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Transmissions and final drives

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02_ZF_EcoLife_Offroad_Schnitt.jpg

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IDEX 2017: ZF’s New Generation

ZF is a global leader in driveline and chassis technology as well as active and passive safety technology. The company acquired TRW Automotive on 15 May 2015, which was then integrated within the organisational structure as the Active & Passive Safety Technology Division.

The new 7-speed ZF EcoLife Offroad automatic transmission has been further developed and optimized for off-road applications in medium to heavy-duty special vehicles. It makes vehicle operation very cost-effective, handles up to 2,600 newton meters of torque, improves acceleration and changes gear depending on topography. It is the performance-enhanced successor generation of the

ZF Ecomat family which has been successfully used in this area for several decades worldwide.

ZF has developed a transmission system, the ZF EcoLife Offroad, designed for current and future requirements placed on off-road, multi-axle or all-wheel-drive special vehicles as well as heavy off-road vehicles. Tailored exactly to the particular vehicle, it relieves the driver from having to operate the clutch and gear lever – thus preventing any incorrect operation. ZF EcoLife Offroad measurably improves acceleration, shifts gear depending on topography and handles up to 2,600 newton meters of input torque which are transmitted without tractive force interruption during gear changes. With this transmission system, one is perfectly equipped for the new high-performance engine generation.

The high spread of ratios of 10 facilitates high speeds, while significantly improving the respective vehicle's climbing ability and reducing fuel consumption at the same time.

The dry weight of the ZF EcoLife Offroad basic transmission – despite all the application-relevant reinforcements – is just 450 kilogrammes. It is also very compact, just approximately 900mm long, which saves valuable installation space. Another advantage is that the automatic transmission operates remarkably quietly thanks to the helical-cut planetary gearsets.

The ZF retarder, which is integrated directly into the transmission, proves its worth particularly on long downhill gradients. This hydrodynamic, wear-free continuous service brake effectively slows down the vehicle thanks to a maximum 1,900 newton meters of braking torque and relieves the strain on the service brakes, thus reducing wear by up to 90 percent.

 

Durable and Future-Proof

With EcoLife Offroad, the successful concept of the ZF EcoLife for city buses was further developed and adapted to the tough use in off-road vehicles. ZF EcoLife Offroad does not only use the advantages of the economical and efficient basic transmission, but is also equipped with reinforced components.

ZF EcoLife Offroad also comes with a dual cooling system which comprises an integrated transmission oil cooler and a separate oil cooler for retarder and torque converter operation.

 

Tailor-Made Electronics

An electronic control unit forms the brains of the ZF EcoLife Offroad. To minimize necessary wiring, this control unit is directly mounted onto the transmission. Programmed specifically to each particular vehicle, it communicates via a standardized CAN bus interface (CAN SAE J1939) with other vehicle components.

For further information please visit: www.zf.com/special-transmission.

http://www.monch.com/mpg/news/14-land/837-idex-zf2.html

I just think the photos look nice.

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Not sure if what I'm writing now is needed (or wasn't posted before), but I'll make a little contribution of my own.
I always thought of Russian 2nd gen MBTs having "very special" transmission arrangement as a well known fact, but constant confusion and numerous gaffes (like wikipedia articles claiming T-72 transmission to be a synchromesh, or Al-Khalid being equipped with SESM ESM500, which are both garbage) drove me to write this.
I do not have much time and haven't been able to find any decent articles, so I'll be brief. Long story short - Soviet/Russian tanks from T-64 through T-90 (and Ukrainian T-84) do not have a transmission per se. All the shifting is done in final drive assemblies instead - so called BKPs - "half-gearboxes". There is no main clutch - when clutch pedal is pressed, clutches in both BKPs are disengaged, and there is also no steering mechanism. Steering is done by switching one of the half-transmissions to the lower gear, or braking with disengaged clutch if it already was in the first gear. It's easy to deduce that this way you get a unique turning radius on each gear.
Here's an excerpt with description from T-72A manual:
72_1.jpg
72_2.jpg
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72_5.jpg
And a gorgeous picture from Rolf Hilmes' "Kampfpanzer Heute und Morgen". Unfortunately I don't have a scanner, so the quality is medicore to say at least.
IMG_1410.jpg
The interesting part is why did they come up with such a system to begin with. BKP was originally designed as a part of Object 430 tank's powerpack, and later used on it's successor - T-64. In both of those tanks BKPs were coupled each to a different end of the "briefcase engine's" crankshaft. One of crankshafts actually, since briefcases (both 5TD and 6TD) are horizontal transversely mounted opposite piston engines. The simple schematic of this:
trans72ml.jpg
(and here's why 6TD-equipped Al-Khalid couldn't possibly have a SESM transmission)
All of it was done in favor of saving space - T-64 was and is easily the most compact main battle tank ever produced. And the tradeoffs were considered acceptable. The obvious downside to this is a principal inability to insert a torque converter in such a power train, attempts to introduce hydrostatic steering also didn't produce any viable results. None the less BKPs were carried onto many subsequent Soviet MBT designs, in favor of both uniformity and space saving. Here's an example of North Korean Chonma tanks model 215 and 216 I've made some time before. Transition from synchromesh to BKP was most likely made because of latter ability to handle more torque, but difference in engine compartment size is also obvious:
tz0_TL.png

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2 hours ago, Collimatrix said:

I'm surprised that a design that essentially duplicates the entire transmission ends up being that compact.

