Inventor Demonstrates Infinitely Variable Transmission 609
ElectricSteve writes with this excerpt from Gizmag:
"Ready for a bit of a mental mechanical challenge? Try your hand at understanding how the D-Drive works. Steve Durnin's ingenious new gearbox design is infinitely variable — that is, with your motor running at a constant speed, the D-Drive transmission can smoothly transition from top gear all the way through neutral and into reverse. It doesn't need a clutch, it doesn't use any friction drive components, and the power is always transmitted through strong, reliable gear teeth. In fact, it's a potential revolution in transmission technology."
Brilliant. Go Steve! (Score:5, Interesting)
This is the kind of thing you like to see -- I hope this man has all the capital he needs and gets that prototype up and running for demonstrations. Plus it's a small time plumber inventor
Fuel economy (Score:4, Interesting)
Because right now the gearboxes are rubbish, they haven't evolved much in the last decades.
So... (Score:4, Interesting)
...when can I fit this on my bicycle?
(I'm serious. Proceeding to read TFA...)
Electric motors (Score:2, Interesting)
The article notes that the motor runs (or can run) at a constant speed, which isn't always the case for gas powered engines, although I'm sure they each have a good zone where they produce power effectively. It seems this type of transmission would be perfect for electric motors which can operate at a full constant level of power right off the line. It still seems like you would want a few power settings; one for heavy traffic, one for the city, one for the highway (at least).
Clever, but he has a lot of work ahead of him (Score:5, Interesting)
I think the weakness in this design is the need to rotate the "bottom" shaft at a speed equal to the input shaft for neutral. While indeed it doesn't need a lot of power, it's a lot of rotation where, in competing designs, a clutch disengages or the drive motor is idling. I could see a lot of things going wrong if the synchronization was imperfect, or if something went wrong.
How do you start this up from a dead stop? Somehow you have to exactly match the shaft rotation speeds to keep it in neutral before you start moving forward, otherwise there will be a lurch.
I look forward to seeing how this is developed further. It has a lot of potential.
A few notes... (Score:4, Interesting)
While quite elegant, this solution requires power input... So not so great on a bicycle...
And as far as cars go, you have to spin a shaft in order to achieve neutral. Which means that you still need a clutch or something for a car to be safe. (If the engine's running and the electric motor spinning the shaft fails the car will go forward... Not nice.)
(Am I the only one who thought that the TFA's statement that understanding these mechanics is dumbing it down? I think it's simple, honestly. I'm not claiming I would have invented it, but I do understand the principle...)
Turbines? (Score:3, Interesting)
Newton's Third Law? (Score:3, Interesting)
For every action, there is an equal an opposite reaction. So, when your monster torque motor is spinning the input shaft, surely it is pushing against the counterspinning shafts with exactly that amount of power? In other words - won't the mechanism (electric motor, flywheel, etc.) that keeps the counterspinning shafts running at the desired speed ratios have to overcome this reaction? It's possible that the frictional and mass inertia of the system helps some, but how much?
I'm not an ME, but the explanation of what the required control motor power is relative to input motor power is very thin here. Be very interesting to see what the detailed input / output / control torque & power measurements end up being.
Re:So... (Score:1, Interesting)
It already exists. It is put out by Fallbrook Technologies and is called NuVinci.
http://www.fallbrooktech.com/nuvinci.asp
Re:Brilliant. Go Steve! (Score:3, Interesting)
It is a very interesting approach, the problem that may happen (I don't know, just guessing here) is to locking the lower shaft while trying to go full force, isn't the entire premise of friction basically shifted (sorry for the pun) to the device that will stop or let go of the lower shaft, which needs to be stopped for the torque to be transmitted to the wheels for example? So there are these 2 small black gears if you look at the video, these gears are perpendicular to the lower shaft, sitting on it sideways, is that the one that will be locking the shaft or driving it, because then all of that power difference (either goes to the wheels or goes to the shaft) will be at a point of failure right there, how will they stop and start that one, is there a reliance on the electrical motor there to hold against the driving shaft? If there is, then the electrical motor will have to produce as much power and torque as the main driving engine.
