Spektrum DX9 Mixing

[Tosh McCaber]

I am having difficulty in mixing motor control to elevator trim. I have found that my Phoenix motorglider flies very well as a glider with power off, but climbs progressively steeply as I push on  full throttle. I want to be able to control it more as though it was a normal power plane – that is, I want to have a proportional and progressive elevator trim down mix as I increase power, so the model flies level, unless I pull back on the elevator.  The Spectrum DX9 transmitter instruction manual is absolutely useless for any detail.

I'm enclosing a photo of the Mixing Tx screen that I'm using.  (By trial and error, and guesswork!),I've set the rate to 45% in the first Rate entry, with 0% In the second Rate on the top line.  I believe that they are respectively the elevator settings for each end of the throttle movement i.e., 45% down elevator for full throttle, and neutral elevator for low throttle. As I understand it, adjusting the second figure in the row would give me positive elevator to start with, which of course I don’t want. (I don't know  what Offset and Trim in the second and third rows do!)

However my main problem  now is that I've found that the elevator does not kick in until around the 45- 50% mark as I push open the throttle. I need the elevator to proportionally depress as the throttle opens from zero!

 

Can anyone clarify what I should be doing with these rows and boxes to achieve a gradual transition of down elevator as I move the throttle stick to full ?

Any clarification appreciated!

[Denis Watkins]

Do you use the Mix1 set out above Tosh, for a existing purpose?

As there is a lot going on there

Most of what you want will be 0 or 100 and can finally arrive + or -

I can't see why L and R aileron should be -5%

And Flaps? Would be zero or 100 if no flaps

The motor is already at -150% so will this still work at normal 0 or 100?

As set, switch A would make the mix live or not

Set rate to 0 for the time being

Try MOT to Ele watching the monitor to see progress

Edited July 25, 2021 by Denis Watkins

[Steve Dunne]

Hi Tosh,

 

Set both sides to 45% (sounds a lot, I rarely use abve 10%).

Then use the OFFSET to move the elevator back to its neutral position.

That's all you need!

 

I strongly recommend:

 

 

The most detailed and readable manual ever for an RC transmitter. I have no connection with the author, but I have a copy. Best £25 I ever spent in modelling...

Google it.

 

Steve.

[Tosh McCaber]

These are the trims that I ended with after my first flight Dennis.

 

Steve, I also spent money on the Rather Good Guide- I find it goes into far too much detail unfortunately!  I have much better results with You Tube videos- unfortunately, I haven't found one that answered my query.  What I'm trying to sort out is- how to have the progressive elevator compensation starting from low throttle, rather than half throttle?

Edited July 25, 2021 by Tosh McCaber

[Steve Dunne]

Exactly as I said above.

Set both sides to the same value - you suggested 45% (sounds a lot, I rarely use above 10%).

Then use the OFFSET to move the elevator back to its neutral position at low throttle.

That's all you need!

[Tosh McCaber]

What doeds the OFFSET do, Steve?

[Nigel R]

you can set the offset so that (e.g.) a quarter throttle, gives no elevator movement

[Steve Dunne]

The Offset allows you to move the neutral, or centre, position of the elevator to the neutral, or centre, position that it had before you introduced the mix.

Thus when the motor is off, i.e. at its lowest position, the elevator is at the neutral position. The mix is then introduced gradually as the throttleis advanced.

[Robert Putley 1]

I also have experienced the exact same problem, and had given up on finding a solution. So, I shall be following this with keen interest.

[Frank Skilbeck]

Make up a test memory and try it. 

[Glenn Philbrick]

Hi Tosh

I do not have solution for you but have this model and same tx, so interested in your set up. I use the three position switch and retract  switch. Retract switch gives a little bit of down for initial power climbs but then switch it out once I have reasonable contro!, I want it to climb anyway. The three position switch has normal trim, slight down flaps to aid thermalling then spoilers up for shortening the landing

[Romeo Whisky]

 

I have used throttle to elevator mix on my DX9 with no problems at all although I would have thought that 45% mix is excessive - I would suggest 20%, and be ready to switch it off if even that is excessive.  (I see you've designated switchA).

 

However, I am intrigued that your mix says MOT>ELE instead of THR>ELE Tosh. 

Surely it is Throttle>Elevator mix you want, so would suggest you try that.  Set offset if you want the elevator to only start mixing in at a higher throttle setting than zero.

 

 

[Tosh McCaber]

14 hours ago, Steve Dunne said:

Exactly as I said above.

Set both sides to the same value - you suggested 45% (sounds a lot, I rarely use above 10%).

Then use the OFFSET to move the elevator back to its neutral position at low throttle.

That's all you need!

