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Feb 19, 2020, 02:06 PM
Balsa Flies Better!
Thread OP
Discussion

Decent servo for a 6 lb airplane?


Hi all

I'm hoping for some suggestions as to what a decent set of servos for my Curare would be. I'm going to need 4 servos- aileron, rudder, elevator and flap. I'm looking for a competent servo- I'm not planning on flying competition and my eyesight isn't great- but I know enough to realize that a servo with lousy centering is no bargain. Currently I'm using a DX-7 Tx- thinking about a Jeti, but that's in the future.

What I used in my Integra- a 7.5 lb ship-are Hitec HS 5475BBs and from what I recall, these seem fine. I don't think my flying skills warrant $100/piece servos- but am I missing something?

Thanks,

Sam
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Feb 19, 2020, 02:14 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by Megowcoupe
Hi all

I'm hoping for some suggestions as to what a decent set of servos for my Curare would be. I'm going to need 4 servos- aileron, rudder, elevator and flap. I'm looking for a competent servo- I'm not planning on flying competition and my eyesight isn't great- but I know enough to realize that a servo with lousy centering is no bargain. Currently I'm using a DX-7 Tx- thinking about a Jeti, but that's in the future.

What I used in my Integra- a 7.5 lb ship-are Hitec HS 5475BBs and from what I recall, these seem fine. I don't think my flying skills warrant $100/piece servos- but am I missing something?

Thanks,

Sam
I didn't believe it at first but after using them I found them to be surprising good.

https://www.f3aunlimited.com/kingmax...rs-mini-servos

These are also very good. Not quite as crispy as the King Max and not as fast but perfectly adequate. I use them in my Tower 60 Kaos ARF because they recommended them and the servo mounting holes are the perfect size.

https://www.towerhobbies.com/cgi-bin...?I=LXDKDX&P=ML

No you no longer need $100 servos to fly pattern planes. The 3D guys flying large gasoline powered 40 to 50 percent scale planes may need $500 servos but not us.
Feb 19, 2020, 02:58 PM
Registered User
I've also been using the Kingmax servos from F3A unlimited for the last couple of years. I have them in the last 4 planes I've built, some old time .60 pattern planes (La2, super Kaos and Bellaire) as well as a 50 cc plane. I've had zero problems with them and they really have impressive specs for the price point. Previously used mainly Hitec.
Feb 19, 2020, 03:10 PM
A man with too many toys
I have a set of the new Hitec D (D485HW) series servos that I started using late last year. They are excellent and reasonably priced. I like the electronics better than the old HS series.

These are my new favorite full size servos.

Looks like the will be back in stock in a few days https://www.towerhobbies.com/cgi-bin...p?I=LXHDHK&P=7


Not sure why Tower does not have servo specifications any more. Servo City has all the details. https://www.servocity.com/d485hw-servo

.
Feb 19, 2020, 04:36 PM
Registered User
Quote:
Originally Posted by Megowcoupe
Hi all

I'm hoping for some suggestions as to what a decent set of servos for my Curare would be. I'm going to need 4 servos- aileron, rudder, elevator and flap. I'm looking for a competent servo- I'm not planning on flying competition and my eyesight isn't great- but I know enough to realize that a servo with lousy centering is no bargain. Currently I'm using a DX-7 Tx- thinking about a Jeti, but that's in the future.

What I used in my Integra- a 7.5 lb ship-are Hitec HS 5475BBs and from what I recall, these seem fine. I don't think my flying skills warrant $100/piece servos- but am I missing something?

Thanks,

Sam
I've had 5 -8 lb planes with the normal regular size servo, I also have used some heavy duty metal geared ones but they would'nt center back up. if you are troubled about the loading put one servo on each aileron and 2 on the elevator
Feb 19, 2020, 07:11 PM
Balsa Flies Better!
Thread OP
Hi guys

Thanks for the responses- very helpful!

I'm not really concerned about control surface loading (well, I suspect the flaps need higher torque, but speed is not of the essence)- but back in the days of nickel cells, I had some HS-85 MGs that were fast, had plenty of torque, but couldn't center worth a plugged nickel. I went to HS-81s and was much happier.

I must admit, I don't get metal gears- I must be missing something. I thought nylon gears have less wear so they last longer. I thought metal gears are for when you're really slamming into something- like flaps on a glider where the flaps contact the ground first. Or are the titanium gears better?

On this airplane, maybe I'll back it into a door or something, but I'm not really worried about stripping gears.

While I've had good luck in the past with Hitec, I'm tempted to give the KingMax a try if people like them. But the other concern is the ESC- I plan on sticking with Castle stuff, and I don't want to use a second battery for the radio- nor am I crazy about a separate BEC if not needed- although I have plenty. My current ESCs are probably all limited to 5V (and I'll bet so are my BECs), so that probably means a new ESC for higher V. And will the Spectrum rx tolerate something over 6V?

Sam
Feb 19, 2020, 10:03 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by Megowcoupe
Hi guys

Thanks for the responses- very helpful!

I'm not really concerned about control surface loading (well, I suspect the flaps need higher torque, but speed is not of the essence)- but back in the days of nickel cells, I had some HS-85 MGs that were fast, had plenty of torque, but couldn't center worth a plugged nickel. I went to HS-81s and was much happier.

I must admit, I don't get metal gears- I must be missing something. I thought nylon gears have less wear so they last longer. I thought metal gears are for when you're really slamming into something- like flaps on a glider where the flaps contact the ground first. Or are the titanium gears better?