But I maybe wrong completely and just misunderstood this thing totally.
How a planetary-based IVT system works in general (Score:5, Interesting)
At first blush, I'd say that both Toyota and John Deere have already produced something similar. What he appears to have, however, is a system that can smoothly transition (with power) through neutral and reverse. That indeed could be the cool, patented part, as the rest of his transmission is pretty well understood and actually in production already in many of the applications they list for their invention. I don't see any patent application listed, so I can't tell for sure exactly where his breakthrough is.
Here's the fundamental principle by which his transmission works, though: Basically the idea is you supply driving power to a planetary gear system and then use another variable system such as an electronic motor or, in John Deere's case, a hydraulic motor, to take speed (but not power) away from the output shaft by spinning part of the planetary system. If you understand how a planetary gearbox works, this makes sense. So in John Deere's case, the less-efficient hydraulic motor uses a tiny amount of power to control how the actual, geared, power is transmitted to the wheels. Using this system JD has a completely variable system with a particular gear range (this is a tractor after all) that has a powered neutral stop. In the pictures and video you'll note he has two electric motors that control the ratio.
Toyota does something similar with their hybrids, although it's more of a way to efficiently (and brilliantly, I might add) blend the gasoline motor's power with the electric system in an infinitely variable way.
Another way of implementing an IVT, though I don't think it is as efficient, is to use a differential. Power comes in the normal part of the differential (IE spinning the entire gear assembly), and then power comes out one side, and an electric or hydraulic motor attached to the other side (Where the wheels would normally go). You can then use the motor to change the apparent gear ratio, and even reverse it.
Better with diesel piston engine Re:Turbines? (Score:3, Interesting)
Turbine without regeneration cycle have approx 30% efficiency and can up 40% efficiency if hot exhaust is returned into the cycle (regeneration). Diesel piston engines actually achieve between 40% and 45% efficiency at optimal constant speed. If you consider turbine systems at optimum efficiency with regeneration and high operating speed are quite large, noisy and need tight maintenance cycles for the finely adjusted and physically resistant blades, this is not suitable for small vehicles. By the way this new gearbox design would be very suited to diesel engines.
Re:Brilliant. Go Steve! (Score:4, Interesting)
Transmission innovation (Score:5, Interesting)
The Thompson coupling [youtube.com] was invented not long ago, and I remember being amazed that there was anything new to be done in the area of mechanical power transmission. And now this. Are we all done now, or is there more still?
Lot of misinformation, this IS the way Prius works (Score:3, Interesting)
I see a lot of people have chimed in without knowledge of how the Prius HSD works. There is NO conventional belt CVT in a Prius.
Prius works almost exactly like this demo. Gear Driven Planetary and Sun gears.
The HSD with its robust gear system without friction drive is what makes it so special.
Here is a simplified demo of how the Prius HSD works:
http://eahart.com/prius/psd/ [eahart.com]
Sorry - People Hate It (Score:1, Interesting)
We tried this on a the Freestyle and Five Hundred (Taurus) a few years ago then dropped it because people didn't like the separation in engine sound vs vehicle speed. It had a spooky feel when driving that they never could get used to. A great idea but too different for the masses.
Re:Brilliant. Go Steve! (Score:5, Interesting)
The new aspect is that this planetary gearset actually has TWO inputs, and the output is determined by the *difference* in speeds between the two. That's how it can go from reverse to forward seamlessly. V1 > V2 is Forward, V1 V2 is Reverse, V1 = V2 is Neutral. Assuming there are no practical limits on the velocity of either input, the possible difference between them is infinite.
