RC Servo’s & RC Motor setup’s from RC Universe
How to get a good basic servo/geometry setup.
What’s servo resolution?
Servos have a resolution of 1024 points per 60 degrees of rotation. That means although even when moving the stick slowly servos look fluid in motion they are actually only able to stop at one of these points. They look fluid because of the high resolution. This is the reason you don’t want to run low percentage ATV or D/R settings. You would end up with a control surface that has very low resolution. This would make the control surface less fluid in motion (more jumpy) and also less accurate all round including centring.
Servo horn setup.
First zero your sub trims, trims, any mixing or mixing offsets on the channel you working on before you screw the horn onto the servo. Unless you purposely trying to create differential on that control make sure the horn is square to the pushrod. Rotate the horn on the splines to see which one of the arms gets closest to being square, this will minimize the amount of sub trimming you need to square the horn from your TX afterwards. When you fix the control horn to the control surface make sure the horn holes are square and in line with the hinge point.
For 3D setups, big control surfaces or servos that are marginal for the application.
Here you want to dial up the ATV on your transmitters. Most radios can go to 150%. I take mine to 140% as this allows 10% for a small amount of sub trim and or flying trim. This is also the reason you want to zero your trims and sub trims on your TX before you set your servo horn. If you exceed that 10% when trimming you will have a dead spot at the end of your servo travel.
Trainer, sport and other general planes with smaller control surfaces & deflections.
Here I use my ATV at 100%. The reason I do this with a smaller control surfaces with less deflection (let’s say less than 25 degrees) is that the suggested servo will have sufficient power and resolution for this type of setup but would be 40% slower if you set your ATV to 140% like a 3D setup. With that said sometimes even small surfaces could do with increasing the ATV settings higher. An example of this would be an aileron that shows signs of wanting to flutter at high airspeeds or a flap / airbrake surface that is working hard. Increasing the ATV and then setting the throw back to normal deflection mechanically will make this surface more rigid and powerful. Careful when using dual rates, if you using low percentage D/R (lower than say 70%) it a good time to consider increasing your ATV settings a bit to compensate for the low D/R. Remember that your D/R setting is a percentage of your ATV and low percentages means low resolution.
Setting up the throws mechanically
Using the above information, decide and set your TX ATV’s to what you require. Now that it’s done lets mechanically set your pushrod to get the required throw. By doing it in this order you will get the best power/resolution from your servo for your control surface requirements. Once you have the servo and control surface horns fixed correctly, connect the pushrod to the very outside holes of the horns. If the surface movement is too much then move the pushrod on the servo horn inwards one hole and check again, repeat if it is still too much. If the surface doesn’t move enough then leave the servo horn hole at the outside and move the control surface horn in one hole and again repeat if it is still too little. The reason for doing it this way is that you end up with the push rod as far out on the horns as possible which gives you the most rigid slop free linkage. By doing it in the above order you will generally end up with the control surface horn being longer (measured from horn hole to hinge pin) than the servo arm which is a good setup. It is not always possible with a 3D setup but as a general rule you should try not go to a point where you have a longer servo arm than control surface horn.
Setting up the throttle for proportional power.
With computer radios it has become very simple but for those who are using old or basic radios you can still set a throttle linkage mechanically so it gives you a smooth throttle response curve. Generally a throttle is very sensitive at the bottom half and from half throttle upwards almost does nothing. To correct this with computer radios adjust the throttle curve mid-point to 30% and adjust the other points so it makes a smooth exponential curve. To do it mechanically, undo your throttle linkage at the servo. With the throttle stick at half move the servo arm on the spline so that it is around 30 degrees off square in the same direction as when closing the throttle. Adjust the pushrod length so the carb won’t bind at either end when moving the throttle stick and then reconnect. You might have to adjust the length of the servo arm slightly to get the correct range of movement for the carb. When you finished you should have a carb that opens to about 1/3 when your throttle stick is at half. Electric motors are the opposite and although I am not sure if newer ESC have corrected for this I have always had to adjust the throttle curve for about 70% at half throttle to give a proportional throttle response.