25-06-2003 18:46

WernerNYK

Hmm, looks interesting. Perhaps some 2D orthographic views though? I can't quite make out exactly what is going on...

25-06-2003 19:00

Tytus Gerrish

Ortho-What now?

25-06-2003 19:15

WernerNYK

The standard in presenting mechanical parts. 2D Top, Front, and Side views....

25-06-2003 19:38

sanddrag

A very interesting concept indeed. There is a lego differential that looks exactly like that, just minus the motors on each side and the final drive gear on top. But since that is a differential, it would compensate for the rpm differences in the motors. I'm just not sure how well it would work with a 14,000 rpm difference.

25-06-2003 19:43

Tytus Gerrish

Thanks

But, Where Am I going to find a 14,000 rpm diffrence?

25-06-2003 19:51

FotoPlasma

He's referring to the difference between the Atwood's speed and the drill's. The Atwood is supposed to be ~5000 rpm, and the drill is supposed to be ~19000 rpm, hence the 14000 rpm difference.

25-06-2003 19:59

Madison

...I'm not sure I understand how this would work.

Shouldn't a differential have two outputs? I'll admit, though, I'm really not clear on how they work.

But, again, since the motors would each have varying RPMs. . . well, how does it work? The Drill output is 19,470 RPM or something. The Chiaphua is 5,500 RPM. They're each connected to a unique shaft and miter gear? Then those two shafts input into a single miter gear there at the bottom? That does nothing to compensate for the difference. Then, I guess, one of those original two miter gears is attached to the larger miter gear, with then gears *up* to the output?

I don't know that I follow what this is meant to do at all.

Perhaps an explanation coupled with a few less fancy drawings is in order?

25-06-2003 20:04

rlowerr_1

I did some tests with this theory out of legos.

On one side of the differential I geared a Lego motor up (40 tooth on motor shaft meshed with 8 tooth gear going to differential). On the other side I geared a Lego motor down (8 tooth gear meshed with 40 tooth gear going to differential).

The differential spun at the speed and torque of the geared up motor. The geared down motor did not have any effect on until I held the differential until the geared up motor stalled. That is when the geared down motor kicked in and spun the differential with the speed and torque of the geared down motor.

So from my findings it seems that this does not work, unless anyone can prove it correct.

25-06-2003 20:08

Gadget470

I studied it for a few minutes.. and I think it's more for a pretty picture with 3DMax than anything else.

25-06-2003 20:31

sanddrag

Well, I guess differentials don't work in reverse then where there are two motors and one output instead of one motor and two outputs. It was an interesting concept to toy with though. I wonder if there would be better results if the speed difference was not so much.

25-06-2003 22:16

Adam Y.

Yeah it really doesn't work that way. It is just the way that a differntial is designed. That same problem can be rather quite problemsome backwards also if you loose all traction in one tire. Btw After watching a few episodes of junkyard wars can someone tell me what it means to lock a differntial??? From the way it sounds it might just fix the above problem though it would probably defeat the purpose of it.

25-06-2003 22:22

Madison

Locking a differential is accomplished by physically connecting the two, otherwise separate output shafts so they act as one. In situations where an open-differential would result in getting stuck. . .where one wheel is sleep and the other is getting no torque, locking the differential would make the rear axle act as a solid piece, giving torque to the wheel that's not stuck.

25-06-2003 22:29

Tytus Gerrish

Sorry

If it is not clear how this device works i will make a more clear and understandable render with labels for now i tell you it has two inputs (the motors) and one output (the shaft on top)

25-06-2003 23:21

Madison

Re: Sorry

After spending the last few hours reading a lot about differentials and their hellspawn, I'm pretty sure that what you're attempting here will not work.

The entire point of a differential is to vary the speed and torque of two output shafts . By reducing it to a single output with two inputs, you're not creating a differential anymore. After all, what's "different" about the output(s)? Nothing. It's a single output operating at single speed at any given time.

Now, though, I think I understand what you're trying to accomplish. You're using the concept of a differential in reverse to mate two motors, and then you need two of these modules on a robot to operate both sides independently.

Based on this the mathematical relationship at work in a differential with 1:1 gearing is input = (outputA + outputB) /2.