Personally I find this really exciting, because i've always been in love with the idea of a variable transmission. Ignoring electric motors for a minute, there are some absolutely INSANE things you can do to a small motor with cams, turbocharging, etc, to extract absolutely massive amounts of power from teeny engines. Like, 1000+hp from sub 2 litre motors. The problem is they end up being extremely peaky (power is only made at a narrow RPM band, or a terribly high one)... but with a variable transmission you can let the engine hunker down in it's sweet spot and let the tranny worry about all the fiddly bits. Hell, you can even do the same thing with a big engine... I wonder if its possible to make five figures of power from a 7 litre? With this we just might find out.
Re:Uh... (Score:3, Interesting)
Or more specifically: Whatever's driving the control-axle will be fighting whatever's driving the main axle, so it has to be as powerful as the main motor. In which case, why not just use that in the first place?
Actually he says it does not act against the control axle. It only needs enough torque to defeat gravity resisting that metal ring gears weight.
A tiny radio controlled car motor can clearly be driven to fast speeds at enough torque to defeat gravity resisting the car from moving, which arguably will weight more than a metal gear piece at this small scale.
And at larger scales with heavier gears and parts, you just scale the small motor up too.
Re:How a planetary-based IVT system works in gener (Score:2, Interesting)
Re:Newton's Third Law? (Score:4, Interesting)
I agree.
His next phase prototype should have a 10-20 HP IC engine (lawn tractor motor, etc.) for the prime mover, and the output shaft of his device needs to be connected to a dynamometer/load absorber of some type.
Can he still control it with the small DC permag gearmotor he appears to be using?
Re:Brilliant. Go Steve! (Score:3, Interesting)
What I don't get is how exactly this is distinct from a differential gear.
For those without: A Prius Simulator (Score:3, Interesting)
http://www.wind.sannet.ne.jp/m_matsu/prius/ThsSimu/index_i18n.html [sannet.ne.jp]
Neat-o, and works fine with IcedTea!
Slider controls for accelerator and brake with 'PRNDB' selector, plus individual sliders for motor, engine, and generator and a visual representation of the work/relation of each..
Fun!
Re:Brilliant. Go Steve! (Score:4, Interesting)
The new aspect is that this planetary gearset actually has TWO inputs, and the output is determined by the *difference* in speeds between the two.
You just stated the definition of a differential gear. It is not new in any way, and describes exactly how a planetary gear works and is normally used. For a real world example take a look at the Hybrid Synergy Drive [wikipedia.org] used in Toyota Prius. It has precisely that: A planetary gear with two inputs summing up to one output, allowing the engine to operate at optimal rpm regardless of wheel speed.
Re:Brilliant. Go Steve! (Score:5, Interesting)
Not to worry about 'infinite' or 'frictionless' - these characterizations are not the intent of the device so we can just evaluate it as a normal continuous transmission being controlled by the ratio of speeds between a control shaft and the drive shaft. Efficiency for low-torque cases can be quite decent as eccentric bearings, gear-qualities and diameters can be controlled well with current techniques.
So... with a real torque, there will definitely be significant forces between the two shafts. Clearly, the full torque will be on the central, driving shaft, while some smaller fraction will be on the upper shaft. As we bring the distance between them down, then the torque between them can decrease, but then there will be more stress on the smaller pinions' teeth. Planetary gears are great for this class of problem and he's throwing decent diameter eccentric bearings in where he can too. The bloke seems honest, and has clearly thrown a fair amount of time and energy into the problem.
There are other approaches to controlling gear ratio via the speed differences between two shafts - he's not trying to do something impossible, he's just trying to do something difficult, successfully. Whether the cost of the bearings and gearing will be favourable when compared to the other approaches is the question. I think his system will work - and decent sealed bearings, high strength pinions, planetary systems - these already exist and are stable tech in current transmissions, even in relatively dirty industrial environments where the transmissions aren't as protected as in cars. In particular, the cost of electronic control for motors has fallen massively over the last years, so if nothing else, the general class of solutions using differential speeds of low-torque motors to control a high-torque transmission is more appealing now.
So, 'genius', no. Hard-working, self-taught engineer? Yes.
