# What makes a connecting rod turn a crank one way?

This may be the most awkward unexpected question ever concerning the reasoning for which I ask it.

I begin with explaining the reason because I think you should know why I ask this question to begin with so you can understand what underlying basic principle of this mechanic I want to understand. Namely the fundamentals of it and how it gets physically transferred internally.

I need to actually understand how it works rather then be told what makes it work.
I'm not a car mechanic and have never worked with combustion engines, pistons or cranks ever before in my life.

Reason: The reason for what I'm about to ask actually involves a video game that is called Kerbal Space Program. It is normally intended to build rockets and aircraft out of individual parts. Each of these parts having physics properties to them with which you can build vessels.

There is a holy grail in this video game to find methods of self sustaining physical generators by the use of a few parts and mechanical setups to basically cheat the physics engine of the game and create methods of propulsion with little energy or no energy input at all. You have to play the game for quite a while and be involved with the community to know how that could be done in the first place but there are already methods to do so just not working concepts to do much with it other then to build slow propeller aircraft.

I have worked long on something and made a reciprocating piston that can deliver potentially infinite impulse only limited by the custom cylinder housing and the custom spring that is supposed to retract the cylinder that repeats the process.
The actual part that creates the energy is a rotating part that creates infinite torque which can be nested inside the cylinder that combines with another custom spring to push and retract the piston.
The reason I use this infinite torque part to drive a cylinder and not transfer the torque directly is because the infinite torque part will break any custom gearing while with the piston setup I can kill the motor where it can still spin freely.

To this piston design I can make a connecting rod turning a wheel. Because the rotating parts torque is infinite driving the cylinder the cylinders impulse is infinite and because now the wheels torque is infinite a gear system driving the propeller also has infinite torque and this should theoretically create a infinite torque propeller (a.k.a. high speed aircraft) to lift very heavy payloads into the air.

The reason why I explain that whole story above is if you were interested. But more importantly so that you understand how fundamentally I have to understand the actual mechanism what drives a crank through a connecting rod one way as I have to replicate it in a game where some parts of the physics are arbitrary and where I have to recreate the same system out of individual parts not intended to be used for what I try to build.

MORE ON TOPIC:

The problem is the connecting rod turning the wheel. Whenever I stop the infinite torque motor the piston rests in it's retracted position because the spring retracts the piston.

In a actual combustion engine this is done with air/gas pressure through combusting fuel, in this game it is mechanical force and there is no other way to do this.

Problem: The problem is when the piston becomes fully retracted the connecting rod rests on the center of the wheel in the very middle. Whenever I restart the engine there is a chance that the connecting rod starts turning the wheel the other way and any propeller/impeller or other propulsion mechanism attached to it will then make the vessel go backwards.

Question: So how does this work in real life then? I don't know...

Why does a piston that moves a connecting rod always turn a wheel or crank one way and not the other way around after it rests and then restarts?
The connecting rod rests on one side of the wheel in the pistons retracted position where it can push the wheel one way or the other. I don't know what to create so it always starts pushing it in a forward motion.

How does this function work internally and why is this always successful in real life engines?

Is there any difference how this works in let's say a steam engine like that of a train locomotive opposed to a piston engine? Either of two methods may be applicable to engineer in my video game.

There's a lot of clever appliances one could use in this game to create various mechanical interactions to recreate real life mechans using the parts available. So if the physics of the real life mechanics are part of the physics calculations in the video game that I play there should theoretically be a method to replicate it just as I created a piston and connecting rod to begin with.

But there's also a chance that it is impossible, or rather, me unable to find a way lol.

What do I need to learn?

CWatters
Homework Helper
Gold Member
I built a crude steam engine once and it would run equally well in either direction. I have also had model aircraft engines accidentally run backwards.

Car engines have an electric starter which turns the engine in the correct direction initially and flywheel that provides inertia which keeps it turning that way.

