Let's Make Robots!

Stall Detection

Ok, here's my problem for you guys.  How do you use a MCU(Arduino, PIC, Stamp, etc) to detect if the bot has a motor stalled on it. I know it can be done, because I've read about bots that are bumperless and detect which motor(s) are stalled for collision detection.  Yes, I know you measure the amps that the motor is pulling, but how do you use the microcontroller to do it?

 

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Just thought this might be of interest to you. I recently put together a homemade wheel encoder. Check it out and off course you're welcome to ask questions...

It's works pretty well though :)

Looks awesome, mine will be encoded, but going to use hall effect sensors to do it with. I got the idea from looking at tachometer circuits. It's not as precise as what you did, but it will work I think.  I know it will be fun though, figure if nothing else I will have figured out a way to not do it.  

I'll have the sensors in next week, I hope then the wheels can be encoded. Encoding will be the hardware part of the solution and adding a few lines of code to check the last known tick against the current reading of the timer, and checking if the motor is supposed to be turning or not.  Just a few variables to plug in. I know there is never an easy fix, but was hoping somebody had already came across it and had a solution for it.

 Happy building!! 

I have seen people make an encoder ring, alternating white/black segments and attach to a wheel. Then use a #QRB1114 IR transceiver to send signals to processor chip. A steady on or off signal for more than .xx seconds (depends on speed of your wheel and number of encoder lines) would signal a stalled motor.

I recently did something similar (with SERVOS). Check out this tread for more info: letsmakerobots.com/node/10960?page=2

I just use a shunt/sense resistor, like this (I don't even use the op amp cause I don't need full resolution):

lowside.jpg

But remember it's a bit more complicated with DC motors cause they change direction = poles...

UPDATE: BTW I recommend using the Serial Oscilloscope I made recently when studying/plotting the current draw patterns. The processing based one I started out with performs awfully.