Voltage adders for custom mixing?

[KaneTheMediocr]

I was looking into buying a transmitter for a scratchbuilt quadrotor, and having a very hard time finding the mixing capabilities I want. I'm considering buying a cheap-ish transmitter/receiver, and then hardwiring the mixers I want with voltage adders. This will only work if 1. the sticks use variable resistors to send a DC voltage signal to the transmitter, and 2. I can get at the interface between the sticks and the transmitter. Has anyone tried this, or have good reason to believe it will/won't work?

[rc404]

I was looking into buying a transmitter for a scratchbuilt quadrotor, and having a very hard time finding the mixing capabilities I want. I'm considering buying a cheap-ish transmitter/receiver, and then hardwiring the mixers I want with voltage adders. This will only work if 1. the sticks use variable resistors to send a DC voltage signal to the transmitter, and 2. I can get at the interface between the sticks and the transmitter. Has anyone tried this, or have good reason to believe it will/won't work?

Yes, this will work. I had a cheap four channel transmitter that I wanted to use for elevons but it did not have a mixer. I built a mixer from op-amps, essentially an analog computer. Fed the output of the sticks to the op amps and the output from the op-amps to the transmitter encoder.

My circuit works well and is a bit complicated. About a year after I build mine, this one was published that is easily five times simpler than mine.

http://www.uoguelph.ca/~antoon/gadgets/mixer.htm

A couple things to watch for. In my case (Futaba Conquest) it was not quite as simple as breaking the wire from the center lug of the stick pot. There is a separate trim pot and I wanted trims to be mixed as well. The stick pot and trim pot went to separate resistors on the encoder board but are common after those resistors. That is where I tapped into the line to get both stick and trim mixed.

The other problem I ran into was interference from the RF. I had to shield the circuit and add caps and ferrite beads to get rid of the interference.

Good luck

[KaneTheMediocr]

thanks 404, I was basically waiting on someone to say they had done it before I bought a transmitter to play with, because if it wasn't going to work then I'd need to buy a different and drastically more expensive radio.

I'll post the results (good or bad) here when they come.

[rmteo]

Take a look at this TX and RX for $29.95:
http://www.mpja.com/prodinfo.asp?number=17044+MI

[arneansper]

http://www.uoguelph.ca/~antoon/gadgets/mixer.htm


I've built this mixer. Here are my results:

http://home.cyber.ee/arne/mixer/mixer.html

I had same experience: it needs good shielding. And adjusting took
lots of time. Better (multiturn) potentiometers would probably help.

Arne