So, for example, let's say input is 10. Therefore, it's 2(10) = outputA + outputB. While driving in a straight line, outputA and outputB would be equal at 10 each -- or the same as the input. If there is resistance against one output, more power/speed/torque will go to the output with lesser resistance. This might end up being a 12 + 8 or a 3 + 17 or even a 20 + 0 scenario.

Your idea here reverses this concept. So, therefore, out equation would read more like this:

output = (inputA + inputB) / 2

So, again for example, let's look at the motor RPMs for the chiaphua and drill under no load.

output = (5500 + 19000) / 2
2(output) = 24500
output = 12,250

Simple enough, right?

Well, now let's look at this in terms of torque.

inputA = 2.2 Nm
inputB = 1.2 Nm

2(output) = 2.2 + 1.2 = 3.4
3.4/2 = output = 1.7 Nm.

So, as you can see, the output of your differential is actually less than what you'd get from a single motor.

I'm unsure if there any circumstances where this wouldn't be the case, but it doesn't appear that there are.

I'm also unsure how things would be affected if the gearing were something other than 1:1.

If I've made some grossly wrong assumption here, please correct me. Thanks.

25-06-2003 23:34

Tytus Gerrish

OK take all that stuff And Turn it around . Look! this thing didnt come off of a truck! It Will never have to do what a diffrental on an automobile does, IN FACT it does the exact oppsite. the Cg model works, the Lego model works, the popcicle stick model works, AND THE PRODUCTION MODEL WILL WORK!

25-06-2003 23:40

Madison

If you'll read the explanation I provided at the end of my post, you'll see that, assuming I've done this correctly, the math shows that what you're doing is actually less powerful than using a single motor.

It will work, yes, but it will be completely unnecessary and act as a burden! Something working on a computer is meaningless if you're not using some hefty software to run your analysis. It looks like you're using 3D Studio MAX. That's not in the same ballpark by any stretch.

The Lego version will work, but again, you're actually outputting less torque than you're inputting on a single side. The second motor/finger/whichever is dragging on the system.

There's no need to scream. I'm sorry I wasted my time trying to explain what's actually happening here. I'll remember that for the next time.

25-06-2003 23:47

jason wright

what made you come up with the idea

25-06-2003 23:55

Jnadke

Re: Re: Sorry

You're on the right track, but you've made a few wrong assumptions. I've done some work (and a lot of math) thinking of a way to use a differential in reverse as a gearbox.

In the end, I came up with several conclusions:
1. A differential is merely a planetary gearbox, designed differently.
2. A differential is less efficient due to the bevel gears needed.

With a differential, the housing is the input, with the two sides being the outputs. A differential allows either the two sides to have the same speed and torque. It also allows torque and speed to shift to one output for the sake of turning. One of the outputs could have twice the input speed, while the other has none.

Unfortunately, with such a design, as Paul Copioli said, the power of the second ("control") motor is basically lost.

In using a differential as a gearbox, you basically put yourself back at the Thunderchicken's problems, because it behaves like a planetary transmission. You cannot have two motors with dissimilar torque and speed characteristics hooked up without experiencing motor fighting. The motor with higher torque will stall the other motor and will win every time. The result is that your robot won't go anywhere. The only way to make such a design work is using worm gears. I then determined that the Thunderchicken's way of using the worm gears would be more efficient.


If you have two motors with similar torque and speed characteristics (or geared to match), you can, essentially, create a continuously variable gearbox similar to the Thunderchicken's CCT. Using one motor to spin the housing, and the other as a control on one of the side outputs, you can simulate a load on that output. Thus, it will behave normally as a differential, achieving a variable gear ratio anywhere from 1:1 to 1:2. The maximum torque is that of a single motor, while the maximum achievable speed is twice that of a single motor, without all the quirks.

26-06-2003 00:07

Madison

So, for my reference, which of my assumptions were incorrect?

I've said exactly what you have, but without drawing the parallel to a planetary gearbox.

26-06-2003 00:13

Jnadke

Mostly the part about the power output being less than a single motor. Although, if working incorrectly, this can be the scenario, it can produce a power output that is the sum of the two motors if working correctly.


The design is hard to make out so until I can get a more detailed view, I will refrain from mentioning whether or not it will work.

