How to hook up the current-sense shunt?

[vadrian]

Hello,

I have two questions regarding the current-sense "shunt."

Question 1:

The "motor.ino" in the tinypilot/pypilot image states: "adc pin1 goes to .01/.05 ohm shunt to measure current."

I have no resistors which are 0.01 or 0.05 ohms.  And that seems really low-resistance, so I'm concerned it's a misprint.  And "sense.sch" specifies a 560 ohm resistor.  So that raises for me a question: What resistance should I be using here?

Question 2:
To where does the shunt go, exactly?  The file "sense.sch" shows a wire from A1, through the 560 ohm resistor, to a symbol simply labeled "shunt".  Exactly how does it get hooked up?


Best regards,
Adrian Vrouwenvelder

[seandepagnier]

the resistance to use is 0.01 ohms. You may have to buy a current measuring shunt resistor. The high power controllers use .0005 ohms (500 micro ohms) with an amplifier.

Which schematic are you looking at?
the 560 ohm or 2.4k resistor is part of a lowpass filter (with 0.1uF cap) See:

https://pypilot.org/schematics/wp_controller.pdf

[vadrian]

I was referring to https://pypilot.org/schematics/hbridge_controller.pdf. I will familiarize myself with current-measuring shunt resistors. Thanks.

[seandepagnier]

also consider you could maybe do without current feedback. It is mainly used to detect stall and prevent motor from burning out.

The controller also supports motor temperature sensor. so while not usually used, if you had this without current sensor, it would prevent burning the motor out but waste a lot of power at end of travel.

A better way would be to have end stops or rudder feedback which are usually both optional. Ideally both (endstops in case rudder feedback fails) then it should be fairly reliable without current measurement. There are other advantages to measuring current though.