Selecting Servos for a New Model

[Sebby]

I have just bought a Seagull Zero. The kit is great, the manual detailed except it gives no clue as to what size, type etc servos are required for the flying surfaces, retracts and throttle. My model is 69” wingspan, 1.20 FS, weight around 4.75kg (9 1/2 lbs) and has mechanical retracts. The manual says 8 servos and the box 9! How do I choose the right servos. Apologies if a forum already exists for this topic, please repoint my enquiry to the right space, thanks

[Former Member]

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[flight1]

Hi this question always comes up so no worries there.

See this calculator to work out torque required, it has a good built in margin of error.

with this plane good standard servos will be fine and i would use metal gears on rudder if sterable and if using mini/thin servos in the wing .       4kg+ torque would be good and 6Kg for retracts

 

Edited By flight1 on 03/11/2018 12:20:53

[Sebby]

Thanks for the responses and the information. Maybe I expect too much but you would think the manufacturer would give the owner a clue. Looking at the torque figure of 5kg would it be best to get metal gears and bearings in the servos?

[Former Member]

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[Jon H]

if you set them up sensibly and fly scale then standard 3.5kg jobs would work fine. I used 148 futaba servos on a 72'' 155 powered P40 and had no trouble at all running a 6v battery.

Personally, i would use standard servos as they are more than adequate. That said, if you want peace of mind by using 5kg servos as Percy suggested then go for it, just dont feel you have to and dont get suckered in by tales of 9kg digital etc.

Metal gear or digital is nice, but certainly not required for a model this size.

If you want a little more than standard give savox 351's a try. 4kg at 6v and more than adequate. I use a few of these on the rudder's of my 80'' 50cc class warbirds. Ailerons on these models get 6.5kg savox 352's.

[Jon H]

Posted by Percy Verance on 03/11/2018 18:42:46:

Hi again Sebby

Personally I usually prefer bearings in my servos. Regarding metal gears, it's perhaps slightly less clear cut. Metal geared servos are usually considered to be more robust, but there can be a downside. If the model has a petrol engine, then vibration can sometimes lead to premature wear on the brass gear trains. An alternative worthy of consideration may be the HiTec servos with Karbonite gears. These are proven to be quite robust as well as reasonably priced....

As per the previous post, get a good strong retract servo, used with it's own battery.

Edited By Percy Verance on 03/11/2018 18:47:35

cant fault any of this advice

[SIMON CRAGG]

I have got similar sized models.

Futaba 3001's all round, less proper "retract" servo, and Futaba digital for elevator.

Life Po4 1700mah packs.

I have changed a few to servoless retracts MUCH better than the mechanical type.

Hope this helps.

[Former Member]

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[Martin Harris - Moderator]

It might be worth pointing out that retract servos differ from standard types as they are designed to drive from one end to the other - usually switching when the pulse width crosses the mid point. In other words, they are not proportional. This means a fair bit of thought and planning to drill the servo disk in the best points to allow the geometry to minimise any load on the servo at each end of the travel - you cannot use adjustable end points in your transmitter.

[Engine Doctor]

Whatever servos you decide on only buy from reputable supplier as there are fake servos on eBay openly being sold as genuine ! If the price looks too good to be true it usually is !

[Former Member]

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[Stearman65]

Posted by flight1 on 03/11/2018 12:19:05:

Hi this question always comes up so no worries there.

See this calculator to work out torque required, it has a good built in margin of error.

with this plane good standard servos will be fine and i would use metal gears on rudder if sterable and if using mini/thin servos in the wing . 4kg+ torque would be good and 6Kg for retracts

Edited By flight1 on 03/11/2018 12:20:53

That's a cracking bit of software.

[Ultymate]

Karbonite geared servos are not recommended for petrol models at all, karbonite will shatter under vibration

[flight1]

Posted by Ultymate on 04/11/2018 15:43:25:

Karbonite geared servos are not recommended for petrol models at all, karbonite will shatter under vibration

well if you got that bad a vibration it's not a good thing for anything and should be built out or designed out.

The thing for carbonite gears is that no anaerobic based glues should be used as it not compatible ( ie; thread lock /super glue etc) . never had a carbonite gear 'shatter' they can break like anything else if put in a inappropriate situation for its design peramaters   If needed grip washer or split washer should be used

as mentioned in a previous post hs485 is a good reliable servo

Edited By flight1 on 04/11/2018 16:20:28