Train Assembly

Fig. 1

Instructions:

Be sure to have the parts for the Train completed before attempting this tutorial. Start a new Assembly File (Standard.iam). From the right click menu, select Isometric View. From the Assembly Panel Bar Menu, select Place Component.

Fig. 2

From the Open File dialog box, select your trainbody.ipt, and press Open. When the instance appears on your screen, use the Right Click Menu and select Done. You should now have a train body on your screen. The train body

being the first placed component will be Grounded. This means the train body will be in a fixed position.

Fig. 3

Select Place Component again and select your trainwheel.ipt. Left click in four places near each other to place 4 instances of your wheel. Now right click and select Done from the menu. Your assembly should look like this.

Fig. 4

Use the same procedure to place the four wheel pins into the assembly. At this point it might be easier to attach the wheels and wheel pins before placing all the components in the assembly and constraining them. When applying Constraints, you will have to rotate the assembly to see what you are doing. You can use the Rotate command any time during the process by selecting the rotate button, rotating the part, and finishing by right clicking and selecting Done. This will leave you in the command where you left off.

Fig.5

From the Assembly menu, select Place Constraint. Select the Insert button. Select the hole on the flat side of the wheel. If the arrow doesn't point out, go

back to the dialog box and depress on the Number 1 button and position the cursor over the center hole. Right click and select Other, and click on one of the arrows until the constraint arrow is what you want.

Fig. 6

Select the check mark in the center of the box.

Fig. 7

Now select the hole in the train. The wheel will fly into place. Change the Offset to .01 and click the Apply button. Repeat the process for the other three wheels. If you forget to change the offset to .01 just edit the constraint from the browser. We will now place the pegs in the holes to hold the wheels on. From the Assembly menu, select Place Constraint. Select the Insert button. Select the peg at the widest point. Be sure the arrow points toward the narrow end. Select the center of the wheel and point the arrow out. Again you want .01 as an Offset to allow clearance for the wheel to turn.

Fig. 8

Do this for all the pegs. At this time you should be able to rotate each wheel individually. With the cursor pick a wheel and spin it. Later we will constrain all the wheels to move in relation to each other. Place Component and select the trainstack.ipt .

Fig. 9

From the Assembly Menu, select Constraint.

Use the Insert constraint. Select the bottom of the small part of the stack, and the bottom of the hole in the top of the train body. The Offset should be set to 0.

Be sure to click on Apply or OK. Either choice will make the constraint permanent. Note: It is very helpful to have the Show Preview check box selected when placing Assembly Constraints.

Fig. 10

You should save your File periodically. Sometimes you need to change the color of the parts so you can see them more easily or to better represent a design. To accomplish this, highlight the part name in the Browser or select the part itself. Right click and select Properties>Occurrence. Select the color of your choice.

Fig. 11

You can make a choice. You can place the linkage arms with pins and constrain them to the wheels or constrain the relationship of the four wheels to each other first. To make trouble shooting driving constraints simpler you may find that the later easier. Constrain the wheels to each other based on the Work Plane on the wheel defined earlier. In the Browser, Double click on one of the Wheels. This will activate the Wheel and cause the rest of the Assembly to become inactive.

Fig. 12

Find the Work Plane that was defined based on the center axis of the wheel and the crank pin. Right click on it. Select Visibility.

Fig. 13

You should now have the Work Planes visible.

Double click on your Assembly file at the top of the Browser to make it active. From the Assembly Constraints dialog box, choose an Angle constraint. For Selection 1, choose the Work Plane of the rear right wheel. For Selection 2, choose the Work Plane of the left rear wheel. It is critical that the direction arrows point to the front of the train and that the Directed Angle solution is active. You can cancel the constraint command and rotate the wheels to the appropriate position. Rotate the right rear wheel so the crank pin is at the top and the left rear wheel to the bottom. Repeat the constraint process.

Fig. 14

Set the Angle to 0 degrees. Select Apply. Use the same operation to constrain the back right wheel Work Plane to the right front wheel Work Plane. The angle should be set to 0 degrees. Repeat the same process for the left side. The right side crank pins should be at the top and the left at the bottom. Select one wheel and rotate it. The other wheels should follow. If they do, you have defined the relationship of each wheel to each other. If they do not you may have had one of the work plane direction arrows facing the wrong direction or had the wrong solution option for the Angle constraint. We can now finish the assembly. Place two crank arms and four crank pins into the assembly. To constrain the crank arm between the two wheels start with the Insert constraint. Select the Hole in the link.