Re:Electric motors (Score:3, Interesting)
Right, that's called 'gas-electric', or 'diesel-electric', or 'turbo-electric', or if you want to associate a good design like that with an abomination, 'series hybrid'. It has been used in production for decades on locomotives, and is becoming more common on ocean vessels. There are even a couple vehicles using such a configuration.
The problem is that the speed of induction motors is relative to the frequency they are being driven at. It requires some complex circuitry to provide high power at a variable AC frequency. That said, it is still probably cheaper, lighter, and more efficient to do that electronically in the speed controller, rather than mechanically in a variable gear box.
Re:Lot of misinformation, this IS the way Prius wo (Score:5, Interesting)
The way I understood it (could be wrong), the Prius drive is only one half of what this guy came up with. The clever bit is the other half. The Prius transmission would not work well without significant torque input/output(electric breaking) on the electric side. The way this works, there is almost no load on the ratio selection element, the only input it needs is enough to create a difference in speed.
Re:Hydrostatics... (Score:5, Interesting)
It's loud. Plus you have to have a heavy hydraulic system (pump, oil reservoir, valving, etc). In practice an electric motor gives you most of the same benefits of a hydrostatic system, but it's a lot lighter and doesn't require an oil system. Of course batteries are heavy, but aren't strictly needed (as in a locomotive).
A few years ago I heard of a design that used small hydraulic motors connected to each car wheel via clutches that would efficiently overcome the propensity of a differential to send power where you don't need it. Basically when slippage was detected, the clutches would engage and the faster wheel would act as a pump, sending fluid to drive the other wheel. The beauty was that if you tied all four wheels into the same system, you could get on-demand four wheel drive as well.
Another prototype I heard of used a hydrostatic system to charge up a nitrogen accumulator in a form of regenerative braking system.
Hydrostatics also has limitations in the amount of power you can transmit. Every large combine harvester we've ever owned has had a hydrostatic transmission, but no tractor ever has had. Combines typically don't pull things; driving power is minimal compared to the power consumed by threshing. Whereas in a tractor, it's all about driving power (outside of PTO applications). You just can't really put 500 HP of pulling power through hydrostatics. Most hydraulic motors are gear motors, which means the oil spins little gears. Under high load, oil slips past the gears without turning them. Compare that to electric where on a daily basis Locomotives pass thousands of horsepower from big diesel engines to the wheels with electric motors.
Re:Brilliant. Go Steve! (Score:2, Interesting)
You just stated the definition of a differential gear. It is not new in any way, and describes exactly how a planetary gear works and is normally used. For a real world example take a look at the Hybrid Synergy Drive [wikipedia.org] used in Toyota Prius.
I don't think it is the same as that. In the HSD the electric motor is contributing a large part of the output power, whereas TFA seems to be saying that the control power is significantly less that the power being transmitted, and hopefully will be less than the energy wasted in a friction based CVT.
Re:Brilliant. Go Steve! (Score:4, Interesting)
The real icing on the cake is (as mentioned near the end) the secondary drive doesn't require a whole lot of power so it can be run by a flywheel
This is something that bothers me as I look at this demo. The secondary drive doesn't require a whole lot of power, because there is literally nothing attached to the output to counteract the little motor's selected ratio.
To simulate the forces of what it'd be to have a car attached on the output, you can just use your hand and try to hold the output from moving, while the ratio is not in neutral. If there is a weaker motor and a stronger motor, what do you think will happen? The stronger motor may feel a pinch, and the small motor will be completely unable to stop the output from distorting the ratios, making the entire setup unusable.
Now, I hope I'm wrong, but there better be something hidden from view That Changes Everything.
Re:Fuel economy (Score:3, Interesting)
Unless you consider the negative environmental impact of disposing/recycling all those used cars and the manufacture of newer ones. We would have done less damage to the planet by forcing everyone to drive the car they had an additional year before they could buy a new one.
