Well it's nice to be allowed to post threads. I guess I passed my probationary time with success. :notworthy Having read replies as: "The 960E is still in testing. We have one up here that hasn't run in months since they blew all of the wheel motors they had for it. I guess they are doing a redesign before they put more motors into it and just blow them up." or "...For example, the 960E we have here has the Siemens drive system on it and it has not stood up at all. Typically Komatsu runs GE drive systems, but went a different route with this truck. They built one prototype with a GE drive system and one with the Siemens system. The Siemens truck blew up 4 drive motors in about a month and a half...........this should show it has MAJOR flaws in the design. Our Liebherrs have the Siemens drive system as well and a lot of the trouble we have with them comes from the drive system." BOTH POSTS COURTESY TO -alco- and for the fact that I wondered myself a great deal of time without finding a proper answer here's my big question: Why did the haul-truck biggies (i.e. the likes of Liebherr, Terex, Komatsu or Hitachi) go to the diesel-electric power packs while Caterpillar stuck with good old-days mechanical drive? I personally like the mechanical one better, but to the ups and downs of each system, i must confess, little do I know. I mean, I know the workings; I just can't see the reasons CAT has, to stick with the mechanical drives. Please, enlight me.
OK, what little I know about the differences. Electrics are more complex because of the electrical components involved. You have all kinds of computers, with little electrical switches and breakers and other fragile small parts that have to be maintained and repaired. There is a ton of wiring involved big and small. All of it has to be very well protected. Besides the big generator, you have a pair of huge electric motors, plus all kinds of ducting for cooling, and I almost forgot, there is a huge carbon pile for absorbing energy and acting as a retarder, plus all the controls for that. Now, the electrics have to have a large and complicated planetary gearing system inside each drive wheel. These parts are rare and very expensive and in the past, prone to severe wear and breakage. Now then, for maintenance on electrics, you have to ad some well educated and experienced high voltage electricians. These guys are scarce, very good ones are scarcer still. They need some expensive tooling to diagnose electrical problems, and they have to be able to understand the functions of all the little circuit boards in the controllers plus be able to follow the schematics. Electricians in times past were not commonly available in third world countries, and electrical components were not available either. Many mines were and are union operations, so electricians were often limited to working on electric parts only, to the point a mechanic had to remove and install covers and do all the other work that was not strictly electrical in nature. So what you wind up with is a larger work force than might otherwise be the case with mechanical drives only. Then there are the repair and rebuild shops for electric generators and motors. There haven't been a lot of them around capable of handling the big components, (still aren't) and repair and rebuild of these items isn't so simple as one might think either. I was surprised when I got involved with electrics how carefull some repair steps have to be, and of course, they take completely different tooling, some of it quite large in it's own right. None of the larger electric construction and mining equipment manufacturers ever developed the excellent dealer and parts network that has been so successful for Caterpillar. Not even today are these facilities available for the other brands. There have been some advantages with electrics working in fixed position mines. An overhead electrical line can be rigged to assist the trucks with stationary electrical power on haul roads, thus lessening the load on the on-board generator package and engine. This is similar to an electric trolley line for trains. I saw one of these in Northern Michigan some years ago. The electric retarder's were also more successful at keeping loaded trucks slowed down without burning up the brakes. You also do not have to have huge transmission oil coolers. With the development of modern computers and controllers, electrics have been given a huge boost to be sure. Mechanical drives have been, up till recently, relatively simple affairs that were easier to diagnose and repair or maintain. Leaks were easy to see, controls were simple and mechanical in nature, and third world and other maintenance people were able to keep these rigs going mostly with simple hand tools and diagnostic equipment. Frankly, mechanical drives, in my experience, are more robust and less prone to break down overall. My comment about modern electrical devices goes for mechanical drives too, most of which are now controlled entirely by electric over hydraulic components. I see that Cat is entering the market with electric drives after a long hiatus. Their initial attempts at electric drives were not successful at all. That being the case, they made the simple decision to stay with the mechanicals and other than keeping an eye on the competition, have stayed well away from electrics till recently. Cat also, fortunately for them, developed a well thought out and designed planetary transmission system that even today is little changed from it's forbears in the very early sixties. This enabled them to use this transmission system in several different models of equipment over the years with some modifications to allow for different uses. It wasn't foolproof I can attest, but it was more dependable and lower cost to use than electrics. Cat also developed a workable system of oil cooled brake retarding, that, mostly with up-sizing, works very well on all sizes of their trucks. That was a very important addition that enabled Cat to move beyond the 50 ton class with regards to braking. I've heard and seen all kinds of statistics concerning fuel economy between the two drives. I don't know that there is enough of a difference to select one or the other based on economy only. There are so many variables involved. It will be interesting to see some test results by Cat and end users of the two models working side by side in the same pits. But it all comes down to proper operation and proper maintenance. Do neither and you will suffer the consequence no matter which way one goes.
