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Many small portable devices have a native requirement for mechanical power: screwdrivers, pumps even drills.
The principle behind the torque-battery is simple: high-tension coil-springs are stacked within a cylindrical housing, attached to the housing and to a common central shaft. It's wound up
to charge and let go to discharge.
As an application example we'll use a battery powered light-duty portable screwdriver. Normally this would be reasonably light device, driven by a small forward/reversing DC motor and using one or two "D-Cell sized rechargeable batteries. A NiCad D-Cell in good condition can hold ~ 6 Watt-hours of electricity.
By contrast a torque-battery driven screwdriver would be much cheaper to build and have a lower-parts count for the drive, ie: a gearbox.
The torque battery for such a device would consist of a 2" long section of 1" pipe, to the inside of which are attached 12 spring-steel/kevlar laminate coil-springs, which attach to a central shaft The springs are separated by dividers, each of which has a bushing for the shaft at the center. The spring attachment points on both pipe and shaft are opposing-staggered (like a radial engine firing order) for best tension distribution when it's wound up. We've used 12 small springs instead of one large one for safety reasons: a small spring can break without causing massive damage (in fact the battery can probably still be used, albeit at 11/12 capacity). The chamber is filled with a very light machine oil as well and capped. The bottom cap has a fixed hex attachment point, the shaft protrudes from the top and is capped by a hex head.
To use the battery, flip open the lid on the screwdriver and insert. Closing the lid locks the ends of the battery in place and pushes the front connector inwards; this releases the pawls on the shaft and allows the energy to be released into the gearbox. To take the battery out, flip open the lid which re-engages the pawls, and remove the battery.
For this particular model, winding it up by hand won't be very effective. A power drill could recharge it to some extent, but returning the battery to it's base-charger allows it to be fully recharged in as little as one minute.
Energy density
http://en.wikipedia...wiki/Energy_density
Spring is at the bottom. [spidermother, Feb 25 2009]
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Annotation:
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pretty much... like a stack of very heavy duty watch mainsprings on a common shaft. The "goal" would be to get comparable power to a rechargeable battery of similar size (I'm not trying to advocate usage for motor-vehicles). Lifespan would be on the order of decades (especially if you let it wind down before you put it back on the shelf), recharge time is minutes compared to hours, totally repairable and recycleable. |
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[+] I like this but fear that there are now very few suitable applications for most people going about their daily lives. I can only think of ceiling fans and food processors. Stair lifts may be possible but the possibility of the spring running out part way makes this a bit worrying. It would be a nice touch to add a wind-powered charging unit; basically a windmill or turbine suitably geared to wind torquebats whenever the wind blows. Hydromechanical or wave-power systems would work as well. |
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6 Watt hours in 1 minute means 3,600 watts. About the same as a small domestic garden shredder. That's a little scary, isn't it? |
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//vastly overtorquing// currently the tool would provide the stopping force until just prior to removing the battery when the pawls would be engaged. |
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//applications// portable screwdrivers, pumps, motorized toys.... |
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[sm] that's actually 360watts. and 6 watt-hours is about what you get out of a rechargeable D-Cell, scary or not. |
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I like the concept of mechanical energy storage, but there's a problem here: in a wound up spring, torque is initially strong, and gets weaker as the spring unwinds. Devices using the battery would thus need to be designed to cope with steadily decreasing torque. |
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//torque is initially strong, and gets weaker as the spring unwinds.//
A spring returning to shape must become either 'wider' or 'longer'; the difference depending upon the form of the spring. This translation effect could be effectively used to provide differential magnification of torque as the spring unwinds. |
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For example, clamp the middle of the spring not the outer edge; now run a crank from above the center of the spring past the outer edge. Attach to this radial part a sliding connection to the end of the spring. As the spring uncoils by turning the crank, the sliding connection gets further and further from the center of rotation, increasing the leverage produced and hence helping maintain the torque. |
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If you could find a good enough conversion mechanism, you might have the spring power a generator, which in turn, provides electrical energy for output. |
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A complementary product might be plug-innable to the battery, and provide variable levels of spinnage with dial adjustments for torque and speed of rotation. |
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[zt] since all applications would require differing set ranges of torque, gearboxes should be integral to the device not part of the battery (and for economy purposes also: at any given time you'll always have more batteries than devices), but a generic all-purpose cvt would be a good idea for hobbyists and one-off applications. |
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Could power a generator in a pinch, though if you have a set electrical application, surely an electric-battery would do better. |
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//...you might have the spring power a generator, which in turn, provides electrical energy for output// that can be used to power a motor to wind up the spring (use a gearbox here to make sure that the motor winds the spring as fast as it unwinds). Harvest the extra energy and solve the world's energy crisis. |
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Ha, funny - solve the world energy crisis with springs. |
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Obligatory WIFRT: Maybe it's because I'm Canadian, but when I first read this I thought it said "Toque Battery" and I wondered why the heck would anybody need to keep a battery in their knitted headgear? Boy, do I feel silly right now... |
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We had developed a backbacon battery but they kept disappearing... |
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//360W// Correction accepted. The same as a power drill, then. Not so bad. |
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(Determined to find scary numbers). Assume your battery to weigh 100g, and to be made of iron. Specific heat = 0.449, energy = 6WH * 3,600 S/H = 21600J, => temperature change = 480.5K. If it discharged internally, it would reach about 500ºC from room temperature. Different materials would not greatly change this value. Granted, lithium ion batteries are also pretty nasty if they self discharge. You'd need to be careful, is all. |
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[sm] my concern is what to use as a governor to limit discharge rate. |
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Two words for you, discounting the other problems.... Energy Density (see springs languishing at the bottom of the table in my link) |
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The figure given is 0.0003 MJ/kg, which is 0.08333 Wh/kg, meaning you'd need 6 Wh / 0.08333 Wh/kg = 72kg of spring to 'slot into your handheld screwdriver', assuming you still want to tighten as many screws as you would with a single D or C cell. |
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Boy, I hope you're strong! |
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The concept I like :¬D , the maths just doesn't work :¬(. |
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wot is this "math" u talk about?.... what was your <link> btw ? |
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I've added what may have been [Skrewloose]'s link. Note that the 0.0003 is not necessarily the most that could be achieved. |
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Filling the device with a relatively high viscosity oil might provide enough internal resistance to prevent catastrophic discharge, while not reducing efficiency much at lower speeds. |
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