4
$\begingroup$

I have a Micro Magician v2 micro controller. It has a A3906 Dual FET “H” bridge motor driver built in.

In the manual it states "Electronic braking is possible by driving both inputs high."

My first question is, what is the purpose of these brakes? If I set the left/right motor speed to 0, the robot stops immediately anyway. What advantage is there to using these brakes, or am I taking the word "brake" too literally?

My second question is, the driver has "motor stall flags that are normally held high by pullup resistors and will go low when a motor draws more than the 910mA current limit. Connect these to spare digital inputs so your program will know if your robot gets stuck." But when my robot hits a wall, the wheels just keep on spinning (slipping if you will), I take it these stall flags can be used on a rough surface where the wheels have more friction?

$\endgroup$
  • $\begingroup$ Just to note: this type of break does not static hold a load, it needs a small rotation to break, thats dynamic break. For static breaking you can use a servo loop and use the motor power to react to the load, or a mechanical break, that is used in cable elevators. There's other types too of course. $\endgroup$ – Diego C Nascimento Jan 2 '14 at 17:58
6
$\begingroup$

Question 1: If you are satisfied with your robots stopping distance, than you don't need electronic braking. With a heavier or faster robot, its quite useful. The larger the machine, the more inertia becomes a important design factor. For example, a form of electronic braking is used by open-pit mining dump trucks. Ordinary dump trucks, being much smaller, make do with ordinary brakes.

Question 2: The stall flags are useful to detect that the wheel is not moving despite full power being applied. I'm presuming we're still talking about a small robot here - what would happen if the wheel got tangled in something like a long hair or thread?

I had a two-inch long robot once that got its powered wheels jammed on a tiny piece of toothpick it encountered while crossing a carpet. Freak luck, but it does happen. If you only run your robot on clean surfaces, and it'll spin the tires when it bumps into something, than you probably don't need the flags. Personally, though, I would use them -- but I'm a belt AND suspenders kinda guy.

$\endgroup$
  • $\begingroup$ Thanks that makes a lot of sense! Small robots yes, and controlled from the internet so need lots of safety measures in place :) $\endgroup$ – Titan Jan 1 '14 at 2:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.