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servo's size

  • Beverik
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6 years 10 months ago #13 by Beverik
servo's size was created by Beverik
Hi Jindrich,
for the flying surfaces you use mainly 2 36kg/cm servos, like you said in a other topic they could be reduced if the plane would be lighter. The servo's you are using, for the 50 KG plane, do think that is the minimum requirement to make it fly save?
I like the 2 servo set up and want to stay whit the 2 servos for ever flying surface but I will reduce the Total weight of the plane. do you have any suggestion what size servo’s ( Torque) to use for light acrobatics ?

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6 years 10 months ago - 6 years 10 months ago #14 by jindrich
Replied by jindrich on topic servo's size
Hi Beverik,

this is not an easy question. Asking two modellers you can get three different opinions :)

However, there are several guidelines that you can follow. Please consider these as my personal opinion only:

1, Analogue or digital servos - I believe it doesn't really matter. Both can be used. However the digital servos have higher torque in general.

2, Voltage - that it's important, because it affects the concept of your board electronics. The higher voltage the higher torque, which means the 7.4V (2 LiPo battery) are an ideal option. Combining this with a receiver capable of using the same high voltage provides the easiest wiring, This assume a receiver capable of providing sufficient current to supply ALL servos. That is critical. A digital servo when it starts moving can take easily more than 10 Amps. If you have more servos (7) connected to such receiver than if more servos need such current simultaneously, apparently the receiver might get overloaded. While a bus of some receivers can support 20 Amps permanently and 40 Amps for a short period of time (in my case www.jetimodel.com/en/katalog/Duplex-2-4-...odukt/Duplex-R18-EX/), still the total current is limited by the used power supply connectors of the receiver, a diameter and length of the power supply and servo cables. If any of these components is underestimated than a voltage supplied to the servos can get below their minimal voltage and they start messing. Well, I'm getting here out of the scope of your question, however, my recommendation here is 7.4V. When using power box the output voltage provided by the power box for servos should be considered as well.

3, Plastic, metal (steel), carbon or titan gear? My recommendation would be steel or even better titan gear. Nothing is more frustrating than changing a servo gear wheel on the airport.

4, Speed is not critical for this type of airplane. It is aerobatic but not 3D competition model. I prefer higher torque rather than higher speed. This goes hand in hand, Faster servos have lower torque and vice versa.

5, Torque is important. We play with big models so we should use strong servos. The torque is driven by the factors listed above. If you take high voltage, titan gear, digital servo, the torque is going to be progably high as well. The servos I used can be considered to be on a very safe side of the choice for 50 kgs model. Personally, I wouldn't recommend using servos below 20kg*cm torque on the used voltage for a model with an expected weight of 35 kgs, assuming 2 servos per controlled surface.

6, Vendor isn't critical. Multiple vendors supply good quality products. Go for brand you know with a good local support and available spare parts. I like Hitec servos, that's why I used them.

Well, I'm not sure it the above would be of any help to you, but those are the guidelines I've considered during my choice.
Last edit: 6 years 10 months ago by jindrich.
The following user(s) said Thank You: Beverik

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