Strange Pitch - comments please

[gorlandheli]

I have a Trex 450 Sport V2 which I have converted to DFC. Having ironed out teething problems it appears to function well. The point is that this is my build experience (original kit build, then conversion/3GX set up etc.)

I had the chance to acquire a Trex 600 pro DFC kit.I have built it and have bought John Salt's set up e-books.

My measured pitch is -4, 0, 4, 7, 10 degrees - that's what I want for now. The concern is that the transmitter settings for this are: 32%, 51%, 70%, 74.5%, 79%. This seems a little strange.

I have (now) roughly equal +/- pitch at set up time but its pretty wild (about 18 degrees)

Do you guys have any comments?

[Gladius]

Did you set the pitch value you want by using a pitch gauge? Is that where the transmitter settings came from? I do agree that it looks a little strange. Are you using any expo, or dual rates?

[gorlandheli]

Yes, carefully levelled the heli itself then used RC Logger pitch gauge. No expo. No dual rates on/applied for this set up...

[Gladius]

If you set your pitch curve to 100%, what pitch do you get? That's your max pitch. Do you have equal positive and negative max pitch? If so, then to get your desired pitch range, your negative pitch value below 50% should be 40% of your positive pitch value above 50%. In other words, if you need to set 30 to get -4* of pitch, then you should need to set 100 to get +10* of pitch. The pitch curves you posted look like they will give you more equal amounts of positive and negative pitch, just skewed so that 0* pitch happens at quarter stick, instead of half-stick.

[gorlandheli]

Thanks Gladius - I will set TX pitch curve back to 0%, 25%, 50%, 75%, 100% and report measurements shortly - your comments are appreciated.

I am certainly not looking for equal pos and neg pitch for flight - I am following rchelicopterfun flight school. This suggests that hover is around mid stick whilst learning - adjusting to an equal pos/neg pitch curve later is not a big issue.

[onemorecrash]

I was going to coment the same to leave the pitch curve linear.
the only one you should be concerned with would be your first pitch point
in normal mode the first pitch should be no more than 3 degrees of pitch.
if you leave it at 0 you will slam the heli to the ground when trying to land too fast.
and on a 600 that could be costly.
cheers.

[gorlandheli]

0% = -16.4
25% = -8.2
50% = 0
75% = 7.6
100% = 14.4

Forgot that end points for cyclic servos are UP 100%, DOWN 80%

Swash is
AIL -34%
ELE -34%
PIT -41%

On Futaba 7C (hence minus values on swash)

Any thoughts from this data?

[gorlandheli]

Thanks onemorecrash - I was only returning to 0,25,50,75,100 for the sake of measurement.

I only want -3 or -4 degrees to counter any wind and an upper of 9 or 10 degrees - I think that 15 degrees is asking for trouble in the earlier days of getting used to it.

[Gladius]

Well, I don't have a 600 Pro, so taken everything I say with a grain of salt (or two). You definitely have more negative pitch than positive, which explains the transmitter settings from your first post. The values you posted for your swash; are those sub-trims? It almost looks like you electronically lowered your swash to get zero pitch at midstick, which then caused your end-points to get out of whack. You've lowered your negative endpoints to get them back in line (somewhat).

If it was my heli, I'd be looking to see if I could get my swash values closer to zero, and then MECHANICALLY adjusting my swash and grip linkages to get zero pitch at midstick, and equal min and max pitch with travel adjust set to the same value for both positive and negative. I have my pitch range set to +/-12* (collective) on my 600, which is plenty. THEN, you can set your pitch curve to give you whatever values of positive and negative pitch you would like.

[jmtyndall]

This comes up a lot. If you have more positive than negative, or visa versa, then your swash isn't centered between the head block and the top bearing support. If you you have unequal pitch, you should lengthen or shorten the servo to swash links until it is equal.

With that said, fbl units don't care about this. But if you're a stickler for proper setup, then this is the right way to do it

[goodhunting]

nother thin pops to mind. You say that the helicopter has DFC head. You never mention what FBL controller are you using (or did I miss that). The thing is that with the FBL units you do not set up the pitch in the transmitter but in the FBL unit...

Gh


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[jmtyndall]

I believe it's 3gx. And I've never set one up, but I think pitch may be set in radio for that fbl

[Smoggie]

Originally Posted by gorlandheli

0% = -16.4
25% = -8.2
50% = 0
75% = 7.6
100% = 14.4

Forgot that end points for cyclic servos are UP 100%, DOWN 80%

Swash is
AIL -34%
ELE -34%
PIT -41%

On Futaba 7C (hence minus values on swash)

Any thoughts from this data?

Put the cyclics to 100% up and down travel. In swash adjust pitch % travel down until you have +/- 12 degrees. If it's not equal either way check that your aileron and pitch servo arms are aligned perfectly horizontally at mid stick (the elevator arm will lean forward slightly from vertical due to the linkage)

[gorlandheli]

Thank you all for your comments - very helpful indeed.

It is indeed a 3GX... there does not appear to be any pitch curve set up in the FBL, so it is a TX deal for this set up.

I had problems with the servo links - I had them adjusted per Align, then 3mm longer, then reduced by 2mm (so Align +1mm) in an attempt to get equal pitch either side.

I will retrace my steps. Knowing that the FBL does not care unduly will be useful. I did get zero pitch each time with a swash plate leveling tool. Servo arms are 90 degrees at zero - no problem there.

The values for the swash are not sub trims, they are under "swash" menu and appear to operate more like a swash gain. I will head for +/- 12 degrees. Once there I can set the TX to have a more sensible pitch curve.

Your help is very much appreciated - every comment has added to my understanding. The forum is invaluable for the practical help given. I only hope I can help others in the electronic domain (my strong suit).

[gorlandheli]

Final results:
End points UP & DOWN 100% on AIL, PIT & ELE
Swash -30% on each
+/-12 degrees on 0-100% linear curve
Final pitch curve is a far more reasonable 33%, 50%, 67%, 77%, 87%

Thank you so much.

[jmtyndall]

Wow you got it dead on? Usually when I get like +13/-12 I give up and call it good :p

[gorlandheli]

Yes - dead on - no I couldn't believe it after all the grief but I did check it and it followed through later on the pitch curve setting - just dialled the pitch % whilst looking at the pitch gauge.

Without the head on swash plate stays level (perfectly) from max to min.

Now I just need some favourable weather! Thanks again - so pleased.

[Gladius]

Awesome to hear, and good luck on your step-up in size!