26-06-2003 00:16

Tytus Gerrish

YES! THE RPM AND THE FPT GET AVREGED bUT tHE HORSEPOWER IS ADDED AND AFTER YOU take into account the fricton from the bevls wich BTY dont rotate too much Anyways I still have the most powerful robot ever!

26-06-2003 00:22

Jnadke

Currently, from what I see, your design connects both motors to the output shafts of the differential (which is connected to the bevel gears), without any attempt at matching them.

Overall, your maximum speed will be an average between the two motors while your maximum achievable torque would be twice that of the weakest motor. Once it stalls, and the breaker trips, all torque will go to the spot with least resistance, which is there.


When designing things, remember that for every action there is an equal and opposite reaction. I see too many people look at the actions and not the consequences. If something can rotate freely, it will, and the device will fail.

26-06-2003 00:35

Madison

...I think what I've discerned, and probably didn't explain to well, is that such an arrangement is capable of outputting more torque at a higher RPM than a single motor would, but not more torque overall.

Also, as best as I can tell, this new output isn't the sum of the two motors, but some average.

I don't know right now. This kid has me so confused I'm practically guessing. I'll have to think about it more using real motor data and draw some better conclusions. It seems that without gearing the motors to one another at some level, while there may be a potential benefit at some point, there'd be a greater overall loss in performance across the entire operating range.

26-06-2003 00:43

sanddrag

This seems like the sort of thing that is just easier to build and test out rather than make guesses or calculations about it's performance.

/me takes out his old lego sets

26-06-2003 01:25

Andy Baker

Tytus,

You could be on to something here. Your basic idea of coupling two motors through a differential is good and could be used in a compact manner on a FIRST robot.

However, in my opinion, you have some more work to do in order to turn this concept into a working model. I'll try to give some suggestions and clarify what Maddie and Jeremy are saying above:

1. Your 1:1 bevel gear mating of the CIM and drill motor is very inefficient. This pair of motors will run at an rpm that is higher than the 5,500 free speed of the CIM, but you need to realize that once the CIM motor gets near or over 5,500, it becomes very inefficient. Electric motors, in general, run most efficiently at about 1/2 of their rated free speed.

Since the free speed of the drill is about 20k, then you should incorporate a ratio between 3.5 and 4:1 in order to couple these two motors together.

2. Realize that bevel gears are less efficient than spur gears. I don't know the exact numbers, but I am guessing that spur gears are around 97% and bevel gears are around 90-92%.

3. It appears that you are actually speeding up your rpm's through a smaller bevel gear on your output shaft. I would suggest slowing your rpm's down. Most FIRST robots operate their wheels around 150 - 500 rpm, so you are gonna want to definitely reduce the speed of your output shaft and then do another reduction in order to get a manageable rpm.

Keep designing and good luck.

Andy B.

26-06-2003 01:45

sanddrag

Okay, I am back after a bit of playing with the Legos. I had two identical motors hooked up to the same power source. One motor was directly driving one side of the differential. The other motor was geared down 24:17 (or 17:24 depending on how you look at it). First, I ran one side at a time with the other side motor disconected and axle locked in place. I felt with my fingers the torque of the system and listened to the pitch of the sound to indicate speed. Then, I ran the system with both motors together. The speed was more than that of the geared down motor alone but less than the direct drive motor alone. The torque of the system was more than either motor alone.

So, my guess is that this design does work. The speed is averaged and the torque is added.

As for Andy Baker's post above, perhaps use a planetary differential instead like this one

EDIT:
The way that one in the pic works is the top left and bottom right planetary gears are in contact with the sun gear which is attatched to the output on one side. All the planetary gears are in contact with each other. There is another sun gear that is not pictured that comes into contact with the bottom left and top right gears in the pic. That second sun gear is on the output shaft on the other side. I hope that helps explain it. I have the unit opened up here on my desk if you have any questions.

26-06-2003 02:29

Jnadke

Really, the design isn't a whole lot different from the functionality of a planetary system. The output shafts are akin to the sun and ring gears. The housing would be the planet carrier. These similarities are in terms of functionality. If you rotate both the sun and ring gear in the same direction, the carrier will rotate at an average of both speeds. The torque will be combined.

