better motor braking

[ikalogic]

hi, i know the method comonly used to brake DC motors is to short the windings.

But in my application i need to pull objects to a certain height with a very simple system consisting of a mottor turning a wire around its shaft and the object is attached to the other end of the wire, i hope you see what i mean.

If i use this classical way of braking i think it wont overcome the weight of the object being pulled.

So, wouldn't i get much better bracking if i keep inversing the current in the winding (Fwd-Reverse) at a relatively high frequency? in such way that the motor doesen't have time to response or move according to any of the 2 currents, but in the same way it would be kind of being braked by a foce as strong as the one that raised it..

is this theory true?

if so, what frequency would be suitable..?

thx a lot

 

[Nigel Goodwin]

hi, i know the method comonly used to brake DC motors is to short the windings.

But in my application i need to pull objects to a certain height with a very simple system consisting of a mottor turning a wire around its shaft and the object is attached to the other end of the wire, i hope you see what i mean.

If i use this classical way of braking i think it wont overcome the weight of the object being pulled.

So, wouldn't i get much better bracking if i keep inversing the current in the winding (Fwd-Reverse) at a relatively high frequency? in such way that the motor doesen't have time to response or move according to any of the 2 currents, but in the same way it would be kind of being braked by a foce as strong as the one that raised it..

is this theory true?

It would probably have some kind of 'locking' effect, but it's highly likely to destroy the motor through over heating. I would suggest you use a worm gear from the motor, this will greatly improve it's resistance to movement from the load, even without braking - plus give you much greater torque.

 

[Klaus]

Further to Nigel's suggestion, a mechanical brake is often used too. You'll find small band type brakes inside every cassette tape recorder or in the older VCR machines. Another way is external brake shoes around a narrow drum on the shaft, this system is used on lift motors.
the mechanical brakes are solenoid activated.
Klaus