Mathew Boulton And James Watt Steam Engine

Mathew Boulton, 1728-1809, financed and worked with James Watt, 1736-1819, to improve Steam Engines. They entered a partnership in1775.

The design below uses a gear-pair to rotate a flywheel at twice the speed of the crank. Why was this useful? It made him a lot of money. When the flywheel rotates at twice the angular velocity, a smaller flywheel can store the same amount of energy. The energy in the flywheel keeps the engine turning as the crank moves though the bottom and top dead centres. A smaller flywheel is useful when you need to install the Steam Engine in a small spaces - such as a coalmine. On a train, you might get the engine closer to the ground to make it more stable.

A different innovation by Watt was his straight-line mechanism. (This is in Tutorial 12). He added a pantograph mechanism to amplify the straight-line motion, and so reduce the size of the engine for a given stroke of a piston. I show this in the video.

This is the Bolton and Watt Gear-Pair.

The flywheel is attached to the gear at the centre of the crank - on the right..
The straight-line and parallel motion mechanisms are on the left.
The parallel motion amplifies the straight motion with a pantograph mechanism.
Compare how straight it is to the radius of the beam arc.


STEP 1: Add a Crank - Slider Mechanism

See Tutorial 2, Step 3.

Make the SliderRed-14-1b vertical.

Apply the Motion-Dimension FBRed-14-2 to the CrankRed-14-3

Make sure the Connecting RodRed-14-4 is longer than the CrankRed-14-3

Step 1 is complete.



We need a Part for the Flywheel. Before this Patent, the Flywheel was attached to the Crank.

In this new Engine, the Flywheel is not the Crank. It is a different rotating Part that is centered at the centre of the Crank.

STEP 2: Add a PartRed-14-1b

Step 2 is complete.


We join the Part Flywheel) to the centre of the Crank with a Pin-Joint.

When you add the Pin-Joint, you must select the PointRed-14-1b at the end of the new Part, obviously, and then the Point that is a child to the centre of the Crank - not the Base-Part.

STEP 3: Add a Pin-Joint


Step 3 is complete.

We have joined the New Part with a Pin-Joint to the Crank.


STEP 4: Add a Gear-Pair

Select, in order:

4.a. The connecting Rod as the kinematically-defined PartRed-14-1b
4.b.The new PartRed-14-2
4.c.The CrankRed-14-3
4.d. The Dimension that defines the length of the CrankRed-14-4


Step 4 is complete

STEP 5: Cycle


The FlywheelRed-14-1b rotates at twice the speed of the CrankRed-14-2.

Straight Line Mechanism for Engines 1: Cartwright's Geared Engine


The Line-of-centres is horizontal.

The Gears have the same number-of-teeth

Step 1 is complete.


STEP 2: Edit Gear 2 to add a LineRed-14-1b
STEP 3: Edit the Angle of the Line in the Part so it counter-rotates the CAD-Line of the input PartRed-14-2
STEP 4: Edit the Length of the Line so it is the same Length of the Gear 1 Part.

The Line is in the –X Axis direction to the CAD-Line of the Part in Gear 2.

Step 4 is complete.


STEP 5: Add a vertical Line in the Base-Part
STEP 6: Constrain it to the Midpoint of the Line-of-centres
STEP 7: Add a Part and Slide-JointRed-14-1b
STEP 8: Add a Line so it is HorizontalRed-14-2 relative to the Base-Part (but vertical in the Part)

It is best to add the LineRed-14-2 mid-way along the CAD-Line of the new PartRed-14-1b

Step 8 is complete.


STEP 9: Add a PartRed-14-1b, approximately 2.5 times longer than the Gear 1 Part, with Pin-Joints, between Gear 1 and the Line in the Sliding-Part.

Step 9 is complete.

We would want to add a Part that mirrors PartRed-14-1b, between PointsRed-14-2Red-14-3

However, the kinematic-chain is fully defined. MechDesigner will not let you add one more Part to this kinematic-chain.

In reality, the mechanism would be constrained too much. However, backlash, play, in the bearings and gears let the machine work.

When a Kinematic-chain is Green, it is a kinematically-defined chain, and we cannot add one Part to it. We must add two Parts. That is, a Dyad.


STEP 10: Add a Dyad with PointsRed-14-2Red-14-3

I have chosen to add an R-R-P Dyad.

In the image, the Joints are:

R = Red-14-1b

R = Red-14-2

P = Red-14-3

The kinematic-chain can now cycle. The Slider in the new R-R-P does not move, but it is still needed to make the kinematic-chain. THIS IS NOT A CHEAT - IT IS A KINEMATIC REQUIREMENT. You must design the Mechanism like this or add backlash to a joint.

Tutorials and Reference Help Files for MechDesigner and MotionDesigner 14.2 + © Machine, Cam, Mechanism, and Motion Design Software by PSMotion Ltd