 

So, how does reverse work?

Reverse works pretty much the same way it does in your road car (see ZF transmission above for example) - by locking one of the carriers onto the case. Only it has to be turned on on both sides here. BKP is essentially not very different from any automatic transmission - it's a planetary gearbox with 4 planetary gearsets and 6 wet clutches. The only two things it lacks to become a proper automatic transmission are torque converter and governor - walve box is already there.
It's small size is mostly the consequence of each gearbox transmitting only the half of the summary power output. This, plus the fact that there is no steering mechanism.

I must also add that T-80 wasn't very different from T-64 and T-72 in this department. It also didn't have neither any differentials, nor steering. It's BKPs were slightly smaller with 3 gearsets instead of 4 (it had 4 ranges instead of 7). Probably along with the fact that gas turbine doesn't have many auxiliaries reciprocating engines require and occupies less space, this was the motivation behind the idea to equip T-80 with hydrostatic ivt steering. The system was developed (see schematic below), tested, but never went into production.
transmission_t_80um_bars.gif

Edited by Levi

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17 minutes ago, Collimatrix said:

Wait, that means that on the GTD-1250 equipped T-80s the entire damn transmission is different?  Wow.

There were two types of power train for GTD-1250 equipped T-80s. First - for domestic use, and it wasn't different from any other version of T-80 (with no steering, see below). And the second one (posted above) was marketed for international customers.
image.jpg
Regardless of the choice of steering, BKPs on all T-80 tanks were different from those used on T-64 and T-72.

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I meant that the GTD-1250 transmission would have to be completely different than the GTD-1000 transmission, which does appear to be the case.

So, correct me if I'm wrong, but couldn't you get a sort of poor man's neutral steer with the BKP by setting one to first gear and the other to reverse?

 

Do you happen to know which transmission the Oplot has?

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1 minute ago, Collimatrix said:

I meant that the GTD-1250 transmission would have to be completely different than the GTD-1000 transmission, which does appear to be the case.

So, correct me if I'm wrong, but couldn't you get a sort of poor man's neutral steer with the BKP by setting one to first gear and the other to reverse?

 

Do you happen to know which transmission the Oplot has?

GTD-1250 transmission on tanks in Russian inventory is not different from GTD-1000 transmission. At least not fundamentally, probably the ranges are slightly different, I'm not entirely sure about that. Again, I should strees it that transmission with hydrostatic steering was never produced - Russian military was not interested in it, and no foreign customers have been found.

Neutral steer is possible with BKP mechanically wise, but iirc control system does not have this option.

Oplot has pretty much the same transmission setup as T-64, but with external gearset for reverse, so that the vehicle can move backwards on any range.
There is also a bizzare version with hydrostatic steering, that doesn't have any links between BKPs other than engine's crankshaft. It has two IVTs each paralleled to the mechanical part of respective BKP so that reduction can be made continuously without shifting down. But it is forever in development and was never produced. No schematics available.

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I've been thinking about projecting a electric transmission just for fun, so I was wondering if you guys could tell me about the different steering systems in tanks.
A short explanation of the concept would be enough, though you could link me to a article or post if you got one. 

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55 minutes ago, Collimatrix said:

This article is very good.  I wrote an article on the WOT forums a while back, which I think is also decent.

The overwhelming majority of western MBTs use double differential steering with a hydrostatic steering drive.

Thanks Coll, just what I needed. 

So if you don't mind I have a few questions on some points:
The ideal tank steering mechanism is as simple as possible; or else the tank will be hard to maintain in the field.  A tank that's stuck in the repair shop most of the time is no good for fighting.

From my point of view at least, a electric transmission would be the most simple of them all, a little ironic considering that the dual drive system is one of the most complex ones.
Why? Because the system can be broken into a few parts:
2 electric motors
2 VSDs
1 generator
1 engine
Wires.
And the control system. 

Electric motors are very simple in construction, the casing, stator and a rotor. And the only part that needs maintenance is the two bearings on the motor shaft.  You can simply view the motors as a module, since if a enemy round pierces the motor, you can probably guarantee that it needs replacement, or rewinding, like a transmission. So when it comes to maintenance, you can probably ignore the motors. And when you need to maintain them, you simply lift out the powerpack or electric motor, loosen a few bolts on the front and rear, pull out the rotor, and inspect the stator. And switch the bearings if needed, which are located on each side of the rotor.

The Variable speed drives or VSDs would most of the time be integrated into the motor. They last just as long as the motor if not longer, and again comes in a module form. They are simply electronics.

The generator is in practice a electric motor in reverse, to say it in a simple manner. 

The wires can be made to simply be plug and play, so when one is severed you can just unplug it, and add a new one, and it should not require a crane or removal of any parts. You could also combine the severed ends if needed. Also, wires last forever, almost. 

Lastly, the control system, quite simply, 1 PLC or computer, two high speed pulse counters and a few sensors. All of them lasting practically as long as the VSDs, except the pulse counters which may need a bearing switch.

If we could remove the IEC, the we could remove the generator, which would make the system MUCH simpler, but that is not possible with the current battery technology. 

(Just a note, there are a few small sub components in the system which are irrelevant that i did not mention)

 


The ideal tank steering mechanism should be as mechanically efficient as possible.  There's no point in having a massive, powerful engine in a tank if its transmission wastes most of the horsepower.

I think a electric transmission scores best here, when I calculated it I think we ended up with the system being roughly 3% more efficient, not considering regenerative breaking and such. 

 


The ideal tank steering mechanism makes driving in a straight line easy; the tank should not tend to veer off course.

This should not be hard to accomplish with modern electronics.  With a sensor on each sprocket, we can measure the RPM and then adjust the motors accordingly.  Alternatively we could have a clutch in between them, however this would be more complex and only work when driving straight forward, and not during turning. If we oversize the electric motors, we can simply transfer power from one motor to the other, and measure the load on the electric motor to avoid the track slipping on the terrain. 

 


The ideal tank steering mechanism is additive; that is, when transitioning from moving at full speed forwards to a turn, the mean track velocity remains the same.  This helps a tank maintain its speed as it turns, instead of bleeding it off.  In addition, tests have shown that additive steering works better when the tank is in deep mud, since keeping both tracks moving helps prevent the tank from getting stuck.

By oversizing the electric motors, we can make them adaptive, simply allocate more power to the other electric motor. A alternative would be to overload the motor. A electric motor can produce 250% of its max torque, well at the cost of reliability and a no so slight chance of catching fire and/or melting. The higher the overload, the worse. Though by adding extra external cooling you could overload the motors for short periods of time like turning, without impacting the motors. This option has to be compared to a conventional transmission to weigh the pros and cons though when it comes to bulk. Or you could make the steering subtractive and make it more compact and lighter. 


The ideal tank steering mechanism allows neutral steering, that is, that the tank can turn within its own length.

By simply adding a neutral mode, you can just make one of the electric motors go in reverse, and throttle them according to how fast you want to turn.


Additionally, a tank steering mechanism should be regenerative, which is to say that the kinetic energy from the inside (slowed) track should be transferred to the outside (sped up) track.  This also helps the tank maintain its speed as it turns.

As you said, by running the electric motor in reverse, you can recover the power for later use, same with braking. 


Tank steering works best when it is continuous, that is, that power is delivered constantly to the tracks while the turn is performed.  This is especially important when driving in hilly terrain, as the loss of power can cause the tank to slide downhill.

A digital system should allow 255 states, which for the human mind is continues. 


Finally, the ideal tank steering mechanism provides multiple turn radii.  Sometimes the driver needs to make a wide turn, while at other times they might need to turn quickly.  In the most refined tank steering mechanisms, the steering is infinitely variable, which means that arbitrary, fractional turn radii can be selected, just like driving a car.

Don't quote me on this one, but it should have infinitetly variable turn radius. 
 

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4 hours ago, Xoon said:

Thanks Coll, just what I needed. 

You're welcome.  I am pretty awesome and perfect and fantastic.

 

4 hours ago, Xoon said:

So if you don't mind I have a few questions on some points:


The ideal tank steering mechanism is as simple as possible; or else the tank will be hard to maintain in the field.  A tank that's stuck in the repair shop most of the time is no good for fighting.

From my point of view at least, a electric transmission would be the most simple of them all, a little ironic considering that the dual drive system is one of the most complex ones.
Why? Because the system can be broken into a few parts:
2 electric motors
2 VSDs
1 generator
1 engine
Wires.
And the control system. 

Electric motors are very simple in construction, the casing, stator and a rotor. And the only part that needs maintenance is the two bearings on the motor shaft.  You can simply view the motors as a module, since if a enemy round pierces the motor, you can probably guarantee that it needs replacement, or rewinding, like a transmission. So when it comes to maintenance, you can probably ignore the motors. And when you need to maintain them, you simply lift out the powerpack or electric motor, loosen a few bolts on the front and rear, pull out the rotor, and inspect the stator. And switch the bearings if needed, which are located on each side of the rotor.