You can't overlook these similarities, because then you will easier understand what will work and what won't. Although the torque with such a system is combined, you have to see that the maximum torque you can ever exert (for an extended period of time) is twice that of the weakest motor (stall torque). If you exert more than this, the breakers will trip due to excessive current draw. All torque will be spent on spinning the (now) dead motor, instead of accelerating your robot.

I wish I had my laptop out. A few months back I was talking with a teammate about prototyping a drivetrain with a similar idea of using a differential as a gearbox. Though, I realized these limitations, which is why I went with the idea above (using two similar motors on the housing and side input).

In all practical applications, lego "prototypes" have no usefulness for a FIRST robot beyond design concept. We have various restrictions, both electrical and mechanical, that cannot be modelled accurately. The Thunderchicken's found this out last year - the hard way. They blew motors and tripped breakers like crazy, all using a similar design. You are only doomed to repeat their failures if you fail to heed my warnings.

I do believe such a design would work, and well, but not without substantial thought and time in creating a simple and efficient design.

26-06-2003 07:58

Joe Johnson

Dr Joe speaks...

Wow, a lot of good discussion.

Here are some of my thoughts.

Jnadke is 100% correct in saying that the a differential is mathmatically the same as planetary geartrain.

Those of you who say, "the torques add and the speeds average" are essentially correct (assuming you account for ratios -- and don't forget the SIGN of the ratio too, sometimes you are adding in a negative number... ...also known as subtracting!).

People need to keep in mind that motors have a speed-torque curve for every voltage. For a given voltage and torque, each motor will run at a given speed, period. Don't forget that the speed-torque line extends into negative torques and negative speeds. By this I mean that if you can run a motor faster than its free speed by applying a negative toque. Similarly, if you apply a high enough torque, a motor will run backwards!

This second idea (that a motor can be made to run backwards even if it is trying to run forwards due to the voltage being applied), is why Paul C. has said you can only use a worm gear to drive your ring gear. Worm gears with low lead angles have the property that they are like mechanical diodes for torque -- by this I mean that torque can drive from worm to worm gear but not the other way around (it is not an exact analogy -- to be honest, I just thought of it and I have not noodled through whether I like it or not). Essentially, a worm/worm gear combo prevent the weaker motor from being driven in reverse.

IN ANY CASE... ...I will state again that there is no real magic to 2 motor systems. They act like one motor with a different speed torque curve. This is not to say that there are not advantages -- there are -- but that they do not allow you to make bricks without straw.

Here are my benefits in order as I would rank them:

1) Higher current limit (due to multiple circuit breakers)
2) Higher power (more torque at the same speeds or more speed at the same torque)
3) Cooler motors (for a given amount of mechanical power, you have more surface area to dissipate the electrical power lost -- HEAT-- AND you have the potential to run the motors nearer to their peak efficiency point which means that you have less heat generated per unit of mechanical power)
4) The ability to shift the speed-torque operating point between the two motors (this can be done in software by giving different voltages to the different motors OR in hardware by mechanically have load sharing as in the case of a differential or planetary geartrain OR by both software and hardware) -- note that this does not make a "continuously variable gearbox" but it does give you some properties of a CVT (provided that you don't look too closely at it).

I really need to write a white paper on this subject.

Joe J.

26-06-2003 12:14

Tytus Gerrish

Thanks andy and joe

I like hearing this and id like to add ThAt this Is a Demonstration Not a production The Final 2:1 bevel output is to show where the power goes In the end (now that i know bevel gears are less efficvent) they will probaly be chabges to somthing else Like a spur , Or if i could mill it a helical geer , Im sorry i use caps so mych with these guys ,there useing math to prove their point But I think they left Somthing out I take what they have said And it looks like they say I am destroying Energy Wich I Obviously cant do The idea of this device is to have the motors work in harmony at any powre arc and while being slowed down wile pushing Where normel 2-motor gearboxes Fight themselves

26-06-2003 15:51

Tytus Gerrish

ok Brandon, here is one of my better attempts at a gear, in this cace a helicial

26-06-2003 16:00

Madison

More math.

Okay, I've played with real numbers for a bit today and I've come up with this very ugly, marginally useless spreadsheet of data. It's attached to this post.

Again, this is all based on the initial equation for a differential that I mentioned earlier in the thread, but reversed for the purposes of this design.

