Saturday, May 17, 2008


We will discuss different ways of braking in the robots , there are 3 different ways as usual which goes from mechanical to electrical .This is basically needed when u want to go down the slope r up the slope, though these are not tat great braking as comapred to the real vehicles but of much help to us.

Mechanical Method :
The mechanical method is what is used on cars today. Basically you need something with very high friction and wear resistance, and then push it as strongly as possible to your wheel or axle. A servo brake works well.People think of using door stoppers but they are not of much help , I tried it n they just wasted my money and time .
Controls Method :
This method requires an encoder placed onto a rotating part of your DC motor. You will have to write an algorithm that determines the current velocity of your motor, and sends a reverse command to your H-bridge until the final velocity equals zero. This method can let your robot balance motionless on a steep hill just by applying a reverse current to your motors.

Electronic Method :
This method is probably the least reliable, but the easiest to implement. The basic concept of this is that if you short the power and ground leads of your motor( connect both the +ve leads of the battery to the two terminals of the motor), the inductance created by your motor in one direction will power your motor in the opposite direction. Although your motor will still rotate, it will greatly resist the rotation. No controls or sensors or any circuits overheating. The disadvantage is that the effect of braking is determined by the motor you are using. Some motors brake better than others.

So how do you short the leads when it is on a robot? Simple. Connect a MOSFET (transistor) and a relay as shown. The MOSFET turns on the relay, which creates a short between the motor leads. Turn the MOSFET on (set C high) with your microcontroller when you want to brake. Basically your motor will still have an H-bridge for normal control, but when you brake you turn the H-bridge off and use the braking circuit. And don't forget the heatsink and flyback diode! Important, or your circuit will melt/blow up.

No comments: