[BillTodd]

Fascinating gearing ideas:


EC-gearing

Videos


Bill

[RICHARD ZASTROW]

Bill, Very interesting!!!! I especially like the idea of the free piston engine in the video section. That should perk up the guys in IC Engine forum.

Dick Z

[handlewanker]

Gulp.....now we're gonna have to try and make this, in the average DIY garage workshop......on a 7X20 lathe......where's the smelling salts.......LOL.

Just when I thought everything had been done with gearing, up comes another gear drive form.....very ingenious.

It was fascinating to watch the EC type worm gear mesh with the ring gear.....worm and wormwheel but both in the same axial plane.

One thing I'd like to point out...In the EC "gearing" set-up the rollers are all sliding contact whereas in involute form gearing it's rolling contact....rolling is better than sliding for transmission without friction.

They cite the design as being very compact ratio for ratio in comparison with a similar worm geared device......this is very true, it's the low ratio pinion and gear gearbox you get when you really want the low ratio of a compact worm drive type set-up, however nothing is mentioned with regards to the backlash elimination which on examining the motion must be there or the gearing would wear itself out in a very short time.....in all cases of sliding contact you have backlash due to running clearances.

The main virtue of the design is compactness.

I get the feeling that the sun and planet gearbox, which is pure rolling transmission members using standard design involute gearing for a low ratio output is the better of the two, but if'n it proves otherwise, expect to find one of the EC gearboxes in all of the next generation of portable electric screwdrivers and maybe cordless drills too.
Ian.

[NEATman]

Bill -
Fascinating! Thanks for posting this link...

Hi Ian-
I would think that with a 4 axis machine, like in their videos, these could be made in a home shop - maybe not to the same level of precision, but they could be made. The funny thing is that this is the same machining technique that Art has been using on his Gearotic software:
Gearotic Motion Main Page

I'm not so sure it is sliding contact - it certainly appears to be, but I think it is really rolling contact. The claimed efficiency is 90% to 99%, which would be difficult to achieve with sliding contact. Also, it appears that the wider teeth in this type of gearing can transfer more load with less bending, which is where I think the increased load capacity comes from.

I agree with your thoughts on seeing this in drills, screwdrivers, etc. Especially if they could be made as powdered metal/injection molded metal parts.

Keith

[BillTodd]

One thing I'd like to point out...In the EC "gearing" set-up the rollers are all sliding contact whereas in involute form gearing it's rolling contact....rolling is better than sliding for transmission without friction.

That's exactly what I thought when I first looked at it !

It is supposed to be a rolling contact with 90-99% efficiency (i.e. at least as good as involute) Have a look at the videos of the cylindrical models - the worm is actually an infinite stack of cylinders.

Bill

[handlewanker]

Hi Bill, Unless I've got it wrong, the "cylindrical" roller rolling in a rack comprised of cylinders too can not be rolling as the form for rolling contact is involute....when the flank form becomes rounded it starts to slide and that is friction, one of the reason that ballscrew technology outclasses the Acme/bronze nut technology, rolling versus sliding......even though both have their uses.

Sliding technology comes into it's own when the parts are seperated by a pressurised oil/air film, provided the surface area to load ratio is sufficiently low so that metal to metal contact never, or seldom occurs, whereas a rolling ball will eventually fail due to it's high loading point contact.

I wonder how a drive would perform if'n the rollers were mobile and able to rotate on each other.....no sliding contact just pure rolling....Hmmmmm....it would probably fail from impact loading at the moment of engagement and load transfer.

On the topic of loading and sliding.......I think that if'n you had an Acme thead and nut with minimum clearance, you would have backlash which is an inescapable factor, but supposing the nut was enclosed in a housing and an oil pressure applied to the middle....would this then emulate an engines big end plain bearing set-up and render the backlash non existent?

The same would apply to the rotary table....pressurise the interface between worm and wormwheel and you have no backlash.....hmmmmm.