The Variable speed drives or VSDs would most of the time be integrated into the motor. They last just as long as the motor if not longer, and again comes in a module form. They are simply electronics.

The generator is in practice a electric motor in reverse, to say it in a simple manner. 

The wires can be made to simply be plug and play, so when one is severed you can just unplug it, and add a new one, and it should not require a crane or removal of any parts. You could also combine the severed ends if needed. Also, wires last forever, almost. 

Lastly, the control system, quite simply, 1 PLC or computer, two high speed pulse counters and a few sensors. All of them lasting practically as long as the VSDs, except the pulse counters which may need a bearing switch.

If we could remove the IEC, the we could remove the generator, which would make the system MUCH simpler, but that is not possible with the current battery technology. 

My post was written for the WOT forums, which are mostly concerned with WWII and early Cold War tanks.  By the late Cold War, tank transmission construction was good enough that even extremely complex transmissions like the Renk HSWL 354 out of the Leopard 2/MBT-70 could be made acceptably reliable.  Technology of Tanks has a schematic diagram of the HSWL 354, and it's freakishly intricate.

I agree that modern electrical motors are potentially very good for tank transmissions.  Historically they were bulkier, heavier and less efficient than their mechanical and hydraulic counterparts.  Their prodigious use of strategic copper was also a concern.

4 hours ago, Xoon said:


The ideal tank steering mechanism makes driving in a straight line easy; the tank should not tend to veer off course.

This should not be hard to accomplish with modern electronics.  With a sensor on each sprocket, we can measure the RPM and then adjust the motors accordingly.  Alternatively we could have a clutch in between them, however this would be more complex and only work when driving straight forward, and not during turning. If we oversize the electric motors, we can simply transfer power from one motor to the other, and measure the load on the electric motor to avoid the track slipping on the terrain. 

 


The ideal tank steering mechanism is additive; that is, when transitioning from moving at full speed forwards to a turn, the mean track velocity remains the same.  This helps a tank maintain its speed as it turns, instead of bleeding it off.  In addition, tests have shown that additive steering works better when the tank is in deep mud, since keeping both tracks moving helps prevent the tank from getting stuck.

By oversizing the electric motors, we can make them adaptive, simply allocate more power to the other electric motor. A alternative would be to overload the motor. A electric motor can produce 250% of its max torque, well at the cost of reliability and a no so slight chance of catching fire and/or melting. The higher the overload, the worse. Though by adding extra external cooling you could overload the motors for short periods of time like turning, without impacting the motors. This option has to be compared to a conventional transmission to weigh the pros and cons though when it comes to bulk. Or you could make the steering subtractive and make it more compact and lighter. 


The ideal tank steering mechanism allows neutral steering, that is, that the tank can turn within its own length.

By simply adding a neutral mode, you can just make one of the electric motors go in reverse, and throttle them according to how fast you want to turn.


Additionally, a tank steering mechanism should be regenerative, which is to say that the kinetic energy from the inside (slowed) track should be transferred to the outside (sped up) track.  This also helps the tank maintain its speed as it turns.

As you said, by running the electric motor in reverse, you can recover the power for later use, same with braking. 


Tank steering works best when it is continuous, that is, that power is delivered constantly to the tracks while the turn is performed.  This is especially important when driving in hilly terrain, as the loss of power can cause the tank to slide downhill.

A digital system should allow 255 states, which for the human mind is continues. 


Finally, the ideal tank steering mechanism provides multiple turn radii.  Sometimes the driver needs to make a wide turn, while at other times they might need to turn quickly.  In the most refined tank steering mechanisms, the steering is infinitely variable, which means that arbitrary, fractional turn radii can be selected, just like driving a car.

Don't quote me on this one, but it should have infinitetly variable turn radius. 
 

I agree with the above points.  You could also make a tank transmission with a double differential transmission driven by two electrical motors, but I think you make a convincing case that it's possible to simply have two motors, one at each drive sprocket/final drive.  I'm not sure which of those two alternatives would end up being smaller.

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I don't know if it's well-founded, but a concern I'd have is that electric transmissions could be more finnicky and less resilient than hydraulic transmissions. A fucky brush/brush spring, a wire prematurely grounded, a short or open in an armature, or anything in-between could bench a tank. Don't know enough about hydraulic systems to know if they might be just as susceptible to fuckery

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1 hour ago, Vanagandr said:

I don't know if it's well-founded, but a concern I'd have is that electric transmissions could be more finnicky and less resilient than hydraulic transmissions. A fucky brush/brush spring, a wire prematurely grounded, a short or open in an armature, or anything in-between could bench a tank. Don't know enough about hydraulic systems to know if they might be just as susceptible to fuckery

It's definitely a problem, although IIRC all the fancy new high-efficiency motors are brushless.  Additionally, you can make the environment an electrical motor lives in extremely sterile, since it isn't breathing in air or fuel.  It does need some sort of cooling, but that can be closed-loop liquid.  In older electrical vehicle transmissions pushing the transmission beyond its design limits, or operating at near the design limits for a prolonged period of time was a good way to burn the motors out.

