Design Projects

The rest of this post will reference engineering school projects.  However, I believe that most of this is also valid to open ended real world projects.

Many engineering schools require semester design projects.  The design project’s goal is to demonstrate to your professor that you learned the key opints of the class.  Typically, demonstrating these core competencies requires being more explicit and thorough in your analyses than you are naturally inclined to be.

The biggest mistake most people make is to assume the “real” work comes late in the process.  It doesn’t the real work in any successful project is done up front.  Serious effort must be given to the choice of projects.  Even more thought and effort must be put into determining the essence and purpose of the project.  The rest of this post will explore this further.

Design Project – the purpose…

The purpose of any design project is the design of a product which can manufactuered.  But what is the real purpose of the end product?

One common mistake is to assume that your end product must be everything to everyone.  For example, in my senior design project (years and years ago) we designed hardware to help movie studios move their sets around the studio more safely and with fewer people.  The first inclination for the group was to design the hardware be able to move any set the studio might build.

Ultimately this turned out to be ridiculous.  We couldn’t levy requirements back on the studio so we couldn’t keep the studio from attaching delicate items to the set right where we needed our clamps to grab the set.  The end result being that we had to scale back our ambitions such that we were capable of picking up the majority of the sets.

A more subtle mistake, related to this one, is that if 90% of the sets were less than 400 lbs but the remaining 10% could be as heavy as 1000 lbs do you let the 1000 lb sets drive the design?  The answer most of the time is no.

This is why determining the essence of a project is so important.  In industry this is why is takes months to write requirements.  The cost of a design can be driven up and up by any single requirement.  Obviously you’d like to avoid having the cost of the design be driven by a requirement that doesn’t need to be as demanding as it is.  In other words, do you really design hardware to meet the 1000 lb sets if hardware to move 400 lb sets is half as expensive?  or requires half as much analysis?

The lesson…

The lesson in all of this is to boil down the project to its essence.  The previous examples essence was the ability to move most sets more safely with only a couple of people instead of the previous ten.

Since the essence is most sets not all sets we were able to keep the design simple with C-clampes, square tube frame aluminum, and a manually operated jack for lifting the set.  Had our design required the ability to lift 1000 lb sets then we would have need to design the hardware with an electric jack instead of a manual jack.  We also would have had to add twice as many C-clamps meaning twice as many attachment points.

If the design had been for all sets such that we had to avoid delicate parts of the set then we also would have needed to design the hardware with a telescopic arm for the C-clamps.  This would have required a wholesale change to the design for allowing the telescopic positioning and then fastening down those telescopic attachment points.

MEMS Gyro models

MEMS gyroscopes are becoming common in Aerospace systems.  They are small, low power sensors accurate in frequency ranges good for Aerospace applications.  Often, MEMS gyros are the only sensors commerically available that provides the necessary frequency response, mass, power and environmental.

I’ve found 2 types of MEMS gyro modeling.  Both of these modeling types are for the design of the MEMS gyro.  A MEMS gyro sensor requires design of some key parameters - resonant frequency, driving frequency, and quality factor.  These articles are not on the frequency response of the sensor.    The frequency response and noise are the primary items to model for control systems.  So these design articles are high fidelity models and information purposes.

Traditional modeling of MEMS Gyros

Traditional design modeling of MEMS gyros often starts with an FEM of the sensor.  However, the FEM is often too large for feasible modeling.  FEM modeling can be infeasible for memory reasons or simply the length of time it takes to produce results.

The next step in traditional design modeling is to create an equivalent electrical circuit for detailed analysis in various software packages.  Again producing results from these equivalent circuit models is time consuming.

Wiki article on Traditional MEMS Gyro modeling

Simplified lumped parameter model for MEMS Gyros

I found a journal article describing a lumped parameter model for MEMS gyroscope design suitable for running in Simulink.  The  benefit of the Simulink lumped parameter model technique allows for much faster MEMS gyro design results through simple gains and trnsfer function blocks.  The results present in the journal article looked encouraging.

Wiki article on Simplified lumped parameter model for MEMS Gyros

More articles coming…

Accurate sensor models are necessary for any good control loop design.  So I have a couple more sensor model/design articles coming.  After that I will start adding details of MEMS gyros as I find them on the web.