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Let's talk about servos - Whatever is on your mind

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Old 11-07-2012, 06:07 PM
  #26
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Default RE: Let's talk about servos - Whatever is on your mind

Yes they are way over kill for the plane. It is an old Model Tech Formula 3D. It is a 70 to 90 powered aerobat. I had one with a 91fs in the nose and she was a pure pleasure to fly. Would hang on a 10 mph breeze. Would hover with ease. After it went in, took me another year and a half to find a replacement. I am going to put a Tacon 60 in the nose with a 6s 5000mah battery. I get just over 1100 watts with a 18X8 prop. The plane flew just fine with SG 5010analog servos that put out 150 ounces of torque. There are digital, metal gear super power servos. I figure this would be a good test for them after I get done with the bench testing. I am planing on building a test rig this weekend so I can mount my dial indicator, just to see how well they center.

If they turn out to be good servos, they would be hard to pass up for the price.

I was checking them out of the package. They seem to have a good fit and finish. Still do not like the stiff plastic servo leads. They are the standard red, orange, brown 3 wire servo lead. They seem a little stiff. They are not the nice teflon coated wires.

http://images.rcuniverse.com/magazin...79/formula.jpg

http://www.rcworld.com.au/media/cata...d_front_34.jpg
Buzz.
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Old 11-26-2012, 02:07 PM
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Default RE: Let's talk about servos - Whatever is on your mind

Did you get those servos?   What do you think?
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Old 04-12-2013, 07:24 PM
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Default RE: Let's talk about servos - Whatever is on your mind

Anyone have experience with Spektrum servos?
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Old 04-13-2013, 02:06 PM
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Default RE: Let's talk about servos - Whatever is on your mind

Yup.

Which ones specifically? Many of them are rebadged JR or Savox
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Old 04-13-2013, 03:02 PM
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Default RE: Let's talk about servos - Whatever is on your mind

Just looking for general feedback on Spektrum servos.  Nothing in particular.
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Old 04-13-2013, 04:33 PM
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Default RE: Let's talk about servos - Whatever is on your mind

Oh boy. I had forgotten about this. Hang head in shame.

I did get them and they are really nice servos. Have not had a chance to build the test rig. Have flown them and they work very well. Super strong.

I have another servo I have been using. These are small digital servos. I picked them up for a Mini 3DX. Was I surprised at the first power on. They are a little noisy, but only because they are trying to center. They are strong and very precises.

http://www.hobbypartz.com/exi-servo-s0820.html

I have since ordered 8 more. They are good servo's. I have 10 flights on them and they work great.


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Old 11-12-2013, 07:10 AM
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What determines how strong the servos need to be? Speed and deflection.

There is a servo calculator spreadsheet on the first page of this discussion. Bring it up and play with it and you come to understand how little or how much torque you need.

I was helping someone in another thread. He is building a 12' wing span sailplane for slope soaring. He asked advice on the aileron servos.

Well, it all depends on how you are going to fly it, I told him.

Based on his aileron width and depth and assuming a maximum of a 30 degree deflection, if he hit that deflection at 50 mph he needs about 37 inch/ounces of torque. So I recommended some that were about 50.

If he did that same 30 degree deflection at 100 mph he needs about 150 inch/ounces of torque.

The numbers have nothing to do with the weight of the aircraft or the span of the wing. It is all about surface area of the control surface and the angle of deflection.

That is why most 3D planes can use fairly light servos. 3D planes are typically flown at fairly low speeds even thought they have large surfaces.
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Old 11-23-2013, 08:52 PM
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What does most people use to test there servos, especially when not in the plane?
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Old 11-23-2013, 10:34 PM
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Hi, this is a very good thread. I wave two questions I've head on my mind 4 a while;

1- mid size servos and their use in larger (.90) planes. The rated torque would be OK, but the smaller gear make them vulnerable.
My question; if they are rated for a specific force, the gear should also withstand that force right ?

2- is there such a thing as "low cost" (under $30) regular servo that centers well ?

Thanks, V.
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Old 11-23-2013, 11:02 PM
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G'day I have been running Hitec 225 servos I have had 3 that have blown or shorted out not sure what causes this to happen but it didn't happen while in the air!
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Old 11-23-2013, 11:08 PM
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hi I have been running hitec 225 servos in most of my planes I have had 3 of them bow up and seize but not while flying what could cause this to happen?
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Old 11-24-2013, 03:23 AM
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I have an old analog type servo tester made by Custom Electronics. Reads up to 500 ma and has a joystick for movement. HK carries digital ones that I would grab if something happened to mine. Questionable servos with dirty pots will show up with the needle twitching as you move the stick slowly. Also shows if control surfaces are hitting their stops before the servo hits the end. by drawing more than 500 ma.

I mostly run JR 821 servos on my sport planes for a good all around servo.
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Old 11-24-2013, 09:22 AM
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Quote:
Originally Posted by 5regal View Post
What does most people use to test there servos, especially when not in the plane?
I have a receiver and a battery pack on the bench just to test the servos. I power them up, move them through their full range to look for smooth operation. Then I do the same with finger resistance to see that there is no clicking, drag or other bad behavior.

For matched surfaces like flaps, I will test all the servos to find the two that most perfectly match. Normally it doesn't matter but occasionally there is one that is slightly off. Fine for Rudder but not to pair with another on the flaps.

Lastly I look for centering. If they won't center with no load they will never center under a little drag in the push rods.
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Old 10-22-2014, 07:07 AM
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Quote:
Originally Posted by izzy-israel-73 View Post
hi I have been running hitec 225 servos in most of my planes I have had 3 of them bow up and seize but not while flying what could cause this to happen?
Looks like no one ever responded. This is an old question but worth a reply.

Serovos fail for a variety of reasons.

Defect - stuff happens

Wires too small - if the wires going to your servos are too thin they will cause a voltage drop under load. As the servo tries to do its job it will have to draw too much current, will heat up and fail.

Broken gears - This is usually caused by impact with a surface. Common on flaps on gliders. Or it could be that the servo being used is really too small. As a result the gears on the servo are too small for the stress being applied.

Overload - The servo is not strong enough and as a result it is working hard causing it to draw more current than it should which generates heat and can eventually cause in internal failure.


These last two are the most important because they can cause problems with more than just the servo.

Draggy push rods - If your push rods are draggy the servo is working hard just to move the rod, forget about the surface. This can be caused by a dirty guide tube, something rubbing along the push rod. If you disconnect the push rod from the servo and the surface it should move smoothly and without drag. If it is dragging or stiff you have a problem.

Miss aligned push rods - This is similar to the draggy connection rod issue above. The miss aligned rod will cause a side load on the servo. This can stress the bearings or the case as well as the motor. If it is severe enough it can even cause the servo to get locked in a position which will draw a lot of power and eventually burn up the servo. The servo has to work harder to overcome this issue meaning it will pull more current than it should. You will either end up with worn sloppy gears, worn bearings, or burn out the servo.

These two problems often cause the servo to not be able to center properly. This can leave the servo under load even when you have the sticks centered. This can cause the servo heat up and eventually fail.

This can also put a high drain on your flight pack or the BEC of your ESC causing rapid pack drain. If your flight pack voltage gets too low it can cause a shutdown of your receiver leading to loss of control and a crash. This is a common cause of crashes that are blamed on the radio system but which are really a power issue .that may be caused by a poor servo installation.

If the BEC of your ESC gets too hot due to this constant load it can cause a thermal shutdown, you lose power to the receiver and you lose control of the plane. Again, This is a common cause of crashes that are blamed on the radio system but which are really a power issue that may be caused by a poor servo installation.

Last edited by aeajr; 10-22-2014 at 07:12 AM.
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Old 09-19-2017, 08:56 AM
  #40
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Anyone have any tips on servos? Any new servos that are especially good or bad?

How about high voltage servos? Traditionally servos run on 4.8 or 6V but many of the newer ones can run on higher voltages so you can use a 2 cell lipo without a voltage regulator.

As many current receivers can also run at this voltage it can simplify your set-up. If you don't need a BEC or a regulator, that is one more thing to leave out of the plane and one less thing to fail.

What tips do you have for the community? I always welcome updates from the members of RCU.

Last edited by aeajr; 09-19-2017 at 09:04 AM.
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