.  Look at volvo penta interceptors. Whilst they are a different design they do the same thing.
Cheers
Reece
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The Old Fart

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Re: Trim Tabs
« Reply #12 on: January 10, 2018, 12:15:43 pm »

Fitted MG90S servo to rear of Tamar. I made a test bracket to go behind servo and clamp to support. It works but flexes the support. Will make a support that goes all the way across and glue to rear of the hull and support.
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