Is there a difference between air and surface servos?

[josh9mille]

Im looking for a new servo for my flux xl but doesnt seem like any of the servos made for cars or trucks have the torque i want for the amount i wanna pay. Futaba has some very high tq servos for around $100 that i like but they say they are for airplane use. I just want to make sure they will work for my truck before i decide to buy one. Here are a few links to what i am looking at. Also does the MMM have enough gumption to run one of these?

http://www3.towerhobbies.com/cgi-bin...?&I=LXRAX0&P=0

This one says to use NiCd only, anyone know why?
http://www3.towerhobbies.com/cgi-bin...?&I=LXVPF0&P=0

[whitrzac]

no, and it "says" NiCd only because it draws a lot of amps that early Nimh batts couldn't deliver


HK has some awesome servos for under $50...

[JERRY2KONE]

That looks like an interesting pair of servos and could start a good debate. They both look up to the job from the specs, and that note about using Nmh batteries ONLY is confusing. Restricting it to only nmh seems kind of weird, but maybe BrianG can come up with a good reason. Either way I would think they will both work, but at $120 a pop you do want to know if there are any issues using them in a Savage. I don't see why either one wouldn't work. Pretty powerful servos. Have you tried looking on EBay for maybe the hitec 7955?

[BrianG]

The only thing I can think of is the gearset, despite being metal, maybe isn't as durable as surface-specific servos? Electrically-speaking, servos operate on the same pulse stream scheme (not like air vs surface ESCs).

[Overdriven]

Originally Posted by BrianG

The only thing I can think of is the gearset, despite being metal, maybe isn't as durable as surface-specific servos?

That was always my understanding of it. The gearset not being able to withstand the shockloads a land vehicle would see in say the steering system. Aircraft servos see loads that are more steady (or ramp up more slowly) instead of shock loads (like hitting a rock while driving). I'd imagine the gearsets for land based vehicles are wider to better deal with shock loads.

I think the nicd thing is just a holdover from the old days. Most planes were almost always 4.8v when nitro and gas was king. Keep the input voltage within the servos limits and everything will be ok either way.

[simplechamp]

This might be a little off-topic, but what does it mean when a servo is labeled as cyclic? Does it mean they are constant rotation or something else? They seemed to be used in helis mostly.

[JERRY2KONE]

Dose anyone have an inside man at Hitec or Futaba that they can post these questions to them for us. I mean I can understand that yes wheeled vehicles are under more pounding pressures than plains are, but how much different can these servos really be inside to make them special for one or the other? I am curious now as well.

i have a hitech 7955 im looking to sell... pm me if u want it

[JERRY2KONE]

Well there ya go. It sounds like it is time for "LETS MAKE A DEAL". Now you can get the right servo, and hopefully at a discounted price. I believe the 7955 sells for around $125 new. You can find them on the T/H site for $100 as a super saver member sometimes. Good luck.

[_paralyzed_]

Originally Posted by simplechamp

This might be a little off-topic, but what does it mean when a servo is labeled as cyclic? Does it mean they are constant rotation or something else? They seemed to be used in helis mostly.

Originally Posted by JERRY2KONE

Dose anyone have an inside man at Hitec or Futaba that they can post these questions to them for us. I mean I can understand that yes wheeled vehicles are under more pounding pressures than plains are, but how much different can these servos really be inside to make them special for one or the other? I am curious now as well.

servos are servos are servos. Cyclic just refers to moving swash plates on helis. It's no different than saying steering or throttle servo.

Air/land/sea/cosmos they are all the same and just renamed for a broader sales spectrum.

[JERRY2KONE]

Not sure what your references are Harold, but that is pretty much what I was thinking as well. i mean really, what could they possibly do to one servo from another that would make it propriatary to only one R/C field and not another? Metal gears are metal gears, right? Seems to me that all of the specs depend on what you plan to use it for, and how much you are willing to pay for it.

The only other question still looming is why would a servo have a spec that says nmh batteries only? I don't really see what difference it would make where the stored energy comes from as long as the voltage is within the specs of the servo requirements, right? After all we are not talking about rocket science here. The only real issue is whether you purchase the right size servo for your application, and also that you get a servo strong enough to hold up to your pounding on it. Case solved Professor Paralyzed.

