ESC circuit

Hi, I'm thinking about using RC outrunner/ESC as spindle drive for CNC. Reading about ESC with Arduino a standart suggested connection seems signal and ground to Arduino, while havnig common ground of arduino and ESC.

The thing is - there will be 12V 20-30A PSU and motor varying between 0.5-15A and switching on/off, so I suspect PSU output might get not be very stable plus I'm not sure about PSU quality itself. So I'm thinking about using separate PSU for Arduino. The question is how to connect ESC then? Might there be any complications using optocoupler for signal transfer?

The thing is - there will be 12V 20-30A PSU and motor varying between 0.5-15A and switching on/off, so I suspect PSU output might get not be very stable plus I'm not sure about PSU quality itself.

That doesn't mean it won't work for an Arduino. Recall that the external power connector wires to an on-board +5vdc regulator chip and also there are some filter caps in the input circuit. Nothing else on an Arduino board uses the +12vdc directly, but rather the filtered and regulated +5vdc.

So I'm thinking about using separate PSU for Arduino.

That would be fine also. Try and get a 8-9 volt supply if you have a choice as the less voltage the on-board regulator has to deal with the less heat it will dissapate.

The question is how to connect ESC then?

Pretty simple. The ESC has a 3 pin connection for control. The 3 wires on that connector are +5vdc, control signal and ground. Because you will be providing power to the arduino from elsewhere (through your external power connector on the arduino board) you do not want to wire the +5vdc to the arduino, just the control signal wire to the arduino digital output pin and the ground wire to a arduino ground pin. So just connect 2 of the 3 wires on the ESC/servo connector. Then you provide your 12vdc husky PS to the main positive and negative wires of the ESC. Best if you first draw it out including both power supplies and show the interconnections and let us 'bless it' :D

Might there be any complications using optocoupler for signal transfer?

Complications? Using an optocoupler for the control signal to the ESC will work and that would mean the grounds between the ESC/MOTOR/Husky power supply and the Arduino would not be connected (through that ESC/servo connector ground wire) and can help for noise problems. However they are not used in model RC systems that use ESC/outrunner motors with sensitive R/C receiver that has low level analog and digital subsystems with normally no problem. I would start simple and go with opto isolation only if a problem pops up. Lefty

retrolefty: Pretty simple. The ESC has a 3 pin connection for control. The 3 wires on that connector are +5vdc, control signal and ground. Because you will be providing power to the arduino from elsewhere (through your external power connector on the arduino board) you do not want to wire the +5vdc to the arduino, just the control signal wire to the arduino digital output pin and the ground wire to a arduino ground pin. So just connect 2 of the 3 wires on the ESC/servo connector. Then you provide your 12vdc husky PS to the main positive and negative wires of the ESC. Best if you first draw it out including both power supplies and show the interconnections and let us 'bless it' :D

Surely a dumb question, but is there no chance that there will be some voltage between ground of arduino and ground of signal connector because of different power sources?

Thank you for a detailed reply.

but is there no chance that there will be some voltage between ground of arduino and ground of signal connector because of different power sources?

When you connect two points together like two grounds they become the same point. There is no flow of current because you only get flow between points of different potential when there is a circuit. There is no circuit so no current flow.
see this:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Surely a dumb question, but is there no chance that there will be some voltage between ground of arduino and ground of signal connector because of different power sources?

As GM stated there will be no potential difference after they are wired together. More importantly without having the grounds wired together the control signal to the ESC from the arduino output pin will not work at all as the +5vdc arduino ESC/servo control signal will not be seen as a valid (0v and +5vdc) signal without a common ground reference wired between the arduino and the ESC.

Recall that to have a meter read a +5vdc point the meter has to have two connections to the circuit, one to the signal to be measured and one to the voltage reference for the signal, commonly called ground or circuit common. So for the ESC to sense the control signal voltage if must have a connection to the circuit common of the device generating that signal. Using opto isolators or complex transformer coupling is the only way two different independently powered circuits can operated together without a common ground wired connection between the two devices.

Lefty

Grumpy_Mike:

but is there no chance that there will be some voltage between ground of arduino and ground of signal connector because of different power sources?

When you connect two points together like two grounds they become the same point. There is no flow of current because you only get flow between points of different potential when there is a circuit. There is no circuit so no current flow. see this:- http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

I understand it this far. What I meant is if there is possibility of difference of potentials between grounds of different psus, because as far as I understand there's no real, solid common ground between them - only through transformers etc. After a bit of searching I found that apparently this is impossible because transformer act as "sort of" isolator between input and output circuits. Thanks.

retrolefty: As GM stated there will be no potential difference after they are wired together. More importantly without having the grounds wired together the control signal to the ESC from the arduino output pin will not work at all as the +5vdc arduino ESC/servo control signal will not be seen as a valid (0v and +5vdc) signal without a common ground reference wired between the arduino and the ESC.

Recall that to have a meter read a +5vdc point the meter has to have two connections to the circuit, one to the signal to be measured and one to the voltage reference for the signal, commonly called ground or circuit common. So for the ESC to sense the control signal voltage if must have a connection to the circuit common of the device generating that signal. Using opto isolators or complex transformer coupling is the only way two different independently powered circuits can operated together without a common ground wired connection between the two devices.

So basically I can just connect grounds of psus directly before arduino or any other device?

So basically I can just connect grounds of psus directly before arduino or any other device?

Yes, basically. Doesn't matter that the common connection is through the ground wire on the ESC's servo connector to a arduino ground pin or if done with a direct external wire between the ESC's power supply negitive terminal and the external negitive terminal of the Arduino's voltage source.

Note that this is specific to isolated (transformer isolated) DC power supplies or battery sources. When dealing with AC power there are other issues one needs to deal with and I offer no universal rule about how to wire up between different AC voltage sources. The principle remains the same but there are differences in AC power between 'ground' and neutral and code requirements that needs to be understood before playing with.

Lefty