Fig. 15

Now select the base of the small protrusion from the wheel.

Fig. 16

Use an Offset of .01. To place the crank arm on the front wheel, use the Mate constraint.

Fig. 17

Select the Axis of the pin on the Wheel and the Axis of the unused hole on the link.

Fig. 18

If you have trouble selecting the Axis, right click and use the Select Other option.

Use an Offset of 0.

Fig. 19

Repeat the process to place the other Link. Use the Insert constraint to place the four Link Pins.

Fig. 20

It is a good time to try to rotate the wheels again. Select a wheel and rotate. The wheels and the cranks should move in a proper manner. If not, the link arms may not have been constrained or modeled properly. Correct problem and test again. You have completed the assembly of the train. Save your file. Now use the Save Copy As function to save a copy of your assembly file with a different name for later use.

Driving Constraints

By Driving Constraints, we can create motion. In the next section, we will explore more constraints, and then create motion with those constraints. Apply an Angle constraint between the back of the Train Body and the Work Plane of the right rear Wheel. The Angle should be set to 0 Degrees. Make a note of the angle constraint number located under the train body in the browser. Later the parameters for this constraint will be edited. At that time you can hover the cursor over individual parameters and a description will appear.

Fig. 21

Let’s make the train wheels move.

Expand the Train Body in the Browser by clicking on the plus sign next to it. Right click on the Angle Constraint under the train body. Select Drive Constraint from the Options.

Fig. 22

Click on the More Information button in the lower Right Hand Corner of the Drive Constraint Dialog Box. Set up the dialog box similar to Figure 21. When you are done, select the Play button.

Fig. 23

If the wheels rotate in the wrong direction delete the last Angle constraint between the wheels and the back of the train body. Redefine it using the alternative selection definition. Unless this constraint is driven, the wheels should be locked in place. They will not rotate.

Select Parameters by clicking on the Parameters Icon in the Assembly Panel Bar.

Fig. 24

When the Parameters dialog box opens, you will see all the Offsets and Dimensions you have used. The last one on the list should be the 0 degrees of the Angular Constraint you applied between the Wheel and the Train Back. Remember you can hover the cursor over the parameter for information. The Parameter Name will be a number (d12 for example). Your Parameter Number may not match what is shown. Click on the Number; it should turn blue. Type the word "Crank" and click on Done. This parameter is case sensitive.

Fig. 25

Hide the Work Planes again by double clicking on one of the wheels in the Browser. Right click on the Work Plane and deselect the Visibility option. Double click on the Assembly in the browser to make it active again. Save your file.

Forward Motion on Track

Use the Place Component tool to place three pieces of Straight Track on the screen. Right Click and select Done. Place a Mate Constraint between a peg end of a track and the slot end of another track. Use 0 for an Offset distance.

Fig. 26

Now apply a Flush constraint between the top surfaces of the two tracks. Use 0 for an Offset distance.

Fig. 27

To finish removing the Degrees of Freedom, apply a Flush constraint between the two edges. Use 0 for an Offset distance.

Fig. 28

Repeat the process for the next piece of track. Use the Mate constraint between the surface of the track and the bottom of the train assembly. Use an Offset of .4.

Fig. 29

Use the Flush constraint between the side of the Train body and the Side of the track. Use an Offset of .7

Fig. 30

Apply a Flush constraint between the back of the train and the back of the track. Use an Offset of 0.

Fig. 31

In the Browser, right click on a piece of track and select Grounded from the options.

Fig. 32

This will keep the track from moving. Now right click on the Train Body in the Browser. Uncheck the Grounded option. This will allow the train to move on the track. There are two ways to get the train to move. In the first method, we write a formula tying the Flush constraint between the Train Body with the Angle constraint between the back of the train body and the wheel. The second involves using a Motion constraint. To write the formula, we can edit the Flush constraint between the Train Body and the Track.

Fig. 33

We now change the Offset from 0 in to (Crank*3.14*2.25 in)/360 deg. Crank is the name we give the parameter for the Angle of the Wheels to the Train Body. Every time the wheel goes around once (Crank/360deg), we want to move the circumference of the wheel (3.14*2.25in) forward.

Fig. 34

We could have done the same operation in the Parameters dialog box. To move the train down the track, Right click on the Angle constraint in the Train Body in the Browser and select Drive Constraint from the options.