Hydraulic systems are in a perpetual state of leaking, which significantly increases fire risk.  There's a report out there somewhere of a panther taking a hit to the glacis, and then burning.  Presumably a spark got into the transmission lubricant.

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8 hours ago, Collimatrix said:

You're welcome.  I am pretty awesome and perfect and fantastic.

 

My post was written for the WOT forums, which are mostly concerned with WWII and early Cold War tanks.  By the late Cold War, tank transmission construction was good enough that even extremely complex transmissions like the Renk HSWL 354 out of the Leopard 2/MBT-70 could be made acceptably reliable.  Technology of Tanks has a schematic diagram of the HSWL 354, and it's freakishly intricate.

I agree that modern electrical motors are potentially very good for tank transmissions.  Historically they were bulkier, heavier and less efficient than their mechanical and hydraulic counterparts.  Their prodigious use of strategic copper was also a concern.

Yes, efficiency of electric motors have dramatically increased. Probably the main reason the motors were so heavy is because the cast iron frame. Nowadays we can use aluminum and titanium. Though, a hybrid electric drivetrain would probably be a bit bigger than a conventional transmission.  If money was not a issue, we could wind the motors with silver, and make casings out of ceramics or some high strength alloy and the transmission would probably be around 40% more efficient and twice as light. Though the price would be around 20 times as high.

 

8 hours ago, Collimatrix said:

I agree with the above points.  You could also make a tank transmission with a double differential transmission driven by two electrical motors, but I think you make a convincing case that it's possible to simply have two motors, one at each drive sprocket/final drive.  I'm not sure which of those two alternatives would end up being smaller.

Electric motors in general don't need gearing. Simply because of their excellent torque curve and output. Considering anything that is done in a differential or transmission can be done though a control circuit I see not reason to add unnecessary complexity. 
Though, for optimal efficiency, you should have a single gear, converting down the electric motors high RPM to something the sprocket can use. At least in AC motors, to reduce the RPM of the motor, you add more pole pars, however this also reduces the efficiency of the motor. A better alternative is to just use as little poles as possible (1 par) and then use a single gear, since from what I have learned, it should be more efficient. 
To give a overview, a AC electric motor with 1 pole par runs at 3000RPM, minus slip. And I think the sprocket has to rotate at 800ish RPM for the tank to reach 80-100km/h . So a ratio of roughly 1:3,75 should be enough.

 

5 hours ago, Vanagandr said:

I don't know if it's well-founded, but a concern I'd have is that electric transmissions could be more finnicky and less resilient than hydraulic transmissions. A fucky brush/brush spring, a wire prematurely grounded, a short or open in an armature, or anything in-between could bench a tank. Don't know enough about hydraulic systems to know if they might be just as susceptible to fuckery

When you start working on these things, you will realize how resilient these things are.  And no need for a soldier to be precise, just plug and play.
A brush motor would be a very bad idea in a tank, since Brushless DC or AC motors are MUCH better. If you are concerned about springs and switches, we have solid state versions or all components, no moving parts. Grounding would not be a issue either, since you can't ground a 400V+ system into the chassis of the vehicle, you just double isolate it. Unless the engine compartment takes some damage from enemy fire, which breaks the protection of the equipment, shorts should be impossible, since all military spec electronics need to be dust proof and waterproof.  And if a winding is partially severed, you just lift out the motor, unbolt a few bolts, remove the rotor, remove the broken winding, and add a new one. 

 

4 hours ago, Collimatrix said:

It's definitely a problem, although IIRC all the fancy new high-efficiency motors are brushless.  Additionally, you can make the environment an electrical motor lives in extremely sterile, since it isn't breathing in air or fuel.  It does need some sort of cooling, but that can be closed-loop liquid.  In older electrical vehicle transmissions pushing the transmission beyond its design limits, or operating at near the design limits for a prolonged period of time was a good way to burn the motors out.

Hydraulic systems are in a perpetual state of leaking, which significantly increases fire risk.  There's a report out there somewhere of a panther taking a hit to the glacis, and then burning.  Presumably a spark got into the transmission lubricant.

As long as the electric motors are IP67 or higher, you can lose as much crap you want into the engine compartment without worrying. Engine compartment flooded? No problem as long as the IEC does not get affected. Dust storm filled it with sand? No problem, dust proof. 

