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Old Dec 05, 2012, 02:08 PM
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MatrixGTI's Avatar
Como - Italy
Joined Mar 2009
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Increase steering at low speed for autonomous rc boat

Hi All,
I'm a newby in Rc Boat but I play with Rc things in the last 20 years (Kopter, Cars etc ).
I'm working on a new project consist in an autonomous Rc Boat based on Ardupilot system to perform 3D bathymetry with echosounder.
Base boat is a surge crusher ep xxl , is a big powerfull boat and I know that is overpowered and big but fit perfectly the stability and the dimension I need.
Boat runs actually at 6S and with 2x5000 mAh runtime is approx 1 hour.
Project is actually at first field test, Autonomous and Manual behavior are good but I need to increse the steering reaction at low speed (that is the scope of the survey as the echosounder need low speed to read good data ).

My question is... what is the easy way to increase rudder response at low speed ?

Bigger rudder ? what shape ?
Double Rudder ?
Bow thruster ?


here you can see the bench and first field test of the ArduBoat

ArduBoat - Bench Test (1 min 59 sec)


Arduboat Field test 1 (2 min 46 sec)
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Old Dec 05, 2012, 03:26 PM
Boaters are nice people.
Sneek, Netherlands.
Joined May 2004
4,746 Posts
Hi Matrix,

The boat you chose is a fast electric, which steers very good when running at speed, hence the small rudder surface.

Making narrow turns with a catamaran at low speed needs a much larger rudder, which will have way too much authority when you run the boat on the plane. The rudder throw must(!) be reduced than, or you'll risk flipping the boat.

A simple way to acheive this would be to mix the throttle and the rudder channel in such a way that the rudder throw is decreased, as the throttle signal is increased.

As a side note; a catamaran is very reluctant to make narrow turns while crawling, due to the hull design.
A monohull will do a much better job at that.

Regards, Jan.
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Old Dec 06, 2012, 12:22 AM
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MatrixGTI's Avatar
Como - Italy
Joined Mar 2009
60 Posts
Quote:
Originally Posted by pompebled View Post
Hi Matrix,

The boat you chose is a fast electric, which steers very good when running at speed, hence the small rudder surface.

Making narrow turns with a catamaran at low speed needs a much larger rudder, which will have way too much authority when you run the boat on the plane. The rudder throw must(!) be reduced than, or you'll risk flipping the boat.

A simple way to acheive this would be to mix the throttle and the rudder channel in such a way that the rudder throw is decreased, as the throttle signal is increased.

As a side note; a catamaran is very reluctant to make narrow turns while crawling, due to the hull design.
A monohull will do a much better job at that.

Regards, Jan.
Hi Jan,
Thanks for the reply.

I know that Surge Crusher is not designed for low speed, but it has other characteristic that are good for my experiment, for example the CAT hull allow me to install the echosunder on the flat part of the bottom and also it tend to turn "flat" that is perfect for the echo transducer readings.

There is no problem if rudder will be oversized because that boat will never go at hi speed , I will limit the throttle at 10/20 % as in the second video to prevent flipping and also for safety reason as it it is autonomous....

For your experience, what size of rudder could be good for narrow turns ?
I plan to build a new rudder based on a standard one, same depth and shape but with double or more lenght to double the active surface. Could be good ?

Thanks

Flavio
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Old Dec 06, 2012, 10:37 AM
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Canada, ON, Markham
Joined Aug 2008
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If you want better low speed handling you should put a bigger diameter and lower pitch prop (more like a scale boat) on it to reduce cavitation and increase smoothness.

For the rudder, also check out scale boats. You'll want something with a lot of blade area right in the prop wash.
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