In a worm drive gearbox rotating at speed the oil film is maintained by the wedge that is generated from the entry clearance of the worm to wormwheel and drags the oil into the interface and forms the cushion that allows it to exist, but in a slow moving rotary table set-up the worm only moves when it does, intermittently practically, both forwards and backwards so the oil film cushion becomes virtually non existant.

I toyed with the idea on paper of a worm wheel that had, in place of the gear teeth, a series of rollers round the periphery, and a coarse worm pitch that made contact between two rollers as the worm rotated....there being no backlash as the worm contacted both front and back of two rollers as it rotated.

The worm in this "design" resembles an auger with it's wide spaced pitching, and the bearings on the wormwheel periphery make contact with the flanks on either side of the "auger" spiral.....all very complicated in the very best traditions....LOL....but it would maintain a backlashless contact closely rolling on a face as opposed to sliding on it.

The EC design would require hardening as well as grinding faciliies to make it work effectively.
Ian.

[BillTodd]

Try this thought experiment .

you are riding along on a nice flat road on horse & cart.

Unfortunately, the wainwright has built the wheels badly, the axle is not in the centre

You bump along, (in a cycloidal motion)

Then your luck changes. You come to a piece of road laid by the wainwright's brother.

The road surface is waving up & down in a way that cancels out the motion of the off-centre wheels.

No wheels sliding

[svenakela]

A gearing that really is producable without extreme machines are hypocycloids.
[ame=http://www.youtube.com/watch?v=cnJCWX2nr4M]hypocycloid reducer - YouTube[/ame]

We are a bunch of people using these for real, with very good result. Tested and approved.

[handlewanker]

Hi, much as I admire the ingenuity of the hypocycloid drive, I get the impression after reading the details that "it fits where it touches, when it touches".....that is, given enough time the sliding faces (they do slide, can not roll) will end up with more clearance than the worm drive which is being projected as a viable backlashless reduction drive replacement.....it can not exist without some backlash eventually ocurring, which is not adjustable, no matter what materials are used and no matter how tight the clearances initially are.

If'n you made the device with hardened and ground lobes, with minimum clearance, enough to allow lubrication and relatively minimum free movement, then by the nature of the materials the life expectancy could be quite satisfactory, but as the wear progresses the backlash would also, and when the backlash exceeds the resolution for CNC rotary table requirements, the device is scrap.....it can not be "tweaked up" to reduce the backlash, for example, as in the worm drive by driving the worm deeper into the wormwheel teeth, a common method used in all dividing heads and rotary tables where the worm is mounted in an eccentric housing to reduce the backlash.

It comes down to lifespan expectancy and reliability......made cheaply and with soft materials and thick grease lube, and you merely have another speed reducer that gives you yet another method to get lower ratios in a compact form cheaply.....very admirably performed too, and in a very neat package, but for CNC purposes, not even a starter.

BTW, if'n you want to see the method that is used very succesfully to eliminate backlash in a practical engineering every day application....I give you the dial indicator.......if'n you have backlash in a dial indicator it is useless for any test purpose.

You can verify this statement by slipping the return spring off of the spindle drive in the dial indicator and try to make sense of the dial movement when you attempt to "clock" a job true.

So, it goes without saying that a reverse loading will always keep the positional tolerance of a drive to very fine limits going forwards or backwards.

This means that if'n the Hypocycloid reducer were to have a reverse load applied constantly, the backlash would be eliminated....very true, but the wear rate would be accelerated and eventually reduce the drive to scrap.

In all forms of sliding face contact, wear is a factor that can not be ignored.
Ian.

[handlewanker]

Hi Bill, re post #5, the EC arrangement is very ingineous....it is virtually a tapered wedge driving into a cylinder against gear teeth, also at an angle, and the wedge driving sideways against the teeth drive it forwards (or backwards) and just keeps reappearing for each tooth at the start as the cylinder rotates.