When speaking about cooling, external cooling would defiantly be the best, since it makes the motor a lot less bulky and makes possible to have a higher IP grade. 

 

6 hours ago, roguetechie said:

With things like Joe Flynn's PPMT technology you could significantly reduce the strategic resources like copper etc for something like that.

He also works with DOD etc already in a number of fields...

Joe Flynn Parallel Path technology

Interesting. 

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2 hours ago, Xoon said:

When you start working on these things, you will realize how resilient these things are.  And no need for a soldier to be precise, just plug and play.
A brush motor would be a very bad idea in a tank, since Brushless DC or AC motors are MUCH better. If you are concerned about springs and switches, we have solid state versions or all components, no moving parts. Grounding would not be a issue either, since you can't ground a 400V+ system into the chassis of the vehicle, you just double isolate it. Unless the engine compartment takes some damage from enemy fire, which breaks the protection of the equipment, shorts should be impossible, since all military spec electronics need to be dust proof and waterproof.  And if a winding is partially severed, you just lift out the motor, unbolt a few bolts, remove the rotor, remove the broken winding, and add a new one. 

I do work on these things, granted, there are some intrinsic differences between the ones I've worked on and the motors you would use in tanks.

It's fair that you wouldn't need brush motors, but, although some more than others, any motor is capable of failing from age, wear, or abuse. My point was that there are a lot of ways that an electric transmission could fail devastatingly, and I'm not sure there are as many ways that a hydraulic transmission could fail devastatingly, with the caveat that I don't know much about hydraulic transmissions. Also, although they are very resilient, MS components are still vulnerable to contamination, corrosion, and chafing. I don't know what backshops do in their free time, but I suspect rotors with broken windings are just trashed and replaced.

Something I'm curious about now that you mention it, it never occurred to me whether or not you could ground the chassis of a ground vehicle with a 400v system. Is there something specific to ground vehicles that makes it impractical?

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50 minutes ago, Vanagandr said:

I do work on these things, granted, there are some intrinsic differences between the ones I've worked on and the motors you would use in tanks.

It's fair that you wouldn't need brush motors, but, although some more than others, any motor is capable of failing from age, wear, or abuse. My point was that there are a lot of ways that an electric transmission could fail devastatingly, and I'm not sure there are as many ways that a hydraulic transmission could fail devastatingly, with the caveat that I don't know much about hydraulic transmissions. Also, although they are very resilient, MS components are still vulnerable to contamination, corrosion, and chafing. I don't know what backshops do in their free time, but I suspect rotors with broken windings are just trashed and replaced.

Well of course, the motors won't last forever. And yes, rewinding electric motors is becoming rarer and rarer, but you can still do it if needed. But most of the time you just replace the entire thing. 

When it comes to hydraulic transmissions, I can't say for sure.  I am used to pneumatic systems, which are very similar. My problem with hydraulics is the chance of leakage, any leakage would cause the entire system to fail, if the pump failed, the system fails. And in practice, you would use the same control systems for the hydraulics, magnet valves and such. Here the sealing could rupture, and they need regular maintenance. 

Honestly, if anyone could cover hydraulic transmissions, that would be great. Does hydraulic system have the ability to recover and store power? Like regenerative breaking?

 

50 minutes ago, Vanagandr said:

Something I'm curious about now that you mention it, it never occurred to me whether or not you could ground the chassis of a ground vehicle with a 400v system. Is there something specific to ground vehicles that makes it impractical?

Well, I am no mechanic (sadly), but I know that 6-48V systems can safely be grounded to the vehicle chassis. I suspect this is because the low voltage is too weak to flow through the steel of the chassis, simply because of the high resistance of steel. This helps dissipating the current, like when grounding a house, you run a wire through the soil, at the dept deep enough so that I can't electrocute a person on the surface. 
When using higher voltage systems however, the chassis is not used to ground the vehicle. I guess 400V is enough to penetrate through the chassis and electrocute a person touching it. 

This is why I suggested double isolating the electric components, which at least by Norwegian standards, removes the need for grounding. 

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Working with pneumatic systems probably makes you more knowledgeable about hydraulics than I am then. I figure in a hydraulics system you ought to be able to limp back to base or out of combat at least, depending on the severity of a leak in a hydraulic system, but it might be that even a small leak would quickly deplete the fluid reservoir, I just don't know. I assume there is a reason why lots of tanks still use hydraulic transmissions, although it might just be tech inertia.

Many transport category aircraft use the body as ground with 400v AC supply and people don't get electrocuted [Correction: 400Hz is pretty standard frequency for transport category electrical distribution, 400v is found on the 787 and 380 and maybe others]. The issue isn't the magnitude of the voltage, but whether current wants to find ground through your body. You can wet your finger and touch either terminal of a car battery and you'll be fine, the excitement only happens if you happen to be in contact with supply and ground at the same time. 