And thats completely ignoring the fact that the fuel saved by cash for clunkers was only about 1/5th the cost of the program.
If I had traded in my 18mpg Oldsmobile for a 30mpg car, I would have only saved about 250gallons a year. At 3 per gallon, that only saved me $750 dollars. How much of my tax money did the government spend on it though? Oops.
Re:Its a con (Score:4, Interesting)
My other concern is the gear tooth size. A traditional transmission uses gears that are quite large and have few teeth. The D-Drive has gear teeth with at least two orders of magnitude smaller teeth in critical places, and they are at a smaller radius. I think this thing will need to be huge to transmit enough power to move a vehicle. Large radius gears are necessary to transmit a lot of power. The planetary design of the D-Drive does not permit large radius gears.
Re:Automatic transmissions fail before engines, no (Score:4, Interesting)
Good point. Well, your numbers are a little off.
My car as 110,000 miles on it. I've raced my car a good bit (legal track racing, of course).
The first clutch (stock) I destroyed was by adding a 150hp NOS system on.
The second clutch (performance) was destroyed by my ex-wife driving it uphill and she slipped the clutch the whole way (like 5 miles). She obviously wasn't very good with a stick.
The third clutch (performance) was actually from old age.
My friend has a comparable car. It's the same engine, transmission, body style and weight. She drives more normally than I do (no racing, just city/highway driving). She had her clutch changed at 100k miles. Labor to replace the clutch is about $350 to $500. Parts are about $150. This car happens to be a bastard to work on, which is why the labor is high. So, $500 to $650 for the job.
This is about the age that an automatic transmission would need to be rebuilt. For this car equipped with an automatic, removal, rebuild, and replace costs about $3,500.
So, with my car, I've improved the efficiency by helping the airflow out (one minor exhaust fix, and a some intake fixing). I enjoy cruising at highway speeds with low RPM's (6 speed). The same car with an automatic would be cruising at a much higher RPM (4 speed), and suffering from losses related to the automatic transmission.
I rarely need to check my transmission fluid (i.e., gear oil). If my gear oil runs low, it could increase wear. A car with an automatic has to have their transmission filter and fluid changed. If their fluid runs low, it can be catastrophic.
There's about a 300 pound difference between the manual 6 speed and the automatic 4 speed.
So, lighter, better fuel economy, and less repair costs. I really don't see why people wouldn't want to drive a stick. The excuse "I don't know how" isn't a valid excuse, except they're too lazy to learn.
I can drive pretty much anything with wheels, and I've proven it. I'm licensed for motorcycles and cars. I've also driven everything including a big truck with a 10 speed air shifter. a neighbor bought a motorcycle, but didn't really know how to drive it. They told me it wasn't driving right, so I grabbed my helmet from the garage (I don't have a bike right now, but I still have the helmet), and took it for a spin. It worked fine. It was operator failure.
Re:Uh...Probably gonna get his server creamed (Score:2, Interesting)
Less than it appears to be (Score:5, Interesting)
The largest value of this device is in its "wow, how does that thing work?" design. By baffling the onlooker and also describing the widget very carefully the illusion of a wonderfully useful device can be created.
It has a problem in the real world, though. The reaction torque is equal to the working torque - and the reaction torque path runs through that "secondary control shaft." This will become obvious as soon as he tries to transmit some significant power through his device. What he's showing isn't a new invention at all, it's just a mechanical "summer" that adds the inputs from two input shafts. All that's new here is some fancy handwaving and creative description.
It might be good enough to fool some people but Mother Nature and those who paid attention in school aren't fooled. Maybe if / when he actually tries to transmit some power through his "invention" and the control motor just spins backwards he'll "discover" a source of electrical energy?
Re:Brilliant. Go Steve! (Score:2, Interesting)
Could we please have a computer analogy to clarify things ?
Re:Brilliant. Go Steve! (Score:3, Interesting)
It would seem to me that this is an ideal application for a (diesel) turbine engine. A turbine has very consistent RPM/torque output: this is why, despite its efficiency, they have not been used in vehicles with any regularity.
