Cyclic vs linear servos

[oldcelt]

What are the pros and cons relating to cyclic/linear servos?

[waveydavey]

You might have to be a bit more specific. Do you mean, cyclic Ie a standard rotational servo as opposed to a linear, such that you find on a board like a 130X tail servo or an MCPX

[oldcelt]

You might have to be a bit more specific. Do you mean, cyclic Ie a standard rotational servo as opposed to a linear, such that you find on a board like a 130X tail servo or an MCPX

Yes, the mcpx has linear servos but most 450 kit builds I've seen being discussed seem to have rotational servos. I wondered if there were good reasons for choosing one design over another?

[Vikki]

HI. Basic reason is those linear servos are custom made by Blade (or their engineering company) to be as small and as powerful as possible to fit a very small helicopter. There are no arms to worry about so no space has to found for them, the actuator actually travels within the confines of the boards footprint.

They are prone to a different kind of damage than rotational servos. The endcap can break and can't be repaired or replaced, the whole servo has to be replaced unless a little enginuity is used (like I did mine). The actuator when hit hard will be forced down the thread, or, if going the other way, breaks the tiny nut at the top of the threaded shaft. I don't think they are anywhere near as powerful as a proper servo since the motor connects directly to the threaded shaft through two gears.

Nope, these guys are made for a very specific purpose so don't even worry about it

[cjcj1949]

Fleet used to make a linear servo (1980s). It was very good and useful. I'm not sure that having a linear output is that useful as usually we are driving a control surface that rotates. They could have an advantage on cyclic as we would not have to position the horn at right angles and the linear mechanism could be easier to replace than the internal gears that currently break. The Fleet servos had a rack and pinion that fitted on top of the basic servo. You would have to mount the servos differently to on a trex 450 as they would need to be vertical on cyclic.

[dillwhacker]

Linear servos have the disadvantage that you cannot select the radius at which you take your output, and so you can't select how much throw you get.

[nobbycopter]

Linear servos have the disadvantage that you cannot select the radius at which you take your output, and so you can't select how much throw you get.

You can in a way...just reduce the endpoints....that's assuming that the linear had as much travel as a rotary when in the outer hole of the horn...

[Varelco]

More torque can be created with rotational servos due to integrating a gearbox within the body.

Linear has the advantage of weight and footprint, hence being used in tiny models.