View Full Version : Highshool technical projects get more difficult every decade.

Loose rivets
18th Jul 2016, 01:07
One of my lot is working with a professor on a detection system that has to be self-powered and work in an extremely hostile environment. His task is to provide the power using the energy from local very rough forces.

So, an axle and a clattering vehicle. Temps -30C to +50C would be my guess. The axle will be pulsing, I imagine, mainly up and down - but not very far in amplitude.

The need is to provide energy for electronics to monitor certain factors of the wheel's wellbeing. Right now, he's looking at an inductance - a coil with presumably a magnet flying up and down in the coil. I don't think this is the way to go, but as yet I haven't given it much thought.

I think it should be entirely self-contained, so no rod anchored to something else. Just a potted lump that can feed off vibration. I'm not sure if there's any quarts devices that could power electronics. Total load not known, but I'd guess at 200 mA at the most. I'm not too sure how Rolex for example, generate power for charging the new generation of self-wind watches. The darn new 'capacitors' are more like a battery, and putting one of those in could see the watch run for 5 years on a corpse. Kind of non-purist in my opinion.

But now, even 5 years it seems is not long enough for this device. It has to pump out a small amount of DC for life. Say, 10 - 20 years, all from residual vibration.

If there is to be a coil, I imagine a magnet springing up and down in the core but springs and indeed the tube would have to be nigh-on indestructible. Also, are magnets that resistant to 50C and a lot of vibration?

18th Jul 2016, 02:59
Tyre pressure monitors work for a year or more with just a small button cell, so the power requirement should be nanowatts rather than hundreds of milliwatts.

There is a line of Seiko watches that generate electrical power to charge the watch battery from movement of the wearers wrist. Presumably the mechanism is shockproof, miniaturised and largely resistant to temperature changes. The battery never needs changing and the quartz mechanism keeps excellent time.

I would be looking at adapting and perhaps further miniaturising one of these mini power generators or at least considering something along those lines.

18th Jul 2016, 06:18
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18th Jul 2016, 11:15
If the environment is that hostile, there's a good chance that there won't be much in the way of cellphone or WiFi signals of suitable strength.

But is the load constant or intermittent? If the latter, what is the load and what is the duty cycle? A piezoceramic would more use than quartz in this application, I feel.

Loose rivets
18th Jul 2016, 11:33
The trouble is, I'm being a bit evasive due to not knowing what I can reveal, or indeed how much I should input on a project.

I recall my son doing A level Electronics and Electronic Systems and feeling uneasy he could come home and have the use of a fairly well-equipt workshop where other kids would have a corner of a busy living room. The latter was me when I was studying, and no dad to help with, well anything.

The shock input would defeat even the finest watch I fear, and the optical side of the device has to monitor the temperature/wellbeing of a bearing with peak loads of tonnes. I'm assuming optical, as I can't imagine trying to put heat sensors near the bearing.

One thing I don't know is how clean the sensor of a thermal sensing device has to be. The 'picture' can be very crude, just a roughly defined area and how hot it's getting so no need for 'imaging'.

One thought. Suppose you had a large iron wheel with spokes. Wouldn't the residual magnetism be enough to excite nearby windings? IIRC, many motors start their cycle with small residual flux.

18th Jul 2016, 12:42
Miniaturisation tends to give greater shock resistance in modern devices. The need to have this device as a totally self contained and self powered item is the biggest problem. An Alnico magnet and a coil mounted between a moving and static part of a vehicle could easily generate enough power, but then the device is not self contained. A wheel implies rotational energy is available, so the most logical step is to harness that rotational energy. A loaded piezo crystal beam might be adequate for power production and robust enough to work in any environment. It all depends on what engineering facilities are available and how small you need to make the device.

Primary batteries that can provide power for up to 20 years are a possibility or possibly something harnessing power from the decay of a radio isotope. Some of the old bomber crews suffered skin burns from the Radium painted dials on their aircraft, so there is clearly plenty of energy available there if it can be harnessed. That may not be acceptable to environmentalists though.

18th Jul 2016, 16:29
At one time in the 1980's, there were pacemakers powered by plutonium batteries and thermocouples - which is why ICAO still has pacemakers in quantity listed as hazardous cargo. They weren't popular with surgeons, who didn't get the income from changing the pacemakers or from those who had to dispose them, and very few, if any, are left. Pacemaker batteries, depending on the demand, can last anywhere between 5 and 20 years, but 5mA for short periods is about the maximum you can get from them. Defibrillator batteries are bit bigger physically, and again, the life depends on demand.

Loose rivets
18th Jul 2016, 22:11
Interesting, but brings back some trying memories. My M-I-L, (so cute I had a blind date with her daughter) eventually developed a bad heart. She didn't let it stop her until on the wrong side of the Atlantic. Well, cost wise. Technology wise, it may have gained her some more years as they fitted her with one of the first A-V sequential pacemakers. I got a surprise briefing from the manufacturers, asking me if I'd convey this information to MIL's surgeon here. I can still remember some of the timings but that's not what really sticks in my mind. It seemed that if she got excited/angry, I could clap a magnet on her chest and it would cause the device to enter tickover mode.

No, I didn't allow my curiosity full rein. :rolleyes:

A mechanicle link to a fixed point? I had hoped to advise against that. Many cars have such links now to send data to the CPU, but it's notable that these fail in the same way as other drop-links. No, I'm hoping there must be a way to have a mono-block device.

I think the battery makes much more sense. I'll try to find out a little more, but of course these days Uni's work with the real world and industrial technology becomes very private. Just don't know yet.

19th Jul 2016, 02:30
Age 15, I once did a high school project using, as inspiration, Frederick Forsyth's description from The Odessa File of how to design a car-bomb. My diagrams from Mr. Forsyth's narrative were pretty impressive. :cool:

Looking back at it now, the funniest thing was my Physics teacher was far more concerned with my proposed use of condoms to prevent the electrodes touching prematurely than with the (viable) device itself! :}

Nowadays MI6 would be interviewing all concerned. :E

19th Jul 2016, 02:47
my Physics teacher was far more concerned with my proposed use of condoms to prevent the electrodes touching prematurely than with the (viable) device itself!

I was at a co-ed. It would have been our biology teacher who would have expressed such a concern.

19th Jul 2016, 11:59
er & Caz: I remember that section of the book and wondering what Freddie Forsyth was on about. When I found out what a condom was I then wondered why he didn't call it a johnny, Durex or one of the many other terms we used at school.