#7 10 years ago

Sailing a straight line

I experimented with shifting the C of G, moving it from 15" from the bow to 13.25" and 16.5". There was no noticeable change in the model's straight line behaviour. I have still to try connecting both props to one ESC. I also plan to increase the size of the rudders (which are already oversize) and reduce the servo/rudder arm ratio to see if that makes any difference.

#6 10 years ago

Sailing a straight line

I will shift the C of G as suggested simply to see what effect it has, but it will be difficult to isolate the effect of the change in hull immersion, from the effect of rudder immersion.
It can only be an experiment and not a solution; it's a scale model and it's loaded down to the correct waterline.

#5 10 years ago

Sailing a straight line

~~grins~~ I never said was easy!!

Seriously the weight up front needs to be enough to move CofG a significant amount ( please note it may make things worse) its a test to see what effect it does have and to try to figure out what's going on. if your CofG is to far aft then the forces you would expect to keep a boat ( or any other vehicle) following a path have too little leverage to compensate for the wayward behaviour of a real world wind/wave/passing bumble bee etc.

The pixhawk is capable of fully autonomous control of a vehicle. it can follow waypoints and depending upon how its configured control many other functions as well.

if you ever saw the BBC tv James May and his glider he used an 8 bit precursor of the pixhawk to control the glider on its 20 mile flight and landing.

http://www.dailymotion.com/video/xw66wd_new-james-may-s-toy-stories-flight-club_shortfilms

"that's not a bug its just an undocumented creature."

Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)

Liked by Colin H

#4 10 years ago

Sailing a straight line

Thanks for the suggestions.
The batteries are arranged in series to provide a single 12V supply. I have also already tried replacing both drive motors and one shaft seal (they are waterproof shafts). You would expect that having independent control of the shaft speeds would enable any tendency to turn to be countered by adjusting relative speeds. The direction of turn is random and defied those attempts.

I will try changing to one ESC and see if that helps. I will also try a weight near the bow and test its effect.

The gyro was about as high-tech as I wanted to go in looking for a solution. The pixhawk looks downright scary!

#3 10 years ago

Sailing a straight line

If your looking to go the HiTEC route get a pixhawk!

https://pixhawk.org/modules/pixhawk

it is your choice as to which one you buy BUT clones are available from ebay. I offer one of these as a solution because it is possibly the most capable of all the autopilot systems.

it is the core of autonomous vehicles in many hobby spheres. You can set it to hold a heading. it has GPS and magnetic compass capability.

Youtube has many many videos on this beast.

Having had time to think ( always a dangerous situation)

Try adding a weight to front of the boat and see effect pls. I am thinking the problem has to be a combination of thrust lines, CofG, and centre of buoyancy.
A radical change of the CofG should change the behaviour of the boat ( for better or worse ) seeing the effect of such a change could indicate way to go .

"that's not a bug its just an undocumented creature."

Sir Terence David John "Terry" Pratchett, OBE (28 April 1948 - 12 March 2015)

Liked by Colin H

#2 10 years ago

Sailing a straight line

Hi Trillium, my thought is the esc's are they feeding of 1 battery or 2??? if 2 maybe they are discharging at a different rate, supplying a slightly different voltage to each motor.
Have you tried 1 esc to both motors??? or 1 battery to both esc's??? just try these to eliminate the possibilities

Hope this give you a starting point

Mark

Etherow Model Boat Club

#1 10 years ago

Sailing a straight line

I have one model which is, by far, the most difficult to keep sailing on a straight course. No model will sail continuously in a straight line if the rudder is untouched, but this one requires continual rudder movements. If I set it sailing straight it will sail a yard or two, and then start to turn in a circle. The direction is random. I've eliminated wind and water currents as causes of the sensitivity. It has two rudders, props, and ESC's with independent control. Tinkering with rudder alignment and prop speeds has not improved it. I have tried a couple of helicopter gyros as a means of keeping a straight course but they are ineffective on this model. I tried adding a 1" deep brass strip below the hull as a keel plate, also with no noticeable change.
Anyone have any suggestions on how to improve this?

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Sailing a straight line

Sailing a straight line

Sailing a straight line

Sailing a straight line

Sailing a straight line

Sailing a straight line

Sailing a straight line

Sailing a straight line