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Futaba mixing


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I’m trying to mix two electric motor’s operating from the throttle stick. I want to be able to switch one motor off.

I have mixed a slave channel and assigned a switch. Both motors work from the throttle, but the switch doesn’t work, it’s just on all the time, even though the mix screen tells me it’s off. Any thoughts would be appreciated.

The transmitter is a Futaba T16SZ.

 

Steve

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Steve, in such situations, please, not only use the mix screen but also the servo monitor. There you will surely see what happens with the slave channel and MOST IMPORTANT, confirm which function you programmed for the slave channel.

 

This is if you took channel 7 for the slave channel but instead of "AUX1", "AUX2", "AUX3",..... you assigned "Throttle", then the slave channel is just a duplicated channel 3 "Throttle" and the mix simply has no effect. This is the "wonders" from when you have a so great liberty defining and assigning channels.

 

On lower Futaba radios you do not have the Function menu and it is impossible to run into such error, but today most top level radio users ask freedom of function assignation but then you MUST be very, very careful so as not to incur in software contradictions and/or avoiding logic. 

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16 hours ago, Steve Howe 2 said:

 I want to be able to switch one motor off.

 

 

Why? it is generally accepted that twins fly better on both engines! 

 

If you can explain what it is you are trying to achieve there might be a better way to do it than a channel mix. 

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55 minutes ago, Steve Howe 2 said:

Jon

This is for a UAV with 2 motors for extra power on take off, then switching to 1 motor for cruise and having the option for switching the other motor back on for redundancy.

 

If the motors are both inline with the fuselage this might work but if it's a conventional twin with motors mounted in the wings then the extra drag from all the rudder trim to fly straight would dramatically effect the efficiency.

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1 hour ago, Steve Howe 2 said:

Jon

This is for a UAV with 2 motors for extra power on take off, then switching to 1 motor for cruise and having the option for switching the other motor back on for redundancy.

 

Ah ok that makes sense, although Andy's point is quite valid. 

 

One thing you could try is to mix the 2 channels but set one on a steep throttle curve so it shuts off below say 60% power. Anything above 60% power the second motor kicks in and you get full power for takeoff. The disadvantage of this is the motors only matching rpm at full power and being out of sync the rest of the time. 

 

Alternatively it should be possible to mix the throttles on a switch. I use much simpler futaba radios and while i cant explain how without the tx in front of me i cant imagine it being that difficult. 

 

In my experience with futaba mixing though my problems have always been forgetting to assign the switch (if its left blank the radio seems to just mix them all the time) and not setting a rate in the mix menu to tell the radio how much i want the slave channel to follow the master. I would have to attempt to set it up myself on my own tx to provide anything more useful. 

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I have a T18SZ which is essentially the same and there are a number of ways to achieve what you want but probably the simplest is:

 

1. Setup your main motor in the usual way

2. Setup the secondary motor on another channel that you are not using and make sure that the control is set to the throttle stick (either J2 or J3 depending on which mode you fly)

3. Setup the throttle curve for the secondary motor to whatever works best, which is probably the same as the main motor.

4. Setup a dual rate function on the secondary motor channel to be operated by the switch that you want to turn the motor off

5. Flick the switch to the 'motor off position' and then use the AFR function to setup a throttle curve on the seocndary motor that is just a flat line at minimum setting (best to use the point or spline type curve).

 

If you are used to using flight modes (conditions), then I would recommend doing the above except for setting up different flight modes and then setting up the throttle curves as per above. The advantge of using flight modes is that you can also change any other thing, like the rates, trims etc all at the same time.

 

I hope thsi makes sense?

 

As I said, this is a very versatile TX and there are many ways to achieve the same thing, what I am suggesting is only one way of getting there and there may be others that work better for you.

 

Good luck

Simon

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