To recap., it's:

output = (inputA + inputB) / 2

This means, of course, that our differential's range of output RPM lies from 0 to ~12,500.

Within that range, there are three distinct spheres of operation.

• In the first, found from 0 to ~2100 (coded yellow) the Chiaphua motor alone is more powerful than the output of the differential.
• From ~2200 to ~8000 RPM (coded red), the differential offers more torque than either motor could provide individually at that RPM. At best, this is ~30% more powerful than the drill and ~90% more powerful than the chiaphua as it approaches its free speed.
• From ~8000 to ~12000 (coded green) and beyond, the drill motor alone provides more torque than the differential.

Out of curiosity, I also looked at what would happen if the drill output was geared down approximately 3.5:1 so that it better matched the Chiaphua's free speed of 5500 RPM.

This is what has me most confused, now. Using the same formula, it appears as if by gearing the drill motor down, the small range where there's a benefit to the system ceases to exist. In fact, in all cases, it appears that a drill motor geared down produces more torque on its own than if it were input into this differential with the chiaphua running at its output speed.

The data for that can be found on the far right. It makes no sense to me, so perhaps there's an error somewhere. Beyond that, the original green, yellow, and red colored data seems to corroborate what Joe Johnson and Andy Baker have said -- as if they need corroborating.

26-06-2003 16:04

Tytus Gerrish

Re: More math.

Thats Because you Havent Calcuated The Hrosepower yet!

26-06-2003 16:13

Jnadke

Then you have already lost, because that's what this gearbox is actually designed to do. Such a design does give benefits over using 2 motors in a spur gear configuration, but if you implement it incorrectly, it will give you less benefits.

In using the output shafts as inputs, one shaft is designed to react off the other. This is why the stall torque of such a system is twice that of the weakest motor. Once the stronger motor attempts to exert more torque, it will overpower the weaker motor, causing it to have negative speed, as Joe mentioned.

Do not fool yourself into thinking such a design is exempt from the rules of a standard 2 motor drive system.

You seem to think that you can defy the laws of Physics with this gearbox. You cannot produce more output power than the sum of the individual motors.

26-06-2003 16:20

Madison

Re: Re: More math.

It doesn't matter. The relationships shown between torque and angular velocity across the three distinct ranges remain true when you're calculating the power output.

In the lower range, at approximately 1250 RPM, the Diff. outputs ~180 W of power. The Chiaphua, on the other hand, outputs ~ 225 W of power.

In the middle range, at approximately 4600 RPM, the Diff. outputs ~503 W of power. The drill outputs ~334 W and the Chiaphua outputs ~ 190 W. Again, this is in line with the expectations shown in my previous spreadsheet.

Finally, in the upper range, at approximately 10500 RPM, the Diff. outputs ~272 W of power. The drill? ~435 W. Again, in line with expectation.

However, despite having written all that, those numbers seem arbitrarily high. But, the relationships I've already established should remain true. Power is, after all, a function of both torque and angular velocity.

26-06-2003 18:57

Gadget470

Tytus, what I think you may not be seeing is how torque is actually there. You seem to be referencing your animation a lot. And yes, the gearbox you've designed could feasibly work. Hopefully with the new nice gears (the one you've just shown) it can be easier for some of us to understand. Even if you animate it with perfect meshing, you still can't see how much torque is coming out of the final shaft.

Relax man, we are all testing it out, physically and mathematically. It's something new, it's gotta be picked apart before it's a) crap, b) awesome, c) another design.

Nobody said you are "destroying" energy, just.. misdirecting it somewhere that you don't want it to be.

When Motor A overpowers Motor B, causing B to stall, your gearbox is basically a normal bearbox reducing Motor A's RPM, but would be less efficiant because A would be also driving B.

Your rotational energy is lost, not destroyed. It's being disapated in noise, friction, and heat. And Motor B is pulling more amps, draining the battery faster.

As has been said, If implemented correctly, this could easily be a very good design.

27-06-2003 12:53

Tytus Gerrish

KRipes! Ive been back on delphi for 3 days And Instead of hearing "Oh whatsup man Long time no see" You guys have to go out and say i am breaking laws Of Physics <LOOK! its JUST A MODEL KiNKS CAN BE WORKED OUT> im working on them all the time just be patient

27-06-2003 13:42

George1902

Tytus: Please don't take offense to anything written here. Your idea has gotten the attention of quite a few people. They're all just thinking it through in their own ways to see if the concept can ever be a reality.

