motor break

how to break dc motor smoothly?

What do you mean by breaking a motor smoothly?

Or did you mean "braking"?

If the latter was meant try PWMing the motor. You can use PWM to smoothly increase and decrease rpm.

Boncuk

sorry for false word. i mean brake the motor. i still have a problem when motor is used in mobile robot and the robot going down hill. if the motor is not braked smoothly, the robot will move down faster

Hi mrdauz,

there is still the possibility to use PWM for the motor. If the robot moves downhill the motor current will decrease. Use the difference between straight and level movement and downhill movement current flow to control the PWM signal.

Just think of driving a car. The same applies here. You just have to reduce throttle position accordingly to maintain speed.

That will only work within a certain range, considering your car won't maintain speed at a downhill slope of 7% without extra braking or shifting gears.

With an electric motor you won't need to apply brakes, but short out the motor for hard braking.

I suggest using an MCU for your project.

Regards

Boncuk

With an electric motor you won't need to apply brakes, but short out the motor for hard braking.

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To expand on this - braking an electric motor via shorting is an effective way to bring the motor to a stop, but if you are more worried about a downhill slope, it might be better to use non-backdriveable gearmotors if you can find them for your application (and if they'll fit); essentially what you want are worm-gear driven motors (like you see in many electric wheelchairs and powerchairs). You can still use shorting to brake such a motor quickly (if it has a high shaft-mass, for instance) - and PWM at lower speeds can help slow things down. Some motor controllers can also perform "PWM shorting" (separate or in combo with PWM speed control) to effect something closer to "engine braking" on an electric motor (lik Boncuk mentions with down-shifting, etc). Normally, PWM control of a motor in many controllers just alternates between freewheel mode and "power applied" mode. The more expensive controllers allow for many other modes of operation. Finally, there are also electro-mechanical brake controls available, if you need to go that route (or add an extra layer of safety).

I knew soft starting, but soft-braking as a terminology... what's the term now for that?

Vizier87 said:

I knew soft starting, but soft-braking as a terminology... what's the term now for that?

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Hi AH Poh,

driving a car and wanting to bring it to a full stop you certainly won't use full braking power which catapults the passengers through the windshield, but use "soft braking" to bring the car to a standstill within a reasonable time and distance.

That's exactly what the OP has on mind with his robot. A very effective (and low cost) way has been suggested by cr0sh when a worm gear is used.

Regards

Hans

Thanks Hans.
A worm gear also takes less space rather than having the motor jutting out in the normal gearboxes, I suppose.