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Mydesign
User Rank
Platinum
BLDC Motor drive using Hall effect sensors
Mydesign   4/24/2012 9:24:33 AM
Sherlock, quiet sometimes back (1998) I had designed similar BLDC motor using hall-effect sensors. There also we had used a photo voltaic transistor for smooth rotating of the motor, but initially it seems that the motor is rotating for a moment then slow down and then rotates. I mean a regular slowdown in between the rotation. Later we identified that at certain instances, the amplitude of the sensor output is not enough for driving the motor. So what we had done is, just injected an external pulse at regular intervals using a timer chip for making the signal strength constant and hence a continuous rotation.

Jon Titus
User Rank
Blogger
Van de Graaff generator?
Jon Titus   4/24/2012 12:37:03 PM
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Sounds as though the motor designers inadvertently created static-electricity generator similar to a Van de Graaff generator often seen in high-school science fairs. Nice solution to the problem.

Rob Spiegel
User Rank
Blogger
Re: BLDC Motor drive using Hall effect sensors
Rob Spiegel   4/24/2012 12:45:33 PM
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1 saves
Sounds interesting, Mydesign. Just so you know, we're always looking for fresh Sherlock Ohms stories. We're also eager to see any Made by Monkey stories of designs gone haywire. 

Send any of your stories to rob.spiegel@ubm.com

DickN
User Rank
Iron
Re: Van de Graaff generator?
DickN   4/24/2012 3:28:28 PM
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The Van de Graaff generator phenomenon is a well-known problem in belt-driven apparatus with no ground connections to the pulleys or to some object near the belt, and in paper-feed or similar mechanisms.  These motors, however, didn't accumulate charge while running.  Once discharged, they showed no further symptoms.  It was during assembly that the charge was introduced.  It might have happened as parts were removed from their stockroom packaging (the shutter wheel in particular), or handed by someone in Assembly with static-prone clothing.

BobGroh
User Rank
Platinum
Re: Van de Graaff generator?
BobGroh   4/24/2012 5:50:30 PM
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Great fix!  Always love it when we 'more experienced folk' use our oft wide ranging experience to come up with a somewhat out of the box fix for a problem.

Charles Murray
User Rank
Blogger
True Sherlock Ohms
Charles Murray   4/24/2012 7:37:39 PM
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I would liked to have seen the expressions on the faces of his colleagues when the author brought it back to life by breathing on it. If ever there was a story that deserved the "Sherlock Ohms" designation, this one is it.

notarboca
User Rank
Gold
Re: Van de Graaff generator?
notarboca   4/24/2012 10:09:39 PM
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This is a great article.  You never know what tidbit of knowledge will help you save the day.  Hail experience!

Mydesign
User Rank
Platinum
Re: Van de Graaff generator?
Mydesign   4/25/2012 5:32:47 AM
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1 saves
Notarboca, you are right. I think if we are listening to the comments and blogs, we can avoid most of design flaws and debugging issues up to an extent. Most of the designs may be theoretically correct, but may not work in practical. This may be due to some ignorance, unseen mistakes or sometimes by complication from components.

William K.
User Rank
Platinum
Static buildup in BLDC motor
William K.   4/25/2012 9:01:51 AM
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The simple fix would have been to change the material and use a plastic that was a bit conductive. ESD-dissipative plastics Are a good fix for the static build up problem. Even though they are not good enough for shielding against interference or EMI radiation, they can reduce the static buildup. Of course not all molders are able to provide this material.

OLD_CURMUDGEON
User Rank
Platinum
BREATHING ON IT ...
OLD_CURMUDGEON   4/25/2012 10:31:35 AM
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This story is an EXCELLENT example of a real life engineering problem which should be mandatory in EVERY science, physics, chemistry, engineering curriculum, whether at the high school OR college level.  Too many students learm the popular linear equations of phenomena (F=ma, e=ir, etc.), but fail to grasp that life is NOT solvable in linear terms.  That's why mathematicians like TAYLOR, LAURENT, La Place, Newton, Leibniz, etal. spent countless hours developing higher order mathematical processes to explain and quantize these phenomena.

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