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Bildo

I am blown away by what you have done so far. Very good use of common sense and old school do it yourself education and practical application. The tractors and work vehicles are great, but how about if you need one that can be roadable? The Mercedes Unimogs of the 50's, 60's and 70's would be a great example. They were actually big tractors, that had road gears, and had every attachment, implement, and toy known to man made for them. A farmer could plow his field with it, then haul the crops to town. Multi-terrain ability, long reach suspension, low speed torque and traction on a flexible frame and able to pull off, say 45 or 50 mph?

Then again, there's still a few of the old ones left out there for a price, and said implements and attachments.

I still like the build your own better.

piolenc

One could do a lot worse than copying the Unimogs, but with the modular approach that this group follows it might be better to view our quasi-Unimog as an incremental development of the tractor/cultivator group of machines, using as many common components as possible. Next major step might be electrical propulsion for the entire group.

Dawg

@piolenc - Yes I agree. Hydraulic propulsion, as far as I know, is not very efficient. I suspect for low speed farm equipment it's great but a street driven car needs to be efficient to be practical. It would be great if someone had some hard numbers to share in this regard.

A standardized electric power cube using the same physical footprint as the original hydraulic one is surely a good idea.

piolenc

I get conflicting information on the potential efficiency of hydraulic propulsion. Apparently it depends on flow rate of the fluid, which suggests that high-pressure systems are better. I haven't checked out the "power cube" project to see what pressure it uses. Whether it matters depends on your goals. If the plan is farm-to-market transport and odd jobs around the farm, low speeds are okay and hydraulics make good sense - excellent control, very high starting torques, quiet...

Dawg

@piolenc The cube is low pressure. 3000 psi.

Dawg

@piolenc - I've been putting some thought into this issue of efficiency. I have a lot of background in electronics. I know that in terms of power transmission, a circuit that is high voltage and low current is the most efficient. Less heat losses along the way. Heat in this case being caused by the resistance in the wires.

To draw some parallels here, I would assume that in a hydraulic circuit, high pressure (voltage) and low volume (current) is the way to go. Heat losses in this case are cause by friction. Continuing in this direction, larger diameter lines would equate to less friction and higher pressures at the motors or cylinders.

So if one was to use hydraulics for a road vehicle, you would want high pressure motors coupled with a transmission to keep the fluid volume low.

The Dawg

Dawg

I did some digging and it appears as though a typical hydraulic system can be as low as 75% efficient. Where as a typical chain and sprocket is around 95%. Quite a difference.

The Dawg

DavidIAm

Efficiency is only important when there is a shortage - for instance - if you have mass production of 3000 PSI power cubes and hydraulic components and sufficient fuel, it hardly matters that it would be more efficient to motivate things via direct drive - its cheaper to drop in the power cube than it is to build a special-purpose direct-drive transmission.

And after all, you can build electric-powered battery-electric power cubes too... and plug them in directly to the formerly gas powered systems. The benefits of a modular power system are significant... particularly in an open source manner. Even at the cost of efficiency.

Dawg

@DavidIAm - Well David I believe that fuel (energy) will always be valuable enough to use sparingly. If this ends up not being the case at some point then you are correct. But even then, there is a point where it would become ridiculous to get involved with a propulsion system that was way too lossy. If the drive motors could be made specifically for this high speed application and the pressures made high enough It might be worth the effort. Who knows?

The Dawg

DavidIAm

Okay, then we need a layer of abstraction consisting of a the throttle control and a universal PTO connector design and torque handling coupler bracket we could probably adopt from somewhere existing.
The existing hydraulic low pressure system would be a simple plugin fixed throttle control module and bolt on the pump.
It would be cool if it was a tool-less coupling, but at the very least it should be like a universal joint flange that anybody can connect or disconnect with a few nuts and bolts and some wrenches. And I'd vote for a bus-bar of wire connection block for the control system *in addition* to a connectorized method of the same.
That way we can attach whatever transmission, pump, sprocket and chain, v-belt, continuously variable transmission, big long driveshaft, whatever is appropriate for the situation.

Jason

While I largely agree that an inefficient car is not worth designing and building (heck, you could practically give me a gas hog right now and I probably wouldn't take it), there is something to be said about modularity. Intermodal shipping containers are a good example of this. You'd think, when it comes to shipping things across the globe, that the most efficient shipping method would be used. However, shipping containers actually hold less and cost more in terms of weight than other previous technologies. The whole benefit was in handling costs. Interesting how a "less efficient" technology could have this kind of impact, which actually increase the volume of global trade:

However, few initially foresaw the extent of the influence
containerization would bring to the shipping industry. In the 1950s,
Harvard University economist Benjamin Chinitz
predicted that containerization would benefit New York by allowing it
to ship its industrial goods more cheaply to the Southern United States
than other areas, but did not anticipate that containerization might
make it cheaper to import such goods from abroad. Most economic studies
of containerization merely assumed that shipping companies would begin
to replace older forms of transportation with containerization, but did
not predict that the process of containerization itself would have a
more direct influence on the choice of producers and increase the total
volume of trade.

Bastelmike

@Bildo,

Unimogs are great because of their versatility. But in high draft application as plowing, they perform very poor. Due to their suspention and the small wheels, compared to a standard tractor.

@Dawg

Efficiency of hydraulic transmissions?

In Dubbel, the german bible for mechanical engineering, the efficiency of best hydr. pump designs is given with a bit over 80 percent. Hydr. motor efficiency is a bit better, more or less in the nineties. Combined this gives the 75% efficiency you mentioned.

There is one big disadvantage from imcreasing the pressure in a hydraulic system. The precision in manufacturing pumps and motors has to be increased. Also pipes, hoses and everything else becomes more expensive with high pressure and will be very difficult to avoid permanent leaking anywhere in the system.

Mike

spike

i love the look oand idea of the unimogs

but for a road car i dont think it can be modular. For a town car id go somthing like MAX (mother earth news im sure youve all seen it) long trips with a large payload would be somthing like a reliant robin and a small truck??

ChuckH

There is quite a bit of industry interest in hydraulic passenger car drivetrains; one research consortium here:

. A strong feature is effective regenerative braking down to very low speeds, which has spawned commercial products in garbage trucks, for example http://www.designnews.com/document.asp?doc_id=236226&dfpPParams=ind_182,industry_auto,industry_machinery,aid_236226&dfpLayout=article . So this is not a goofy idea at all.

I glimpsed a small vehicle on the highway yesterday which appeared to be towing a closed trailer, with exhaust pipes on the trailer. I don't know what it was, but it inspired this thought: a small car designed as two parts, passenger compartment and power trailer, with energy transferred through hydraulic quick connects. (Hydraulics have a lot to recommend themselves as modular power interconnect in the 100 hp range, where mechanical output is the primary load.)

A battery electric hydraulic-pump trailer would be suitable for short trips. A gasoline-powered trailer would serve longer trips. A steam trailer might be developed down the line.

This is really just an aerodynamicised vehicle version of the power cube concept (power cube on wheels) and the vehicle power trailers would be perfectly functional as power cube substitutes around the GVCS infrastructure wherever required.

Chuck

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