Edit: Steam engines control direction by changing the timing when steam is injected to either side of the piston..

https://en.m.wikipedia.org/wiki/Walschaerts_valve_gear

Nik_2213
@CWatters

Thanks, didn't expect such a quick reply :)

There is a method in this video game to kick start the initial motion although it will not make the process automatic and probably hazardous the way the game physics work. A minor inconvenience but I was hoping for a automatic mechanism.

Do model aircraft not have starters? What is done to fix it when it starts running backwards?

How does it work for a steam locomotive?

Maybe besides trying to answer my question as it stands I could have better asked a secondary question which is if there are other methods to turn reciprocating motion into rotary motion in any other way then using a rod and a crank.

As long as it can be devised in the game I play it doesn't necessarily have to be a rod with a crank but that's the only way I know of personally.

CWatters
Homework Helper
Gold Member
Do model aircraft not have starters? What is done to fix it when it starts running backwards?

Some small model engines have spring starters built in. Most are either hand started by flipping the propeller or applying an electric starter to the spinner.

Occasionally when hand flipping the propeller the engine will fire during the compression stroke, kick back and run in reverse. Mainly an issue for diesel or glow plug engines where the timing isn't well controlled. Usually the pilot throws a rag into the prop to stop it or cuts off the fuel supply.

This mechanism appears to do what you want. Unfortunately the video is a bit fast to see whats going on clearly but the centre gear always rotates in the same direction.

HeavenFun
Hi ! IIRC, early steam engine designers went to a lot of trouble to devise 'parallel action' machinery to get around the basic patents for cranked pistons. IMHO, those much-lawyered patents delayed the spread of steam power by several decades, just as the Wright Bros' later almost did for flight.

FWIW, there are some interesting takes on, um, off-beat machinery at...
http://www.douglas-self.com/MUSEUM/museum.htm

( Nike-note: Care, you may lose entire evening browsing there... )

IIRC, Edison (US) and Swann (UK) began a similar patent battle over light bulbs etc, but saw this was bad for business and settled amicably. May be why 'Edison' bulbs have screw thread, yet UK's are 'bayonet'. YMMV...

HeavenFun
@Nik_2213 Any insight regarding any mechanism that includes cranked pistons for steam locomotives could be incorporated in my design. I don't know yet so I'm here more or less to gather any mechanical way to achieve what I'm after. It's a journey to find out what works in the game which could be a multitude of ways. Piston designs are actually already made in the game just not with a spring mechanism that retracts it which is bloody necessary for my design to work which is new and uncharted.

I do want to share some links involving the game and what people like I try to make so people can get a idea. The infinite torque motor is something new I'm not willing to share yet but here are things some people make (not me) with non traditional propulsion methods.

The first 2 are more concept videos then usefull applications but cool nontheless.

FWIW, there are some interesting takes on, um, off-beat machinery at...
http://www.douglas-self.com/MUSEUM/museum.htm

( Nike-note: Care, you may lose entire evening browsing there... )

A evening? Probably much longer lol. Cool source :)

Baluncore
Why does a piston that moves a connecting rod always turn a wheel or crank one way and not the other way around after it rests and then restarts?
As a crankshaft turns, inlet and exhaust valves are opened and closed so as to produce rotation in the required direction.

Steam engines, pneumatic or hydraulic motors, and two stroke IC motors can use simple valves, such as reed valves and openings in the cylinder wall that are uncovered by the piston.

Four stroke motors have a camshaft that is driven at half the speed of the crankshaft. The camshaft operates the valve timing or phase which decides the motor direction of rotation.

Tom.G
Look at the radial engine for a clue. You can use three pistons positioned radially such that only one can be at fullly retracted at a time. You then sense which piston to energize to rotate the crankshaft in the desired direction.

Cheers,
Tom

CWatters
tech99
Gold Member
The little synchronous electric motors used in electric clocks can run either way. But there is a ratchet device to stop this. It has a spring, which, if the motor starts the wrong way, bounces it back in the correct direction.

anorlunda