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3 hours ago, Vanagandr said:

Working with pneumatic systems probably makes you more knowledgeable about hydraulics than I am then. I figure in a hydraulics system you ought to be able to limp back to base or out of combat at least, depending on the severity of a leak in a hydraulic system, but it might be that even a small leak would quickly deplete the fluid reservoir, I just don't know. I assume there is a reason why lots of tanks still use hydraulic transmissions, although it might just be tech inertia.

Well, a small leak would still probably rupture the hose and spew hydraulic liquids everywhere. In a component it would not be a issue, well other than having to constantly refill the reservoir.  Normally, you would have two circuits per sprocket, meaning that if one circuit fails, you can still limp back to base with the other. But of course this comes with the issue of needing two reservoirs, two pumps and two of any control valves per sprocket. Which could get complex. Without a duplicated circuit, the system would be just as vulnerable, if not more vulnerable. 

 

3 hours ago, Vanagandr said:

Many transport category aircraft use the body as ground with 400v AC supply and people don't get electrocuted [Correction: 400Hz is pretty standard frequency for transport category electrical distribution, 400v is found on the 787 and 380 and maybe others]. The issue isn't the magnitude of the voltage, but whether current wants to find ground through your body. You can wet your finger and touch either terminal of a car battery and you'll be fine, the excitement only happens if you happen to be in contact with supply and ground at the same time. 

Ok, so I just found out I was completely off about grounding in vehicles. Turns out, they have nothing in common with house grounding systems. Quite simply, you connect one of the poles from the battery to the chassis, and this way you only need one wire to components in the vehicle. Like headlights, spark plugs, starter motors and electronics. 

The reason electric vehicles do not ground their batteries that power the motors is so that they don't mix the high and low voltage. 
So the reason a 787 or 380 has a 400V system is because the entire system is 400V, while in a car the headlights, starter, electronics and such are 6-48V.

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24 minutes ago, Xoon said:

Well, a small leak would still probably rupture the hose and spew hydraulic liquids everywhere. In a component it would not be a issue, well other than having to constantly refill the reservoir.  Normally, you would have two circuits per sprocket, meaning that if one circuit fails, you can still limp back to base with the other. But of course this comes with the issue of needing two reservoirs, two pumps and two of any control valves per sprocket. Which could get complex. Without a duplicated circuit, the system would be just as vulnerable, if not more vulnerable. 

And we've about hit the end of where I can contribute to discussions about hydraulics

24 minutes ago, Xoon said:

Ok, so I just found out I was completely off about grounding in vehicles. Turns out, they have nothing in common with house grounding systems. Quite simply, you connect one of the poles from the battery to the chassis, and this way you only need one wire to components in the vehicle. Like headlights, spark plugs, starter motors and electronics. 

The reason electric vehicles do not ground their batteries that power the motors is so that they don't mix the high and low voltage. 
So the reason a 787 or 380 has a 400V system is because the entire system is 400V, while in a car the headlights, starter, electronics and such are 6-48V.

I don't know about electric cars or anything (it could be that batteries produce a pretty constant voltage with current that adapts to the load), but transport category aircraft tend to have a lot of different voltages and mixes of AC and DC power buses (400v AC for flap actuators and other things, 115v AC for passenger's outlets and other things, 28v DC for lights and other things, 14v DC for batteries and other things, 5v DC for electronics, etc), and all of it ends up grounding to the same airframe. It works because the generator's amperage output is able to be tuned very closely to the amount of load that the craft is using at that moment, and as long as the load output matches the load, nothing gets an overvoltage or overcurrent condition. It's kind of a pain in the ass because the way electricity is often taught, voltage is the variable, the resistance of the circuit is given, and you figure out current based on voltage divided by resistance, where, when generators are concerned, resistance is the variable and a desired voltage is given, so the amperage has to be manipulated to keep voltage at a given level. 

 

Posting from PC, not quite done with explanation, will pick it up from mobile when I can.

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Xoon, yes there are hydraulic hybrid systems and they're actually very good. However, the nature structure and requirements placed on "green energy and efficiency" subsidies has artificially retarded hydraulic hybrid research development and deployment.

In a hydraulic hybrid system your "battery pack" is called a hydraulic accumulator. This is what would "store" pressurized fluids you don't need right that instant.

You can do series, parallel, and other hybrids more or less the same in a hydraulic system as you would in a battery hybrid.

You can also do regenerative braking, power mixing, and even regenerative suspensions etc!

Personally I can see plus and minus points for each system with hydraulic being more tempting for 50+ ton vehicles 

At the extreme other side of the spectrum battery less ICE electric hybrid technology as is being worked by a couple countries WRT motor scooters and etc that use ultracaps could be phenomenally useful for everything from exoskeletons to things like the Polaris ATV's.

