Mon 26 Apr 2010
Posted by Marcin
A universal mechanical power source is one of the key components of the Global Village Construction Set – the set of building blocks for creating resilient communities. The basic concept is that instead of using a dedicated engine on a particular powered device – which means hundreds of engines required for a complete resilient community, you need one (or a few) power unit. If this single power unit can be coupled readily to the powered device of interest, then we have the possibility of this single power unit being interchangeable between an unlimited number of devices. Our implementation of this is the hydrauilic PowerCube – whose power can be tapped simply by attaching 2 hydraulic hoses to a device of interest. A 3/4″ hydraulic hose such as this
can transfer up to 100 horsepower in the form of usable hydraulic fluid flow.
You may have seen our prior report on PowerCube as the power source for MicroTrac. The question is – how flexible can the PowerCube be? We ask this question from the standpoint of the PowerCube’s suitability as an essential component for building resilient communities – or, how radically small can your infrastructure tool-set be, if your goal is creating a modern, high quality of life?
To shed some light on this question, we mounted the PowerCube on LifeTrac, our open source tractor – to demonstrate the radical interchangeability of parts. This radical modularity is the key to what we promote as the life-size Lego set for real technology. We mounted the PowerCube on the rear receiver of LifeTrac, and ran LifeTrac with it. Here are the results:
One conclusion is clear. The PowerCube concept of power unit interchangeability is sound.
While the 18 hp PowerCube appears to be undersized for the 6000 pound tractor – the motion could really be twice as fast with the same PowerCube. This is an artifact of the LifeTrac hydraulics circuit. This is because in the case shown in the video, 5 gallons per minute (gpm) is diverted in parallel (parasitically) to the steering cylinder (in retrospect, this was not a good idea – see circuit diagram to trace the details) – so we are really using only 5 gpm of the 10 gpm available for the wheels and all other hydraulics outside of the steering cylinder. The steering cylinder is diverting the 5 gpm because this flow divider is in the LfeTrac hydraulic circuit.
The key to the soundness of power unit interchangeability is easy interconnection of the power unit to the device of interest. The hydraulic nature of the power unit accomplishes this successfully. How difficult is it to plug and unplug a set of hoses with quick connects, as shown in the video? In my opinion, this is such a great stride towards optimizing society’s mechanical power infrastructure from the systems perspective – that this should have been adopted by the maintream decades ago. However, geopolitical foul play mandates inefficiency and mediocrity.
Is the potential really as good as it sounds? That depends on your goals. If your goal is freedom, and if you want to build resilient communities without prohibitive equipment and maintenance costs – the answer is yes. If you are a power broker in favor of debt slavery by virtue of high equipment and maintenance costs, the answer is no.
What are the disadvantages of the modular, hydraulic power unit? Hydraulic transmission of power is only 85% efficient in pumping, and hydraulic motors are similarly efficient, so your overall system efficiency is 70%. Automatic mechanical transmission is 90% efficient. This disadvantage of hydrauilics is turned to an advantage over mechanical transmission when doing a task like digging with a loader, where you move back and forth repeatedly. Since it takes time to switch gears, and hydrauilics can switch immediately – hydraulics are actually more efficient in this case. Moreover, you can’t run many devices effectively, such as loaders, without hydraulics.
From the systems perspective, one may claim that the PowerCube is no less fuel efficient than mainstream options – if resilient community autonomy is considered. This holds true if one uses a modern steam engine, which can run on local fuels, such as biomass pellets. Now this is another whole story, and we’ll explore the myths and truths about this option at a later date. For now, suffice it to say that steam engines have a proven track record of being half as efficient as internal combustion engines. However, since fuel is readily available in the form of renewable biomass, the real answer on efficiency depends on your method of accounting, where accounting is not value-neutral. The answer on efficiency simply depends on your values – or what you are including in the accounting – which depends on the extent of your consciousness.
As a side note – I just visited some Amish people looking for square bales for our planned strawbale-CEB hybrid house, and I was amazed to see a perfect example of well-intended bad design regarding dedicated power units. One single farm had a huge round baler, with a dedicated diesel engine, pulled by a horse (these are typically pulled and powered by tractors); another square baler with its own engine; 3 more diesel engines for the house and dairy; and probably several others that were not immediately visible. A single PowerCube or other implementation of an interchangeable power unit, integrated thoughfully into the entire operation, could substitute for most, if not all, of the dedicated engines.
The closest widely-used concept to the PowerCube is the tractor power take-off (PTO), which is a rotating shaft used to power external devices. This is a great idea, but it’s dangerous and less flexible in applications than the flexible hydraulic hoses. Moreover, the hydraulic take-off (HTO) – whcih is what we have on the PowerCube – is found commonly on other power units, such as tractors and skid loaders. Tractors and skid loaders don’t have interchangeable power units, however – outside of LifeTrac.
In summary, from the standpoint of the resilient community creation – the applications of the PowerCube modularity concept have significant potential. PowerCubes can also be made in different sizes. The 20 hp range one – the size of the engine in riding lawnmowers – is a good candidate for a lighter version of LifeTrac, perhaps in the 3000 pound range. The 20 hp range engines are in abundant supply. It is useful to convert from a single-function lawnmower to a multipurpose tractor like LifeTrac. The design can be such that the lighter LifeTrac can still do the same tasks as the larger LifeTrac- such as lifting 1500 pound bales – but the LifeTrac Lite will move slower. In the limit of low size, we can consider Prototype II of MicroTrac as a 4-wheel machine similar to LifeTrac, since the single-wheeled MicroTrac turns out to have balance and traction issues that are yet unresolved. We expect MicroTrac to be similar in size but more flexible in performance compared to another kit tractor, CadTrac.
The next point in this exploration is stackability of PowerCubes, not to mention the use of a PowerCube in a light road vehicle chassis. The latter allows one to use a single engine unit for tractor/utility work and road transportation.This would be the real life-size lego set for autonomy in power equipment, tractors, and cars.
What if we put two small PowerCubes on LifeTrac instead of one? Then we could run with a single motor on small tasks, and two motors on larger tasks. This takes advantage of the fact that small, 20 hp lawnmower engines are typically air-cooled and simple to mount. The difficulty is hydraulic fluid plumbing, and mounting or dismount more than one PowerCube. What are the practical limits to this approach? Two power cubes yield a 40 hp equivalent tractor – which may be sufficient for full and effective sufficiency in power needs for a prototypical, high quality-of-life, resilient community of 100 people. After this, imagine an 80 hp bulldozer using 4 small power cubes. We’re quite curious if this kind of approach will work. The difficulty is that managing multiple power units is like herding cats, so clever interconnection strategies are required.
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