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.
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.
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.
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.
I also would have liked to see the expressions. If this happened today there would be someone with a camera, the breath would have been accompanied by some some incantations and the whole thing would have gone viral. It is a great story.
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.
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.
I am going to take your screen name literally and assume that we are of roughly equivalent ages, and therefore I can agree with your basic premise of practical experiences trumping classic bookwork often. However, there are an infinite number of field problems we run into and it is unrealistic to expect them to be taught in a classroom. It is equally unrealistic to expect the teacher to be versed in all the problems possible. Each field has its own unique set of problems and solutions.
That is why it is the moral obligation of people like you and me and the majority of people who post on this site to pass our knowledge on to the next generation of engineers, no matter how arrogant and smart alecky they are. Remember we were once new to our respective fields and knew everything and had a brand new sheepskin to prove it.
Tool_Maker: It IS very obvious that there has never been a textbook nor course outline that can fully explain ALL the variables that enter into a dynamic system (whether closed loop or open). However, my point was (and still is!) that engineers, designers, technicians MUST always be aware of higher order variables, and that the world does not adhere to the linear model which is too often the only model preached in school.
When I graduated college w/ my crisp, clean diploma, I was hired by a very large & stable radio communications company. After going through the initial interview process, I IMMEDIATELY KNEW that once in the door, IF the CHIEF ENGINEER handed me a broom to swab down the Engineering Dept. floor daily, then that was precast to be my introduction into the fascinating world of product design. So, the day before I started, I checked my bravado at the door, and walked in as a humbly as I knew how. I was immediately assigned to work along side a senior engineer, who was understanding and very willing to show me how the FOURIER TRANSFORM of the course texts fit into the real world of design. I have NEVER forgotten those sympathetic lessons in personal communication to this day, some 50 years later!
When analog meters were the only way to go, the staticly charged meter solution was to wipe the meter face with a weak solution of dishwashing detergent and let it dry. The residue was conductive enough to bleed off the static charge and all was right with the world!
I think that the bigger lesson is considering potential problems during design, and that includes those posed during manufacture. While not the same issue by any means, we have a whole house vacuum cleaner. One day I noticed that it was running and found that the hose was put away, which meant that something had turned it on other than a switch or shorting the outlet contacts. I had to go to the unit to shut it off by unplugging it. This happened a second time, which forced us to unplug it whenever we left the house for any length of time. I called the store owner who sold it to us and he contacted the manufacturer to find that no one else had reported this issue. So, what happened?
When I was rewiring my basement I had to locate the breaker for a circuit I needed to change and started cycling breakers, a quick off/on cycle turned on the vacuum cleaner. I then cycled the breaker for a count of 10. The vacuum cleaner did not turn on. This proved that the issue was one of bad design, that didn't account for a power droop/loss for a short period.
So, while not necessarily in the same category of problem as the static/motor control, a comprehensive spec may help avoid many odd problems, such as unforseen states. But then again, learning experiences are a fact of life precisely because we will always miss something.
I agree completly. Engineers solve "real-life" problems and this should be transmitted to every high school student considering a career in engineering. The most exciting part of my professional life has been solving problems--design and process problems. The most difficult are ones in which the product is used incorrectly or abused. When this happens, you almost never know the real story behind the failure and the "fix" is very alusive.
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