<< Click to Display Table of Contents >> Navigation: Getting Started Tutorials - MechDesigner > Tutorial 14: Gear-Pairs / Rack-Pinions > Historical Applications of Gear-Pairs |
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 centers. 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 10.4). 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 example is a from the Boulton and Watt Steam-Engine. •The Part that is kinematically-defined is the Connecting-Rod of the Crank-Slider mechanism. •The Line-of-Centers is the CAD-Line on the Crank. •The Driven-Gear is on a Part with its axis at the center of the Crank •The flywheel is attached to the Driven-Gear at the center of the Crank. |
||
STEP 1: Add a Crank - Slider Mechanism See Tutorial 2, Step 3. Make the Slider Apply the Motion-Dimension FB Make sure the Connecting Rod
|
||
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 Part that that rotates around the center of the Crank. STEP 2: Add a Part We join the Part Flywheel to the center of the Crank with a Pin-Joint. When you add the Pin-Joint, you must select the Point STEP 3: Add a Pin-Joint 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 Part 4.b.The new Part 4.c.The Crank 4.d. The Dimension that defines the length of the Crank STEP 5: Cycle
The Flywheel |
STEP 1: Add a Simple Gear-Pair - Option 1 The Line-of-centers is horizontal. The Gears have the same number-of-teeth |
|
STEP 2: Edit Gear 2 to add a Line STEP 3: Edit the Angle of the Line in the Part so it counter-rotates the CAD-Line of the input Part 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 5: Add a vertical Line in the Base-Part STEP 6: Constrain it to the Midpoint of the Line-of-centers STEP 7: Add a Part and Slide-Joint STEP 8: Add a Line so it is Horizontal It is best to add the Line |
|
STEP 9: Add a Part We would want to add a Part that mirrors Part We must add two Parts. That is, a Dyad. THIS IS NOT A CHEAT - IT IS A KINEMATIC REQUIREMENT. In reality, because the two sides of the mechanism cannot be an exact mirror, there must be enough backlash to accomodate the differences. In Kinematics, Pin-Joints do not have backlash. |
|
STEP 10: Add a Dyad I have chosen to add an R-R-P Dyad. - I could also add an RRR dyad, with one very short Part at the Point 2 or Point 3 In the image, the Joints are: R = R = P = 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. |