Electronic – basic RF transission in noisy environment

433mhzantennaRF

I built a little quadcopter, and I need to transmit some data to it in a max. 4-5 meters range.
The transmitter needs to transmit in a quarter of a sphere (the quadcopter will newer be "behind" the transmitter, neither under it); the quadcopter will only receive signals in half of a sphere: under and all around it's body.

I built a working communication system based on the RF modules in the picture below. But when the 4 DC motors of the quadcopter start, the electromagnetic noise blocks the communication. The motors are about 6 cm away from the receiver, which is surrounded by them.

My questions:

  • 1) each motor has a capacitor between its terminals, and I read that two additional capacitors, one from each terminal to the motor's case, would help; is that true? I also read "but only if the motor's case is well grounded" (I didn't rellay understand that, does it mean I have to connect the case direcly to ground?

  • 2) I had a couple of cheap 433MHz transmitters/receivers around (I don't mean "transceivers": each module can do only one thing, TX or RX) and I decided to try using them. But many people says they're garbage: I don't mind if that's true in general, but is it possible to use them in my case whit a quite good reliability?

  • 3) I had trouble understanding the antenna I should use. At this very moment I have two identical quarter wavelength straight 6mm copper wire antennas, one on the quadcopter and one on the ground. Are there best antenna types for this kind of transmission? I can have what I whant on ground, but the quadcopter needs a lightweight antenna.

Those are my actualRF modules
433MHz modules

Best Answer

Reduce Common Mode emissions by CM filter choke using either Ferrite torroid around each motor wire pair or all wire pairs or wired dual coil CM choke or ferrite clamp on ribbon wire etc with similar CM choke on radio signals to uC using twisted pair or coax and Ferrite CM clamp. Differential chokes are useful with decoupling caps to isolate conducted motor noise interfering with radio but emission noises are also important to suppress with small RF caps (pF) across motors with CM chokes and twisted pair.

Ferrite beads for motor signals are often needed. http://www.digikey.com/products/en/filters/ferrite-beads-and-chips/841?k=ferrite&k=&pkeyword=ferrite&pv7=3&FV=fff40034%2Cfff802ab&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25

Look at a professional design for ideas.

Consider you will need power common mode, CM chokes and differential mode (DM) chokes (ferrite beads) for motors, data signals, twisted pair and shielded twisted pair as well as RF shunt caps on data inputs.

BTW these are not very powerful radios suited for long range copters.

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