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Help figure out what bend to use

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Old 01-25-2019, 06:49 PM
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mkjohnston
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Default Help figure out what bend to use

Hi Guys. I have a rigging issue when setting up a throttle rod on a new airplane that I built a few months ago. I either make the rod to long or short. I had to use the ATV on my radio to get it to work but it still didnt work right. When I am at half throttle in air its already full bore wide open. I dialed it down to the max and that didn't work at all either. I use Dubro Easy connectors on all controls in every airplane. any suggestions would be greatly appreciated!
Thank You!
Michael Johnston
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Old 01-25-2019, 07:40 PM
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kenlowe
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Michael,

Throttle response of the engines in our toy airplanes (both gas and glow) is far from linear. This is the problem you're describing, right? Have a look at post 8 in this thread:

Power Curve of a gas motor (DLE 30)

Alternatively, dial-in some expo on the throttle channel on your radio to make the response somewhat more linear. Some radios even allow to set a multi-point curve to get even more accurate response. Either way, you want less servo movement at the low end of the throttle stick and much more movement at the top, which is basically what the linkage arrangement in the above link is doing.

Hope this is helpful.

Ken
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Old 01-25-2019, 07:57 PM
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Assuming a nitro motor, right? Usually, the throttle arm is comparatively short, so that means a short servo arm. Measure the throttle arm from the center to the furthest hole, then find a servo arm that has a hole no more than the same distance from its center. Less is better, never more to start. Do the best you can for this, sometimes it just isn't possible to find an arm that matches. But pick the one with the closest inside hole you can. Use a clevis (preferably nylon) on the throttle end, in the furthest out hole. On the servo end let the rod initially be 3-4" too long. Slide it into the EZ connector, and put the arm on the servo. Leave the rod loose. Fire up your radio with default setting for the throttle. Move the throttle stick to high. Manually slide the wire through the EZ connector forcing the throttle to full open. Tighten the connector screw on the wire to hold it in place. Test to see if the radio will just fully close the carb at full down and full down trim. If it wants to move too far, dial down the radio settings a bit, and reset the rod for full stick/full throttle again. Retest. It may take a few attempts until you get it right. If you can't get it with just the radio, then move the EZ connector in one hole, and try again.
IF, on the first attempt above, the servo won't fully close the throttle, and you have no way to increase throw via the radio, then move the connector out one hole and try again. Repeat as needed.
After you get things working, you can then trim the excess rod. Or leave it, if it is not causing any problems.
Of course, if your radio has independent adjustment of both end points, that can help a lot to get things dialed in perfectly after getting it close above.

Some with gas engines like to set things initially so the throttle is fully open, and the servo arm is set to almost point straight forward at full stick. At throttle kill, it would be back somewhere past 90 degrees, but nowhere near as much as a flight surface servo arm would be. This produces a somewhat more linear response from the engine, sort of like using expo or setting up a throttle curve. But I haven't found it to be really needed for most glow engines.
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Old 01-26-2019, 12:04 PM
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Hi Ken , Ted, Yes these are nitro power engines and I have tried everything to get this to work right. My problem started 2years ago when I started flying after a 20 year hiatus. I had standard RC equipment with no bells and whistles 25 years ago and now I have one 8channel TX and 6 Rx's. I had set up the Throttle in my RC cars with TX and had no problems but when I get back to airplanes it is totally different. I will look into both of your suggestions and fix my airplane today.
Thank You
Michael Johnston
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