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Turning a wheel eccentric to the motor drive without gears/belts

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Mark Fry11/02/2016 09:55:42
19 forum posts

Hi all

I have a small setup (~20cm) in which a wheel-like part (green) is turned with an eccentric drive (grey wheel) as below

The position of the green wheel is adjustable along the two grey points.

My current idea is to cut a radial slot on the wheel and design a planetary part with a slot and pin (yellow). The wheel turns the yellow part by the pin.

With the depicted position, the wheel can no longer turn anti-clockwise due to the wedge action of the yellow part.

Is it possible to have this adjusted such that the yellow part somehow gives way?

Here's the wireframe view, if it helps:

Mark

Jeff Dayman11/02/2016 13:38:18
2189 forum posts
45 photos

What wheel are you reinventing here?

You might google search "shaper bull gear stroke adjustment" for a similar but simple and proven mechanism.

(Invented in the 1880's or thereabouts by some folks much smarter than me)

Mark Fry11/02/2016 13:53:10
19 forum posts
Posted by Jeff Dayman on 11/02/2016 13:38:18:

What wheel are you reinventing here?

You might google search "shaper bull gear stroke adjustment" for a similar but simple and proven mechanism.

(Invented in the 1880's or thereabouts by some folks much smarter than me)

Hi Jeff,

I've just looked it up. Are you referring to this?

But this slides the bar horizontally whereas I'm hoping to turn a wheel eccentrically, whose axis is adjustable.

Mark

KWIL11/02/2016 14:04:49
3447 forum posts
66 photos

Just goes to show that although you can draw it in CAD it does not always work without a designer's mind as well.wink

Mark Fry11/02/2016 14:09:12
19 forum posts
Posted by KWIL on 11/02/2016 14:04:49:

Just goes to show that although you can draw it in CAD it does not always work without a designer's mind as well.wink

Well, I don't doubt that for a second. I'm very new and CAD's merely a tool.

Tim Stevens11/02/2016 14:11:44
avatar
1502 forum posts

If we knew what you were trying to drive, achieve, etc it might be easier to see what the options are.

'Turning a wheel eccentrically' might simply mean make the hole not in the middle and roll it along.

Does the wheel need to turn in a way which is not circular but (eg) elliptical?

Does it need to rotate as conventional but at a varying speed?

If you can explain what you actually want, more help might be available.

It is very frustrating to be told the bare bones of a problem ...

My wife keeps hitting me, what can I do about it?

Cheers, Tim

MW11/02/2016 14:14:20
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2051 forum posts
51 photos

Bear in mind that they probably ran these machines at fairly low RPM by todays standards (like less than 500 RPM) and with good reason also; the sliding bar/slotted lever is taking the whole force of the drive and if you're not careful it could break or shake itself to pieces at high speeds, just think of what a pulley does thats out of balance with the other.

Its very neat looking design which i applaud, but would also like you to consider the required strength in the materials and good fits to minimize the risks involved in a real working piece, there's no harm in using emery paper to improve the fit.

You could improve the movement of the Yellow component by using a roller bearing on the supporting shaft below made to fit that particular slot.

I'm assuming the "wedge" action is what also helps the momentum of the driven component and in order to change direction, it would be easier to position a kind of small"idler" wheel between the wedge and the "wall" of the bigger wheel that rubs against it and spins freely on its axis this would give you the room needed to change direction of force on the wedge without it ceasing when trying to move backwards.

I know half the stuff i say is ramble so, take what you want from the utterance, if anything

Michael W

Ajohnw11/02/2016 14:22:41
3631 forum posts
160 photos

If the pivot point of the larger wheel is fixed and adjustable that could do the sort of thing you seem to want. As drawn there isn't anything actually determining what the larger wheel rotates about so it might do any old thing.

Say you have a T slot running across the larger diameter and use that to locate the position of the pivot the larger wheel is going to spin round on. That locates the point it will revolve around. Your slot wont.

John

=

Mark Fry11/02/2016 14:42:30
19 forum posts

Hi Tim,

Sorry, I certainly can provide more detail. I'm just trying to turn the green part/wheel using a base wheel. The rotational axis of the green part is eccentric w.r.t. the base wheel. Also, the position of the green part can be slightly adjustable along the X axis intersecting the centre of the grey wheel, i.e. the red line

Note that the red line doesn't span across the entire diameter of the grey wheel, as the allowed adjustment is relatively small.

As to your questions:

- No, the green wheel needs to turn in a circular motion.

- The green wheel could rotate at any speed and the speed could vary.

Hopefully my issue is better explained. Let me know if I'm missing anything.

Thanks

Mark

Ian P11/02/2016 15:54:56
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2537 forum posts
102 photos

What rotates the green wheel?

What diameter is the (thin looking) green spindle?

When the 'Base Wheel' rotates is it the driver or the driven?

Green wheel 'Circular motion', is that rotational or orbital?

Does the 'block in slot' device traverse the slot every revolution?

Ian P

Muzzer11/02/2016 17:11:11
avatar
2904 forum posts
448 photos

Obviously you aren't going to be able to achieve any kind of reduction ratio, so the question is whether you need both wheels to rotate continuously? In the same direction? And at reasonably constant speed? In which case something like an Oldham coupling might do the trick.

Difficult to know what you are trying to achieve here. Perhaps you might show what lies beyond?

Mark Fry11/02/2016 17:24:06
19 forum posts
Posted by Ian Phillips on 11/02/2016 15:54:56:

What rotates the green wheel?

What diameter is the (thin looking) green spindle?

When the 'Base Wheel' rotates is it the driver or the driven?

Green wheel 'Circular motion', is that rotational or orbital?

Does the 'block in slot' device traverse the slot every revolution?

Ian P

Hi Ian,

Here are the answers to your questions:

- The green wheel is to be driven by the grey base wheel.

- The green spindle is about 3MM-5MM in diameter.

- The base grey wheel is the driver for the green wheel.

- The green wheel is to be rotated in circular motion. It will not orbit.

- The block in slot is part of the wheel. It's attached to the spindle, so it rotates with the spindle.

Cheers

Mark

Ian P11/02/2016 17:27:41
avatar
2537 forum posts
102 photos

Murray

Surely an Oldham coupling is going too far off topic. In any eventy I dont think the OP is trying to get any reduction ratio, it just seems he has accidentally created some sort of one way drive.

Maybe all will be revealed in time.....

Ian P

Muzzer11/02/2016 18:19:31
avatar
2904 forum posts
448 photos

Yes, I must admit an Oldham coupling does seem an unnecessarily simple solution. But we like puzzles...

Mark Fry11/02/2016 18:46:05
19 forum posts

Hi Muzzer,

Indeed, reduction ratio isn't needed. The two wheels don't have to move continuously, but need to move in the same direction.

The Oldham coupling is certainly interesting! However, my understanding is that the misalignment between the input and output shafts needs to be defined so that the coupler is manually shifted accordingly. In my case, manual configuration isn't possible, so I was hoping for a mechanism that could self-adjust to the misalignment.

I wonder if there's a self-adjustable coupling mechanism.

 

Thanks

Mark

Edited By Mark Fry on 11/02/2016 18:46:46

frank brown11/02/2016 20:00:06
436 forum posts
5 photos

The only way I can think off is to have a mutilated star and planet type drive. It could be a friction drive though. Imagine your big disc has internal teeth cut in it. If a planet wheel is mounted on the backing disc, then the star wheel's position can be varied depending where its centre of rotation was. Normally it would be fixed on the same centre as the big wheel but the the star wheel can be rotated around the planet wheel and still have proper engagement but with a different position. This would give it a different radial distance, but its angle would change wrt to the big wheel. The other slight ( !) problem is that of its speed and direction, another set of gears might be required?

Frank

Howard Lewis13/02/2016 18:01:28
5562 forum posts
13 photos

The Whitworth Quick Return mechanism was used as the drive to ram of shapers.

If a varying speed of rotation is needed and IF space is available, why not use the Whitworth Quick Return Mechanism (shown earlier) and couple it to a Con Rod and Crank to change the linear motion into rotary?

Or have I missed something, in the objective?

Howard

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