Servo Mounting

[Maurice Dyer]

I've been doing rc a long time. Back in the day, it was generally accepted that mounting servos sideways i.e. 90 degrees from normal, was a bad idea. Is this still true, or has it ever been disproved ??.

Maury

[john davidson 1]

Probably stems from the leverage on the mounting  points being less longitudinally mounted ,which still applies .

[Andy Gates]

Me too!

 

Personally I think it still holds true.

If a servo is screw mounted 90 degrees to the direction of the drive (pushrod direction), it only has a small mounting foot - the width of the servo.

With a servo mounted in line with the drive, the mounting foot is the length of the servo so it is therefore better supported with less give so more accurate surface deflections.

[PatMc]

Surely the force is rotational (i.e. torque) therefore the leverage is the same no matter what the servo mount orientation is.

[Nigel R]

There's a vertical distance between the underside if the lugs and the servo horn. This will cause the servo to lean when it is acting against any sort of resistance. Obviously degree of lean is kind of proportional to said resistance.

 

You cannae change the laws of physics. 

[Paul De Tourtoulon]

45 minutes ago, PatMc said:

Surely the force is rotational (i.e. torque) therefore the leverage is the same no matter what the servo mount orientation is.

Yes but no, it's the vertical force of the the output shaft levering against the lower serve mountings,, hoping you know what i mean,,,

[Paul De Tourtoulon]

Damme you got there 5 seconds before me,,,

[Nigel R]

Quick on the draw!

[Maurice Dyer]

Thanks all: just as I thought. Featuring to check though.

[Eric Robson]

I prefer the mounting of the Seafury servos to the Hanger 9 Corsair.

I always try to mount the servos sideways in the wing and have never had any problems doing so.  They were mounted upright for many years when we used torque rods with a single servo which made a very neat installation but not so efficient.

[Ron Gray]

Assuming that the 'box' that the servo is mounted in is not actually touching the servo then the restraint for the servo is through the lugs. Therefore I can't see that, as in Eric's photos, it makes any difference?

[J D 8]

   Bit of confusion with this one I think, servo lying on its side as in the Seafury wing fine. Servo as mentioned by Andy mounted upright but turned 90 degrees not good. Having said that I do have some mounted that way due to space available but they are just doing throttle.

[David Ovenden]

Personally I agree entirely with what has been said so far . I'll always mount my servos in-line with the pushrod axis for all the reasons previously stated.

However, back in the day(1981) R.H.Warring no less was suggesting either method was OK. Photo from his book "Radio Control for Modellers". 

 

 

[Ace]

When servos were 3kg the forces transferred to the mountings were negligible, however power could now be far greater and those mounted at 90' will have a very small distance between the mounting screws greatly increasing the twisting load compared to the wider spread of longitudinally mounted. Situation would be exasperated if they were single lug at each end possibly inducing a rocking motion.  Just my 2p worth.    

[John Lee]

We may be using more powerful servos now but that is largely irrelevant - it is the aerodynamic forces on the control surfaces acting back through the control linkages that will act on the mountings. As long as a servo has not stalled that will be the same whether the servo is rated at 1Kg or 100Kg.

 

Whilst there is a theoretical advantage in mounting longitudinally I would defy any normal (as opposed to World class) modeller to detect a difference in practice on any small to medium (say 7kg) models. I know I can't.

[Nigel R]

1 hour ago, David Ovenden said:

Photo from his book "Radio Control for Modellers". 

 

Noting that the sideways mount used to be the easiest, neatest fit for a small (20 size) model using 3kg servos of the day. And a four lug servo would likely not twist much on a small model.

 

Bigger fuselage, 3 abreast would be easiest. And mechanically better under the  higher loads.

 

Nowadays we have tiny servos for small stuff anyway.

 

[Martin Harris - Moderator]

Conversely, any angular servo movement due to the flexible mounts (I would hope my airframe mounts don't deflect to any meaningful degree!) will be less in the unconventional direction. 

 

While we're on the subject of flexible mountings, how many people put the top hats in the wrong way?  Virtually every second hand model I've had has them the wrong way up, which destroys the designed pre-loading of the rubber grommets by allowing the tube of the top hat to dig in to the bearer - for avoidance of doubt, the rim of the top hat is NOT designed to fit under the screw head!

[leccyflyer]

That's right Martin - quite a few pre-owned models that I've had have had the servos mounted with the top hats upside down. Some have had servo lugs broken off - how do you break the lug off a standard sized servo?

[Paul De Tourtoulon]

6 minutes ago, leccyflyer said:

That's right Martin - quite a few pre-owned models that I've had have had the servos mounted with the top hats upside down. Some have had servo lugs broken off - how do you break the lug off a standard sized servo?

I also found that 90% of servo are not properly mounted,

 And how do you break a servo lug, I have included an illustration,,,?