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[Mike M]

Hi, Can anybody recommend a servo for my Fairmount Alpine build.Power supply is going to be a 12V 7A lead acid Battery. Also a couple of 30 A esc to control 2 Brushed motors.Thank you

[malcolmfrary]

Action do a rather nice two ESC and mixer combo. P94, probably best used with a P95 board to easily run on a 12 volt battery.
I have almost always used standard size servos for steering where there was room to fit them, 1 metre yachts down to plastic kit conversions.  If this is the 1:75 Alpine, probably easiest to use one servo for each rudder.

[Des]

For servos, I've used a Futaba 3003 in one AZIZ model, and a Hitec HS-311 in another.  I've also used the Action P94 twin ESC + mixer in both models, with a P93 switcher module for the bow thruster.

I think your Fairmount Alpine is only slightly bigger than my AZIZ's, so I'm not sure that I'd go to the trouble of installing and setting up 2 servos (1 for each rudder) - but it might be worth selecting a servo with metal gears and top bearing - versions of Futaba and Hitec servos are available with these options - check out the Hobby King (Hong Kong) website.

Des

[DBS88]

Re servos either one or two or considering a heavy duty servo with ball bearings and extra load capability, at what size hull or displacement weight does this become a sensible / safer thing to do to avoid stalling the standard servos?

[clockworks]

Standard servos like the Futaba 3003 are perfectly capable of handling the steering of 1/10th electric buggies, so should be fine in any boat that you can lift on your own. Back when I used to race, a few of the fastest guys in our club used the cheapest electrics in their cars.  The cheap servos were powerful enough, and the gears only break if whatever it's controlling takes a really hard knock, like clipping a barrier at 30mph. Shouldn't be a problem in a tug.

[Mike M]

First thank you everybody for your great advice. So... I'm thinking one servo for both rudders one esc for each motor 30A each.Then I would like to mix both stern and aft bow thrusters linked to reg props. Does that make sense?? Any suggestions for esc, servos, mixer etc.  I will be using a 12V 7A lead acid battery.I have nor bought a Radio or Receiver yet.


Your help so far has been great,Like I said earlier electrical not my strong point..    Cheers Mike

[Des]

I would go bigger on your battery - say 12V, 12A.hr.  You'll need lots of ballast in that hull to bring it down to her waterline, and a bigger battery will provide some of that mass along with a longer run time.  As a guide, I used a 12V 10A.hr battery in both of my AZIZ kits.  Use a standard AGM battery - less expensive, more weight.  A LiPo will do the job, but you'll end up adding more lead anyway.

Des.

[derekwarner]

Mike.....I believe, stern & bow thrusters on lifesized vessels [such as these] have independent control to each thruster......and reversible/ variable speed again for each thruster


Angled bething, positioning and the critical holding of an angle relative to structures and winds/sea state is usually performed at relatively low fwd/aft speeds


Derek

[malcolmfrary]

First thank you everybody for your great advice. So... I'm thinking one servo for both rudders one esc for each motor 30A each.Then I would like to mix both stern and aft bow thrusters linked to reg props. Does that make sense?? Any suggestions for esc, servos, mixer etc.  I will be using a 12V 7A lead acid battery.I have nor bought a Radio or Receiver yet.


Your help so far has been great,Like I said earlier electrical not my strong point..    Cheers Mike

As said in reply#1, standard servos will do, Action do good speed controls. 
My thinking for one servo per motor is that the mechanical arrangements are much simpler.  If both are to operate together, a Y lead will take care of that, but you get the chance to operate them individually if there are two servos.
If 30A ESCs are really needed, no Lead Acid battery that will fit in the boat is going to last, either in terms of run time or charge cycles.

[Des]

30A ESCs don't mean 30A current draw by the motors - this is a max current condition that the ESC can tolerate for a short time - usually only 1 or 2 seconds.  This rating should be higher than the stall current of the motor so that jamming the prop won't cause the ESC to self-destruct.  If a motor has a stall current of around 30A, it will have a full-load current rating of around 5 - 8A;  and a tug will rarely require full power to the motors and props in order to achieve a realistic hull speed with corresponding realistic wave pattern.  So, for 2 motors each with full load current rating of say 6A, a 12A.hr AGM battery will give at least 30 minutes run time - more if you ease up on the throttles.