The wedge principle displayed here would have to reciprocate in and out for each tooth of the gear wheel to reproduce the cyclic motion, but in the EC design this has been accomplished by the curvy worm shape that rotates as it "caterpillers" forward and sideways simultaneously.....LOL.....I've seen something like this in the spiroid gear design.

I don't think I'd like to attempt making the worm, or even the internal slanted tooth worm wheel, and the thought of trying to measure the fit in both is enough to bring on an attack of the vapours....LOL.
Ian.

[BillTodd]

HW have a read of the patents here:

Patent US20100095792 - Toothed Wheel Gearing (Variants) and ... - Google Patents

It seems to me reasonable to describe the 'worm' a rolling point contact .

Bill

[handlewanker]

AHHHHHH, now that's better.....fig 4 on page 3 of 22 shows the eccentric rolling roller in the external gear teeth, which is just like you describe the motion of the cart with wobbly wheels running on a road that matches the up and down wobble....very interesting.

It would seem from the patent illustration, re fig 4, that the roller does indeed roll cyclically on the gear teeth and not slide as I first thought.

The fig 4 illustration in the patent, although for a single 2D "slice of the action" very neatly puts the whole principle into perspective.

Keeping it simple, and referring to the fig 4 drawing for a single roller, it would appear that a single straight eccentric roller with rounded tooth form, rolling on a wheel with multi straight rounded teeth, would generate a backlashless forward or backward rotation....reversal of the roller would not mean lost motion.

The disadvantage of the single straight roller would be when it reached the top of the gear wheel tooth, and the gear wheel tooth could then slip past it......but with the phased series of rollers in a helical form and the same for the gear wheel round the gear wheel this would not happen.

This means that the roller could be "screw cut" with a rounded tooth form to give a helix that would mate with the gear teeth, which are more difficult to cut, but not so for a CNC guided tool path.

Perhaps this is the answer to the worm drive replacement.

I wonder if a stacked tooth roller could be made DIY by wire cutting hardened segments with multi tooth elements, staggered to simulate a helical roller, and be made to mesh with a similar stacked tooth gearwheel that also had the teeth staggered round the periphery, as in the original illustration of the EC design.

I don't think many of us could envisage cutting the helical form in both roller and gear in one piece and mating them together successfully, but in phased segmented slabs.....very doable.

CNC wire cutting can give you a very accurate series of "slabs", each one identical and accurate to form, that could be assemble together, and staggered to make the drive, and I would think that for practical purposes the slabs at 6mm thickness and 5 of them would yield gear of 30mm width to match a similar width worm assembly.

I think a worm is the wrong term for the helical roller, even though at first glance it appears to be a worm, as it really is a helical cranked pinion with rounded teeth rolling on the periphery of a helical gear wheel also with rounded teeth.
Ian.

[svenakela]

Hi, much as I admire the ingenuity of the hypocycloid drive, I get the impression after reading the details that "it fits where it touches, when it touches".....that is, given enough time the sliding faces (they do slide, can not roll) will end up with more clearance than the worm drive which is being projected as a viable backlashless reduction drive replacement.....it can not exist without some backlash eventually ocurring, which is not adjustable, no matter what materials are used and no matter how tight the clearances initially are.

...

FYI, they do not slide, they roll. I use a bunch of hypos and the backslash is not noticable.

[handlewanker]

Hi Sven, if'n it rolls as you say, is there any reason why a rotary table drive of 60:1 ratio without backlash couldn't be made, or is made, and how would it compare to the conventional steel worm and bronze wormwheel set-up cost wise.

I can understand the EC set-up as it is easy to see the rolling motion from the patent notes that Bill Todd posted, but the one you showed in the video of the drive is difficult to envisage.....do they both follow the same principle of the eccentric gear with rounded teeth rolling round another internal gear also with rounded teeth, but one less than the pinion?
Ian.

[svenakela]

The biggest problem to overcome with hypo's are vibrations from the assymetrical position of the internal driver. It requires counter weight and/or reduction of material to rebalance the shaft. I have a fourth rotational axis with a hypo drive.

Google or search here at cnczone, they've been discussed before.

EDIT: Great summary here.

[handlewanker]

Hi, I don't think the vibration would be a problem if'n the drive was used in place of a rotary table's worm drive with bronze worm wheel to reduce/eliminate backlash....probably only if'n you were "fast forwarding" the table round to the next co-ordinate etc.

I can not see any way that any backlash can be taken out if'n it develops from wear.....not important in a reduction drive, but totally necessary in a rotary table/positioner application, and 4th axis work is totally reliant on a backlash free device.

What would the highest reduction be in this device?

IE, can you get as high as 1:2 reduction?....this would lend itself to the 1:2 reduction that is required in a 4 stroke engine to drive the camshaft at half engine speed, so making a very compact and simple crankshaft/camshaft geartrain as opposed to the two gears that otherwise puts the camshaft to one side of the engine due to the diam of the second driven gear.....the reducer would then just be a virtual collar that fits on the crankshaft centrally, with the rotors inside it.
Ian

[svenakela]

Yes, the vibrations are there if you have higher rev's, if you stick to lower revs it's not a problem but as I said a balancing is doable. You will have high rpms's pretty quick as the gearing ratio is low. 1:2 will not be doable, for any type of oscillating gear reduction.

Wear is not an issue, my hypo's are stuffed with grease and they will run forever before backlash will become a problem. They're made in a Cincinatti CNC, and we kept the tolerances really low. Also, the contact area is way larger than for example in a worm gear or rack/pinion. There are other guys out there who made hypo's in home made CNC's and they still perform very well.

[handlewanker]

So, if'n the rotors are made initially to a slack fit, and then hard chromed to inject longevity for wear and then ground to also control the clearance, I would think that the rotary table with one as the resolver would be practically indestructible, and maybe handed down from father to son like a family heirloom....LOL.

What is the max reduction you could get from a hypo device......four ring gear lobes and three rotor lobes?.....that would be 1:4 reduction...perhaps?.....that would suit my design needs as the 1:4 ratio could be utilised with two sets of cams at 180 deg to one another.

On second thoughts, for the engine timing gear arrangement, I think that a pinion with 20 teeth and involute tooth form, running inside a ring gear of 40 teeth would do the job of 1:2 reduction without having to go to the extremes of making a hypo drive for a relatively simple problem that does not care if some backlash was present.

I think the hypo solution would also suit the drive for a chain block which at present requires a set of planetary gears to make the reduction.
Ian.

[vegipete]

Try this thought experiment .

you are riding along on a nice flat road on horse & cart.

Unfortunately, the wainwright has built the wheels badly, the axle is not in the centre

You bump along, (in a cycloidal motion)

Then your luck changes. You come to a piece of road laid by the wainwright's brother.

The road surface is waving up & down in a way that cancels out the motion of the off-centre wheels.

No wheels sliding

I don't believe this. "No wheels sliding" can only occur if all 4 wheels are in phase. (I'm not sure, but I suspect the cart would actually get 'stuck' on the section of road made by the wainwright's brother if the wheels can't slide.) The EC-gearing has created essentially a single tooth pinion. All 'layers' of this pinion rotate at the same speed yet the radius varies. With varying radius comes varying tangential speed, yet the meshing gear obviously does not move with locally varying surface speeds.

Still, a really neat mechanism. Gotta think about fabricating one...

[BillTodd]

I don't believe this. "No wheels sliding" can only occur if all 4 wheels are in phase. (I'm not sure, but I suspect the cart would actually get 'stuck' on the section of road made by the wainwright's brother if the wheels can't slide.)

You're quite correct That's where my analogy breaks down. (But who in their right-mind would make a four wheel drive Horse'n'Cart :LOL

Novikov's modification is to change the road so only one wheel touches down at a time. when this is integrated into a 'worm' the result is a smooth rolling motion.

Bill