I was using two Simple Motor Controllers (SMCs) to control two brushed motors in an RC car - controlled from an Arduino. I have decided to switch to a Qik2s12v10 becasue that gives me visability into each motor’s current draw. However, I forget about the cool feature in SMCs to limit over-discharging a LiPo. This feature doesn’t exist in the Qiks. Is there another way to limit the over-dishcarge rate? Or do we just run the barttery until it runs out of charge? Doesn’t this hurt the battery? What does everyone do in this case?
You should definitely avoid over-discharging your LiPo battery. What are you using to send serial commands to the qik?
I’m using an Arduino with NewSoftSerial.
Is that what you were looking for?
I haven’t received the Qik yet - it’s in the mail. Prioir to this, I have been using a pair of SMCs using the NewSoftSerial interface. All has been working fine.
Sorry, I just noticed you already said you’re using an Arduino as a control source. One reason the SMCs have a low-voltage shutoff feature is because they can be controlled manually from RC or analog voltage sources. Since the qik is controlled only through serial commands, you can typically use your control source to monitor the battery voltage and react accordingly. In your case, you can connect your battery voltage to one of your Arduino’s analog inputs and monitor it yourself; if it drops too low, command the qik to stop driving the motors. Note that if your battery voltage can ever be above 5 V (e.g. if you are using two LiPo cells in series), you should use an appropriate voltage divider to keep the voltage on the analog input below 5 V. Does this make sense?
Thanks Ben - that makes sense.
Since I’m using a 3S LiPo, it will always be above 5V so I was hoping I just missed a secret battery voltage status command in the Qik command summary. Oh well.
Voltage divider it is.
Thanks for your help.
Unfortunately, the qik doesn’t monitor the battery voltage. If you have three of the same-value resistor lying around (ideally something between 1k and 10k), you can make a 1/3 voltage divider pretty easily and safely connect the output to one of your arduino’s analog inputs. You can get back to the original battery voltage by converting the reading to millivolts and multiplying by three (to undo the divider):
or you can simplify this to
Since each ADC count corresponds to 0.00488 V, which is pretty close to 5 mV.
Thanks much Ben. This is a good tip.