circular movment into linear

[JekylHyde]

Hi!
i have a big motor i took from a mixer (kenwood).
i want to translate the circular movment into linear (to make it move a metal bar forward & backward).
any PRACTICAL ideas? (step by step?)
i need to be able to push 5Kg objects (at least)...& to move 20cm back & forward, back & forward, back & forward... endlessly.
thanks

 

[Nigel Goodwin]

A crankshaft, like in a petrol engine - it's really a VERY simple (and obvious) technique.

 

[dknguyen]

Like on a locomotive train or car engine, except backwards. Instead of the linear piston driving the rotating wheel, the rotating wheel drives the piston.

**broken link removed**
https://auto.howstuffworks.com/engine1.htm

 

[Mike_2545]

Here is an animation of a crankshaft:

**broken link removed**

 

[Menticol]

This is very cool
https://en.wikipedia.org/wiki/Hoekens_linkage

And check his "brothers"
Straight line mechanism - Wikipedia, the free encyclopedia

 

[dknguyen]

That's pretty neat. We take a lot more things for granted now....like machining straight lines.

 

[ke5frf]

Another way to do this, same principle as the crankshaft but somewhat different, would be an obtusely shaped cam.
A rod guided by a track or guideposts of some sort is held against the rotating cam by a return spring. As the more obtuse (longer) part of the cam is turned by the motor (usually gear reduction), it pushes the rod and stretches the spring, moving it outward in a linear fashion. As the cam moves around toward the shorter, rounder part of the cam, the spring pulls the rod back to its original position.

I wish I had an animation or the ability to animate it myself.

 

[grim]

trouble with a crank shaft is that the rotation to distance ratio varies, and the toque you can get out of it is inverse to that.

how about rack and pinion?

 

[Mr RB]

Yeah but he did say it has to move back and forth endlessly, so a cam or crank arrangement means the motor does not have to be continually reversed.

A properly design "pin in groove" cam can push and pull, and can have a cam shape to give more linear force than a crank, but the crank wins outright for ease of build and reliability. If he can use the middle portion (say 50%) of the stroke range it will be close to constant force.

 

[ke5frf]

Trying this out.

Had some time, so I drew up a diagram for the linear cam model.
Maybe someone can use it.