Mechanical Design

Simulation
1

Hello Community,

I am looking for help with the design of a mechanical system.

Conceptually, I have an arm attached to one end on a device that oscillates 45 degrees to the left and 45 degrees to the right from its vertical position. At the other end of this arm, I have an axis. I would like the arm to rotate from its left position to its right position, which is about 90 degrees, and when it rotates 180 degrees and when it goes from the right to the left position, which is still 90 degrees, the axis this time rotates 360 degrees.

I'm looking for a mechanical solution without putting a motor on the axis.

If anyone has an idea, I would appreciate it.

Have a nice day 

2

A small simplified diagram would surely help to understand the subject.

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3

Hello Nicolas,

Indeed, a small diagram could allow you to better understand your problem.

But if I understood correctly, I would propose this concept:

an arm with a double set of belt/freewheel by playing with pulley diameters to vary the angle of rotation of the axle at the end of the arm.
- a freewheel that drives the left belt when you pivot to the left, with a 2:1 ratio between the pulleys to amplify your rotation from 45° to 90°
- a freewheel that drives the belt on the right when you pivot to the right, with a 4:1 ratio between the pulleys to amplify your rotation from 45° to 360°
 

Provide belt tensioners that fit well. It's 100% mechanical, without an actuator, but be careful with the size, torques and speeds!

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4

Thank you Icome for much appreciated help. Indeed I should have made a diagram for a better understanding.

Based on your diagram (thanks to you), I'm trying to make the axis at the end of the arm do 180° when you go from position 1 to position 2 and 360° when you go from position 2 to position 1. I think that with your belt/freewheel system, it must work but how to go from one belt to another depending on whether the arm goes from position 1 to position 2 and vice-versa? 

Thank you again for your attention.

5

@icome gave you a solution:  freewheel

https://fr.wikipedia.org/wiki/Roue_libre

6

It's a solution in 2 parallel belts (1 for each direction) hence the problem of clutter that it can pose described by icome.

Small precision, should the movement of the axis be proportional to that of the arm? (which is the case with the belt system)

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7

Hello again to all and always thank you for your contributions.

I can now see a little more clearly. And yes FUZ3D, the proportionality of the axis/arm movements is what I was looking for.

I'm going to move forward in this direction on my prototype. I will keep the community informed of my progress

Thanks again

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8

Hello

As the transmission ratio is different depending on the direction of rotation of the arm, only the solution by pulleys and belts (or chains, or gears if slippage is not allowed) can be suitable, associated with two freewheels of the pulleys in connection with the frame.
The attached video illustrates the principle of operation.
The pulleys are exaggeratedly magnified, in order to better distinguish movements. In fact, it all depends on the size of the mechanism...
Important note: Since the axle-linked output pulley is driven by the arm, the gear ratios are not 2 and 4, but 3 and 5.

Kind regards.


conception.avi
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