As for me, I get a headache when I look at it for too long. It's like one of those "Magic Eye" things.

(On a partially related note, 10 points to anyone who can trace this "Magic Eye" movie quote to it's movie:

"Oh, it's a sailboat."

"Brenda?"

"Jerk!")

27-06-2003 21:37

Ianworld

Good thing i found this thread. I was about to try to build something like this without knowing the short comings.

From what i can tell though the real success of this type of drive would be where you put two drills( or another pair of motors) in conjuction.

Then drive one forwards at 100% power and drive the other in the other direction at 95% power. In a simplified system this would cause one to drive at its rated 19,470 rpm and another at 95% of that or 18500. The result combines these two rpms.

It would be 19,470 minus 18500 because that one is going backwards which results in a sense a negative rpm. This gives an rpm of about 1000 with twice the torque of the weaker motor or 190% of the torque of a drill motor. All the power with a 19.5 to 1 reduction.

you can then of course put both those motors driving forward at full power together to get about 40,000 rpm at full power with 200% torque. 40 times faster than the example i showed above. The problem of course then is finding ratios in the middle that work well by providing adequate rpm's and torque.

[edit] Hours later... I built a small differential out of legos and from what i can tell the first experiment is a failure. The torque appears to be much less when one is run backwards and rpm i subtracted from one motor. The result appears to be that it slowed down as predicted by adding the rpms together BUT the torque appears to have dwindled. Unfortunatly i don't have a way to measure the torque so i can't say how much.

28-06-2003 00:30

Gadget470

Tytus, as I said in my post... we aren't saying you are breaking the laws of physics. The "lost" energy, isn't really lost. It's just not where you may want it (if implemented incorrectly).

By "Lost" we mean "Not going where we want it to be"


And for My 10 Points... the movie is "Mallrats"

28-06-2003 01:54

Ianworld

okay i think i've found an answer? solution? complexity? idea?

Either way its called the torsen differential. The whole point of it is to overcome the limitation of only being able to supply 2 times the torque of the weaker motor. A torsen differential which is used on the Hummer allows the motor to supply up to 6 times more torque to one output shaft than to the other output shaft. The question i have though is what happens if we use it like these other differentials are thinking of being used?

here are some links about the torsen differential:

A white paper on the Torsen differential: http://www.sonic.net/garyg/zonc/Tech...ferential.html

and Howstuffworks.com's comments on the torsen: http://auto.howstuffworks.com/differential8.htm

28-06-2003 13:35

Tytus Gerrish

ErrehhH! I need asprin....
Ill work it out!

But still In spite of its disadvantages it will Combine the force of two motors over a larger power arc than any ideas ive seen yet ,wich Work! but when theyre slowed down By puching Or accelarating They will not Be as efficent as My device

28-06-2003 13:41

FotoPlasma

Not that I want this not to work, but just out of curiosity, do you have any pieces of mathematical proof of your statements and assertions?

29-06-2003 12:09

Tytus Gerrish

You need the math Huh!

Well, I dont have the numbers BUT!, why dont you ask the people who make Dual-engined Helicopters and helicoptor engines and the gearboxex that merge their power. ie, General Eletric, Sickorsky, Alison, Lycombing ,Textron, Etc....

Dont Get me wrong The constructive critisim is good But some of you can ,Realy Push it!

29-06-2003 14:49

Madison

Re: You need the math Huh!

I'd bet that those people did a lot of math and analyses of things before they ever set pen to paper, so to speak.

I'm not one to throw around praise of respect lightly and I think most people aren't. Show us something that proves this concept works, either through your own calculations or by those of someone else, and you'll earn more respect.

If you don't want people to offer suggestions, criticisms, or flat out tell you that your idea sucks, don't post it online. That's the nature of the internet. You've given nobody any reason to expect that your idea he has any worth.

I see a nice picture that copy-cats something you may have seen somewhere else. It shows no appreciation for the knowledge required to pull it off. Sure, there's a potential for it to evolve into something useful, but that potential is completely meaningless unless you're willing to harness and go to the next step. Making grammatically horrendous claims that we ought to trust you and that it will work is a waste of my time.