Another case of cat letting the market become developed and then dive in. Basically the cost of manufacture in the 60,s and the lack of success of the 779,s in the field seemed to kill the ED program back then, Cats belief i feel is that they wanted to go a different route to the rest and the development of more mechanical drive powertrains fitted in with the current manufacturing facilities and the technologies could be extended to other product lines back then. Of recent times they have marketed mechanical drive as having a broader range of use and delivering more power to the ground, now with the advent of digital controls and A/C drives the ED system is a lot more viable and for Cat the timing is right. Now when the 797 was being developed a Cat plant manager was asked why and he answered "two words - tar sands" and i think what you will find with the ED Cats being developed would also come down to 2 words "Rio Tinto" There preference for ED leaves Cat in the cold for 150 ton and above sales with the very small exception of a couple of sites, Bingham Canyon being one of them. There is a big population of ED through Rio and if you dont have a product to sell, well you make one if you want to get that business. I have seen as much info as is around for the ED truck and it looks a good thing, time will tell though and Minexpo should see at least 3 F series trucks on the stand and one of them will be an AC drive.
The mechanicals in the small ranges made sense because the transmission technology could be built pretty much standard and just scaled up to fit the next larger machine. Anyone who worked on a 769 would recognise the parts in a 785 and be able to fix it with larger lifting equipment. When you get to a certain size range though, scaling up by a percentage just doesn't work. Everything has to be redesigned. Transmissions, drive lines and final drives just were not able to handle the increased amounts of horsepower required to move that massive weight. As I recall for years the Cat mechanicals ended at 85 tons while Terex, Westinghouse and Leiberr were running 150 ton units on DC current. On the other hand electrics have a large problem getting started moving. Put them on a steep hill at a dead stop with a load and they burn up the motors. Put them is mud and the same thing happens. The slippage between the output of generator and the huge amount of eletrical current necessary to start the motor turning can't be carried in the wiring. I'm told the new electrics don't have this problem anymore which would seem to take away the advantage the mechanicals might have had. With the advent of computer diagnostics, the need for licensed electricians has been lessened to a large extent. When I worked for the HaulPak dealer we had mechanics that went to the factory for training and we never did have electricians working on those machines.
First of all, I really do thank you guys for giving your inputs. It helped a lot! I can see now the main diffrences (at least some of them) between the two drives and also the factors that might have an impact on them. To me though, the main factor that affects the future of transportation in general, is the fuel. Today we have the fossils fuels or electricity. It's tue that at this moment, electricity is a more "survivable" mean of power. It's simply more efficient nowadays to produce it with various methods used, of which, nuclear power is a most effective and durable one indeed. The fossils ones are just too streched at the moment and way too much surounded by political play. I must add though, IMO, that the apparent "launch" of bio-fuels can, eventually come to the mechanical drives rescue. In this case, perhaps, the competition will continue. End users' preferences/demands (e.g. RioTinto as Gavin84w mentioned) or simply the crucial advantages of one system's over the other will, in the future decide the winner. Which one will be on the long run? What do you guys think? Once again, thanks for your inputs.:salute