Question Re: BoeBot Servo Current Draw

bobledoux

The idea is to use motor current draw as a secondary obstacle detector.

I'm trying a 0.47 ohm resistor to monitor current draw on a BoeBot. The voltage drop through the resistor will be used with a comparator to test for a motor stall condition.

Question: What is a reasonable upper current limit for this function? For example, should I assume a battery draw of more than 1 amp as signifying a "stalled" conditon? I'd prefer to use a single resistor that is connected in series with the battery terminals. So heavy current draw could also indicate an electrical short condition.

bulkhead

I have something just like this on my project too. I found my continuous rotation servo has around a 2 amp current draw when it was stalled (running on 6V). I used a 10 ohm resistor (the smallest I had) in series with the power (red) wire of the servo. I compared the voltage on that to a set voltage (created using a 3K ohm and a 2K ohm resistor connected in series to the battery terminals).

I found it helpful to test the actual current draw and actual voltage change on the 10 ohm resistor using a multimeter, before creating a voltage for the comparator to compare too. It also helps to hook up an LED to the comparator's output signal, so you can easily test to see if it works. Just use your hand to stall the servo, and see if the LED turns on.