Right guys,

Thanks to all your input, and as a matter of trial and error, I think that I may have resolved it?

 

Steve, your input  quote above started my train of thought in hopefully the right direction!  I realised that the top "Rate" line in the DX9 has two Rate inputs which could be used for each side of neutral- Right/left for Aileron, Rudder and Elevator etc.

 

Throttle requires Rate adjustment on both sides of a nominal "neutral", which is the 50% throttle setting. If you look at my original screenshot above, I have only used the first of the two Rate adjustments in the top line.  I have now inputted (perhaps a more reasonable?) 15% into both boxes, which gives me a gradual down elevator input as I increase the throttle from zero throttle , rather than down elevator starting the input at mid throttle.

 

In the Offset line, by trial and error, and for whatever reason(?), I found that I had to input 100% to bring the elevator back to its former neutral position, as shown by the Tx monitor screen.

 

At present, I have this elevator compensation controlled on switch A, (for safety reasons!).  However, if all goes well, I'll simply revert to set the bottom Switch line to "On".

 

Any further input and info welcome!

[Tosh McCaber]

22 minutes ago, Romeo Whisky said:

 

I have used throttle to elevator mix on my DX9 with no problems at all although I would have thought that 45% mix is excessive - I would suggest 20%, and be ready to switch it off if even that is excessive.  (I see you've designated switchA).

 

However, I am intrigued that your mix says MOT>ELE instead of THR>ELE Tosh. 

Surely it is Throttle>Elevator mix you want, so would suggest you try that.  Set offset if you want the elevator to only start mixing in at a higher throttle setting than zero.

 

 

Hmm Romeo Whisky,

 

I have checked the range of posible inputs on the Mix table- can't find THR- just MOT!  I guess that they come to the same thing!!?

I'm still trying to get my brain to understand the Offset- see my input above!

[Romeo Whisky]

Hi Tosh,

 

Mine is probably an older DX9 than yours - it doesn't give MOT as a mix option and also THR is Channel 1, whereas your MOT seems lower down the list.

I notice you also have MOT set at -150% - why is that?   I presume it might be for Throttle Cut, but that -% is not necessary for Throttle Cut (should be -100% with Throttle Trim Setting set to zero) and that might be affecting the mix. 

[Steve Dunne]

Hi Tosh,

With the mix now set up, just watch the monitor to see how the elevator reacts to the throttle stick movement.

Hopefully it now does what you expect...?

[Tosh McCaber]

It does indeed, Steve. (I hope)

 

I'll let you all know after my next flight, (which may be a good few days, looking at the weather around Aberdeen- wind and/or rain!)

ps. I'm still wondering the mathematics of having had to key in 100% in the OFFSET line?

[Frank Skilbeck]

You are basically wanting a one sided curve that runs from -100% to +100% throttle, so offsetting the start point does that. 

[Tosh McCaber]

Thanks Frank!  I'm getting there!

[Robert Putley 1]

Steve Dunn,  Hi, Have a Spektrum DX9. I have a Discus glider with 3 servo wings. Having real problems setting this up. The manual you recomend does not cover sailplanes.  Mr knight does howver do a manual to cover sailplanes using Spektrum DX9 to Dx18 TX`s.

 

 I have found this website but i cannot see how one can prchase or download the manual.

 

Do you have any ideas?

[Andy Gates]

I may be being a bit old fashioned here but why not add some washers or packing between the motor and bulkhead at the top of the motor mount to increase down thrust and relieve the problem at source?

[Tosh McCaber]

Andy, Can't do it, due to lack of clearance on my Phoenix motor bulkhead-(things start to rub).

 

Robert,Can you give a little more clarification of your Discus set up and problems?  Lots of guys here to help, as you can see from this topic.

 

With regard to the Rather Good Guide- at last I found a page in the 600 odd page volume that was pertinent to my cry for help here.   As I mentioned above,  I found that it goes into a great amount of  detail and technicalities unfortunately- I have to really look for the situation that I'm needing help with- much easier discussing it here!

[Don Fry]

Tosh, be aware that your solution can have aerodynamic consequences. I would expect, if you are at low speed, and you open the throttle suddenly, the auto down elevator input will give a good dose of dive until the speed comes up. 
So get used to it at height, as an aborted landing might give you an interesting few moments at least

[Steve Dunne]

Robert,

 

Sherman's great sailplane programming guides are available at:

 

https://red-sailplane.myshopify.com/

 

These are also great instruction manuals for use of the DX transmitters in general, as well as sailplane setup guides.

 

Steve.

[Tosh McCaber]

Excellent guide, Robert.  But be aware, as the name implies, and as I found out, the Sherman book purely relates to sailplanes, as opposed to powered sailplanes!