osxpro,

I was looking into Jr recently. It just so happens not too long ago I figured out twin programming for a friend with one. First decide what features you want. The minimum I want is to be able to “hold” either engine at idle while the throttle stick runs up the other. This makes mixture adjusting on the ground easy and allows practicing single engine flying in the air.

Every radio brand’s programmable mixers work a little differently. The Jr Pmixers work very simply. The 2 basic Pmix concepts are slaving one channel to another and holding or freezing a channel from responding to its Tx control input. Then build up whatever functionality you want from these 2 basic applications. There are many possible arrangements.

Switch assignability is where Jr falls short. They still haven’t made all switches and switch positions available for any function, like the other brands do. They took a big step in that direction with their new 9, but still didn’t go all the way. The ability to turn features on/off is what makes add on features selectable during flight. The number of switches available limits the number of features that can be independently selected. So with that said Jr gives you only these choices (with flight modes off): E-F, M-D, L-D, MX, AU, GR, SNP, STK. Basically any position of the flap switch, only the top position of the Aux2 switch, the mix switch, and the gear switch. Other brands give every position of any switch – much more flexible! This is the only limitation holding me back from buying Jr.

Here is a simple twin throttle setup where engines can be throttled together or individually from the main stick. For simplicity I’ll use the gear channel (ch5) for the left engine and the main throttle (ch1) for the right. The gear switch will control the left engine operation and the mix switch will control the right. Another channel must be used for gear (alternately the engine control could be put on the 3 position Aux2 switch where up gives both engines, mid left only, and down right only):

Step one is to program the main (right) throttle channel (ch 1) with a hold. For Jr, to hold a channel, just mix the channel to itself, set mix values at -100%, then set mix offset for hold position desired. Select one of the standard (non multipoint) Pmixers. Input ch1 as master and slave. Choose the mix (MX) switch in the switch selection submenu. Set mix both values for position one (Pos1) -100%. Leave Include and Origin off and Trim on. Basically the throttle is now mixed to itself in reverse canceling out its own input. Flip the gear switch and the throttle servo will stop responding to the stick. Changing the Offset changes what position the servo will hold at. Note, if you want to reverse the direction to flip the switch for hold, return Pos1 mix values to zero and set Pos0 values at -100%.

Next, set up the second throttle. Adjust gear channel so it switches the left engine from idle to full throttle. Then adjust the full throttle ATV to zero, so gear switch commands idle and servo centered. Activate a second Pmix with throttle Ch1 as master and gear ch5 as slave. Choose the gear (GR) switch in the switch selection submenu. Leave the Offset at zero (center stick), Include and Origin off, Trim on. Flip the gear switch to mid throttle. Set whichever mix value comes on (Pos0 or Pos1) to -100% each way. So basically when the gear switch is one way the mixer is off and the left engine is at idle, the other way the gear channel is centered and slaved to the main throttle.

The setup I programmed had more features like differential throttling with rudder control and an auxiliary throttle instead of fixed hold position, so was more complicated. There may be a problem with zeroing out the ATV in one direction, for this simple program. It might not allow the slave mix to drive the gear channel to full position. But this is enough to give you the basic ideas and get you going. The rest is just play with these ideas till you get what you want.

Let me know what you come up with?

Multiflyer