Graupner MZ-24 and Differential thrust

[Dicktator]

Listen up lads

I've been pulling my hair for the past few days trying to set up differential thrust with Graupner MZ-24 and I can't seem to get it to work. I am connecting two motors to a single battery and then the ESC's to the receiver. One of them is connected to the throttle, the second to the second AUX (ch6) channel. Ideally I'd like to use the right stick to control the craft turning. I tried mixing the channels thusly:

Throttle -> Aux2
rate 100%, offset 100%, always on

Ruder -> Throttle
rate 100%, offset 0%, switch to left stick

Rudder -> Aux2
rate 100%, offset 0%, switch to left stick

This seems the logical setup, but it won't work. Rudder won't control anything. Motors don't even turn on and they sure as hell don't spin up with different rates. Any tips would be helpful at this point.

 

[Craftydan]

Hey Dicktator, Welcome to the forum.

Not sure about the won't turn on . . . the Aux channel or both?

First, what is normally mapped to control Aux2? If a switch or other input is mapped there, then the throttle and rudder mix are adding onto another unlisted input. Might be 0, might be mid-stick, might be max. If it's mid-stick, the ESC will never arm (and won't until the signal goes to "0"). That binding will either need to be broken and reconnected to the throttle (not sure if Graupners can do that, but I think they can) or that input will need to be canceled in another mix (Aux2->Aux2, rate -100%, offset 0)

Second . . . why are you offsetting your THR-> AUX2 mix? Throttle will already be at minimum at bottom stick, now you're telling aux2 to go 100 points below minimum.

Third . . . one of your two rudder mixes will need to be reversed -- Rudder -> ???, Rate -RATE, Offset 0. Which? depends on which motor gets which channel. try it out first.

And finally . . . 100% rudder?!? Sorry, that's a strong throw. Start with ±30% on these rates and go up/down from there.

One last suggestion . . . If your radio has a monitor screen, it's a valuable tool. They generally show what the radio outputs are being sent to the RX, sometimes with bar-graphs, sometimes with numbers, sometimes with both. If the signals aren't right there, they won't work on the plane. If they are, but the plane won't behave, your problem isn't in your transmitter.

 

[Dicktator]

This is all Greek to me, mate... Let me tell what I do know though.

Aux channels have nothing mapped to them, they are free channels. If I connect one motor to the rudder, I can kinda sorta control it when moving the stick left or right, but when releasing the stick it returns to the midpoint and that makes the motor spin at 50% speed. Moving the stick right turns the motor off and moving it left makes it go full speed.

All things aside, let's forget my failed method -- what would be the correct path to take in order to get differential thrust? This is not for an airplane mind you, it is for a boat I'm building. The boat has no servos, only two motors on the sides which I plan on using for both moving it forward and steering. I have 6 available channels to work with.

By the way, the MZ24 has a touchscreen but it is so user-unfriendly that every time I look at the screen, I get punched in the face by the menu and then as I continue to work down the options, it keeps swearing at me. That's how bad it is. The manual is no different either. The radio expects you to be the god of RC, basically.

 

[Craftydan]

Ok, the rudder-stick behavior makes sense. I'm going to assume you don't have a rudder and you're using the differential in it's place, and then use that.

So take it from the start . . .


On the airframe, connect left motor to throttle, right motor to rudder and mix:


Throttle->Rudder, Rate 100%, offset 0 (adds the signal from throttle stick over to the rudder output 1-for-1)
Rudder->Rudder, Rate -100%, offset 0 (cancels out the rudder stick movement -- 100%-100% = 0% -- leaving only the mix above)


That should make both the throttle and rudder channels follow the throttle sticks, and the rudder stick will have no response. The unspoken "mix" here is the stick's binding -- rudder will give the rudder channel +100% (assuming your rudder dual rate is set to 100) -- which the second mix cancels out.

Now pick a rudder rate you want -- we'll say 30% to start (full rudder throw will cause one motor to go up by 30% and the other to go down by 30%).

Now the mixes will be:


Throttle->Rudder, Rate 100%, offset 0 (adds the signal from throttle stick over to the rudder output 1-for-1)
Rudder->Rudder, Rate -70%, offset 0 (100%-70% = +30% rudder stick to throttle)
Rudder->Throttle, Rate -30%, offset 0 (-30% of rudder stick to throttle)


First one is unchanged. Second one combines the cancel-mix used before with mixing in little bit of rudder throw to speed up the right motor as the stick is moved right. Third one mixes negative rudder stick to the throttle output, slowing down the left motor when the stick is moved right.

To get this working on Aux2 will probably require mapping aux2 to something or the channel will be locked out. See if this works or not and we can go from there.

 

[Dicktator]

You sir, are a bloody wizard! I got it working just the way I wanted. I'll post photos and videos of it ripping through a lake soon. Thank you very much.

 

[Dicktator]

Sorry for the double post,

This is what you helped create. I hope you're as proud as I am

https://www.facebook.com/al.igaiter/posts/556123147883117