Mini Maestro and Contra Prop Unit

Hi guys I have designed and built a Contro Prop Unit (15" dia. props) intended for a 90" span RC Fairey Gannet. Basically it is controlled by 2 ESC,s for the two brushless motors and two servo,s for the pitch control of the props. The reason for for 2 ESC,s and 2 servo,s is that during flight the pilot of the Gannet would shut 1 engine down and cruise on the other then after 30 minutes or so would swap engines and cruise on the other and repeat this during the flight. this was for fuel economy and so that both engines would accumulate about the same running hours for maintenance reasons.
I am trying to reproduce this sequence on my unit controlled by my transmitter, from the throttle stick and a 3 position switch. Problem is my RC transmitter is only 8 channels and no sequencers at all only mixers which will be used up by other things like undercarriage, wing folding etc. So what I was hoping to do is use an Arduino UNO to take the signals from my receiver throttle and 3 position switch channels and pass them to the mini maestro 12 to start the appropriate sequence depending on the 3 position switch.

I have created suitable sequences on the maestro but at the moment they are just in one sequence with a short delay in between each just to seperate them. I have also built a mimic panel with 5 servo,s, 2 to mimic the pitch of each prop, 2 to mimic each ESC and 1 to mimic the Master throttle from the Tx and a 3 position switch to mimic the switch on the Tx. I did this because I think it would be a bit scary to try to sort this out using the Prop unit itself, and I think the sequencing will get a little more complicated than I have at the moment.
What I don’t know is how to connect up the 3 position switch on my mimic panel to simulate the switch on my Tx and a pot to simulate the throttle from my Tx. I can leave out the Arduino for the moment until I,ve done some more experiments with sequences and just use the maestro connected to my PC. and look at the interfacing later on (slowly slowly catchy monkey as they say) or a bit at a time.

Can you help out here at all as this part of it is all new to me so I,m struggling a bit.

Hope I,ve explained this well enough for you, sorry about the long post.


Hello, Rod.

That sounds like a fun project! From your description, I am not entirely sure what kind of output you plan on connecting to the Maestro from your 3-position switch, but we have a connection diagram and instructions for how to connect a basic switch and potentiometer under the “Attaching Servos and Peripherals” section of the Maestro’s user’s guide, which you can find under the “Resources” tab of its product page.

If you tell me more about the output of your specific 3-position switch, I might be able to help you connect it to the Maestro.


Hi Jon thanks for responding. I did see the diagrams but at the moment I’m not really sure I think I just need high or low inputs from the switch. I have a double throw centre off switch which I thought I could use. When the switch is centred would be both props, when forward would be say front prop only, and when back would be rear prop only. of course each one of these positions would start a different sequence that is programmed in the maestro. It is quite difficult to explain the required sequences for shutting down one prop and starting the other but I’ll give it a go.

Take Off.
Switch centred.
both ESC,s full throttle, both props set at fine pitch. Throttle on Tx effects both ESC’s.

Cruise, on say front Prop.
Switch forward.
Rear ESC would shut down, Rear prop would then go to feathered position. (Front prop will need an increase in pitch here I think) throttle at 3/4 say. Throttle on Tx would then only effect the front ESC.

Prepare to change to cruise on rear prop.
Switch centred again.
Rear prop goes to fine pitch, Then rear ESC goes to say 3/4 throttle. Throttle on Tx now controls both ESC’s again.

Cruise on Rear Prop.
Switch back.
Front ESC would shut down. Front Prop would then go to feathered position. (Rear prop will need an increase in pitch here I think) throttle at 3/4 say. Throttle on Tx would then only effect the rear ESC.

To go back to cruise on front prop the above 3 sequences would be reversed. This change over could happen several times in a flight.

Back to cruise on both props to prepare to land say.
Switch centred again.
Front prop goes to fine pitch. Then front ESC goes to say 3/4 throttle. Throttle on Tx now controls both ESC,s again.

Hope this helps explain a little of what I am trying to achieve.

What I can’t see at the moment is how to connect the 3 position switch on my mimic panel to the maestro to simulate this. Do I need to use three channels on the maestro, 1 forward, 1 centre and 1 for back or can this be done on one channel also the centre position on the switch is the off position so can I actually use this position anyway. I think the pot for simulating the Tx throttle will basically be as the diagram in your manual on its own channel.

As I said I have got these sequences working in the maestro but all in one sequence with just a delay between them to separate them a bit and make them obvious.
I’m pretty sure these will need changing but at the moment its a starting point.

Once I have got most of this sorted on the mimic panel to ensure nothing is going to go silly I’m hoping to take the signals from the receiver Throttle and 3 position switch channel with a Arduino and pass them to the maestro.

Hope I have’nt confused things to much.

Thanks Rod

Since your switch has two outputs, one thing you could do is connect each of those outputs to a channel on the Maestro like we suggest in the user’s guide, and then you could create a set of conditional statements that reads the status of the two channels and looks for conditions when the switch is centered, forward, and back.

If you continue having trouble wiring your switch, could you post a schematic that shows how you plan to connect it?


Thanks Jon was unclear on wether I needed 1 2 or 3 channels on the maestro but what your saying I think is I use 2 channels 1 for forward switch 1 for back switch and centre position would give no signal and then look for positions with if statements in the script. I have never done any programming before so thats gonna be a challenge. Can these conditional statements be created in the status window or do I actually need to manually write a script for them.
Sorry if I,m sounding a bit dumb here but as I said this is all new to me.

Thanks for your help here.


You would need to write a script for them. If you have trouble coding it, feel free to post here with what you have tried, along with the schematic that shows how you are connecting everything (pictures of your setup would be useful, too.).

Also, your project sounds pretty cool, so if you have pictures or a link to a blog about it, we would love to see them!


Sorry for not responding earlier Jon but with christmas looming and 4 kids 13 grandchildren and 1 great grandchild things get a bit hectic.

Ok as I said this could prove a bit of a challenge for me but I’ll give a go. I have looked at some example scripts and the script created by the status window but at the moment it looks a bit daunting and I can’t quite make out what’s happening yet but I’ll study it all a bit more and see if can make it all out.

I don’t have a blog for this but I do have some photos so here are couple sorry if there not very good but I’m no photographer either.

This has run a few times the sound is quite unique and the power is quite awesome too. I controlled it using the Tx throttle for throttles with the mode switch to change between front prop, rear prop or both props, and 2 servo test units to control the pitch of each prop, however this was extremely scary as there was always a chance that you could put a prop into feather while at 10000 revs, not a good idea at all. So I need to sort something better out before running it again. I did intend on purchasing Spektrum DX18 which I probably could have done this with but at about £600 funds dictated otherwise, then I came across the Mini Maestro,s and it looked pretty doable with one of these and a Arduino. Its just whether I can get my head round it now.


One more that shows things a bit clearer


Sorry I,ve not been around for a while guys but someone else’s project has got in the way at the moment. Be back to it as soon as I,ve finished with that.

Thanks Rod.