Would EXPO help this?
07-29-2008 | 01:39 AM
#26
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From: Rochester,
NY
RE: Would EXPO help this?
ORIGINAL: chashint
Well, I am going to disagree with those saying not to use the expo.
Since your throttle opening is linear to throttle stick movement, I see no reason not to experiment with the expo to see if you can tune the rpm to match the throttle stick position.
While I think the method Minnflyer showed you with the servo arm positioning is a good place to start, it will only get you part way there.
I say copy your setup that has now been test flown into a new model memory and try adding the expo to the throttle on the new memory location, that way your original setup will be intact and your experiment won't cause you any grief if it does not work.
The worst that can happen is it won't work the way you want it to.
If that is the case just blow the model out of that memory location and you have lost nothing.
I am surprised that the 7c does not have an adjustable throttle curve in the ACRO programming, but my quick look at the online manual indicated it was a HELI only program.
It was years before I had a radio that had the adjustable throttle curve, I did what I could with the mechanical expo but there has always been a lot faster throttle response at the low end. When I finally programmed in that linear response I found out I did not like it at all.
Maybe it is because I have never had linear throttle response, but it did not suit my tastes so I went back to what I am used to.
Well, I am going to disagree with those saying not to use the expo.
Since your throttle opening is linear to throttle stick movement, I see no reason not to experiment with the expo to see if you can tune the rpm to match the throttle stick position.
While I think the method Minnflyer showed you with the servo arm positioning is a good place to start, it will only get you part way there.
I say copy your setup that has now been test flown into a new model memory and try adding the expo to the throttle on the new memory location, that way your original setup will be intact and your experiment won't cause you any grief if it does not work.
The worst that can happen is it won't work the way you want it to.
If that is the case just blow the model out of that memory location and you have lost nothing.
I am surprised that the 7c does not have an adjustable throttle curve in the ACRO programming, but my quick look at the online manual indicated it was a HELI only program.
It was years before I had a radio that had the adjustable throttle curve, I did what I could with the mechanical expo but there has always been a lot faster throttle response at the low end. When I finally programmed in that linear response I found out I did not like it at all.
Maybe it is because I have never had linear throttle response, but it did not suit my tastes so I went back to what I am used to.
Jim
07-30-2008 | 11:43 AM
#27
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From: Rochester,
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RE: Would EXPO help this?
Here's where I am now and I think this is a good solution for anyone with a similar problem.
I worked from the half way point and then out from there in either direction.
To get the carb barrel open half way with the stick at half I turned on the plane and radio with the wing removed, put the throttle stick at half on the radio, and removed the servo arm screw. I lifted the servo arm off the servo and put it back on while watching the carb such that the carb barrel was halfway open when I found the right tooth on the servo. Then I screwed the servo arm back down tight.
Next, I moved the stick on the radio to full throttle and adjusted the end point on the radio until the carb barrel was open 100%!
Last, I moved the stick on the radio to idle and adjusted the end point on the radio until the carb barrel was barely open.
Now, idle is idle on the carb, half stick is half open on the carb, and full stick is full open on the carb and full rpms on the engine! Before I was getting half open on the carb barrel with just a couple clicks above throttle on the stick. Didn't have to use any expo at all as most suggested. Incidentally, I ended up using the outermost hole on both the carb and servo ends.
This worked perfectly!! It's raining today so I'll have to fly the plane next and will report on how it works out.
I worked from the half way point and then out from there in either direction.
To get the carb barrel open half way with the stick at half I turned on the plane and radio with the wing removed, put the throttle stick at half on the radio, and removed the servo arm screw. I lifted the servo arm off the servo and put it back on while watching the carb such that the carb barrel was halfway open when I found the right tooth on the servo. Then I screwed the servo arm back down tight.
Next, I moved the stick on the radio to full throttle and adjusted the end point on the radio until the carb barrel was open 100%!
Last, I moved the stick on the radio to idle and adjusted the end point on the radio until the carb barrel was barely open.
Now, idle is idle on the carb, half stick is half open on the carb, and full stick is full open on the carb and full rpms on the engine! Before I was getting half open on the carb barrel with just a couple clicks above throttle on the stick. Didn't have to use any expo at all as most suggested. Incidentally, I ended up using the outermost hole on both the carb and servo ends.
This worked perfectly!! It's raining today so I'll have to fly the plane next and will report on how it works out.
07-31-2008 | 09:30 AM
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From: Rowlett,
TX
RE: Would EXPO help this?
ORIGINAL: cappaj1
Now, idle is idle on the carb, half stick is half open on the carb, and full stick is full open on the carb and full rpms on the engine! Before I was getting half open on the carb barrel with just a couple clicks above throttle on the stick. Didn't have to use any expo at all as most suggested. Incidentally, I ended up using the outermost hole on both the carb and servo ends.
Now, idle is idle on the carb, half stick is half open on the carb, and full stick is full open on the carb and full rpms on the engine! Before I was getting half open on the carb barrel with just a couple clicks above throttle on the stick. Didn't have to use any expo at all as most suggested. Incidentally, I ended up using the outermost hole on both the carb and servo ends.
ORIGINAL: cappaj1
The opening in the carb barrel IS proportional to the throw of the throttle linkage and arm. In other words, when the stick is at idle the barrel is barely open, when it's at 1/4 the barrel is 1/4 open, when at 1/2 the barrel is 1/2 open and so on. But the engine response isn't proportional. This is what I was trying to explain before. With only a few clicks (now) above idle, the engine begins to race too quickly. We put a tach on the prop and sure enough it showed the rpms of the engine were not proportional to the stick movement. There is a logarithmic response where the engine rpm's climb their most at the lower end of the stick movement.
The opening in the carb barrel IS proportional to the throw of the throttle linkage and arm. In other words, when the stick is at idle the barrel is barely open, when it's at 1/4 the barrel is 1/4 open, when at 1/2 the barrel is 1/2 open and so on. But the engine response isn't proportional. This is what I was trying to explain before. With only a few clicks (now) above idle, the engine begins to race too quickly. We put a tach on the prop and sure enough it showed the rpms of the engine were not proportional to the stick movement. There is a logarithmic response where the engine rpm's climb their most at the lower end of the stick movement.
