Choppernext slide to start...

A DESIGN CASE STUDYor “Tales of an engineering design consultant”

Presented by:Prof. Will DurfeeDepartment of Mechanical EngineeringUniversity of Minnesotawkdurfee@umn.edu

• Please sit with your team• Take one index card, one sheet plain paper

• Stimulated Muscles = Power • Brace = Trajectory guidance • Brake = Control, stability

HUMAN/MACHINE DESIGN LABDepartment of Mechanical EngineeringUniversity of Minnesota(www.me.umn.edu/divisions/design/hmd/)

Fu

x,vT

X

PE Force-Velocity

CE Force-Velocity

Fscale

IRC

CE Force-Length

Activation Dynamics (2nd order)

PE Force-Length

u

V

X

V

X

Force

Passive Element

Active Element

Muscle mechanicsSmart orthotics +

electrical stimulation for gait restoration

Haptic interfaces for virtual product prototyping

The case begins

At 2 pm on an otherwise ordinary day, you get a phone call...

So the first question is...

What the heck is “roof ventilation”???

http://ogrowald.home.texas.net/ogalleryindex.htm

What’s the rest of the obstacle course look like?

How about a close-up of a firefighter chopping a hole in a roof?

Test chopping

• 3004 Cedar Av, destroy the roof• Video taped 12 firefighters, 4x4 hole• Time: 1:47 -- 13:28• Blows: 47 -- 268• Conclusions

– the task: hit hard enough and often enough to break through roofing material

– few, heavy blows, or lots of lighter blows– light tapping does nothing– bigger people take less time– roof surface is at feet

Design requirements

• Task = sum of blows• Accuracy of blow• Weight and feel of ax• Endurance• Reliability• Cost• Ease of operation• Operates outdoors• Reliability• Reliability

OK, time to brainstorm

You be the consultant.

As a team, brainstorm on at least three different ways to solve this problem. Quick sketch the “best idea on the blank paper. Deliver to Durfee in 12 minutes.

The competition

My design...

Da Vinci notebooks: 4,000 pages of notes and sketches

Early ideas

The saga of the strike surface...

8 layers of 3/4” BCX plywood

top with 1/4” lexan + 1/8” vinyl

2” nylon

1/4” lexan + neoprene

1/4” lexan + carpet

1/4” neoprene + 1” lexan ==> held up…more or less

Over two years, machine worked well…sort of...

Parts and materials

Estimated

$1,330

Actual

$3,198

Labor

Estimated

$1,370

Actual

who knows...

Major shortcomings

• Cable breaks• Top plate cracks• Complicated recalibration

involving a laptop and reprogramming the microcontroller chip

• A pain to maintain

You be the design critic

On your index card, list 3 ways to improve the design. Deliver to Durfee in 3 minutes.

Ref What Vendor Vendor PN Cost NotesShock accelerometer, 5K G range Dytran 3200B5 330.00$ Shock accelerometer, 5K G range Dytran 3200B2 350.00$ Cable, mini coax, 10-32 stainless plug to BNC, 10 ft. Dytran 6469A10 28.00$ Constant current diode, 2 mA Dytran 6123 4.00$ Connector adaptor, 10-32 to solder Dytran 6115 15Cable, new type, mini coax, 3 ft Dytran 6011A03 26

Tech Tools PIC programmer Digi-Key MP-PROG-ND 199.00$ Tech Tools 40-pin ZIF adapter Digi-Key MP-ZIF40-ND 49.00$ IC, PIC16F876-20/SP, microcontroller Digi-Key PIC16F876-20/SP-ND 9.38$ Resonator, ceramic w/ caps, 4.0 MHz Digi-Key X902-ND 0.56$ Resonator, ceramic w/ caps, 20.0 MHz Digi-Key X909-ND 0.68$ PCM C compiler CCS PCM 99.00$ Palm IIIxe CompUSA 3C80304U 249.99$ Palm HotSync cable Best Buy 10104U 19.99$ Null modem cable (9 pin), Belkin CompUSA F3B207-10 14.99$ IC, MAX536A, RMS-to-DC Maxim MX536AJQ 15.30$

Temp IC, Dallas DS1620 Jameco 114382 5.49$ ZIF socket, 28 pin Jameco 104002 8.25$ IC, MAX233 CPP, TTL-to-RS-232 Jameco 106163 4.95$ Neoprene rubber sheeting, 12"x12", 1" thick, firm, 60A durometer McMaster-Carr 8568K719 36.96$ 5/8-11 x 1-1/2 HHCS, grade 8 Jerry's5/8 lock washer, grade 8 Jerry's1/4-20 x 3/4 SHCS, stainless Jerry's1/2-13 stop nuts, nylon insert Jerry's1/2-13 x 3 HHCS, grade 8 Jerry's1/2 washer, grade 8 Jerry'sCalibrator sledge, 20 lb, fiberglass handle Home Depot 42904202227 48.78$

Lessons learned

• For one-of, overdesign• Design for strength, stiffness• Mechatronics is a great skill• It’s all in the details• Budget wisely• Continual communication with client• You learn by building it yourself