# Train Engine Tutorial

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Train Engine Part 1 | Train Engine Part 2

With the rigging parameters explained in the Train Overview video, Rich goes about explaining his 'best-practices' for organization and naming in this video. With the use of his 'Rig Sketch' technique he explains his thought process to resolve the problems at hand and then set out applying the tools modo has available to create the rig for the train. User can follow along by opening the models directly from the resources tab below or simply watch and learn as a master rigger teaches his craft.

Users can jump ahead to a specific section by using the Chapter selection widget on the right side of the player or by directly clicking any of the Chapter Title links below.

Tab | Time | Chapter | Description
1 | 00:00:00 | Introduction | Introduction to Locomotive Engine and explanation of what needs to be done.
2 | 00:02:41 | Organization Plan | How to organize the model for a production environment.
3 | 00:05:41 | Naming Standards | Best practices to use for when naming items and layers.
4 | 00:06:30 | Organize Model | Actual process of organizing the different layers needed for the train rigging.
5 | 00:15:58 | Placing Centers | Positioning of 'Centers' is important preparation for animation.
6 | 00:24:09 | Rig Planning | Rig Sketch walkthrough or what is necessary to rig the action at hand.
5 | 00:35:06 | Rig Prototype | A basic prototype to decide if the technique outlined in the Rig Sketch will actually work.
| 01:02:15 | Total Video Time |

Frequently Asked Questions--

Q.) He quickly changes the how the background items are drawn, how is he doing that?

> A.) He is using a hot key to set the display preference for the viewport, its called "Inactive Meshes". He goes over the default settings that he uses in the "Preferences" section of the Foundation, please refer to it for more information.

Q.) He spends a lot of time naming things, is it really THAT important?

> A.) YES!!!! We cannot stress enough how important it is to build yourself a naming standard and apply it to your rig AS YOU GO. It prevents a lot of confusion later while you are trying to debug and adjust your rig as well as making it easier for other people to crack your rigs open and make changes as required.

Q.) He calls items "Layers", what is that about?

> A.) In the early modo days before there were "Items" everything was a mesh "Layer" and you would work in various foreground and background layers to build your model. That idea is a cornerstone for how modo was developed and is how modo internally sees "Items". It's nothing that will affect how you work, it's more that I keep using the old term instead of the new one.

Q.) I found that when I was working with my centers that the last item I had selected center was being affected and not the one I wanted, why?

> A.) If you select a 'Center' in Center mode, it will remain selected until you select another item and actually select its Center directly. It can be confusing because you see the new center on the newly selected item but the last center is still selected but not visible. Just make sure the center you want to work with is highlighted in the yellow selection color before proceeding.

Q.) He mentions setting up an "expression", what is that? Does modo have "expressions"?

> A.) The term expressions is just a quick way of describing building complex relationships between values in the scene. So if you wanted to make the value of a channel be twice as much you could build an "expression", which is a line of specially formatted text, to tell the system to double the channels value. Modo does not have the traditional "Expression" that is text based, it uses "Modifiers" to allow you to build complex relationships, such as doubling the value of a channel. For more information check out the Modifiers section.

Q.) He mentions "precision" issues, what does that mean?

> A.) Sometimes in computer graphics values generated by different elements will fall out of sync. If the amount of accuracy between two elements that are depending on each other is great enough you may see things shift in your 3D scene. Sometimes its related to how a value is derived other times it can just be a vast difference in scale. When you know this might be possible, it's a good idea to try and find ways to prevent this from causing problems in your scene.

Q.) He mentions a "Cycle" or "Circle" as being a problem with using modifiers, what does that mean?

> A.) If you have two items and they both depend on each other in some way, lets say Item A needs to get Item B's position before it can set its own. If you try and get Item B to depend on Item A's position modo would complain about there being a "Dependency Loop". How can you get the value of Item A's position if it is connected to Item B's position and in turn, Item A is depending on Item B's position. This is a very clear example, others might be more subtle but still require that you take steps to prevent the "cycle", "Circle" or "Dependency Loop".

Q.) He uses the term "Parametric" when talking about a curve, what does that mean?

> A.) Simply put a curve is measured by a value of 0 to 1, 0 being the beginning and 1 being the end. So its not a measure of distance its just a "Parameter" or value. In 3D graphics a lot of things are considered "Parametric" another example being UV values. They are parametric because they are also 0 to 1 and not a measure of distance or actual surface area. So its big word that just means, in the 3D context, that something is always a measure from 0 to 1 no matter what its real world size in the scene may be.

Q.) He talks about the "Floating Point" or a "Float" channel, what does that mean?

> A.) "Floating Point" number just means a number that has a decimal place. So a value of 1.004 could have its decimal point moved to change its value to 10.04. Its decimal "point" can "float" to different positions in the number to change its value. See the Channels section for more information.

Resources--

Links to the modo in-line help system
Docs: Viewport visibility settings
Docs: Parenting
Docs: Centers and Pivots
Docs: Work Plane
Docs: Direction Constraint
Docs: Path Constraint
Docs: Action Centers
Docs: Scale Tool (negative scale option)
Docs: Locator Display Options

Links to other pages in this training
Training: Preferences
Training: Parenting and Hierarchies
Training: Centers and Pivots
Training: Align Set Drop Tools
Training: Modifers
Training: Constraints
Training: Action Centers
Training: Curves
Training: Locator Mesh Display
Training: Channels

File--

Links to the modo scenes used in the video
(click to open in modo)
File: Locomotive_00_Organize_01.lxo
File: Locomotive_00_Organize_02.lxo
File: Locomotive_02_RigPrototype_01.lxo
File: Locomotive_02_RigPrototype_02.lxo

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