2019-08-30, 01:21 AM
Hi Skeyeyedoc,
Hope I can be of some assistance. With this controller there is no need for a shunt resistor (but it is still one off the possible ways to measure the current).
This controller has an output (IS Left and right) that gives a certain current that is related to the current running through the motor.
According to the specs with an 1k resistor from IS to ground the factor to the voltage on IS with this resistor will be 8.5 so with 15 amps going through the motor (and a resistor of 1k between IS and Ground) there will be a voltage of 15/8.5 = 1,764 volt on IS.
As indeed the voltage in current limit mode might be 7 volt and you want to get a good reading on pypilot and keep the arduino alive you should then use a voltage divider. The downside of this is that these resistors will be parallel to the 1 k resistor and will be of some influence (resistance will be lower than 1k) to the 8.5 factor that is why I suggest to keep a high value for these resistors (174k) so you should have a 100K resistor on IS as well in series with a 74K resistor connected to ground.
The point where the 100k and the 74K resistor meet will be the current sense input on the arduino. With these values you should be good if you keep the current up to 20 Amps. Just as in the software low current 20 Amps max will be 1.1 volt (Vref). If you do go above 20 Amps (you do get above the 1.1 Volt) you can use one of the other settings in the software by putting the pins D4/D5 (see motor.ino) high or low and/or chance the voltage divider accordingly.
Off course using a shunt according to motor.ino is another good option as you can use IS but you don't need to.
Beholder77 does not mention the 1k resistor from IS to ground and I doubt if he gets a good current reading without changing calculations in motor.ino (also a possibility to get the readings right)
Hope this gives a bit more explanation,
Greetings Rob
Hope I can be of some assistance. With this controller there is no need for a shunt resistor (but it is still one off the possible ways to measure the current).
This controller has an output (IS Left and right) that gives a certain current that is related to the current running through the motor.
According to the specs with an 1k resistor from IS to ground the factor to the voltage on IS with this resistor will be 8.5 so with 15 amps going through the motor (and a resistor of 1k between IS and Ground) there will be a voltage of 15/8.5 = 1,764 volt on IS.
As indeed the voltage in current limit mode might be 7 volt and you want to get a good reading on pypilot and keep the arduino alive you should then use a voltage divider. The downside of this is that these resistors will be parallel to the 1 k resistor and will be of some influence (resistance will be lower than 1k) to the 8.5 factor that is why I suggest to keep a high value for these resistors (174k) so you should have a 100K resistor on IS as well in series with a 74K resistor connected to ground.
The point where the 100k and the 74K resistor meet will be the current sense input on the arduino. With these values you should be good if you keep the current up to 20 Amps. Just as in the software low current 20 Amps max will be 1.1 volt (Vref). If you do go above 20 Amps (you do get above the 1.1 Volt) you can use one of the other settings in the software by putting the pins D4/D5 (see motor.ino) high or low and/or chance the voltage divider accordingly.
Off course using a shunt according to motor.ino is another good option as you can use IS but you don't need to.
Beholder77 does not mention the 1k resistor from IS to ground and I doubt if he gets a good current reading without changing calculations in motor.ino (also a possibility to get the readings right)
Hope this gives a bit more explanation,
Greetings Rob