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Drive Line Components


In this section, I will cover how you take the rotational motion of the motor and convert it to smooth linear motion.Using some simple parts, you can have your machine running in no time!

For the sake of simplicity, I am going to start at the motor shaft and works towards the "toy-end" of the machine...

1: Shaft Collar

Your first task is to attach something to your motor shaft. To do this, you need to get something called a shaft collar. Like the name suggests, this is a collar that simply goes around the end of the shaft. You order these by matching the shaft size to the inside diameter, or ID, of the shaft collar.


How do they work? If you look down the shaft, you will see there is a flat edge ground in... To provide some grip, there is a screw on the side of the shaft collar. Line that screw up against the flat edge, and tighten down. Done!

To make life a little easier, you can also use a flanged shaft collar. These collar have built in mounting holes. I order these in bulk from China (they can take up to 4 weeks to arrive so patience is a must), use them in the majority of my builds, and I have them in stock if you need one. The only come in milimeter sizes, so you'll need to covert your shaft size SAE. 

2: Flywheel/PinArm

You will attach the shaft collar to the flywheel.  This will be your first step in translating rotational motion to linear motion.  The shaft collar attaches the flywheel (or pinarm) to the motor.  When the motor is turning, the flywheel will also.  You will want the the flywheel to be as balanced as possible, and therefore your pivot should be as close to center as possible.  The picture to the right is a flywheel made of oak, but they can be made of almost any type of material, including aluminum, steel, and plastic.  Depending on the strength of the material, you will probably want to offset the stroke length holes so as to not weaken the flywheel.  This is normally done in something of an "S", instead of a straight line, as shown in the picture.

How do they work? The center hole is your pivot point or rotational axis, and each hole to the side will determine stroke length.  Due to the circular motion of the flywheel, you will double the distance from the center for your stroke.  If you only want a six inch stroke, you would only have to put one hole three inches from the center of your pivot point to achieve this.  The pinarm (pictured below) has holes drilled at 1/2", 1", 1 1/2", 1 3/4", 2", and 3".  This will give you stroke lengths of 1", 2", 3", 3 1/2", 4", and 6", in that order.  It should be noted that with each jump, you should alternate sides, or you will end up with a long slot (which can be done, also, but requires a little more engineering.)


To the left is a picture of an aluminum pinarm, most of which was discussed in the paragraph above.  It should be noted that some pinarms have a set screw and attach directly to the shaft of the motor without the use of a shaft collar.

3: Rod Ends

To the right is pictured the most common rod end type, though there are many varieties.  It is instrumental in connecting the first drive arm (number 4 on our list of things to talk about) to the flywheel.  You run a bolt of some style (pictured below) through the bearing and screw it into the flywheel.  Then, the first drive arm screws into the base of the rod end.

Wing, knob, hex.jpg

Again, these bolts come in many varieties.  The picture shows a wing bolt, hex head bolt, and threaded knob.  Other options are available, but these are the most common, and you only need something to attach the rod end to the flywheel.  A note of advice, The easier it is to unscrew and select a different stroke length is normally considered a bonus.

Rod End.jpg

4: First Drive Line

The first drive line is probably the most basic and simple component the entire machine.  It is also referred to as a linkage arm, and is just a basic threaded rod that you can get from most home improvement stores or hardware department of your favorite chain.  The only notes on this piece are that it needs to be longer than the diameter of your flywheel and has to be threaded to match your rod end.

5: Universal Joint

Linkage Arm.jpg

This linkage allows the rotational motion of the wheel to be translated into a smooth linear motion along the second drive line.  It is a smaller version of the "U-Joint" in automobiles, and can commonly be purchased at hobby shops near the RC cars.

U Joint.jpg

6: Second Drive Line

Second Drive Arm.jpg

The second drive line is the last piece before we get to adapters and toys, the fun parts.  It can be a wooden dowel, a plastic rod, a broom handle, or whatever you can make work.  To the left is pictured an aluminum rod that is threaded female on one end and male on the other.  This allows it to connect to the universal joint on the male end, and platforms and adapters to screw into the other side.  Note:  whatever you choose for the second driveline has to be capable of attaching toys to it.  Almost anything can be used, as long as you have patience, imagination, and a willingness to engineer.

7: Linear Guides

Linear guides are used to stabilize the second drive line, and essentially keep the aim true.  Without these, the linear motion will tend to wobble and pivot causing stress on every linkage in the chain and possibly cause harm to the user, or at least discomfort.  Pictured to the right is a Thompson pillow block bearing, but you can use different items, such as a hole drilled in plywood or a hole drilled in a sheet of delrin.  As long as the second drive line is stable, the sky is the limit.



I will sometimes get asked if all these components are necessary to build a machine... Fair question. To the right is a video that shows exactly what you get when you don't properly turn the rotational motion into linear motion.


This is a great example of why you need the primary and final shafts... The shaft bounces up and down because there is no second hinge point. This is NOT what we want!

Bring this machine in to the bedroom and you'll find yourself sleeping on the couch! 

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