Looking for information on longevity of servos

BradC

G'day All,

As part of the automation of my ancient iron chariot, I've replaced the heater valve with a manual one controlled by a tiny 9g model aircraft servo (controlled by a Propeller).

At first I had trouble with the servo buzzing at various setpoints, but I've fixed that by driving it about .002mS past the desired point and dropping it back. I now get dead accurate positioning with no apparent complaints from the servo.

I just wonder how long this contraption is likely to last in an environment where it is called upon to make periodic adjustments to the valve while the vehicle is running.

Has anyone used cheap(ish) servos in long term environments? How do they last?

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Release the hounds!

LoopyByteloose

Generally, the servos have plastic gears. I believe they are nylon. These seem to be okay for hobby R/C control, but they do wear out if any substantial load is placed on them. And so, two solutions have come along. One is higher priced metal gear servos and the other is a replacement set of gears.

How long will yours last? Much depends on the context. Is it an extreme environment? Are you loading the servo excessively. Nobody can tell you for sure.

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Ain't gadetry a wonderful thing?

aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

W9GFO

I was testing servos the other day and realized that one of them was very old. I cant say how old but it is the kind that had the older style connector - which had been replaced so that it could still be used. It could be over 25 years old, wish I knew how many RC aircraft and boats it had been in. In those days I couldn't afford to buy a new servo for each model I built so they got reused frequently.

Aside from it being noticeably slower than a modern standard servo, it is still working just fine and is quieter than most.

Rich H

p.s. Karbonite is another material that servo gears are made out of.

Wikipedia said...
Karbonite gears are commonly used in RC servos. The material that these gears are made from offer almost five times the strength of nylon gears and also better wear resistance. Cycle times of well over 300,000 have been observed with these gears with virtually no wear. Servos with these gears are more expensive than those using nylon gears but are highly durable.

Post Edited (W9GFO) : 7/11/2009 4:47:43 PM GMT

LoopyByteloose

Well, the Carbonite appears to be a black material. Nylon is a translucent white and that is what I have. Generally, the quiter the gears - the better they wear. Yes, newer servos have enhanced speed and possibly finer control. Some newer ones even have ball bearings.

Due to R/C models being propelled by nitro fuel, the servos are somewhat resistant to chemicals and heat. But they are mostly a thermoplastic that might soften and melt at temperature extremes.

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Ain't gadetry a wonderful thing?

aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan

W9GFO

Ball bearings in servos have been available for many years.

As to the original question - I don't know. As long as the servo isn't worked too hard (gear stripping), too often (wear) or isn't being cooked - assuming a descent quality servo - I see no reason for it not to last as long as any other similar car part.

If you want to reduce the chance of failure, if it were me, I would replace the 9g servo with a standard size Futaba or JR servo. Or if standard size is too large, a smaller high torque Futaba or JR. On my multi-thousand dollar aerial photography helicopter I use only Futaba digital servos.

Eeek! That's not true - I use a Parallax (rebranded Futaba) continuos rotation servo (not digital) for the tilt mechanism on the camera.

Rich H

BradC

Hrm.. well the unit is in the vehicle cabin hidden under the dash, so it's away from all the nasty heat and solvents under the bonnet. I was initially using a valve coupled to a servo as I was playing with fuzzy logic control algorithms for the heater core, but recent testing has shown bang-bang control is pretty much just as effective as the core has loads of thermal inertia, so I might substitute my contraption for a genuine vacuum operated heater valve and three way vacuum solenoid. I'll leave this in-situ in the mean time and see how long it lasts.

I actually replaced the 9g servo with a genuine Futaba unit yesterday W9GFO. It'll be interesting to see how it lasts. The load is not great, and the movement frequency is anywhere from nothing to once every 10 seconds. As it's operating in bang-bang mode, I'm just rotating it about 60 Degrees to the same points each time.

I was more concerned about the sensor pot wear than the gears to be honest. I'd heard rumours that servos tended to wear excessively when they were jittering as it tears up the track on the pot.

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Release the hounds!