I'm not going to blindly praise you. Show me a real reason or leave me alone. A lot of the mentors here, me being in a different, lower realm entirely, work their behind off to make sure that their students have a real grasp of the concepts at work and that they're not making stuff up and getting lucky by it. It's insulting to them that you write off their contributions with your assumptions and crass attitude.

29-06-2003 15:49

Tytus Gerrish

M. Krass

Although I do Love your Critical essays To me All you realy had to say was....

"So tytus, You dont have the numbers?"


And here is an intresting pdf...
www.army.mil/usapa/doctrine/DR_pubs/ dr_a/pdf/fm1_514.pdf
id like to point out the part on the combining transmition
Im still looking for more info... so its on the way

29-06-2003 18:07

Gadget470

... and she's right. You just say "add everything and it's better"

Perhaps create a white paper, one with calculations, better (and by better, I mean easier to understand) drawings with less fancy textures, and then really ask what people think.

29-06-2003 19:19

Ryan Dognaux

Hey Tytus - just curious, did you make all that in 3D Studio Max, or did you import some stuff from CAD/Inventor into 3D Studio Max??

Also, taking in some of what people have said here.. it is true that you can't really judge any real-world attributes of objects in 3D Studio Max... unless you have certain add-ons/settings that allow that... Inventor/CAD would be a much better help if you try to do some math and test some things before ya build it.

Design looks interesting, keep at it

29-06-2003 19:56

FotoPlasma

Re: M. Krass

Here's a working URL for that PDF.

<edit>
Because of the fact that that PDF is image based, you can't search through it. Also, actual information pertaining to a "combining transmission" seemed a little lacking. This irked me a little, so I searched around a little.
</edit>

Other than that, upon my own investigation of "combining transmissions," it seems they're only used in rotary aircraft (helicopters [namely the Chinook] for the most part).

Here's another website that explains the CH-47 drivetrain's usage of a "combining transmission," or "C-Box," as they like to call it. The images on their website are artificially shrunk, so here're some links to the actual full-size images:

Diagram of CH-47 drivetrain, focusing on how the assembly is integrated into the body of the aircraft.

Conceptual diagram of the actual mechanical set-up of the system.

Assuming the engines are the same, in the concept diagram, they output 15066rpm, which goes through a ~1.23:1 reduction, taking it to 12263rpm, which goes through another reduction of ~1.77:1, taking it to 6912rpm, which goes to the two independant (somewhat) rotors, which have their own ~30.72:1 reduction, before the output shaft (the rotor) which is a nice and manageable 225rpm.

I have no idea what I added to this thread, probably nothing, but there's a little more information about practical usage of this kind of system. *beats a dead horse*

And just for the record, I still love Google.

29-06-2003 20:26

Madison

Re: M. Krass

Well, whatever. I'm tired of this, so I'm done.

If you can manage to build it and make it work, good for you. If you happen to manage to do that by pulling it straight out of your behind, I don't care. I've done what I can to provide a better explanation as to how and why this may operate and how and why it can be improved. If you're not interested in learning from that, I'm not interested in providing it.

You have a lot to learn about everything.

Good luck.

29-06-2003 20:35

Tytus Gerrish

ok... Ill build it, ill prove it works, Ill change the way multi-motor drives are built Forever!

(ok, getting a little ahead of myself there.... ,At least ill build it)

30-06-2003 00:31

Ianworld

A friend of mine directed me towards the Toyota prius (and i suppose other hybrid cars.) They have two inputs at varying speeds and combine them to produce one output. Unfortunatly i haven't been able to find a good source of information on the topic of their transmissions but i'm still searching. Might be good place to look for more info.

I'm starting to edge towards beltless CVT though...

30-06-2003 10:17

Matt Attallah

I was under the impression that they used one or the other - not both. When it needed heavy acceleration it used the gas engine - but when it was coasting or anything like that - it gave the power from the engine to the generators so the gens. can charge the battery while the electric motor was being used...


But if they do use both at once - they can use a viscous coupling, and I'm sure that can help in its moments...

