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[catengineman]

Hi, is there any help out there for me to cure a small problem I have found in my build of the Tito Neri.

On the first 'wet' test of the build I found that the thrust from the prop's could hold the ASD's over at full lock and they would not return to neutral until the power was reduced or removed, some of this problem was I thought to poor connections between receiver and servos getting glitches and causing wrong signals etc.
Wire route replaced and even a 'Y' lead fitted to control both ASD's from the same stick but the problem is still evident when at 'full' power through the prop's.

I am only running 720 turbo instead of the recommended 900 turbo motors and had fitted heavy duty servos
Should I invest in yet stronger servos (if they are available) or do I need to rethink on how I control the tug?

Richard,

[Sub driver]

Hi...I'm not into tugs...but have you tried reducing the throw on the servo...I had a similar problem once when the servo went too far then wouldn't pull the rudder back to neutral..not the servo at fault but the linkage.I reduced the throw and it cured it...as I said not into tugs but thought it may help a slightly over throw on the servo and the full prop wash may be too much worth a try at least...good hunting. :)

[catengineman]

Thanks Sub driver,

The throw on the servo has been tried and the operation of the servo to the ASD is via gear wheel drives though in my own opinion the ratio is wrong for the type of application.

The servo head has a large cog and the ASD shaft has a small cog this gives a very quick turning movement of the ASD thrust but in this the strength required to hold or control it has to be quite high.

Now I have even tried to have 360 degree movement on the ASD units, yes I can control them while it is out of the water and then again I can SEE where the unit is at any given time. but as soon as the tug is in water then ? unless thrust is seen the ASD could be pointing in any direction......?

So reverted back to normal servo operation and limit the throw to 60 degree from center (outward swing) 50 degree from center (inward swing) OK so some people will ask why the difference between in and out.

Prop wash over the second ASD will cause prop slip and with cavitation set a greater thrust to the outer side of the affected ASD, inturn giving a greater strain on the servo to hold at the set angle.

I think I may be right but then what do I know about models.....

Richard,                                                         answering his own question after thinking about it

                                 With that in mind is there a really strong servo out there which is a standard size?

[Tug]

Oh yes bigger servo's exist but your wallet will not stand the strain,

Look at the list on Prestwich's site,

Are you using servo's on 6 volts?  lots more torque that way.

[FullLeatherJacket]

Richard

I have one of these which I used for the large, unbalanced rudder on my Envoy:

http://www.jperkinsdistribution.co.uk/detail.php?JPNO=7720220&activepage=1&Navmain=R/C%20equipment&subcatname=Servos

Plenty of oomph and would be quick on 6 volts. J Perkins supply through most model shops.

FLJ

[funtimefrankie]

My "Nangee" hull with twin ASDs has just had it's first run.
I've fitted high thrust servos from Howes at £9.99 each. The servos are powered from their own battery pack of 4 AA cells.
The motors are Model Motors Direct 777s, it has a good turn of speed, you wouldn't want it to go faster.
No sign of the drives sticking over.
It will spin on it's own length and do hand-brake turns...sort of.
Frank

[HS93 (RIP)]

Any chance of a picture of the linkage to the servo.

Peter

[funtimefrankie]

No linkage as such

The servo is mounted on a bracket, which is attached to the drive. The servo has a large gear mounted on top which meshes with a smaller gear on the verticall leg.
So when the servo moves the leg moves more.

Picture to follow......
Frank

[HS93 (RIP)]

Thanks for that Frank I was wondering if it was a link that was a bit to straight when on lock , but as it has none It wont be that . back to sleep.

Peter

[Bluebird v2]

catengineman hi there,

Just by your last posting, I understand that you are still using the geared drive to the ASD unit? if so, have you still got the ratio the same, where the big cog is mounted on the servo unit, driving the small cog on top of the ASD unit. Just out of curiosity, have you tried a 1:1 arrangement where the cogs are of equal diameter and teeth??

aye
John e
bluebird

[funtimefrankie]

The gear on the drive is bespoke, if that's the right word,
I have two units and they do have different size gears on the drive, so one swivels a bit more that the other.

But  are no way near 1:1
I don't think you could fit a much bigger gear on the drive, but then a smaller one to match on the servo would bring the servo too close to the drive to fit it.

The arrangement on this one is different to mine

http://www.cornwallmodelboats.co.uk/acatalog/voith_schottel.html

I don't know if this is  new or older model or just a different model.

Frank