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Multiplex 3030 - Throttle Pitch Compensation

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Old 07-17-2003, 11:48 AM
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wildblueyawner
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Default Multiplex 3030 - Throttle Pitch Compensation

Hi all,

Need a little help. I want to program a MPX 3030 to add pitch-compensation of throttle, however I'm messing up neutral elevator trim in the process. Specifically, elevator jumps when entering / exiting the Center function. I've got neutral elevator established from previous flying, so would be nice to add pitch comp w/o affecting current elevator trim.

I feel a bit silly :stupid: asking this, since I previously posted a similar inquiry re servo centering in a user mix involving flaps and spoilers, and the solution provided was to ensure that the NormPos option was set to the proper state, which worked fine, thanks

Since throttle is similar to spoilers in that there isn't a "neutral" position to speak of, I'd have no problem if Throttle also had a NormPos option. . . . . . but it doesn't.

What to do?

TIA for assistance.
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Old 07-17-2003, 03:13 PM
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HarryC
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Default Multiplex 3030 - Throttle Pitch Compensation

I suspect that you are using the servo centre parameter? That is what is causing your problems. Either leave it at 0% or at minus9% to compensate for using non-Mpx servos. Throttle mixed to elevator is set independently for both sides of throttle from the mid throttle position but you can't alter the location of that centre like the normpos. You could have 0% from throttle below mid, and X% from throttle above mid, but that's all.

If you are not already using Gx, you could assign it to throttle at some point and use Gx to switch the mixer on, so that it offsets the point at which mixing becomes active, but at that point the mix value will come in with a little jump.

If you want down trim to come in all the way from idle to full throttle, alter the ele mid point by using the control trim parameter, not the servo centre parameter.

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Old 07-17-2003, 05:40 PM
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wildblueyawner
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Default Multiplex 3030 - Throttle Pitch Compensation

Thanks much Harry, esp. for providing several solutions depending on operating modes / preferences.
I suspect that you are using the servo centre parameter? That is what is causing your problems. Either leave it at 0% or at minus9% to compensate for using non-Mpx servos.
Yes, am (was) using Servo Center. Just curious re the 9% ==> Is this to cancel the 110% MPX "expanded" travel limit?, since 110% - 9% = 100%
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Old 07-17-2003, 09:48 PM
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Default Multiplex 3030 - Throttle Pitch Compensation

The minus9% servo centre is to correct the different centre that Mpx uses, not to correct the travel. To correct travel, use travel values of 73% each way.

Servo centre and control trim centre do slightly different things and it is useful to understand their differences. Mpx trim is centre biased so it has no effect on the end travel which remains the same, except for throttle trim which has an idle bias. If you set a travel of +/- 1 inch, then adjust the trim lever so the surface is 1/2 inch down, you will then only get 1/2 inch down movement and 1 1/2 inch up movement. The end points are relative to an absolute centre, not to the floating centre defined by the trim lever. If you adjust the neutral by altering the control trim parameter, you are in effect moving a trim lever electronically so it has the same effect, it is centre biased and does not alter the end points.

The servo centre parameter however is the absolute centre. If you move the surface to be 1/2 inch down by altering servo centre, you will still get 1 inch down and 1 inch up from that point.

When you activate the centre parameter the servo will go to true 0% centre and not move while you alter the value.

So control trim center operates within the existing travel window, servo centre shifts the entire travel window. Bear this in mind if setting up flaps on a 3 pos switch, with servo centre defining the mid position. You may have the end points correctly set. Then decide to alter the centre e.g take off flap. Both up and down flap end points will move as well, so you may get flap not going fully up or alternatively try to go too far and binding and stalling the servo.

Mpx uses servo timing centre of 1.6ms, compared to Japanese centre of 1.5ms. So when you plug in a Japanese servo, or an Mpx "uni" servo with JR plug, it goes to the wrong centre. You can get it back to the correct centre by setting servo centre to minus9%. This is only for the 3030, the 4000 and Royal Evo have a "uni" timing switch.

Mpx travel is 0.55ms either side of centre. Although popular belief is that Futaba/JR use 0.5ms either side of neutral (1 to 2ms) it is not true, JR uses +/- 0.4 ms and as far as I can tell Futaba uses +/- 0.43ms. A JR Tx set to normal 100% travel generates a signal of 1.1 to 1.9ms, Futaba from 1.07 to 1.93ms. In order to get the same travel, the Mpx travel must be set to 0.4/0.55 = 73% to match JR or 0.43/0.55 = 78% to match Futaba.

The 4000's uni switch does not correct this travel, it only corrects the centre.

Interestingly all three brands meet at +/-0.6ms. JR's max travel is 150%, 1.5*0.4=0.6ms. Futaba's max 140% travel gives 1.4*0.43=0.6ms. Mpx normal max of 109% gives 1.09*0.55=0.6ms.

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