Zephirus79

Hey guys, been in the hobby 6 months and after the wind claimed my trainer last saturday (Way too windy and it was my fault). I am going to get a 2nd plane. It is probably goign to be a sig four star .60 size.

My question is regarding servos.

Currently I have the cheap tower hobbies servos in my trainer and I have had to replace the gears inside of them once already due to broken teeth.

there are so many options when choosing a servo. I dont need high end stuff because I dont intend on competing anytime soon. There are options like ball bearing, non ball bearing, resin gears, karbonite gears, digital, high performance, YAHHHH!

What does all that stuff mean? Somone wanna give me a quick rundown? Basically I want servos that are pretty standard. Ball bearings I guess are smoother than non ball bearings. What about the gears? I dont want cheap flimsy plastic gears like the ones that are in the tower servos. Whats stronger resin or karbonite or what other materials are there.


so much stuff!

KC36330

ball bearing are very slightly faster when all else is equal and they also have less shaft free play over the life of the servo. high torque is required when the control surface size and airframe speed are increased, your standard low end tower servos will stall out and fail to move the surface at high speed on larger surfaces like the 4* 60 has (in extreme conditions). different gear strengths can get had all the way up to metal gears but there has to be a weak link in the chain to 'give' during incidents, those times you broke gears in the servo you most likely saved control surfaces, it's much easier to change a gear set then a control surface so make your choices wisely and base them on the application they are intended to be placed into. high end servos aren't for competition, they are application specific and you may or may not need them in your application. on the 4* 60 standard servos will work fine as long as you don't get to carried away and try to get max speed (which isn't a 4*s strong hand) acrobatics out of it.

kc

majortom-RCU

My Feedback: (40)

Standard servos, even Tower Hobbies standard servos, ought to stand up to just about any trainer. But crashes and hard landings do take their toll on any mechanical device. If you do everything at wide open throttle, that puts more of a load on the servo. Save your wide open throttle for climbing; cruise straight & level somewhere around half-throttle; reduce throttle when coming down. Bushed servos are cheaper, less accurate relative to bearings. Two bearings are better than one, also more expensive.

Hitec's Karbonite is supposedly more durable than nylon for gears, but Hitec gives warnings not to overload their karbonite servos by putting them in planes where their torque ratings suggest they should be OK. Metal gears are stronger, but grind away at each other with the vibration of the engine. Some lightweight servos don't have the gear strength suggested by their manufacturer's torque rating. Some mfrs torque ratings don't stand up well to inspection. I've never had any servo (use all the majors, high and low end) that didn't need gear replacements sooner or later... more from wear than breakage, although I've broken a few teeth. You'll know you have gear wear when the slop becomes noticeable. Slop being that the servo arm will wiggle back & forth with no resistance. Installation slop is another problem, using linkage that has multiple wiggles, resulting in lots of free movement of the surface with no input from the sticks. This leads to flutter, which often leads to in-flight destruction of control surface and consequent crash.

Metal gear servos are typically used on the most demanding applications. They cost more. They weigh more.

A trainer--even a big trainer--should not be a demanding application. Try a set of standard Futabas, or Hitecs, or JR. Try connecting your linkage for elevators & ailerons at the furthest hole out from the hinge line on control horns, and the closest hole in on the servo arms. This will give you reduced but more than adequate throws, more flutter resistance, less problems from whatever slop is in the linkage. It will make the flying loads easier on the servos, give you longer times between gear replacements. Also it makes the plane easier to fly, smoother, less jumpy. If your transmitter provides for expo, dial some in for smoother response to stick inputs.

Take care in adjusting your linkage so that your surfaces are exactly neutral with no trim one way or another on your transmitter.

PJ_TankPilot

When you replace servo gears because teeth are broken, make sure you get all the teeth out. All it takes is one tooth hiding in the grease to jam the gears. You know what probably happens next.

KC36330

sounds like the voice of experience speaking

i also change all the gears in the set not just the ones that are broke, i have seen allot of people who only change one or two from a set because 'the others are fine' but they too have been stressed so change all of them.

kc

sfsjkid

Those cheap Tower servos are actually either Futaba or Hitec standard servos and as someone pointed out, well up to the job of controlling your trainer under normal conditions. I'm curious, when did the gears fail? The only problem I've had was with one Avistar powered by a .46 engine. Plane was in a full speed dive, ailerons were loose for the speed, fluttered and stripped the gears.

Rodney

Any of the common brands of low end servos (the Tower brand included) should be more than adequate for any sport flying. When teeth are broken, it is almost always from a shock load like a hard landing or physically banging the moveable surface against something. Yes, metal gears are a little stronger than the plastic but they wear (get sloppy) much quicker than the plastic gears do. They are also audibly noisier if that makes a difference. Until you get quite experienced and/or get into 3D flying, the standard sleeve bearing servos will perform as well as the others at a much reduced cost.

barryadam

Well, this certainly looks like the time & place to pose my questions. The last time I was building/flying, there were few options for servos. Now it seems like there are endless possibilites. In the "old days", you used the standard servos that came with the radio for all applications except those extreme ones like ultra light, retracts, or maybe a high torque requirment.
Now that I want to get back into flying, I need help selecting the correct servos for some old planes. Is there any science to picking the appropriate servos with lightest weight but sufficient torque? I understand the features that provide response speed or durability, but what about basic sizing? I have searched the forums, but using the same as someone else (if you could find that) may not be the optimum choice.
The radio manufacturers seem to publish technical servo specs, but how to chose?
Any suggestions?

Thanks

Barry

BobH

My Feedback: (2)

Take a look here for some answers to how much torque..

http://www.coloradogliders.com/servo...calculator.htm

P-40 DRIVER

For what your doing, Hitec 425's are a real good servo for $15. For what your doing, any standard servo will work, past that it is a waste of money. Breaking gears happens but usaully because you crashed or hit something.

rlmcnii

My Feedback: (3)

Zephirus 79,

My third airplane is a Bruce Tharpe Venture 60. It is very similar to a 4-Star 60; it is the same size, but a little lighter. Mine uses a Saito.82 for power and Hitec HB475 servos. The HB475s have what Hitec calls Karbonite gears. These gears are apparently much more wear resistant than plain nylon gears. The servos have plenty of power for sport planes of the .60 to.90 size and do have ball bearings on the shaft. I run mine on six volts just for a little extra speed. Although, I do not believe I could tell the difference if they were running on 4.8 volts!

There is a lot of talk about the Karbonite gears being brittle. I have never had an occurence of a spontaneous gear failure. Hitec recommends one servo/surface/11 or 12 pounds of plane. A 4-Star 60 (or anything similar) will be nowhere near 12 pounds.

The HB475s are just a few dollars more than the 425s.