On this airplane, maybe I'll back it into a door or something, but I'm not really worried about stripping gears.

While I've had good luck in the past with Hitec, I'm tempted to give the KingMax a try if people like them. But the other concern is the ESC- I plan on sticking with Castle stuff, and I don't want to use a second battery for the radio- nor am I crazy about a separate BEC if not needed- although I have plenty. My current ESCs are probably all limited to 5V (and I'll bet so are my BECs), so that probably means a new ESC for higher V. And will the Spectrum rx tolerate something over 6V?

Sam
You are talking about ESC's, are you flying electric powered or wet fuel powered. These servos are very tolerant on voltage. I run anything from 4.8V to 6.6V (2 cells LiFe for wet fuel engines). All the receivers nowadays can run over 6V no problem. Some can go up to 12V.
Feb 20, 2020, 05:37 AM
Balsa Flies Better!
Thread OP
Hi Hansen

Me- I'm flying electric. I think the ESCs I have in my drawer are all good for 5V or so. The specs I saw on the servo though, looked like it got a lot snappier at higher V. The Kingmax specs went up to 8.4V which is a 2 cell lipoly. Any of my current servos would probably have magic smoke leaving at that V.

So in practice, maybe I should ask which servos are people happy with at 5V or so?

Sam
Feb 20, 2020, 08:12 AM
Registered User
Standard servos all round. I'd use HS485. They'll be way more than you need in terms of torque. Flaps on Curare are tiny, won't need anything special to drive them.

Remember fancy fast digitals need a big battery and use more power.
Feb 20, 2020, 08:19 AM
Registered User
Jet_Flyer's Avatar
Quit using Futaba radio gear years ago, but I like their servos and still use them. They have a good selection and are very reliable. Plus the plugs are keyed and match the key slots in my receivers.

Mike
Feb 20, 2020, 09:55 AM
Balsa Flies Better!
Thread OP
Umm- about the flaps....I think they're supposed to be able to go 90 degrees- and that means that there will be a fair load on them. I'm pretty sure the flap loads will be much higher than all the other surfaces combined. Ideally the flaps should work on a downline- at least, I'd like to try them that way. I wouldn't be surprised if there's 5 lbs load on them- basically, you're putting the brakes on a six lb airplane and if they slow the airplane down appreciably- which I've heard that they do- then there's a fair amount of load.

Sam
Feb 20, 2020, 11:51 AM
Missileer Extraordinaire
Mel Duval's Avatar
I have had trouble using over 4 servos with the ESC powering them. Digitals have been particularly problematic for me because of the high current draw. Check out the ESC specs closely to make sure. The available current is more important than the voltage.
Feb 20, 2020, 12:18 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by Megowcoupe
Hi Hansen

Me- I'm flying electric. I think the ESCs I have in my drawer are all good for 5V or so. The specs I saw on the servo though, looked like it got a lot snappier at higher V. The Kingmax specs went up to 8.4V which is a 2 cell lipoly. Any of my current servos would probably have magic smoke leaving at that V.

So in practice, maybe I should ask which servos are people happy with at 5V or so?

Sam
The servos may spec to go up to 8.4V but they still work very well in lower voltage. As mentioned I run at 6.6V with a LiFe pack and they are quite quick. You can use 5V and they will be fine.
Feb 20, 2020, 12:23 PM
AMA 46133
SeismicCWave's Avatar
Quote:
Originally Posted by Megowcoupe
Umm- about the flaps....I think they're supposed to be able to go 90 degrees- and that means that there will be a fair load on them. I'm pretty sure the flap loads will be much higher than all the other surfaces combined. Ideally the flaps should work on a downline- at least, I'd like to try them that way. I wouldn't be surprised if there's 5 lbs load on them- basically, you're putting the brakes on a six lb airplane and if they slow the airplane down appreciably- which I've heard that they do- then there's a fair amount of load.

Sam
Flaps don't necessarily have a lot of load on them. The reason is that flaps are not used when the plane is at full speed. You typically don't drop the flaps 90 degrees while you are flying at full throttle. Flaps on our RC planes are mostly used as air brakes. Some may mix their flaps with elevator to make sharper corners on their maneuvers but the flaps do not move very much in those cases. So no your flaps do not have a higher load than you other control surfaces.

There are control surface load calculator online that will give you some references.

http://www.mnbigbirds.com/Servo%20To...0Caculator.htm
Feb 20, 2020, 01:09 PM
Balsa Flies Better!
Thread OP
Hi Hansen

Let me look at the amp draw I've got on my ESC- think it'll be a 50 amp Castle Edge. If needed- and I'm beginning to think it might not be a bad idea- I'll go to a separate BEC. That way if the servos do draw more current than I think- I won't lose the airplane. I'll likely take your suggestion on the Kingmax servos on the ailerons, elevators, and rudder.

About the flaps- I'm thinking something with more torque- maybe a winch servo? The flap on a Curare is really a speed brake-so I think the idea is that it could be used at high speed. It's not going to add a lot of lift on landing- it's purpose is to "dirty up" the airplane. The flaps are also directly in the prop blast. Worst case is that the airplane is in a full throttle dive with the flaps extended. Yes, that shouldn't happen- but I don't want to break something if it does. Hence, I want lots of torque- speed/accuracy not so important.

Sam


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