 

Damnit double edit:

WRT brushless motors, you can do some really interesting and amazing things with them these days including using them as parts of your suspension system with adjustable damping and rebound rates on the fly and much more!

This is why we see Boston dynamics going from big dog using hydraulics or pneumatics to the demon hellspawn recent development that's half wheeled donkey half great ape!!!

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26 minutes ago, Vanagandr said:

I don't know about electric cars or anything (it could be that batteries produce a pretty constant voltage with current that adapts to the load), but transport category aircraft tend to have a lot of different voltages and mixes of AC and DC power buses (400v AC for flap actuators and other things, 115v AC for passenger's outlets and other things, 28v DC for lights and other things, 14v DC for batteries and other things, 5v DC for electronics, etc), and all of it ends up grounding to the same airframe. It works because the generator's amperage output is able to be tuned very closely to the amount of load that the craft is using at that moment, and as long as the load output matches the load, nothing gets an overvoltage or overcurrent condition. It's kind of a pain in the ass because the way electricity is often taught, voltage is the variable, the resistance of the circuit is given, and you figure out current based on voltage divided by resistance, where, when generators are concerned, resistance is the variable and a desired voltage is given, so the amperage has to be manipulated to keep voltage at a given level. 

 

Posting from PC, not quite done with explanation, will pick it up from mobile when I can.

Yeah, I am a to-be-tradesman, not a engineer, at least yet. So this is more advanced than we are taught. 

We work generally with PSUs (24V, 2.5A) and your typical out-of-the-socket voltage types (230V, 380V, 400V, 440V and 690V).

Here the current is constant, and will fill out the path of least resistance. Burning out anything not strong enough to handle it.  We can manually adjust the PSUs, but we usually just keep them at max. 

And we are thought to never mix voltages, usually to avoid fusing switches and melting coils. 

I have touched on some more dynamic formulas, but never put them into practice. 

 

 

16 minutes ago, roguetechie said:

Xoon, yes there are hydraulic hybrid systems and they're actually very good. However, the nature structure and requirements placed on "green energy and efficiency" subsidies has artificially retarded hydraulic hybrid research development and deployment.

In a hydraulic hybrid system your "battery pack" is called a hydraulic accumulator. This is what would "store" pressurized fluids you don't need right that instant.

You can do series, parallel, and other hybrids more or less the same in a hydraulic system as you would in a battery hybrid.

You can also do regenerative braking, power mixing, and even regenerative suspensions etc!

Personally I can see plus and minus points for each system with hydraulic being more tempting for 50+ ton vehicles 

At the extreme other side of the spectrum battery less ICE electric hybrid technology as is being worked by a couple countries WRT motor scooters and etc that use ultracaps could be phenomenally useful for everything from exoskeletons to things like the Polaris ATV's.

 

Damnit double edit:

WRT brushless motors, you can do some really interesting and amazing things with them these days including using them as parts of your suspension system with adjustable damping and rebound rates on the fly and much more!

This is why we see Boston dynamics going from big dog using hydraulics or pneumatics to the demon hellspawn recent development that's half wheeled donkey half great ape!!!

A few quick questions:
1. For how long can the accumulator keep the stored energy?

2. How much of the energy can the hydraulic regenerative breaks recover?

3. What makes a hydraulic system more suited for heavy vehicles?

4. The ultra caps can only store the energy for a short period of time right? So when traveling downhill for long amounts of time, the energy is lost?

5. Do you know how efficient the system would be?

6. Could you draw a hydraulic circuit to show how you can vary the speed of the motors and mix power?

 

17 minutes ago, Collimatrix said:

Most Western MBTs have a mix of mechanical and hydraulic systems in their transmissions.  The transmissions are a series of planetary gears plus a hydrodynamic torque converter.  The steering drive is usually, but not always, a hydrostatic, infinitely variable motor that connects to the transmission output by a series of mechanical differentials.  There are also usually hydrodynamic retarders that supplement the brakes, like when the tank is going downhill.  The torque converters usually compromise the tank's ability to engine brake.

Pure hydraulic transmissions have been tried once or twice, but I don't think they were terribly convincing.

Though not terribly convincing, it is always worth a look. You never know if a breakthrough makes it viable in the future.

 

 

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Most Western MBTs have a mix of mechanical and hydraulic systems in their transmissions.  The transmissions are a series of planetary gears plus a hydrodynamic torque converter.  The steering drive is usually, but not always, a hydrostatic, infinitely variable motor that connects to the transmission output by a series of mechanical differentials.  There are also usually hydrodynamic retarders that supplement the brakes, like when the tank is going downhill.  The torque converters usually compromise the tank's ability to engine brake.

Pure hydraulic transmissions have been tried once or twice, but I don't think they were terribly convincing.

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