Written By Dave Martin
  • 5/20/2020
  • Read Time : 5 min.

Two Huge Problems with How Teams Manage Calculations

What engineering teams get wrong about managing calculations.

I’ve been an engineer for over a quarter century, and I’ve noticed two huge problems regarding how product development teams manage their calculations.

First, we don’t do a good job integrating and saving our notebooks. Every job I’ve ever had, I used notebooks. Almost all engineers and designers do. We use these to sketch ideas, take notes, and perform calculations.

We use those calculations to derive requirements, size features, and perform basic analysis. We then plug some of our results into model dimensions, but our CAD parts and assemblies are disconnected from our calculations.

What happens to those engineering notebooks when someone leaves a job?

Maybe they get put into a box and placed into storage. Maybe you hand them to your boss. Maybe you leave them in your desk for the next person to find. I’ve worked for some of the biggest companies, and I’ve never seen anyone have a consistent plan for capturing that information. It just gets lost.

Second, it’s still way too easy to screw up design and analysis by messing up your units. In 1999, the Mars Climate Orbiter was lost during entry into the Martian atmosphere. It either burned up or skipped off the atmosphere. Why? One team calculated impulse in English units but the rest of the team used metric.

How much did that screw up cost? The mission cost was $327.6 million, but we know the true cost – the thousands of hours invested, the professional reputations damaged, and embarrassment – was much higher.

I’ve worked in aerospace several times in my career. Mass and weight are two of the biggest driving factors in that field. Unmanned aerial vehicles (UAV) are limited to 55 pounds total. There’s literally a dollar per pound cost you can calculate for rocket launches. You better track your mass properties in CAD and get them right. Yet it’s so easy to screw up mass and weight.

Fortunately, there’s a great solution to both these problems. They’re called Engineering Notebooks. This solution enables us to store our engineering calculations in our CAD models and drive model dimensions from the calculations. And Mathcad Prime understands units; it has built-in functionality that makes working with units practically fail safe.

Here’s how Engineering Notebooks work:

  • We capture our calculations in Mathcad worksheets, and embed these worksheets in our CAD models.
  • We send inputs from Creo Parametric to Mathcad Prime, which performs the engineering calculations.
  • Mathcad sends outputs to Creo Parametric.
  • The Mathcad outputs drive feature dimensions and parameters.

The benefits of Engineering Notebooks include:

  • Our information, our decisions, and our methodology are captured electronically. The worksheets can be shared and reused.
  • Since the worksheets exist inside of our CAD models, we can’t lose track of our calculations.
  • Both Mathcad Prime and Creo Parametric understand units. You can create your model and worksheet in different sets of units and they both understand each other. If you make a mistake with units – such as trying to perform math with incompatible units –Mathcad Prime will warn you.

Here’s an example of a CAD model with an embedded worksheet:

Model with attached worksheet.

See that orange-yellow M icon in the upper right corner? That tells you the model has an embedded worksheet. Double click on it to access the worksheet and update the calculations and outputs. Here’s what the worksheet looks like:

worksheet2

Our engineering calculations are captured inside the assembly and drive our CAD geometry.

Want to learn more? I’ll be presenting at PTC’s virtual conference on June 23, where you can learn more about Mathcad Prime, engineering calculations, and more, including Engineering Notebooks. Register here to join in. Hope to see you there!

Virtual Conference: Ensuring Accuracy of Calculations Throughout Engineering.


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About the Author

Dave Martin is a former Creo, Windchill, and Mathcad instructor and consultant. After leaving PTC, he was the Creo specialist for Amazon; and a mechanical engineer, Creo administrator, and Windchill administrator for Amazon Prime Air. He holds a degree in Mechanical Engineering from MIT and currently works as an avionics engineer for Blue Origin. 


Martin is the author of the books Design Intent in Creo Parametric and Top Down Design in Creo Parametric--both available at www.amazon.com. He can be reached at dmartin@creowindchill.com.

Two Huge Problems with How Teams Manage Calculations
Almost every designer and engineer keeps a notebook. Problems arise when the author is no longer around.