If you could "seamlessly clutch" from "stopped" to full speed, back to "stopped" and then into reverse all while remaining at a consistent, low RPM, you'd have the perfect transmission for a diesel turbine. Very exciting! We might be able to significantly increase the petroleum efficiency of our new production ICE vehicles without being dependent on expensive, radioactive, inefficient rare-earth metals! (That's only a very short-term solution, anyway: it'll only last a couple years longer until people realize the overall cost is significantly higher.)
Furthermore, it looks like this transmission might be easily shoehorned into existing (low-RPM) diesel vehicles and realize a performance increase, provided it's not an inefficient design - the video looks like it's got fewer points for energy loss than a traditional shifting transmission, at any rate.
Re:Brilliant. Go Steve! (Score:5, Interesting)
Yeah but eliminating clutches removes a common point of failure. So even if the performance benefits aren't that great it may increase the life of the car/machine.
Re:Brilliant. Go Steve! (Score:3, Interesting)
Not at all. This device has three inputs, GP neglected to mention the main engine. It uses two smaller inputs to affect the main larger input. The prius balances two engines of rougly equal size. This controls a single engine with two much smaller ones. It seems to be a novel and unique transmission.
Re:Just a variable opposition drive? (Score:2, Interesting)
I don't mean to be a skeptic, but I guess I fall into the camp that doesn't understand this. It seems that the control shaft is just used to undo the motion of the main input shaft.
Sort-of/not-really. You can think of what the control shaft does as changing the size of the gear being driven by the main shaft dynamically. Imagine the main shaft is driving the output shaft using a gear with 30 teeth. Now start moving the control shaft, and the main shaft has to move around 40 teeth to achieve a full rotation of the output shaft instead of just 30 teeth. You've "virtually" turned the smaller gear into a larger one by actually requiring an extra quarter turn around output gear, changing its effective size. The situation of this system with the control shaft orbiting backwards at that rate should be the same as a simpler system using the larger, 40 toothed gear directly connected to the main shaft. In theory, the same amount of power should be required, excluding the theoretically tiny amount of power required to orbit the planetary gear. In practice, I'm not sure that that power requirement remains tiny under load, but that's the theory, anyhow.
For instance, to go in reverse, the control shaft has to be going faster than the input shaft and would then be doing all the work.
No, the work is still being done by the main shaft, the only thing the control is doing is reversing the output gear by spinning faster than the main one. It's still the power being supplied to the main gear that's driving the movement of the output gear, and all the control shaft needs is power to keep it ahead of the main gear in terms of speed, it shouldn't need the power to push the output unless for some reason the main shaft is no longer contributing power. All it needs is the power to rotate it's little planet around at speed. As long as it can do that, the power coming from the main engine will push the output shaft around at the desired rate, including in reverse.
Furthermore it doesn't even solve the CVT part of it because the control shaft needs to be able to move through the same large range of speeds that the output does. If you had a control shaft that could do all this, why not just hook it up to the output?
Because the little electric motor running the control shaft doesn't have the power to turn the output, it just has enough to rotate its little planet around. At least in theory. In practice, I'd want to see how well this works with significant power and real loads. Again, count me as skeptical that those power requirements for the control shaft's engine remain tiny under load.
aka differential (Score:4, Interesting)
Not really new. Model T's had differentials. And why are differentials called that? Because they "difference", as in subtraction, rather like Babbage's difference engine. All this thing is doing is distributing the speeds of 3 shafts so any 2 add up to the speed of the other. The wonder is that apparently no one has applied this idea in a transmission. Maybe that's because there's some fundamental problem, like, oh, how to drive 2 shafts so that the 3rd one can be precisely controlled? I suspect the electric motor used to drive the 2nd shaft may need to be so powerful that this idea may prove impractical. The inventor tries to get around that problem by having that electric motor act more as a brake, always running at negative rpm, so to speak. Notice that "top gear" is the 2nd shaft being locked to a speed of 0 rpm. The 2nd shaft could be run forward for an even taller top, but that would take real power, so this invention doesn't do that. We can hope that it works.
