Technical, Techniques, Hints, and Tips > Radio Equipment

BRUSHLESS MOTOR RFI

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RHBAKER:

*   Am in the process of building a model of a fast patrol boat.
 The model uses two 2400 kV brushless motors controlled by individual 50A  ESCs; each motor drives one contra-rotating propeller. Each ESC is driven by its own Li-Po battery and operates within it's own individual electrical circuit. Both ESCs are driven from a common Rx, although use separate control channels. The Rx is separate battery, not BECC powered. The latest ESCs are fitted with small ferrite rings.
 For some time have been trying to resolve a “squeal” and “stutter” which can occur on motor start-up. Each motor powers up quietly and smoothy if operated by itself. If the motors are operated in unison a “squeal” and/ or stutter can occur with either motor. If the control lever is  returned to neutral and the motor stopped and restarted the problem may reoccur or the motor might start up cleanly.
   The vessel can be operated on either 2S or 3S power, on 3S the squeal and stutter is much more pronounced. Since starting the project have now replaced every drivetrain component, excluding the Tx & Rx, yet the problem persists. Those components have worked well on other vessels.
 Hope have explained the issue adequately. Question is, has anybody and idea what is causing the problem and, more importantly how can it be resolved?   

 

grasshopper:
Is it possible that you have too many positive voltages from the three sources?


Run the Rx through the BEC from ESC1, disconnect the 5v supply from ESC2 to the Rx and ditch the separate Rx battery. It may be the supplies from three different sources causing a conflict

RHBAKER:
Thanks for the response. Should have mentioned that the positive leads from both ESCs have been disconnected so the battery is the only power source.
Am sure it is some obscure item such as this though. Just need to find it!
 

C-3PO:
Two pointers...

1.  Create a common ground connection - Tie all the negative (grounds) together for all components (Esc, Batteries,Receiver)

2. To further diagnose the problem use a Y splitter cable from one receiver channel to both ESC and see if you get the same squeal

C-3PO

malcolmfrary:
What C-3PO said, add that the common ground connection might need to be heavier than originally thought.
ESCs only do what they are told, but a varying ground line potential can mess with their understanding of what they are being told, and if the two motors are not starting from the same position regarding the phases that are being generated, they might well produce noise rather than smooth motion.
It is very unlikely to be RFI, but there might be some overhearing between circuits, especially if the high power leads, motor or battery, run near to, and parallel to, any signal leads.

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