April (13&14) 2015

ENGR B47Intro. to Egr. & Design

Lab #12Electric Motor

Schedule / Timing

• Week 11: Introduction, Groups, Delegation• Week 12: Motor Construction• Week 13: Motor Construction & Troubleshooting• Week 14: Troubleshooting & Data Collection• Week 15: Troubleshooting, PowerPoint, “Report”• Week 16 (Finals Week*): Presentations

* Presentations will take place on May 13 from 8:00 - 9:50 am

2

Basics of Magnetism

[walk-through on whiteboard]

• Permanent magnets– Likes repel– Opposites attract– Draw “field lines” represent this behavior

• Electromagnets– Relationship between current & magnetic field– Straight wires and loops

Review

Building a Motor

[walk-through on whiteboard]

• Permanent magnets– Two fixed on the outside– One rotating in the center

• Can get a “motor” to work for half a rotation

• “Flip a switch” and change the magnet?

Review

Building a Motor

What would it look like?

Graphics from pcbheaven.comhttp://www.pcbheaven.com/wikipages/How_DC_Motors_Work/

Review

Graphics from pcbheaven.comhttp://www.pcbheaven.com/wikipages/How_DC_Motors_Work/

Review

How Get Current to Coils?

Graphics from pcbheaven.comhttp://www.pcbheaven.com/wikipages/How_DC_Motors_Work/

Review

Graphics from pcbheaven.comhttp://www.pcbheaven.com/wikipages/How_DC_Motors_Work/

Review

Motor Project Goals

• Construct a motor• Characterize performance (worksheet coming)

– Speed vs. Torque curve– Power vs. Torque curve– Maximum Power calculation

• Create instruction manual– Audience is middle school students– Include assembly guide & component list– Step-by-step instructions (lots of pictures!)– Troubleshooting section

Review

Grading Criteria

Motor Project is 20% of final grade (see syllabus)

• Performance of motor [25%]– Mostly concerned that it works– Little incentive to out-perform other groups– Data is critical

• Presentation [25%]• Instruction Manual [25%]• Peer Evaluation [25%]

Review

To Do List for Today

• Double-check 1st Day Stuff– Exchange contact information– Make schedule to accomplish all tasks

• Continue Constructing Motor– Collect needed pieces from instructor– Starting winding– Start modifying housing– Cut spacer for commutator– Finish wiring– Test function with power source (see instructor)

Motor Construction

General Guidelines• Building the Electromagnet

– Tape the lag screws to the axle– Wind the wire around the bolts– -Windings 4 layers thick– -Leave 6” tails– Test the Electromagnet

• Building Commutator– Building the Commutator– Affix foil tape to the dowel– -Leave ¼” gap between contacts– Place stripped ends of wire under foil tape– Break in foil must be perpendicular to

electromagnet

• “Each time the commutator hits the point where it flips the field in a two-pole motor, the commutator shorts out the battery (directly connects the positive and negative terminals) for a moment. This shorting wastes energy and drains the battery needlessly”

• Forming the Brushes– Try with thin brass sheet– - ¾” wide by 3” long– Wind around nail– Form it to shape shown

12

Motor Assembly

Characterizing Motor Power• See write-up posted on course website• Wind up known mass (provided by instructor)

– Calculate power and torque– Will need timer & tachometer (provided by instructor)– Run with DC power supply (provided by instructor)

• Ideally measurements @ multiple speeds (masses)• Plot data, include in final presentation• Talk to me before taking measurements

13

Power: Watts (Newton·meters/second)Force: Newtons (kilogram·meters/second2)Height: metersTorque: Newton·metersRotational Speed: Revolutions/second (not RPM)

Writing a User Manual

• What to include– Assembly instructions– Operation instructions– Troubleshooting guide

• Format– Step-by-step guide– Lots of pictures / diagrams*– Use plain language (understood by 10-14 year olds)– Probably 3-10 pages (based on font size, # images)– Fairly open-ended as far as style

(How many columns? How many steps? Which orders should I put in the required elements?)

14* Of major components or steps. These are for clarification

of the operation, not to prove to me you built it.