Perhaps most people on Slashdot have never played around with a differential? Jack up the rear wheels of a manual transmission, rear wheel drive car, and see what happens when you spin one wheel by hand. If the transmission is in gear (engine off, of course), the other rear wheel will spin the opposite direction, at the same speed. If the transmission is in neutral, the opposite wheel and the drive shaft will spin at some rate that together adds up to the speed you're spinning. Usually, the drive shaft will spin and the opposite wheel won't, because the wheel has the greater mass and inertia.
Also perhaps most people here have never had the experience of getting one rear wheel of such a car on extremely slippery ice? I'm talking ice right at 0 C, with water on top. (Well, if that's what road conditions are like, just stay home that day.) You might think you're okay if at least one wheel can get traction. Nope! If your vehicle doesn't have differential lock, you're stuck. The one wheel on a dry surface won't move, while the one on ice spins twice as fast.
Re:Less than it appears to be (Score:4, Interesting)
The reaction torque is equal to the working torque...
No, it isn't.
- and the reaction torque path runs through that "secondary control shaft."
If either were the case, then as the secondary motor spun up either the drive motor would have to slow down or the total speed of the two drive shafts would change.
The drive motor never changes speed, and neither does the total speed of the two drive shafts.
In your scenario, the top shaft would not slow down as the bottom shaft sped up, it would simply keep spinning at the same speed. To get the system in neutral, the control shaft (and therefore the control motor that drives it) would have to spin at the same speed as the drive motor and shaft. In order to make the output shaft spin in reverse, the control motor would have to be twice the size of the drive motor!
That is obviously not what is happening, so now you have to look at what is happening. The control motor is spinning the planetary gears around the drive motor's ring gear and the output shaft's ring gear, effectively neutering all the torque the drive motor is applying. This is exactly the same as applying a clutch, without needing two friction plates - just a spinning motor and some planetary gears. When the control motor spins faster, the effect is to reverse the direction that the planetary gears need to spin to compensate for the torque being applied by the drive motor.
The only things the control motor is applying any power to are the planetary gears, and then only to affect their relationship to each other. It is completely isolated from the torque conversion loop, even though it looks like it is right in the middle of it. When the control motor is spinning at full speed (reverse), all of the power is still being supplied by the drive motor. You could swap out a bigger motor on the drive side and apply a load on the output side and the results would be identical. So long as the RPMs didn't change with the larger motor you wouldn't have to change any gearing on the control motor or any of the planetary gears.
Re:Brilliant. Go Steve! (Score:3, Interesting)
Planned obsolescence has been around a lot longer than "current fashion".
There is a story about Henry Ford - probably apocryphal, but it has the ring of truth - and the durability of the Model 'T'.
Story has it that in the 1920s, Ford sent a number of staff around the US to "beg, steal or borrow" as many scrapped Model 'T's as they could get. He then had each one stripped down and inspected to find out which components were failing and which ones weren't. The guys dismantled and micrometer-ed and recorded and collated and statistics-ed and eventually came back to Ford with a report saying, in precís, "Everything wears out apart from the flange sprocket gadgie ; we've not found one of those that's excessively worn."
"Fine," says Ford, "re-design the flange sprocket gadgie and make it cheaper and weaker. It's obviously stronger than the car needs."
Which is ha-ha-but-serious : in an ideal world, something with a 2 year manufacturer's warranty would fall to pieces, every part unusable through wear, after 732 days.
If you want something that's going to last 30, 40 or 50 years, be prepared to pay for it. An occasional acquaintance of mine works in maintenance for the electricity transmission monopoly ; the mean age of his pool of equipment was approaching 40 years the last time I stood him a pint. But you can bet that that gear wasn't brought on a tight budget from a winding shop in a distant country.