Here is what I wrote way back when. Although the general idea is for non-computer radios, the throttle linkage should be handled the same way as a non computer radio because the first setup should be mechanical, with minor trims done with end point.. MINOR trims. Using end points does a real number on you resolution, so leave it alone until you are thoroughly satisfied with the mechanical setup and only need to dial in some minor amounts of trim.

So, with that, here we go.....



I've seen some questions about binds in throttle linkage and proper set up of the throttle linkage especially with non-computer radios, (those without end point adjustments) So I thought I take a few moments and write this setup description and post it here in the beginners forum.

This setup may also be found in other locations, such as in RCKen and Minnflyer's "Getting Started" web site and possibly in the AMA Sport Aviator magazine. My intent is not to re-invent the wheel, but just to offer this as a point of interest to those that may be interested.

I hope this helps.

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Because non-computer radios do not have end points you have make all the adjustments, including centering, mechanically. The stick movement relates to 100% servo movement. So, you have to work with the mechanical settings of the "levers and bell-crank" action of the servo arm and the throttle arm.

First, select the servo you intend to use for your throttle, most likely a standard servo.

Your setup will depend on what position your throttle servo will be in the servo tray on your particular model. The servo can be mounted so the throttle arm points to the front of the servo (short edge) or it can be setup to that the throttle arm is pointing to the side of the servo (long edge). Make sure you do your centering on the side if the servo as mounted in the servo tray slot for the model that you will be using. See the below diagram.

Once you have selected the correct side of the servo you are using, it’s time to zero the servo. You can do this either with the servo in the servo tray or outside of the servo tray. Obviously, if you do it in the aircraft, in the servo tray, you will be all set. If done outside, then you have to make sure the servo is mounted squarely in the servo tray once you are ready.

It’s time to center the servo arm. You can only do this using one of the other channels with trim set to the mid point or at zero (no plus or no minus trim, just set it to the mid point on the TX). Connect the servo to that channel (rudder, elevator, aileron... whatever, but NOT the throttle). Center the transmitter stick and the trim tab of the channel you are going to use for the centering operation. Plug your battery pack into the receiver. The servo will move to the center. If the servo arm is not 90 degrees to the side of the servo, then remove the servo arm and rotate it 90 degrees as shown in the diagram. Each arm is offset somewhat to enable you to find the ONE of the four arms that is correctly centered for that servo. If you do not have a four arm servo, get one. Once you have done this, secure the servo arm into the servo using the servo arm screw and tighten it down. I would also either cut the other arms off or mark the one you intend to use with a permanent marker so that if you remove it, you will remember what one you centered on.

Once you have done that, your servo will be centered with the centerline of the servo arm perpendicular to the side or top of the servo (again, see the diagram). Again, you have set the centering for that servo so use that particular servo for your throttle.

If you have not done so, go ahead and install the servo in the servo tray slot and connect the servo to the throttle slot in your RX.

Now, center the throttle and the throttle trim on the TX. (If using a computer radio, then use the screen for the trim and center the trim so that it is neither + or – trim.) Set the TX aside, yeah, leave it on.

Fully open the engine throttle by rotating the engine throttle arm so the throttle is visibly fully open (goes to the end stop and you can see that the throttle is fully open in the carburetor throat. Set the TX throttle AND trim to fully open (all the way up). Now, connect the linkage using the hole on the servo arm that is the furthest away from the center and the same on the engine throttle arm.

One point here. If you are using a clevis on the engine side of the linkage with metal rods and if your engine throttle arm is metal, do not use a metal clevis. Use a plastic one such as the Dubro Safety Lock Kwik Link (2-56) Dubro part number DUBQ1510 or something like it. You do not want metal-to-metal connections on the throttle. This could create electronic noise with metal to metal connections in a high vibration area such as the throttle linkage. And, I would stay away from using the cheap plastic clevis’ that come with many ARFs and kits.

Adjust your linkage so that they match up (rotate the clevis or ball socket so that the linkage matches up with the hole in the throttle arm without moving the throttle arm). Lengthen or shorten as necessary but be precise and make sure the throttle arm does not move once you put the thing together (plug in the ball socket or attach the clevis).

Now, move the trim to fully closed and slowly move the TX throttle until you go to full closed while carefully watching to see if the servo arms ‘wants’ to go further when fully closed. If it fully closes with no binding, then go to full closed with the trim. Again, if no bind, then you are ok.

If it binds, or the servo ‘wants’ to go further than the throttle will allow it, then choose a next hole on the servo that is closer to the center. And try it again. Leave the linkage on the engine alone for now.

Re-check for binds and that the throttle opens and closes fully with no binds with the TX fully open and closed with both settings for the trim. If no binds then you are ok. If it binds, then more adjustment is necessary. Continue to adjust as necessary until you are happy that it opens fully and closes fully with no binds. Now, you should have correct adjustment and trim settings so that you can close the throttle with the trim to shutdown the engine when finished. The goal here is to have your TX throttle at full open with the trim at full open and the servo arm moving just to the end point, and fully closed with trim at full closed just to the end point. No more, no less. AND using as much of the throttle rotation as you can. This gives you the most throttle resolution with no binds.

One additional point here. There is a device called TXservo that allows you to center the servo and test the full range of any servo with a PC and without your transmitter. But, I won’t go beyond saying that this can be done and that this device does exist. If you want to see what I mean, then do a search on the internet for TXServo.