Strange throttle curve behavior

[psindrup]

On my DX7 I have configured the 3 throttle curves for my T-rex 500 as follows:

Normal: 0-60-80-90-100
Stunt-1: 100-90-80-90-100
Stunt-2: 100-100-100-100-100

With the heli on the ground, and the throttle/pitch stick dead center in normal mode, I should be at 80 (and zero pitch), but if I change to Stunt-1 the head speed increases, even though it should also be 80% mid stick.

It gets even more strange:
When I change from stunt-1 to stunt-2 (still on the ground, mid stick) nothing happens to the head speed, even though the throttle curve should change from 80 to 100

I am totally lost.

Is there anyone who has any idea about what is going on?

Thanks a million.

Peter

[bjosko]

Hi Peter.
Are you sure that you have 0 degrees pitch on half throttle in normal, and not around 3 degrees that are common ? Because, if your radio are set up pr. normal wise, you have 3 degrees positive pitch in normal, and 0 degrees in ST 1, so the blades are running with no lift in ST 1
Do you use any trim in normal mode ? This will disappear in Stunt 1&2.

From ST 1 to ST2, are your batteries OK, (I remember you told that you use some cheap batteries ?), or are you running in governor mode ?

[psindrup]

Hej Bjørn

Yes, I am absolutely sure that my pitch is zero at center throttle stick.
And no, I have not used any trim yet, and my batteries are in top shape. :wink:
And no governor.

Peter
Denmark

[Danal Estes]

Several thoughts:

1) The DX7 has "hover trim", on one of the upper rockers, that is only effective in normal. Be sure this is disabled (and/or set to zero).

2) Trims (near the sticks) are unique to flight modes on the DX7. Do ANY of the trims change when you click between normal and idle 1? Loading/unloading the head from a trim change, even a cyclic trim change, could be causing this...?

3) With the heli itself powered off, power up the TX and go to the servo monitor page. Put the left stick at exactly mid (zero pitch, 80% throttle). Now click back and forth between normal and ST1. What moves? Throttle? All three CCPM servos? This will help narrow down which trims or curves to examine.

Let us know what you find... :)

[psindrup]

Hi Danal

Thanks for some very useful feedback.

I will "investigate" and let you know.

Peter

[psindrup]

Hi again Danal

Here are my findings.

Several thoughts:
1) The DX7 has "hover trim", on one of the upper rockers, that is only effective in normal. Be sure this is disabled (and/or set to zero).

It is not disabled (I can not find where to disable it), but it is dead center.


2) Trims (near the sticks) are unique to flight modes on the DX7. Do ANY of the trims change when you click between normal and idle 1? Loading/unloading the head from a trim change, even a cyclic trim change, could be causing this...?


Nope!
All trims are at center, and none of them moved when changing the flight mode, and the pitch trim is "disabled" it idle-up 1 & 2

3) With the heli itself powered off, power up the TX and go to the servo monitor page. Put the left stick at exactly mid (zero pitch, 80% throttle). Now click back and forth between normal and ST1. What moves? Throttle? All three CCPM servos? This will help narrow down which trims or curves to examine.

None of the values changes when switching from normal to idle-up 1.
When switching from idle-up 1 to 2 the "THRO" changes from 80 to 100 as expected.


This is reallly strange ...:dontknow

Peter

[Socal500]

You wil have a point on you throttle curve where you will not see any difference in headspeed from point A to B.. like from 90 to 100. Im not sure if thats the case in your situation on the 80 to 100.

I would start by going back through the programming process regardless of what ESC you are using. Be sure to set your throttle curve for normal so that it is 0 to 100. During program I think most ESCs use that to determine stick position for full throttle.

[Danal Estes]

Hmmm... if NOTHING moves on the servo monitor screen when you click the switch between normal and ID1 (assuming left stick at mid/zero position), then nothing can be changing on the heli either. That screen shows exactly what is sent. If nothing changes... then nothing changes.

So, what moves on that screen?

[yamahajoe]

as far as the speed not changing from idle 1 to idle 2 . mine did that with the stock esc even though i was not in gov mode. i programmed again and that fixed it. it was even beeping the right mode both times.

[psindrup]

Hi all

Just to follow up: Re-programming the ESC solved to problem.
(I did program the ESC during initial setup, but did not program it again when I was done setting the heli up)

Peter

[ZipZap]

as far as the speed not changing from idle 1 to idle 2 . mine did that with the stock esc even though i was not in gov mode. i programmed again and that fixed it. it was even beeping the right mode both times.

The modes may have been right. One of the things the ESC does during programming is set values to recognize the end-points on throttle position. I'm guessing that your upper end-point on the ESC was lower than 100% throttle from your transmitter.

[psindrup]

The modes may have been right. One of the things the ESC does during programming is set values to recognize the end-points on throttle position. I'm guessing that your upper end-point on the ESC was lower than 100% throttle from your transmitter.

That was my guess too, so I just re-programmed the (stock) ESC, and now it works just fine. And I think that my "max throttle" (flat 100% throttle curve in idle-up 2) was actually only 80% before the reprogramming.

Peter

[ZipZap]

Definitely want to have the 0 - 100 linear curve when doing the ESC on this one.:thumbup: