View Full Version : when is it to much subtrim? whats acceptable
flapjack
02-18-2008, 10:01 PM
Trying to build trex450 using my DX6i. Watched the finless video on CCPM setup. All of the arms seem to be slightly off 90. So i used the single arms, since the ball link fits.
Then centered the arms using sub trim. One of the servos needed about 38 units to center. Went back to monitor and the stick centers are off. Since this is the new center is there a way to center the monitor screen to match stick position?
or is 38 subtrim to much and i should try to mechanically center arms to a smaller value?
also finless sets swash settings at 50% but dx6i defaulted to 60%. Should i be starting at 50%
Guess im stuck
You should be perfectly fine with 38 units of sub-trim. I tested the DX6i and sub-trim does not affect the CCPM mixing at all. I went up to 100 units with my testing.
As for the "stick centers" being off, I didn't even look at that.
- John
DavidH
02-19-2008, 08:49 AM
Don't know if it does the same on the Spektrum. But from what your reporting I would guess it does. If you use a lot of subtrim. For example the 40% or steps you used.
You have 60% one direction and 100% the other direction in travel. That means it has shifted the center about 20% plus towards the 100% side from neutral. Subtrim is nearly the same as using ATV's in the same scenario above.
David
David,
But that isn't how it acted on with a servo or actually monitoring the pulse widths. The data I collected showed that using sub-trim shifted the center and moved the endpoints with it. Here is where I posted some data: http://www.runryder.com/helicopter/t396222p1/?highlight=dx6i
But, as I said above, I didn't even look at the "stick centers" indication because everything else indicated it was just fine.
- John
DavidH
02-19-2008, 01:56 PM
David,
But that isn't how it acted on with a servo or actually monitoring the pulse widths. The data I collected showed that using sub-trim shifted the center and moved the endpoints with it. Here is where I posted some data: http://www.runryder.com/helicopter/t396222p1/?highlight=dx6i
But, as I said above, I didn't even look at the "stick centers" indication because everything else indicated it was just fine.
- John
John,
That is what I meant. I just did not do a good job of explaining it. LOL
Using large amounts of ATV's will shift the center also from my experience with some transmitters. That is one of the reasons AFR's are used on some of the upper end radios.
David
Pinecone
02-19-2008, 05:45 PM
Yes, there is some point where excessive subtrim will cause the range to become skewed. But since JR/Spketrum start with 100 end points and go to 150, and can still use some subtrim, it will be a lot.
And since you should never need more than half a spline's angle of sub-trim, you shoudn't get there unless you want to.
- John
flapjack
02-20-2008, 01:23 AM
Thx for the info. I tried all the servo arms again. And got it set up today. Could only get -10 to +10 on pitch but im a noob so i went with it. Learned a lot building this trex as opposed to an RTF. Ill soon be rebuilding the head after some crashing 1st.
It was crazy how nice it hovered. needed only 1 click of elevator trim. Thx for all the help