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You can also visit a version of this mechanism with dwell in here.

The Scotch Yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice-versa. The piston or other reciprocating part is directly coupled to a sliding yoke with a slot that engages a pin on the rotating part.

The advantages compared to a standard crankshaft and connecting rod setup are:

  • High torque output with a small cylinder size.
  • Fewer moving parts.
  • Smoother operation.
  • Higher percentage of the time spent at top dead center (dwell) improving engine efficiency.
  • In an engine application, elimination of joint typically served by a wrist pin, and near elimination of piston skirt and cylinder scuffing, as side loading of piston due to sine of connecting rod angle is eliminated.

The disadvantages are:

  • Rapid wear of the slot in the yoke caused by sliding friction and high contact pressures.
  • Lesser percentage of the time spent at bottom dead center reducing blowdown time for two stroke engines.

The shape of the motion of the piston is a pure sine wave over time given a constant rotational speed.

30 Apr 2013

Everything about scotchyoke mechanism....i want to know

Johann Wegmann Morovic
04 Aug 2013

Dear Gentlemen,Thankyou very much for this article.I´´ve been Reliability RCM,CAD/FEA and Simulation events user.I am

Johann Wegmann Morovic
11 Aug 2013

Dear Sirs,
1.-¿Cómo controlo el sentido de rotación en Stirling Motores?CW o CCW?
2.-¿Cual es mejor:Rómbico,Yunque Escosés,o slider-Crank,corredera ,cruzeta y biela?Confiabilidad, Tiempo entre Mantenciones. Gracias Johann wegmann

johann wegmann
07 Oct 2013

I am working in Alpha Stirling Engine,reciprocat

01 Feb 2014

""this mechanism is to be high torque to achived so many machines to be used ""

15 Apr 2014

i want to know the full dimensions of the skotchyoke mechanism

Keerthivasan Jayakumar
28 Apr 2014

Thank u for sharing scotch mechanism an it is really useful in my further projects

10 Nov 2014

thanks for sharing this mechanism on it .it is very nice to understood ,

19 Jun 2015

Do you have any calculations or spread sheets to shw velocities and torques acting on the slot

06 Nov 2015

can u pls explain why the rotation occurs always in the same direction. as far as i can see there is no reason for a random direction change at the end of the stroke. tks for explaining more.

06 Nov 2015

Dear Troll,
Thank you for your visit to my channel.
You are right, it can rotate in either way.

25 Feb 2017

I had a question, is the distance between the centre of pin to the centre of rotating disc equals the displacement made by the shaft???

25 Feb 2017

distance should be half of the reciprocating shaft stroke.

mian waqas
21 Jan 2018

i like your work

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