[nativepaul]

It looks like I have a different opinion or maybe just a different viewpoint to the rest of you, in general I would say, yes, there are differences in servos between the R/C disciplines. Cars need an unusual combination of high torque and high speed that requires good motors and ESCs inside them and that makes them expensive, but most air disciplines don't require as much speed (helicopter tails being a notable exception) most of my boats and planes have servos about .15-.22 second travel to maximise torque for the size and weight of the servo, and fly well with that even 3D funfliers, but my cars are around .1 second with as much or more torque but weigh and cost a lot more I usually spend as much for the one servo in a car as I do for all 4 servos in a plane. I love the Ace 1015s in my 1/8th cars, but if someone gave me a bunch free and paid me £10 each to fit them in my models I wouldn't fit any to my planes and only 1 of my boats would get one as they're too heavy and would just blunt performance with the servo speed being of no benefit, if I had any huge planes sure a few would go in there, but on my own dollar I'd buy something slower, lighter and cheaper, for the same torque.

All servos with a few exceptions operate on the same principals and you CAN run a car one in a plane (with a weight penalty), or run a plane one in a car (but you may find you need to get that opposite lock on quicker if your tail happy like me), those exceptions are; retract servos (very low geared for immense torque but very low speed and unusual 180degree rotation lock to lock rather than the normal 120), sail arm servos (low geared for massive torque to move and hold a full sail on the end of an arm several inches long but very low speed), sail winch servos (often regular speed and torque but instead of 120degrees of rotation they have continuous rotation to winch in a sail sheet)

[JERRY2KONE]

Originally Posted by nativepaul

It looks like I have a different opinion or maybe just a different viewpoint to the rest of you, in general I would say, yes, there are differences in servos between the R/C disciplines. Cars need an unusual combination of high torque and high speed that requires good motors and ESCs inside them and that makes them expensive, but most air disciplines don't require as much speed (helicopter tails being a notable exception) most of my boats and planes have servos about .15-.22 second travel to maximise torque for the size and weight of the servo, and fly well with that even 3D funfliers, but my cars are around .1 second with as much or more torque but weigh and cost a lot more I usually spend as much for the one servo in a car as I do for all 4 servos in a plane. I love the Ace 1015s in my 1/8th cars, but if someone gave me a bunch free and paid me £10 each to fit them in my models I wouldn't fit any to my planes and only 1 of my boats would get one as they're too heavy and would just blunt performance with the servo speed being of no benefit, if I had any huge planes sure a few would go in there, but on my own dollar I'd buy something slower, lighter and cheaper, for the same torque.

All servos with a few exceptions operate on the same principals and you CAN run a car one in a plane (with a weight penalty), or run a plane one in a car (but you may find you need to get that opposite lock on quicker if your tail happy like me), those exceptions are; retract servos (very low geared for immense torque but very low speed and unusual 180degree rotation lock to lock rather than the normal 120), sail arm servos (low geared for massive torque to move and hold a full sail on the end of an arm several inches long but very low speed), sail winch servos (often regular speed and torque but instead of 120degrees of rotation they have continuous rotation to winch in a sail sheet)

Yes but what you are describing is obviously determined by the specs themselves on what particular servo you purchase. Of course if you purchase a servo with slower speed, or lower torque for a 1/8th scale truck then it will not cope in your setup. This is an obvious mater of doing proper research and picking the correct servo for your application.

The discussion here is in regards to two identical servos with the exact same specs (speed, metal gears, bearings, high torque, & size) but labled to be specific to boats, planes, or vehicles. The question that was posted is whether there really is any internal differences between these two servos even though they may be labled for boats, planes, or cars, and not all or a combination of them. Unless we get an answer from someone who actually works in the manufacturing of, or works on the internals for warranty repair then we have to assume that they are identical in all aspects. I mean does anyone out there have two servos (one for cars & one for planes) in hand that have identical specs that can open both of them and post up pics for us to anylize? If the gearing is the same, and the motors used are the same, then they must be the same. Then the car/plane labling are nothing more than stocking guidance to keep stocks in balance. Wouldn't you agree?

[nativepaul]

Originally Posted by JERRY2KONE

The discussion here is in regards to two identical servos with the exact same specs (speed, metal gears, bearings, high torque, & size) but labled to be specific to boats, planes, or vehicles. The question that was posted is whether there really is any internal differences between these two servos even though they may be labled for boats, planes, or cars, and not all or a combination of them.

Most of the discussion is indeed in that regard, but that is not what I got from the OP, Josh made no mention of identical servos and to me it reads like he is asking if a high torque plane servo is suitable for cars. I answered the OP rather than adding to the discussion, yes it plane servos can be used but they wont be ideal. If you look at the Josh linked to neither are very fast at .14 and .17 seconds being plane servos (as I mention above) and getting their high torque from low gearing rather than big motors, you wont find servos with identical specs to these sold for car use as they're not fast enough to justify the price.


To add to the discussion if two servos have the same gears torque and speed to me they are the same servo despite one being marketed for cars and the other for planes, its a pure marketing decision trying to get a share of both servos markets while only investing in the tooling to make one servo, however only one of them, or if they go for a compromise between weight and speed neither of them will be ideal for the marketed application.