smoking robot out of control

A project log for autoCut

robot lawn mower on steroids

schuhumischuhumi 08/08/2015 at 18:310 Comments

"Angstwiderstand" (literally "fear resistor") is a German expression for resistors you put in your design that do nothing in normal operation. Here's why you should put them in there anyways:

Today I had a few problems with the h-bridge controlling the height adjustment. Later I foolishly left the robot unsupervised in the garage with the high power circuitry on to let the usb power banks charge. After some time the l298 h-bridge went nuts:

Now that's toast. On the high power side the l298 is connected to the 14.8V power rail (+BATT), the input pins are connected to the microcontroller:

It seems like while bursting in smoke the l298 shorted +BATT to the micro, which destroyed it. Have a look at that bulge:

As you can see in the schematic the micro also controlls 4 FETs, two of which power the mowing motors.

As a result I had a smoking robot running it's mowing blades at full speed despite all controllers powered down

When I discovered that scene gaining control again luckily was as simple as flipping the switch for the high power circuit. Things learned from this: