# Transforming Motion In Opposite Directions

1. Feb 1, 2016

### Sirsh

Hi All,

I have a project I am working on, I'd like to know if anyone knows of/or has seen it been done. I want a mechanism or method that allows me to change the direction of rotational motion that I am applying.

For example, I want to rotate a crankshaft in one direction (say forwards), but want a fly wheel to rotate in the opposite direction. These need to be connected simply if possible.

Anyone have any ideas or suggestions?

Thanks!

2. Feb 1, 2016

### Sirsh

In addition: I want this to be in the sense that if gears are used then they must be 'sandwiched' or parallel to each other.

3. Feb 1, 2016

### billy_joule

I guess you've considered gears or pulleys, so what is it that makes unsuitable?

4. Feb 1, 2016

### Sirsh

I want to ideally have some type of gear mechanism on the crank shaft (the crank shaft can be split into two components with pedals on each section) that allows the flywheel to also be on the same axis of the shaft, I do not know if this can be done by gears? gears seems to have to be on separate axes of each other.

The mechanism of the 'herringbone' gear is the motion I want, but it would require that the crank shaft and flywheel are not on the same axis, if that makes sense.

5. Feb 1, 2016

### billy_joule

A planetary gearset is coaxial and can reverse direction. Though, I don't think a -1:1 ratio is possible.

A herringbone gear reduces thrust force but otherwise functions as any other gear type, so I'm not seeing their relevance.

https://en.wikipedia.org/wiki/Herringbone_gear

6. Feb 1, 2016

### Sirsh

Perfect! A bit of modification to the basic idea of planetary gear sets and it'll serve my purpose.

Do you think that the manufacturing cost for planetary gears would be less than those of herringbone type gears?

7. Feb 1, 2016

### billy_joule

Any gear type can be used in planetary gear train, including herringbone type gears.

8. Feb 1, 2016

### Sirsh

Wouldn't that be bad? As their mechanism wouldn't be utilized and I'd assume that manufacturing their thread type would be more complicated than a normal type of gear?

If you were to have theoretically a planetary gear in the middle of a relatively heavy fly wheel would the heaviness of the fly wheel cause the ring gear to not rotate and cause only the sun gear and planet gears to rotate (given that the sun gear is already rotating)?

9. Feb 1, 2016

### Nidum

One of the sun gear , spider or ring gear needs to be locked to ensure positive drive .

Choosing which component is locked and which is input and which is output of the other two determines the effective gear ratio and direction of output rotation relative to input rotation .

https://en.wikipedia.org/wiki/Epicyclic_gearing

10. Feb 1, 2016

### Sirsh

Thanks for the link, I couldn't see any diagrams that depicted the rotation of the three elements when one of each were locked.

If you lock the spider/planet gears, would the sun and ring gears rotate in opposite directions?

11. Feb 1, 2016

### Nidum

12. Feb 1, 2016

### Sirsh

With all gears freely moveable, it works ideally. But if I had a relatively heavy flywheel as the ring gear and a crank as the sun gear, would the ring gear cease to move, causing the planet gears to rotate instead, along with the sun gear?

13. Feb 1, 2016

### Sirsh

Maybe if I had a plate that fastened the planet gears in place then it would work?

14. Feb 1, 2016

### Nidum

Yes - with the spider prevented from rotating you then have positive drive from crank shaft to flywheel .

15. Feb 1, 2016

### Rx7man

Take a look at a differential gear, you'd lock what is usually the crown gear, and the spider gears would reverse the direction in a 1:1 ratio.. For light loads, 3 gears are needed (2 side gears and 1 spider gear), but additional spider gears can be added to increase load capacity.

16. Feb 2, 2016

### Sirsh

Cheers Nidum, I'm thinking that if i can some how manage to fix the spider gears. Then use two planetary gear sets, with both sun gears attached to my crank (crank is in two equal sized parts), and then connect my fly wheel to the two ring gears, I may be able to achieve the rotation I require.

17. Feb 2, 2016

### Nidum

That seems to be a very complicated arrangement . Post a sketch of the crankshaft , flywheel and bearings and we'll see if something simpler is possible .

18. Feb 2, 2016

### Sirsh

This is a quick representation of what I'm thinking of, which may be unrealistic. The grey is the crank shaft, the magenta is the fly wheel, red is the ring gear, green is planet gears, yellow is sun gear. These aren't the arrangement or number of bearings etc, but shows the general idea.

I want the grey crankshaft to rotate CCW while causing the magenta fly wheel to go CW.

Note the planet gears will be fixed in some manner also.

19. Feb 3, 2016

### Rx7man

Here's what I drew up to clarify how I imagine it... green is your input shaft, the yellow gear (spider gear) is held from rotating around the input shaft's axis , but can rotate around it's own axis, which powers the side gea on the flywheel (blue).. Red is the rollers for the flywheel

You can pair and add more spider gears if needed, I didn't want to clutter the drawing with additional ones.

20. Feb 3, 2016

### Nidum

@Sirsh :

We would probably be able to give you better design help if you told us what you are actually trying to do in your project as a whole .