Des.

[Mike M]

30A ESCs don't mean 30A current draw by the motors - this is a max current condition that the ESC can tolerate for a short time - usually only 1 or 2 seconds.  This rating should be higher than the stall current of the motor so that jamming the prop won't cause the ESC to self-destruct.  If a motor has a stall current of around 30A, it will have a full-load current rating of around 5 - 8A;  and a tug will rarely require full power to the motors and props in order to achieve a realistic hull speed with corresponding realistic wave pattern.  So, for 2 motors each with full load current rating of say 6A, a 12A.hr AGM battery will give at least 30 minutes run time - more if you ease up on the throttles.

Des.    Thanks for the info.Rather confused about Battery choice,Thought a  12V 12 A lead acid battery would be more than enough?I am open to suggestions.Also I am running 2 Raboesch RM 730 TQR 12v motors #109-73. Esc recommended by the Dealer for these is between 35-40A.Do you guys agree with this? Already ordered the motors so there is no turning back.

[Des]

Hi Mike

Yes, I think that a 12V 12A.hr battery should be more than adequate - but leave buying the battery until you are ready to put the hull into the water.  then if you find you need more ballast you can buy a bigger battery.  For my 2 AZIZ kits I bought the biggest battery that would fit through the access hole in the foredeck.

Selection of ESCs for a particular job can be tricky if you don't understand what the numbers mean - and that includes many hobby shop dealers.  For my first AZIZ I used the Action P94, rated 20A on each channel.  But when I measured the actual motor current, at around 3A each, for my next AZIZ I used the P94 Lite, rated 10A per channel - and then installed 7.5A fuses in a motor lead from the ESC to the motor.  So the motor is protected from overload (if the props get fouled with weed, or similar), the ESC is protected, and I saved a couple of bucks.

For my bow thrusters I have used  the Action P93 multi-function controller.  But if your hull has both bow and stern thrusters then I'd be tempted to look at the P94 (lite);  if I remember correctly this can change from spinning the boat, to translating sideways, with a simple "blip" on the throttle stick.

I have noticed on this forum that many members use motors much bigger than those I have used in my AZIZ's, and for them bigger ESCs are both appropriate and necessary.  But for a tug around 1000 - 1200 mm or so they are not usually necessary.  (By the way, what size props & nozzles are you using on your Alpine - that will make a difference).

Des.

[Mike M]

I upgraded the props to 50-R_4bl-M4 Brass 9(#147-17 & #147-18) Upgraded shaft L=236MM4. Don't know what size the nozzles are Whaever came with the kit.Sounds like the ESC's are going to be a bit more difficult to chose.The guy at Raboesch recommended 35-40 a esc. and a 15 & 20 a for bow thrusters?/


Cheers Mike

[Des]

Mike

My AZIZ'z are about 1100 mm length, and about 10.5 kg displacement, and use 50 mm props driven by MFA 919D61 motors (2.85 A at full load on 12V, 8A stall current) with 6:1 reduction;  I found I had to dial back the throttle setting to less than 50% for realistic hull speed and wave patterns.  Your Alpine is somewhat bigger and heavier, but still uses 50 mm props.  To achieve a realistic hull speed and wave pattern you will need to spin your props somewhat faster than my AZIZ's, so you may not need to dial back your throttles at all.

It's possible that the MFA motors maybe a little marginal for your bigger hull - you may need to find something a bit bigger which will drive your props to around 2200 rpm.  But  the motor current will not be significantly higher than 3 - 5 Amps (power is power, regardless of motor make and type);  so ESCs rated at 20 or 30 Amps are way overkill.  Hence why I chose the P94 Lites for my second AZIZ.  If you have an appropriate fuse in one motor lead, between the ESC and motor, that will blow before the ESC if your props become fouled - you don't need to have a 30A ESC just to cater for the stall current of your motors if you have a motor fuse in the circuit.

Just a word about your props - I used the Raboesch 147's on my first AZIZ kit - very expensive, but that may be due to the Australian dealer's markup.  For the second AZIZ I bought a pair of 50 mm Kaplan style props from Simon Higgins (Prop Shop, UK) - nice looking props at only about 60% of the price of the Raboesch props.


Des.

[Mike M]

Thanks Des you are a wealth of information Much Appreciated,    Mike