Fig. 35

Set up the dialog box similar to figure 23. The wheels should turn and the train will move down the track.

The other method of creating motion would be the use of an applied Motion Constraint. To use the Motion Constraint, Right Click on the Angle constraint between the back of the train body and the wheel in the Browser. Select Suppress from the options.

Fig. 36

Select Constraint from the Assembly Panel Bar. Select the Motion tab in the dialog box. On the Motion tab, select the Rotation-Translation option for Type. In the Solutions tab, select Reverse.

Fig. 37

For distance, use the circumference of the wheel: diameter of the Wheel 2.25*3.14 (3.14 is an approximation for PI). Every time the Train Body moves forward 7.065 inches, the wheel will revolve once. Select OK. Right click on the Angle constraint located under the train body in the browser. This is the constraint that we renamed in the parameter editing window. The Angle constraint is between the back of the train and the work plane used on the right rear wheel of the train. Select Drive constraint.

Fig. 38

Set up the Dialog box as is shown in Figure 41 below.

Fig. 39

Press the Play button. Your train should travel down the Track. If the train moves in the wrong direction, change the end length to a negative. However this means that there may have been a minor error constraining the train parts.

Circular Motion

In this assembly, we are going to create a circular track to run the train around. Open the Copy of the train engine you saved earlier. Start by selecting the Place Component icon from the Assembly menu. Place one instance of the circular track. Right click and say Done.

Fig. 40

From the Assembly menu, select Pattern Component.

The dialog box will have you pick a component. Select the Curved Track. Select the Circular tab. Depress the arrow button for the rotation axis and select the inside face of the curved track. This will allow the pattern to use the center line with which we created the track. Set the Count to 8 and the Angle to 45 degrees. Select OK.

Fig. 41

Use the Place Component function to place a Pivot on your screen.

Fig. 42

Use the Constraint tool and select Insert for an option. Select the hole on the pivot and the curved edge of a piece of track.

Fig. 43

Use an Offset of 0. It is time to position your train engine on the track. Since we want the engine to be able to drive in a circle, we will need to leave the one Degree of Freedom that allows it to rotate. The first constraint will position the train the correct distance above the track. Select the Constraint tool. Use the Mate constraint. Select the top of the track and the bottom of the train body. The Offset should be .4.

Fig. 44

The train should be at the correct elevation. We will now align the side of the train with the side of the pivot. Select the Constraint icon from the Assembly menu and choose the Mate constraint. Select the side of the train body and a face of the pivot. Use an Offset of 12 and check Apply. If an error occurs, make sure the body of the train is not Grounded.

Fig. 45

Change to a Flush constraint. Select the rear of the train body and the rear of the Pivot block. Use an Offset of 2.5.

Fig. 46

The Engine is now positioned on top of the track. We need to Ground the track. This will allow the train to go around the track rather than the other way around. Do this by expanding the Patterned Component Icon in the Browser. Expand Element 1 and right click on the Curved Track.ipt. Select Grounded from the options.

Fig. 47

Unground the train body by following a similar process. The final step before we can drive the train in circles is to establish an Angular constraint between the pivot and our Grounded curved track. Accomplishing this step is difficult because we cannot see the end of the track we need to use. Right click on Element 8 in the browser and check the Visibility box from the Right Mouse Menu. The piece should disappear. You can now select the end of the track and the side of the Pivot. Set the Angle to 0. Select OK.

Fig. 48

Go back to the Browser. The Curved track that is invisible is grayed out. Right click, select Visibility and the track should show. Right click on the pivot, select the Visibility option, and make the pivot invisible. To drive the train in a circle, we will create a formula. Open the Parameters dialog box. The last entry should be the Angular constraint between the Pivot and the Track. Change the 0 degrees to Crank/12. If you remember, we named the Parameter for the relationship of the wheels to the Train Body Crank. Every 12 revolutions of the Train Wheels will cause the Train to go around the Track once.

Fig. 49

In the Browser, expand the Train Body. Right click on the Angle constraint. Select Drive Constraint from the options.

Fig. 50

In the Drive Constraint dialog box, change the end degrees to -5400. By selecting the More button located next to the Cancel button, you can increase the speed by increasing the number of degrees in the Increment box. If you check the Start/End/Start option in Repetitions, the train will get to the end then back up.

Fig. 51

Additional Exercises:

- Design a train car to use the same tracks. - Design a coupling system to be used between the train engine and the

additional cars.