servo torque
04-24-2010, 07:02 AM
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servo torque
so we are about to fit out 2 large planes with servos and the question has come up about how much torque is really required.
the planes in question will both 100cc size, 1 is a aus star 120inch Cessna 182 and the other is a 104 inch sukhoi.
Now i know if money and sense will let us we would be putting 7955 servos though out both but at over $100 a servo we will need to take out a small loan to buy them. both plane need 8 each so thats alot of money on just servos.
i have seen plenty of 35% 3d type planes like the suk with 2 5645 on the ailerons. thats about 320 oz of torque per side being 2 on each. i can only assume this is enough as people seem to be doing it?. aswell the rudder will be setup for 2 servos so how much torque is really need if i did 1 7955 thats 333 oz torque or 2 5645 lets say that comes in near the 320oz so not much different. i can not see the need for 2 7955 that being 666oz torque? bearing in mind this plane will be flying 3d?
now the cessna only has rather small surfaces and will only be doing scale type flying how much torque will it need. surly it wont need 7955 though out. the flaps might need a bit more than say the ailerons. but have no idea where to start with how much torque would be needed in the first plane?
can someone with planes in this size let me know what they are using and how it works for them?
thanks in advance custard
the planes in question will both 100cc size, 1 is a aus star 120inch Cessna 182 and the other is a 104 inch sukhoi.
Now i know if money and sense will let us we would be putting 7955 servos though out both but at over $100 a servo we will need to take out a small loan to buy them. both plane need 8 each so thats alot of money on just servos.
i have seen plenty of 35% 3d type planes like the suk with 2 5645 on the ailerons. thats about 320 oz of torque per side being 2 on each. i can only assume this is enough as people seem to be doing it?. aswell the rudder will be setup for 2 servos so how much torque is really need if i did 1 7955 thats 333 oz torque or 2 5645 lets say that comes in near the 320oz so not much different. i can not see the need for 2 7955 that being 666oz torque? bearing in mind this plane will be flying 3d?
now the cessna only has rather small surfaces and will only be doing scale type flying how much torque will it need. surly it wont need 7955 though out. the flaps might need a bit more than say the ailerons. but have no idea where to start with how much torque would be needed in the first plane?
can someone with planes in this size let me know what they are using and how it works for them?
thanks in advance custard
04-24-2010, 02:41 PM
#3
RE: servo torque
Well, I'll have to chime in on the 5645. It has good torque, but on an aerobatic plane I found out the hard way ($$) that they are relatively slow and possibly the centering isn't as good as some other servos. Maybe the Power HD1501 servos would be good for the Cessna. They claim over 200 oz. at 6V. and the speed is faster than the Hitec. And the price is very reasonable.
04-24-2010, 06:23 PM
#4
RE: servo torque
I use the 5645 on jets, on ailerons, flap & elevators, no problem at all. Lesser Hitec servos on the (small) rudders, nosewheel, etc.
Servo speed is less an issue on jets, we don't spend time banging the sticks from one extreme to the other like 3D demons. - John.
Servo speed is less an issue on jets, we don't spend time banging the sticks from one extreme to the other like 3D demons. - John.
04-24-2010, 07:03 PM
#5
RE: servo torque
A lot of people don't fully understand the math/geometry of surface setup. Becuase the Cessna isn't going to need 50* throws like a 3D plane, you can get away with a lot less. Where the math and geometry come in is that you can really amplify a servo's torque mechanically VERY easily. A lot of people don't realize this.
For example:
Servo X has 200oz of torque. Manufacturers come up with this value on a 1 inch servo arm at either 4.8 or 6V depending.
Now consider this. What happens when you reduce the servo arm to 0.5" in length?? YOU'VE JUST UPPED THE SERVO'S OUTPUT POWER BY 50%!!! Thus your 200oz servo is now putting out 300oz! That's a massive increase. Now what happens if you also increase your ATV to the max (like 125 or 150% depending on radio)? Now you have 50% more resolution as well because 1024 steps (common for servos) * 50% = 1548 steps of resolution. Now, also consider running 6.6V a123 RX packs and you've just added another 10% of power and speed to the servo. In the end you can have your 200oz servo putting out 330+ oz of torque all due to setup!!! Not to mention, because you have a shorter servo arm, you will GREATLY reduce servo gear wear/slop and your servos are going to last a lot longer.
I see a lot of guys that have their massive 1.5" arms on 100cc planes and are trying to run them for IMAC. They lose a TON of resolution being that they have to run the throws at 30-40% of ATV thus affecting their precision, accuracy, snap exits are poor (due to blow-back from lack of servo power due to setup), etc.
Anyway, just wanted to make you aware that you'll be abl to get away with a lot less servo if you plan out your setup properly!
Eganwp
For example:
Servo X has 200oz of torque. Manufacturers come up with this value on a 1 inch servo arm at either 4.8 or 6V depending.
Now consider this. What happens when you reduce the servo arm to 0.5" in length?? YOU'VE JUST UPPED THE SERVO'S OUTPUT POWER BY 50%!!! Thus your 200oz servo is now putting out 300oz! That's a massive increase. Now what happens if you also increase your ATV to the max (like 125 or 150% depending on radio)? Now you have 50% more resolution as well because 1024 steps (common for servos) * 50% = 1548 steps of resolution. Now, also consider running 6.6V a123 RX packs and you've just added another 10% of power and speed to the servo. In the end you can have your 200oz servo putting out 330+ oz of torque all due to setup!!! Not to mention, because you have a shorter servo arm, you will GREATLY reduce servo gear wear/slop and your servos are going to last a lot longer.
I see a lot of guys that have their massive 1.5" arms on 100cc planes and are trying to run them for IMAC. They lose a TON of resolution being that they have to run the throws at 30-40% of ATV thus affecting their precision, accuracy, snap exits are poor (due to blow-back from lack of servo power due to setup), etc.
Anyway, just wanted to make you aware that you'll be abl to get away with a lot less servo if you plan out your setup properly!
Eganwp
04-25-2010, 05:09 AM
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RE: servo torque
thanks Eganwp that makes alot of sense. im sure the cessna will be setup with the best possible mechanical setup. hence is now looking like needing alot less servo torque than first thought.
so the 5645 be enough on the rons of the suk. i will be mainly 3d flying and have no want to fly imac. i will have to check the servo arms and see about the length they are. but now i can see this making more of a difference over the torque needed. and yes i want max throws with it so by the sound will need more torque to achieve this
so the 5645 be enough on the rons of the suk. i will be mainly 3d flying and have no want to fly imac. i will have to check the servo arms and see about the length they are. but now i can see this making more of a difference over the torque needed. and yes i want max throws with it so by the sound will need more torque to achieve this