30-06-2003 14:23

FotoPlasma

I am absolutely not an automotive expert, so I apologize in advance if I'm just being stupid (not to mention the fact that I just woke up).

That said, after a little searching, I found this, a comparison between the Honda Insight and the Toyota Prius regarding their drivetrains.

According to the various diagrams of energy flow (mechanical and electrical) in various states of use (stationary, starting up, accelerating, cruising, and decelerating/regenerative breaking), it seems as though both the electric motor and the internal combustion engine are used in tandem much of the time, in the Prius (and obviously less of the time in the Insight, but it still happens).

30-06-2003 15:37

Jnadke

The Prius uses electric generator/motor at different stages in the drivetrain. Primarily, the gas engine exerts power into a planetary gear system. One part of the planet is connected to a generator. The other part is connected directly to the wheels. As the engine rotates, it exerts equal torque on both the wheels and the generator. As the generator produces more electricity, it exerts more torque as a reaction, thus, the engine can exert more torque on the entire system. Basically: The torque is split between the wheels and the generator.

The neat thing, however, is that the power created by the generator (when the batteries are full), is sent to a motor that is directly connected to the driveshaft that, ultimately, leads to the wheels (after the planetary gear system). So, contrary to belief, the Prius planetary gearbox does not have two inputs. Its planetary gearbox actually has one input and two outputs. The only exception to this is when it is using regenerative braking.

1. You can't get any more efficient than 100%. Traditional gearing will combine the torque while still allowing the same top speed. Do the math and you end up with the same power output as the sum of the two motors.

2. If you've learned anything from the explanation of the Prius above, you cannot exert more torque than the weakest motor (believe me, if Toyota could operate at greater than 100% efficiency, they would). Once you do, it will act as a generator. The power output of the remaining motor will be split between the wheels and the generator. The bad thing is, all the speed controllers do with this generated power is get rid of it, as heat. Basically, this limitation makes this system bad for pushing applications (when using motors with dissimilar torques).

3. Actually, I got the idea from a patent when I was surfing the internet. Technically, it's not your device. It belongs to the guy that patented it. Beyond usage for non-profit applications, you have no rights to it.
Differential electric engine with variable torque conversion
Continuously variable transmission system
Continuously variable gear drive transmission
Electric constant speed/variable speed drive/generator assembly

There's a lot of neat stuff floating around in the patent database. All of it is free range to us since we're using it not-for-profit. Sometimes when I have an idea I search there to see if there's a better idea or to see if it's feasible.

Thank you. You really have to realize what the two parts independently are doing, and then piece them together. Instead of being an input, pretend it's a fixed shaft. You'll then realize that such a system does provide some benefits, but also has some quirks. Such an idea could succeed if you could develop an easy mechanism to mechanically stop the shaft and hold it in place. The Thunderchickens did so using worm gears. The bad part is that worm gears are 75% efficient at best. A more realistic estimate is 50%.

30-06-2003 15:58

Joe Johnson

50% is good...

Worm & Worm gear combos are not typically even 50% efficient.

There is a very good match between effeciency and backdriveability so in the case of the the Thunderchicken drive, they were probably way under 50% or else the system would have been backdriveable.

Joe J.

01-07-2003 12:34

Tytus Gerrish

A Dual-engine helocopter Roto-train

01-07-2003 16:14

sanddrag

That's pretty neat however is appears that each motor would be spinning at the same speed. Have you tried it with different gearing on one motor?

01-07-2003 16:27

Gadget470

Urmm.. having them at different speeds (in that orientation) will definitly cause a generator. Give it a whirl, program the rcx so one is going 100% and the other 50-80% Should be some interesting results.

Edit: If you have a rotation sensor, maybe you could get some good feedback?

02-07-2003 16:45

Tytus Gerrish

thats exactly what i did Boyo!

02-07-2003 17:07

Gadget470

And the feedbacks?

02-07-2003 17:07

Jnadke

Then put your finger on the blade and watch what the system does. You'll notice that such a system doesn't stall, which can be good and bad.

03-07-2003 00:01

Ianworld

I tried what you just tried and from using just my hand to feel the torque i was pretty sure the torque was less with one motor geared down a bit, but i don't have a way to measure it unfortunatly so i could be wrong.

03-07-2003 00:06

sanddrag

my studies